Chapters 1 and 2

Standards organizations

Standards organizations issue standards that are important in the field of networking. Standards Organization Description ISO The International Organization for Standardization (ISO) is the largest standards- development body in the world comprising the national standards institutes of 162 countries. It is a non-governmental organization issuing voluntary standards in fields from agriculture to textiles. Of most significance for networking, in 1984, the ISO developed the OSI model. The OSI model is a seven-layered framework of standards and specifications for communication in networks. The short name ISO is not an abbreviation for the name of the organization in any particular language, but was derived from the Greek word isos, meaning equal. Website: www.iso.org IEEE The Institute of Electrical and Electronics Engineers (IEEE) is an organization dedicated to advancing theory and technology in electrical sciences. The standards wing of IEEE issues standards in areas such as electronic communications, circuitry, computer engineering, electromagnetics, and nuclear science. Website: www.ieee.org ANSI The American National Standards Institute (ANSI) is the national standards institute of the United States that facilitates the formation of a variety of national standards, as well as promotes those standards internationally. Individually accredited standards bodies perform the standards development under ANSI's guidance. The best-known ANSI standard in the information technology world is a method for representing keyboard characters by standard four-digit numeric codes. Website: www.ansi.org TIA and EIA The Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA) are two trade associations accredited by ANSI to develop and jointly issue standards for telecommunications and electronics. Websites: www.tiaonline.org and www.eia.org ARIN The Regional Internet Registry (RIR) is an organization that supervises how Internet numbers are allocated and registered in a particular geographical region. There are five RIRs in operation and the American Registry for Internet Numbers (ARIN) is responsible for the United States, Canada, and parts of the Caribbean. The services provided by ARIN include: • IP address allocation. • Registration transaction information with the help of WHOIS, a query/ response protocol that is used to query an official database to determine the owner of a domain name or an IP address on the Internet. • Routing information with the help of RIRs that manage, distribute, and register public Internet number resources within their respective regions. ICANN The Internet Corporation for Assigned Names and Numbers (ICANN) coordinates the assignments of unique identifications on the Internet, such as domain names, IP addresses, extension names, and Autonomous System (AS) numbers. Note: In 1993, an international organization called the Internet Assigned Number Authority (IANA) was established to govern the use of Internet IP addresses. Today, that function is performed by ICANN. Website: www.icann.org ISoc The Internet Society (ISoc) organization coordinates and oversees standards and practices for the Internet. Its mission is to promote the open development, evolution, and use of the Internet for the benefit of all people throughout the world. Website: www.isoc.org IETF The Internet Engineering Task Force (IETF) is an international open committee that consists of working groups, committees, and commercial organizations that work together to develop and maintain Internet standards and contribute to the evolution and operation of the Internet. All published Internet standards documents, known as Requests For Comments (RFCs), are available through the IETF. Website: www.ietf.org

Fiber connectors

Various connectors are used with fiber optic cables. Note: It often takes a specially trained and certified technician, plus specialized equipment, to install fiber optic connectors. This is because the installation requires in-depth knowledge about fiber optic communication systems and fiber optic cables. Additionally, the installation involves various testing processes, which can be done only by a knowledgeable or certified technician. Fiber Optic Connector Description Straight Tip (ST) ST connectors are similar in appearance to BNC connectors and are used to connect multimode fibers. They have a straight, ceramic center pin and bayonet lug lockdown. They are often used in network patch panels. ST connectors are among the most popular types of fiber connectors. Subscriber Connector or Standard Connector (SC) SC connectors are box-shaped connectors that snap into a receptacle. They are often used in a duplex configuration where two fibers are terminated into two SC connectors that are molded together. SC is used with a singlemode fiber. Local Connector (LC) LC connectors are used for both singlemode and multimode fiber and a small form factor ceramic ferrule. It is about half the size of an SC or ST connector. LC connectors use an RJ-45-type latching and can be used to transition installations from twisted pair copper cabling to fiber. Mechanical Transfer Registered Jack (MT-RJ) The MT-RJ connector, also called a Fiber Jack connector, is a compact snap-to-lock connector used with multimode fiber. Because the MT-RJ connector is compact, it is easy to use. It is similar in size to the RJ-45 connector. Two strands of fiber are attached with the MT-RJ connector. Ferrule Connector (FC) FC connectors use a heavy duty ferrule in the center for more mechanical stability than SMA or ST connectors. A ferrule is a tubular structure made of ceramic or metal that supports the fiber. These connectors are more popular in industrial settings where greater strength and durability are required. Fiber Distributed Data Interface (FDDI) FDDI connectors are used for multimode fiber optic cable and are a push/pull-type, two-channel snap-fit connector. Also called a media interface connector (MIC). Biconic The biconic connector is a screw-on type connector with a tapered sleeve that is fixed against guided rings and screws onto the threaded sleeve to secure the connection. When the connector is inserted into the receptacle, the tapered end of the connector locates the fiber optic cable into the proper position. The biconic connector is one of the earliest connector types. Sub-multi assembly or sub- miniature type A (SMA) SMA connectors are similar to ST connectors, and use a threaded ferrule on the outside to lock the connector in place. It is typically used where water or other environmental factors necessitate a waterproof connection, unlike a bayonet-style connector. As with copper media, there are also fiber couplers available. However, fiber couplers work differently than their copper-media counterparts. Fiber couplers are used when a system has one or more input fibers and one or more output fibers that need to be connected. The connection can be created by thermally fusing the fibers so that the cores get into intimate contact.

OSI model layers

The layers of the OSI model, starting from the top, are described in the following table. Layer Number and Name Description Layer 7, Application layer Enables applications on a network node (device) to request network services such as file transfers, email, and database access. These requests are accomplished through the use of Layer 7 protocols such as Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), Internet Message Access Protocol (IMAP), and the like. Proxies and firewalls work at this layer. Layer 6, Presentation layer Translates Application layer data into an intermediate form that both client and server can process. Encryption, compression, character sets, multimedia formats, Multi-Purpose Internet Mail Extensions (MIME) types, and codecs exist at this layer. Proxies and firewalls work at this layer. Layer 5, Session layer Establishes and controls data communication between applications operating on two different devices, regulating when each device can send data and how much it can send. TCP and User Datagram Protocol (UDP) port numbers exist at this layer. Firewalls also work at this layer. Layer 4, Transport layer Performs the actual establishment, maintenance, and teardown of the connection. Optionally divides long communications into smaller segments, including error recognition and correction, and data receipt acknowledgment. TCP and UDP protocols exist at this layer. Packet filtering routers, multilayer switches, and firewalls work at this layer. Layer 3, Network layer Adds logical addressing (network addresses) and chooses the best route. IP, Internet Control Message Protocol (ICMP), and Internet Group Management Protocol (IGMP) exist at this layer. Routers, multilayer switches, and firewalls work at this layer. Layer 2, Data Link layer Structures the data into a format appropriate for the transmission medium. Adds physical addresses such as media access control (MAC) addresses or frame relay data link connection identifier (DLCI) numbers. Usually includes simple error checking. All WAN and LAN protocols exist at this layer, including Ethernet, token ring, frame relay, Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), wireless access protocols, ATM, and X.25. (Some of these protocols extend beyond Layer 2.) Switches and bridges work at this layer. Layer 1, Physical layer Transmits bits (binary digits) from one device to another and regulates the transmission stream over a medium (wire, fiber optics, or radio waves). All electrical and mechanical aspects of data transmission exist at this layer, including cabling, connectors, antennas, transceivers, baseband, broadband, signaling types, voltages, waveforms, modulation, frequencies, and clock rates. Network interface cards, hubs, and repeaters work at this layer. Note: While it is true that a repeater, hub, or network interface card will also be designed to work with a specific Layer 2 protocol (such as Ethernet or token ring), these devices are generally classified as Layer 1 devices because their primary purpose is connectivity rather than forwarding decisions based on Layer 2 addresses. The OSI model is an excellent conceptual model to understand networking and to compare the functionality of different devices and protocols. You will often hear experienced engineers and troubleshooters discuss a problem by referring to the relevant OSI layer. Examples include: "I think it's a Layer 2 problem as opposed to a Layer 3 problem," or "Do we really have to use Layer 3 addressing to carry data across a point-to-point cellular call?" Note: Some network protocols do not map directly to the OSI model. For example, Multiprotocol Label Switching (MPLS) is often referred to as Layer 2.5 because it exists somewhere between the traditional concept of the Data Link and Network layers.

Extranets

An extranet is a private network that grants controlled access to users outside of the network. It is an extension of an organization's intranet. With the help of an extranet, organizations can grant access to users such as vendors, suppliers, and clients to connect to resources on the network.

Device placement

When installing devices in a wiring closet, you need to consider the placement of those devices so that your setup and maintenance activities are not hampered. Make sure that the devices are placed within reach of a power source and that power cords are not in high foot-traffic areas. Devices that need to connect to other devices should be within a reasonable distance of each other. Devices should also be physically accessible by the people who need to perform administration tasks on them. Proper airflow for cooling must be taken into account so that devices do not overheat.

Terminals

A terminal is a specialized device on a mainframe-based network that transmits user-entered data to a mainframe for processing and displays the results. Terminals are often called "dumb" because all required processing or memory is located on the mainframe. Terminals usually consist of just a keyboard and a monitor. Standard client devices that need to interact with mainframe computers can run software called a terminal emulator so that they appear as dedicated terminals to the mainframe. Thin clients are often considered to be related to terminals because of their reliance on another device to provide processing power. The main differences between thin clients and terminals are: • A terminal is typically just a monitor and a keyboard with no processing power. A thin client is typically an actual device with a CPU and RAM, but has no hard drive. • A terminal connects to a dedicated port on a mainframe. A thin client connects to the network like any other device, and it boots from its network card, downloading the operating system from the network and running it from RAM.

Data transmission

Data transmission is the exchange of data among different computers or other electronic devices through a network. Unlike telephony, which involves only the transmission of voice, data transmission sends non-voice information such as graphics, animations, audio, text, and video over the network. Most of the data transmission takes place through networks and the term "data networks" is synonymous with networks. Though data is typically stored as files before being transmitted, there are exceptions to this process. In some forms of data communication, such as online chat or video conferencing, data needs to be transmitted as soon as it is generated. In such cases, data is instantaneously converted into a network-compatible format and transmitted without being stored either in main memory or on a disk.

Baseband transmission

In baseband transmissions, digital signals are sent via DC pulses over a single, unmultiplexed signal channel. As all devices share a common transmission channel, they can send and receive over the same baseband medium, but they cannot send and receive simultaneously.

Multicast transmission

Multicast transmission is a transmission method in which data is sent from a server to specific nodes that are predefined as members of a multicast group. Network nodes not in the group ignore the data. Communication with nodes outside of a multicast group must be done through unicast or broadcast transmissions. A video server transmitting television signals is an example of multicast transmission.

Network media performance factors

Several factors can affect the performance of network media. Factor Description Noise Electromagnetic interference (EMI) that disrupts the signal. The signal-to-noise ratio decreases as the transmitting distance increases. Attenuation The progressive degradation of a signal as it travels across a network medium. Some media types are more susceptible to attenuation than others. Attenuation can also occur when the cable length exceeds the recommended length. Impedance The opposition to the flow of electricity in an alternating current (AC) circuit. To reduce the risk of signal loss and degradation through reflection, it is important that the transmitting device, the cabling, and any terminators have the same impedance. Impedance is measured in ohms (Ω). An ohm is the value of electrical resistance through which one volt will maintain a current of one ampere

OSI model and associated network devices

The applications, operating systems, and network technology you choose determine how the OSI model is applied to your network. The applications will vary depending on the user needs. The operating system will vary depending on the needs or preferences of the organization. The network technology will vary depending on the requirements for the network. The following table summarizes the OSI model layers and the protocols and network devices that are associated with each layer. OSI Layer Protocols or Key Characteristics Network Devices Layer 7, Application layer HTTP, FTP, SMTP, IMAP, etc. Application proxy Layer 6, Presentation layer Encryption, compression, character sets, multimedia formats, MIME types, codecs, etc. Application proxy Layer 5, Session layer TCP and UDP port numbers Firewalls Layer 4, Transport layer TCP and UDP protocols Firewalls Layer 3, Network layer IP, ICMP, and IGMP protocols Multi-layer switches, routers, and firewalls Layer 2, Data Link layer Ethernet, token ring, frame relay, PPP, HDLC, wireless access protocol, ATM, X.25, etc. Switches/bridges and access points Layer 1, Physical layer Cabling, connectors, antennas, transceivers, baseband, broadband, signaling types, voltages, waveforms, modulation, frequencies, and clock rates. Network interface cards, hubs, repeaters, etc. Hubs, repeaters, patch panels, cables, and network cards

Twisted pair connectors

Twisted pair has two common types of connectors: the RJ-45 and the RJ-11. The RJ-45 is an eight-pin connector used by twisted pair cables in networking. All four pairs of wires in the twisted pair cable use this connector. Note: The RJ in RJ-11 and RJ-45 is an abbreviation for "registered jack." An RJ-45 connector can also be called an 8P8C connector. Pin T568A (Legacy) T568B (Current Standard) 1 White/green White/orange 2 Green Orange 3 White/orange White/green 4 Blue Blue 5 White/blue White/blue 6 Orange Green 7 White/brown White/brown 8 Brown Brown You can also connect two UTP cables together by using a UTP coupler . This can be handy when you have some shorter cables and you need to run them for a longer distance. The RJ-11 connector is used with Category 1 cables in telephone system connections and is not suitable for network connectivity. However, because the RJ-11 connector is similar in appearance to the RJ-45 connector, they are sometimes confused. RJ-11 connectors are smaller than RJ-45 connectors, and have either four or six pins. There is also the RJ-48C connector, which is commonly used for T1 lines and uses pins 1, 2, 4, and 5.

Enterprise networks

An enterprise network is a network that includes elements of both LANs and WANs. It is owned and operated by a single organization to interlink its devices and resources so that users have access whether they are on or off premise. Enterprise networks employ technologies and software designed for fast data access, email exchange, and collaboration. Enterprise networks are scalable and include high-end equipment, strong security systems, and mission-critical applications.

Intranets

An intranet is a private network that uses Internet protocols and services to share a company's information with its employees. As with the Internet, the employees can access an intranet via a web browser and navigate a company's web pages. However, an intranet is not very useful if it is not connected with the Internet. An intranet contains information that is segregated from the Internet for confidentiality and security reasons.

Transmission speeds

Data transmission speed is usually stated in terms of bit rate. However, there is another measure of speed known as baud rate. Though the two aren't the same, they are similar. • Bit rate: Bits are the zeros and ones that binary data consists of. The bit rate is a measure of the number of bits that are transmitted per unit of time. The bit rate is usually measured in bits per second. This means that, if a wireless network is transmitting 54 megabits bits every second, the bit rate is 54,000,000 bps or 54 Mbps, where bps stands for bits per second and Mbps stands for megabits per second. • Baud rate: Baud rate measures the number of symbols that are transmitted per unit of time. A symbol consists of a fixed number of bits depending on what the symbol is defined as. The baud rate is measured in symbols per second. If your data encoding uses something other than bits, the baud rate will be lower than the bit rate by the factor of bits per symbol. For example, if there are 3 bits per symbol, the baud rate will be one-third that of the bit rate.

The internet

The Internet is the single largest global WAN, linking virtually every country in the world. Publicly owned and operated, the Internet is widely used for sending email, transferring files, and carrying out online commercial transactions. All information on the Internet is stored as web pages, which can be accessed through software known as a web browser. Most of the processes related to the Internet are specified by the Internet Protocol (IP) , and all the nodes connected to the Internet are identified by a unique address, known as an IP address.

Mainframe computers

A mainframe computer is a powerful, centralized computer system that performs data storage and processing tasks on behalf of clients and other network devices. On a mainframe-based network, the mainframe computer does all computing tasks and returns the resultant data to the end user's device.

Network segments

A segment is a subdivision of a network that links a number of devices or serves as a connection between two nodes. A segment is bounded by physical internetworking devices such as switches and routers. All nodes attached to a segment have common access to that portion of the network.

Broadcast trasmission

Broadcast transmission is a transmission method in which data is sent from a source node to all other nodes on a network. Network services that rely on broadcast transmissions generate a great deal of traffic. Occasionally, nodes use broadcast transmissions to check for the availability of a particular service on the network. If the service is not available, the nodes broadcast a request for the service. If a server is present, it responds to the request. Some servers periodically advertise their presence to the network by sending a broadcast message.

Copper media

Copper media are a type of bounded media that use one or more copper conductors surrounded by an insulated coating. The conductors can be made from a solid wire or from braided strands of wire. Sometimes shielding , in the form of a braided wire or foil, is wrapped around one or more conductors to reduce signal interference from nearby sources of electromagnetic radiation. Two of the most prevalent types of copper media used in networks are twisted pair and coaxial cable.

The Open systems interconnection (OSI) model

The Open Systems Interconnection (OSI) model is a standard means of describing network communication by defining it as a series of layers, each with specific input and output. The model provides a theoretical representation of what happens to information being sent from one device to another on a network. The sending device works from the Application layer down, and the receiving device works on the transmitted data from the Physical layer up. The OSI model was developed by the International Standards Organization (ISO) and has seven layers that are numbered in order from the bottom (Layer 1) to the top (Layer 7).

Structured cabling

The Telecommunications Industry Association (TIA) and the Electronic Industries Association (EIA) developed the 568 Commercial Building Telecommunication Cabling standard. This standard defines the regulations on designing, building, and managing a cabling system that utilizes structured cabling according to specified performance characteristics to create a system of unified communications. Structured cabling is based on a hierarchical design that divides cabling into six subsystems. Subsystem Description Demarcation point (demarc) Contains the telecommunication service entrance to the building, campus- wide backbone connections, and the interconnection to the local exchange carrier's telecommunication facilities. The network demarcation point is usually a foot away from where the carrier's facilities enter the building, but the carrier can designate a different measurement, depending on the needs of the facility. Note: A secondary demarc can be installed to provide redundancy. Note: The telephone wires coming to your house are an example of a demarcation point. Everything outside your house is the telephone company and everything inside your house is your wiring. Backbone wiring Provides connections between equipment rooms and telecommunication closets. Backbone cabling runs through the floors of the building via risers or across a campus. The allowed distance measurements of this cabling depend on the type of cable and the facilities it connects. Equipment room Provides the main cross-connection point for an entire facility. Also provides a termination point for backbone wiring connected to telecommunication closets. Telecommunication closet Houses the connection equipment for cross-connection to an equipment room along with workstations in the surrounding area. It contains horizontal wiring connections, and entrance facility connections. In an office building with multiple floors, depending on the floor plan, there can be as many telecommunication closets as needed. Horizontal wiring Runs from each workstation outlet to the telecommunication closet. The maximum allowed distance from the outlet to the closet is 295 feet. If patch cables are used, an additional 20 feet is allowed both at the workstation and the telecommunication closet, but the combined length cannot be more than 33 feet. Horizontal cabling specifications include: • Four-pair 100 ohms UTP cables • Two-fiber 62.5/125 mm fiber optic cables • Multimode 50/125 mm multimode fiber optic cables Work area Consists of wallboxes and faceplates, connectors, and wiring used to connect work area equipment to the telecommunication closet. It is required that a data and voice outlet be available at each wallbox and faceplate. The TIA/EIA 568 standard also includes recommendations for how network media may best be installed to optimize network performance. • 568A: This obsolete standard defined the standards for commercial buildings and cabling systems that support data networks, voice, and video. It further defined cable performance and technical requirements. • 568B: This standard, some sections of which are now obsolete, defines the standards for preferred cable types and the minimum acceptable performance levels for: • 100 ohm twisted pair • STP • Optical fiber • 568C: The current release is the third in the 568 series. 568C defines the standards for commercial building cabling. It recognizes CAT6a as a media type. It also defines the minimum bend radius for twisted pair cables, both shielded and unshielded. In addition, it specifies the maximum untwist value for CAT6a cable termination.

Grounding

Electrical devices often must be connected to a ground point for safety. In these situations, the ground connection serves as a way to direct high voltages safely away from humans and other devices, sending them instead into the ground. Grounding is the connection of a shield or conductor to an electrical ground point, such as a pipe or wire that is in contact with the ground. Grounding at one point in a segment helps prevent noise on the data conductor by shunting noise signals to the ground. Connecting to the ground at multiple points can introduce noise onto the line, degrading network performance. You should ground networking and other sensitive electronic equipment to dedicated ground points rather than to pipes and conduits. Electricians refer to this sort of ground connection as an isolated ground and will use an orange socket for such circuits.

Hosts

A host is any device that is connected to a network. It can be a client or a server, or even a device such as a printer, router, or switch. Any device on the network can function as a host when other devices access its resources, such as a server computer having its resources accessed by another server. TCP/IP Hosts In the early days of computer networking, all computers were mainframe computers that controlled the activities of network terminal devices. The mainframes were joined together to communicate in the early research networks that laid the foundation for the Internet. As Transmission Control Protocol/Internet Protocol (TCP/IP) was adopted and became ubiquitous and personal computers joined the networks, the term "host" was generalized and is now used to refer to virtually any independent system on a TCP/IP network.

Media converters

A media converter enables networks running on different media to interconnect and exchange signals. Technically, a media converter is considered a transceiver because it transmits and receives signals. Media converters are often built into other devices such as high-end switches. To install a media converter, simply connect terminated ends of the two media you want to bridge to the converter. You may need to provide electrical power to the converter, but may not need any additional configuration. Many converters are available that allow you to convert from one media type to another. The following table describes some commonly used media converters. Converter Type Description Multimode fiber to Ethernet Used to extend an Ethernet network connection over a multimode fiber backbone. Fiber to coaxial Used to convert signals on fiber to a coaxial cable. Singlemode to multimode fiber Used to transmit multimode fiber signals over singlemode fiber devices and links. It supports conversion between multimode segments on a network that spans a wider coverage area. Singlemode fiber to Ethernet Used to extend an Ethernet network connection over a singlemode fiber backbone.

Network configurations

A network configuration is a design specification for how the nodes on a network are constructed to interact and communicate. A network configuration determines the degree to which communications and processing are centralized or distributed. There are three primary network configurations: • Centralized or hierarchical • Client/server • Peer-to-peer

Networking standards

A networking standard is a set of specifications, guidelines, or characteristics applied to network components to ensure interoperability and consistency between them. Standards determine all aspects of networking such as the size, shape, and types of connectors on network cables as well as the number of devices that can connect to the network. For example, the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard is used to standardize Ethernet network implementations by providing networking specifications and characteristics. Standards can be de facto, meaning that they have been widely adopted through use, or de jure, meaning that they are mandated by law or have been approved by a recognized body of experts. Note: To help recall which is which, you can think of words like jury and jurisdiction, which are words related to the legal system. These words, and the term de jure, come from the same Latin root.

Rack systems

A rack system is a standardized frame or enclosure for mounting electronic equipment and devices. They allow for dense hardware configurations without occupying excessive floorspace or requiring shelving. The 19-inch rack format is an industry standard. Each piece of equipment or device is fastened to the rack frame with screws. Equipment that is designed to be placed in a rack system is usually identified as a rack mount, rack-mounted system, rack-mount instrument, rack-mount chassis, subrack, or rack-mountable. All types of electronics and computing devices come in rack- mounted packages, including servers, switches, routers, telecommunications components, tape drives, and audio and video equipment. Rack systems can be two-post racks or four-post racks. Two-post racks are designed for lightweight equipment such as switches. Four-post racks are designed for heavier equipment such as servers. These racks are typically bolted to the floor for stability and security. Server rail racks use rails to mount the systems to the racks. Rack mount systems might include the rails, or you might need to purchase them separately. Some server rail racks are fixed mounts. Others are sliding rails, making it easier to access the rear of the device. Free-standing racks are usually heavier duty racks that don't need to be bolted to the floor for stability.

Electrical noise

Electrical noise , also known as interference in wireless networks, refers to unwanted signals that are present in the network media. Noise interferes with the proper reception of transmitted signals. Noise can come from natural sources, such as solar radiation or electrical storms, or from man- made sources, such as electromagnetic interference from nearby motors or transformers.

Data encapsulation

Encapsulation is the process of adding delivery information to the actual data transmitted on each layer. Encapsulation takes place in the transmission end as data is passed down the layers. At the receiving end, the reverse process of removing the added information is done as data passes to the next higher layer. This process is called de-encapsulation . The added information is called a header if it is before the data or a trailer if it is added after the data.

Shielding

Shielding is the method of placing the grounded conductive material around the media. This prevents the introduction of noise into the media by deflecting the noise to the ground. Because of this, the connection between the ground and the shield is called a drain . Shields are drained in only one location to prevent a ground loop, a phenomenon in which the shield introduces noise in the data signal. All other jacks and termination points must also be grounded. Common forms of shielding include the copper braid in coaxial cable, or foil wrapped around wire pairs in shielded twisted pair (STP).

Premise wiring

Premise wiring is the collection of cables, connectors, and other devices that connect LAN and phone equipment within a commercial building. In a structured cabling situation, the premise wiring will consist of vertical and horizontal cable runs that radiate out from a central location throughout the building to individual devices. Many components are used in premise wiring. Premise Wiring Component Description Drop cable The wire that runs to a PC, printer, or other device connected to a network. Patch panel A connection point for drop and patch cables. Typically, a patch panel has one or more rows of RJ-45 or other connectors. Drop cables are connected to the connectors. Cables run between the connectors to connect drop cables as needed. Patch cable A cable that is plugged into the patch panel to connect two drop cables. They are most often stranded and not solid core. Cross-connects Individual wires that connect two drop cables to a patch panel. Cross- connects are rarely used in modern networks because they are built into the network components. However, they are still frequently used in telephone wiring. • A main cross-connect (MCC) is the connecting point between entrance cables, equipment cables, and inter-building backbone cables. It is sometimes referred to as the first-level backbone. • An intermediate cross-connect (ICC) is an optional connection point between the MCC and the horizontal cross-connects. • Horizontal cross-connects (HCC) provide a point for the consolidation of all horizontal cabling, which extends to individual work areas, such as cubicles and offices. Fiber optic horizontal cabling is limited to 90 meters. Optional consolidation points or transition points are allowable in horizontal cables, although many industry experts discourage their use. • Vertical cabling or vertical cross-connects are generally recognized as cables that run vertically between floors in a building, or vertically between equipment in an equipment rack. They are not defined as part of the Structured Cabling standards. Distribution frames Distribution frames are devices that terminate cables and enable connections with other devices. Many installations will use a combination of a main distribution frame (MDF) and several intermediate distribution frames (IDFs) . • An MDF contains the devices used to manage the connections between external communication cables coming into the building and the cables of the internal network, via a series of IDFs. An MDF is usually a long steel rack that is accessible from both sides. Termination blocks are arranged horizontally on one side at the front of the rack shelves. The jumpers lie on the shelf and run through vertically arranged termination blocks. • An IDF is a free-standing or wall-mounted rack for managing and interconnecting end user devices, such as workstations and printers, and an MDF. For example, an IDF might be located on each floor of a multi-floor building, routing the cabling down the walls to an MDF on the first floor. The MDF would contain cabling that would connect to external communication cables. Wiring closet A wiring closet , network closet, or telecommunication closet is a small room in which patch panels are installed. Drop cables radiate out from the wiring closet to the components on the network. Straight-Through, Crossover, and Rollover Cables There are generally three main types of networking cables: straight-through, crossover, and rollover cables. Each cable type has a distinct use, and should not be used in place of another. In addition to the differing uses, each cable type has a distinct wiring configuration within the cable itself. • Straight-through cables are used to connect unlike devices, such as computers to hubs or switches. All wire pairs are in the same order at each end of the cable. A straight-through cable is also commonly known as a patch cable. • Crossover cables are used to connect like devices, such as device to device, switch to switch, or router to router. In a crossover cable, the transmit conductor at one end is connected to the receive conductor at the other, allowing both devices to communicate simultaneously. • A rollover cable is used to connect a device to a router's console port. In a rollover cable, one end of the cable is wired exactly the opposite of the other end of the cable, going from one to eight on end A and from eight to one on end B. They do not support data transfer; instead, they provide an interface for programmers to connect to and adjust the router's configuration. Rollover cables are usually flat instead of round, and their outer jacket is often a unique color such as yellow or light blue. Some rollover cables have Ethernet connectors on both ends and will need a DB-9 (RS-232) or RJ-45 adapter to connect to a serial port. They are also referred to as Cisco console cables or Yost cables. The RJ-45 cable that is commonly used for network connectivity is also referred to as straight- through cable. In a regular Ethernet UTP patch cable, four wires are used. Pins 1 and 2 transmit and pins 3 and 6 receive. All lines are straight-wired. (Pin 1 is wired to pin 1, pin 2 to pin 2, and so forth.) In a crossover cable, pins 1 and 2 connect to pins 3 and 6, and pins 3 and 6 connect to pins 1 and 2.

Network components

There are several common components that make up a network, each of which performs a specific task. Network Component Description Devices Hardware such as computers, tablets, cell phones, servers, printers, fax machines, switches, and routers. Physical media Media that connects devices to a network and transmits data between the devices. Network adapters Hardware that translates data between the network and a device. Network operating systems Software that controls network traffic and access to common network resources.

Unicast transmission

Unicast transmission is a method for data transfer from a source address to a destination address. Network nodes not involved in the transfer ignore the transmission. Unicast transmission is the predominant mode of transmission on LANs and the Internet. Unicast communications are also commonly referenced as point-to-point communications. Some familiar unicast applications are Hypertext Transfer Protocol (HTTP) , Simple Mail Transfer Protocol (SMTP) , and File Transfer Protocol (FTP) .

Centralized networks

A centralized network is a network in which a central mainframe computer controls all network communication and performs data processing and storage on behalf of clients. Users connect to the mainframe via dedicated terminals or terminal emulators. Centralized networks provide high performance and centralized management, but they are expensive to implement. Note: The term "hierarchical network" can also be used to describe centralized networks. A pure centralized network is rare in today's environment. Most of the network types you encounter will be decentralized to some extent, with the client/server architecture having some degree of centralization and the peer-to-peer architecture being almost purely decentralized. In a decentralized network, each peer can connect directly with other peers without being managed by a central server. A server provides services to the nodes upon a request from them. A peer-to-peer network is an example of a decentralized network.

Client/server networks

A client/server network is a network in which servers provide resources to clients. Typically, there is at least one server providing central authentication services. Servers also provide access to shared files, printers, hardware storage, and applications. In client/server networks, processing power, management services, and administrative functions can be concentrated where needed, while clients can still perform many basic end-user tasks on their own.

Carrier sense multiple access/ collission avoidance (CSMA/CA)

Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) is a contention-based media access method that is primarily used in IEEE 802.11-based wireless LANs. In CSMA/CA, nodes can transmit whenever they have data to send. However, they take steps before they transmit data to ensure that the media is not in use. There are six steps in the CSMA/CA process. Step Description Step 1: Data to transmit A node has data to transmit. Step 2: Check network The node determines if the media is available by polling. Step 3: RTS signal Optionally, the node may send a Request-To-Send (RTS) signal to the access point. Step 4: Wait The node waits until all nodes have had time to receive the jam signal. Step 5: Transmit The node transmits data. Step 6: Monitor for RTS signal During transmission, the node monitors the media for an RTS signal from any other node that may already be transmitting data. If an RTS signal is received, it stops transmitting and retries after a random delay. Note: The 802.11 standard is a family of specifications developed by the IEEE for wireless LAN technology.

Types of media access

Depending upon the traffic on the network media, a node can transmit data on a network. The media access method determines whether or not a particular node can transmit data on the network at a given time. Media access methods fall into two categories: contention-based and controlled. With contention-based or competitive media access, the nodes themselves negotiate for media access time. Depending upon the traffic on the network media, a node can transmit data on a network. The media access method determines whether or not a particular node can transmit data on the network at a given time. Media access methods fall into two categories: contention-based and controlled. With contention-based or competitive media access, the nodes themselves negotiate for media access time. Deterministic access methods are beneficial when network access is time critical. For example, in an industrial setting, key control and safety equipment, such as flow-shutoff sensors in chemical storage facilities, must have a guaranteed transmission time. Deterministic systems ensure that a single node cannot saturate the media; all nodes get a chance to transmit data. However, they require additional hardware and administration to configure and maintain. Contention-based systems are simpler to set up and administer, but timely media access is not guaranteed for any node.

Digital data transmission

Digital data transmissions use voltage differences to represent the ones and zeros in data. Unlike analog signal transmission, they are not modulated over a carrier. On-off keying or Manchester encoding converts data into a digital waveform. Each bit takes a predefined time to transmit, and the sender and receiver synchronize their clocks either by transmitting a bit pattern or by monitoring for the reception of the first bit.

Coaxial cable types

Many varieties of coax cables are available, not all of which are used in networking. The wires used in networking can be solid core or stranded core. A solid core wire is made of a single metal or a single strand. A stranded core wire consists of multiple strands or solid cores. Cable Type Characteristics RG59 A 6 mm (0.25 inch) coax cable with 75 ohms impedance. RG59 is used for low-power video connections such as digital receivers. RG6 A coax cable with 75 ohms impedance. RG6 is preferred over RG59. This type of cable is often used in routing cable television signals. RG58/U and RG58A/U A 5 mm (0.25 inch) coax cable with a stranded core and 50 ohms impedance. RG58/U and RG58A/U are used for Ethernet networking. RG8 A 10 mm (0.5 inch) coax cable with a solid core and 50 ohms impedance. RG8 is used for Ethernet networking. RG9 A 10 mm (0.5 inch) coax cable with a stranded core and 51 ohms impedance. RG9 is used for cable television transmission and cable modems. Note: The RG specification codes come from their page numbers in the Radio Guide manual, the original military specification (Mil-Spec) for coax cables, which is no longer in use. For example, the RG8 specification appeared on page 8.

Punch down blocks

A punch down block can be used to connect one group of telephone and network wires with another group in utility or telecommunication closets. They typically support low-bandwidth Ethernet and token ring networks. There are two primary types of punch down blocks. Type Description 66 block Used in the telephone industry for decades to terminate telecommunications. Supports low-bandwidth telecommunications transmission. 110 block Punch down block or cable termination block used for structured wiring systems. Using the 110 block system, multipair station cables are terminated, allowing cross- connection to other punch down locations. Supports a higher bandwidth than 66 block and is suitable for use in data applications. Note: 110 block (T568A, T568B) supports both T568A and T568B wiring schemes.

Power management

Power management is an important consideration when installing devices in a wiring closet. You need to ensure that there are sufficient power outlets available and that they can accommodate the number of devices that will require power. In addition, those devices need to be protected from power quality problems that can damage equipment and from power outages. Uninterruptible power supply (UPS) systems provide three functions that affect the availability of network equipment. • They serve as a source of backup power in the event of an outage. • They provide power conditioning by removing sags, noise, and other power quality problems. • They provide real-time monitoring and controlled shutdown of protected equipment. In addition to the benefits and efficiencies provided by UPSs, other power management features need to be considered in maintaining a healthy network environment. Power Management Feature Description Power converters In networking, you are most likely to encounter power converters as transformers for devices. You might also see them in voltage regulators and the mains power supply. Circuits Be sure there are enough circuits to supply power to all of your devices without overloading any one circuit. Circuit breakers will shut the circuit down if it is overloaded. Inverters An inverter or power inverter is a device that converts DC current to AC current. For networking you need an inverter that supplies a stable DC power source so that there are few, close to no, power fluctuations as these could harm the networking equipment. Power redundancy Power redundancy is built into many servers in the form of duplicate power supplies. For any device that you rely on to conduct business, you should consider whether power redundancy is available and affordable. Which is more expensive: redundant power or down time?

Parallel data transmission

With parallel data transmission, the transmission of multiple bits takes place by using multiple transmission lines. Many bits—even multiple bytes—can be transferred per clock cycle. The transmission of synchronization, start/stop, and error correction bits does not occur along with data bits. They are often sent over additional transmission lines, thus improving the overall throughput of data. Parallel transmission is commonly used on the parallel port on a computer, to which you can connect printers or scanners. Other uses include the system bus inside a PC and the Small Computer System Interface (SCSI) data bus.

Data packets

A data packet is a unit of data transfer between devices that communicate over a network. In general, all packets contain three parts: a header, data, and a trailer. The header part contains the destination and source addresses. The trailer part contains an error checking code. The data part contains the actual information or data that is to be transmitted. The contents of a packet depend on the network protocol in use. The terms frame, packet, segment, and datagram are sometimes used interchangeably when referring to data being transmitted over a network. Terms such as these are generally referred to as protocol data units (PDUs) . The actual correlation between OSI layers and the appropriate type of PDU is described in the following table. OSI Layer PDU Type Layer 1 (Physical) Packet Layer 2 (Data Link) Frame Layer 3 (Network) Packet Layer 4 (Transport) Segment or datagram Layer 5 (Session) Message Layer 6 (Presentation) Message Layer 7 (Application) Message

Digital signals

A digital signal , unlike an analog signal that can have many possible values, can have combinations of only two values: one and zero. These values represent the presence and the absence of a signal, respectively. Digital data, which is a sequence of ones and zeros, can be translated into a digital waveform. In computer systems and other digital devices, a waveform can switch between two voltage levels: zero at the ground or a zero voltage state, and one at a positive or negative voltage level.

Networks

A network is a group of devices that are connected together to communicate and share network resources such as files and peripheral devices. No two networks are alike in size or in configuration. Each network, however, includes common components that provide the resources and communications channels necessary for the network to operate

Analog signals

A signal is data transmitted as electromagnetic pulses across a network medium. An analog signal carries information as continuous waves of electromagnetic or optical energy. In networking, electrical current commonly generates analog signals, the intensity of which is measured in volts. An analog signal oscillates between maximum and minimum values over time and can take any value between those limits. The size, shape, and other characteristics of the waveform describe the analog signal and the information it carries. The characteristics of an analog signal can be described or categorized using some specific terms. Term Description Amplitude The distance of the crest or trough of a wave from the midpoint of the waveform to its top or bottom. The amplitude is one half of the overall distance from the peak to the trough of the wave. Cycle One complete oscillation of an analog signal. Frequency The number of complete cycles per second in a wave. It is measured in hertz , which is one cycle per second. Frequency is also called the period of the wave. Phase Is where a wave's cycle begins in relation to a fixed point. Thus, two waves of the same frequency that begin at the same time are said to be in phase . Two waves that either start at an offset from each other or have different frequencies are out of phase. Wavelength The distance between two successive crests or troughs in a waveform.

Network topologies

A topology is a network specification that determines the network's overall layout, signaling, and data- flow patterns. Networks are defined by a combination of their logical and physical topologies. Topologies define the way different nodes are placed and interconnected with each other. They may also describe how the data is transferred between these nodes.

Twisted pair cables

A twisted pair cable is a type of cable in which one or more pairs of copper wires are twisted around each other and clad in a color-coded, protective insulating plastic sheath or jacket to form a pair. All pairs are encased in a plastic sheath or jacket. The number of pairs within a cable will vary depending on the type of twisted pair cable. Twisted pair cables typically use shielding around pairs of wires.

Coaxial cables

A coaxial cable, or coax , is a type of copper cable that features a central conducting copper core surrounded by an insulator and braided or foil shielding. The dialectric insulator separates the conductor and shield and the entire package is wrapped in an insulating layer called a sheath or jacket. The data signal is transmitted over the central conductor. A coaxial cable is so named because the conductor and shield share the same axis, or center. They share a common axis or are "co-axial." This arrangement helps prevent electromagnetic interference from reaching the conductor

Twisted pair cable categories

A twisted pair cable comes in different grades, called categories, which support different network speeds and technologies. Category Network Type Maximum Speed Description Distance 1 Voice transmission 1 Mbps CAT1 is not suitable for networking. Not specified 2 Digital telephone and low-speed networks 4 Mbps CAT2 is not commonly used on networks. 100 m 3 Ethernet 10 Mbps CAT3 is currently used for telephone wiring. 100 m 4 IBM token ring 16 Mbps CAT4 can also be used for 10 Mbps Ethernet. 100 m 5 Fast Ethernet 100 Mbps CAT5 supports a signaling rate of 100 MHz. 100 m 5e Gigabit Ethernet 1 Gbps CAT5e supports a signaling rate of 100 MHz. 100 m 6 Gigabit Ethernet 10 Gigabit Ethernet 1 Gbps 10 Gbps CAT6 supports a signaling rate of 250 MHz. 100 m 55 m 6a 10 Gigabit Ethernet 10 Gbps CAT6a supports a signaling rate of 500 MHz. 100 m 7 10 Gigabit Ethernet 10 Gbps CAT7 supports a signaling rate of 600 MHz. 100 m Note: A twisted pair cable's category is typically printed on the cable itself, making identification easier.

Other copper cable types

Although twisted pair, coax, and fiber optic cables are the most prevalent types of cable media used in network installations, you might also encounter several other types of cables. • A serial cable is a type of bounded network media that transfers information between two devices by using serial transmission. Information is sent one bit at a time in a specific sequence. A serial cable most often uses an RS-232 (also referred to as DB-9) connector, but can also use a DB-25 connector. In networking, serial cables are often used to connect routers. • While not as common as other bounded network media, IEEE 1394 , commonly known as FireWire ® , can be used to connect up to 63 devices to form a small local network. FireWire cables use a shielded cable similar to STP with either four or six conductors. Connections to devices are made with either a six- or four-pin connector. • A USB connection is a personal computer connection that enables you to connect multiple peripherals to a single port with high performance and minimal device configuration. USB connections support two-way communications. The USB 3.1 standard increases the signaling rate to 10 Gbit/s, double that of USB 3.0. It is backward compatible with USB 3.0 and USB 2.0. • The IEEE 1901-2013 standard, also known as broadband over power lines (BPL) , is a technology that allows broadband transmission over domestic power lines. This technology aims to use the existing power infrastructure to deliver Internet access to remote areas at a rapid pace. BPL is yet to gain widespread acceptance because of the potential signal interference with other data signals such as wireless transmission and radio waves. The interference of BPL signals with radio waves affects radio operations, which are the main source of communication during times of natural disaster. In addition, there are concerns about the security of data when it is transmitted as plaintext using BPL, because it is easy to detect and intercept data when the signal travels using a common power source. Accepting and implementing BPL will require enhanced encryption and other security measures. Note: Interference and encryption are covered in detail in subsequent lessons. • The IEEE 1905-2013, more accurately, the IEEE 1905.1-2013 standard, provides a common interface for home networking technologies. The Standard for a Convergent Digital Home Network for Heterogeneous Technologies is designed to reduce network complexity for consumers and helps operators manage various networks throughout homes. There are various wired connections that can be used, but the most common under this standard are Ethernet over HDMI and Ethernet over power line. A device with built-in HDMI 1.4 capabilities allows audio, video, and data communication over an HDMI 1.4 cable. Devices that comply with the nVoy hybrid home networking standard can use Ethernet over power line.

Anycast transmission

Anycast transmission is a transmission method in which data is sent from a server to the nearest node within a group. That node then initiates a second anycast and transmits the data to the next nearest node within the group. The process is repeated until all nodes within the group have received the data. Network nodes not in the group ignore the data. Anycast is used for updating routing tables in IP version 6 (IPv6) because IPv6 does not use broadcast transmissions. In addition, anycast addresses are often used with IPv6 DNS servers. You can have multiple IPv6 DNS servers scattered around the network using the same anycast address. When a client sends a DNS query to that address, the client's router would route the query to the nearest DNS server. Note: IPv6 is covered in greater depth later in the course.

Carrier Sense Multiple Access/Collision Detection (CSMA/CD)

Carrier Sense Multiple Access/Collision Detection (CSMA/CD) is a contention-based media access method used in Ethernet LANs, where nodes contend for use of the physical medium. Nodes can transmit whenever they have data to send. However, they must take steps to detect and manage the inevitable collisions that occur when multiple nodes transmit simultaneously. The busier a network becomes, the greater the probability of collisions, and the lower the CSMA/CD efficiency. There are six steps in the CSMA/CD process. Step Description Step 1: Data to transmit A node has data to transmit. Step 2: Check network The node determines if the media is available by monitoring for existing transmissions by other nodes (carrier sense). Step 3: Transmit The node transmits data if no other node is transmitting. When the media is available, the node transmits, starting with a 7-byte repeating pattern of 1s and 0s. This is called the preamble. Step 4: Collision If two nodes transmit at the same time, a collision has occurred. The collision is most likely to occur during the preamble. The transmitting node that detects the collision will continue to send the preamble, along with a 32-bit jam signal. This is a special pattern that warns other nodes to not transmit. In addition, the jam signal will cause the frame to fail its expected CRC check, so that other nodes discard the frame and wait for a retransmission. Step 5: Wait The two nodes that collided wait for a random backoff period (in milliseconds). Step 6: Retransmit After waiting for a suitable backoff interval, the two nodes will retransmit again. Because the backoff interval will not be the same for both nodes, one of the nodes will retransmit first, and the other node will retransmit after. Note: CSMA/CD is the access method for Ethernet formalized in the 802.3 standard, a specification issued by IEEE to standardize Ethernet and expand it to include a wide range of cable media.

Guidelines for installing bounded network media

Note: All of the Guidelines for this lesson are available as checklists from the Checklist tile on the CHOICE Home screen. Consider these best practices and guidelines when you are installing bounded network media: • Create a list of requirements for your network so that you can work toward meeting them. These requirements may include how many users will need to connect, the physical area it will need to cover, external connections, etc. • Consider the factors can affect the performance of network media, such as electromagnetic interference, attenuation, and impedance. • Consider the environment's limitations, such as the amount of ventilation for the network closet, access to power, or space to run cables that can affect your network. • Employ converters that enable different media to interconnect and exchange signals. • Follow the 568 Commercial Building Telecommunication Cabling standard when dealing with structured cabling. • Make proper use of premise wiring components. • Use plenum cables in designated plenum spaces of a building to comply with fire codes, and use PVC in nonplenum spaces. • Employ good cable management techniques to properly support cables and to keep them organized. • Ensure that your wiring closet has adequate power for networking equipment, and that you protect the equipment from power quality problems that can damage equipment and from power outages. • Use rack systems to maximize the use of space for equipment in a wiring closet. • Consider the limitations of the equipment and how they might affect your network. • Consider the compatibility requirements of all of your equipment to ensure that it will all work together the way you need it to.

Polling

Polling is a controlled media access method in which a central device contacts each node to check whether it has data to transmit. Each node is guaranteed access to the media, but network time can be wasted if polling nodes have no data to transmit. The polling process is repeated by giving each node access to the media until the media reaches the node that needs to transmit data. Demand priority is a polling technique in which nodes signal their state—either ready to transmit or idle—to an intelligent (or managed) hub. The hub polls the state of each node and grants permission to transmit. Additionally, a node can signal that its data is high priority. The hub will favor high- priority transmission requests. Safeguards in the protocol prevent nodes from assigning every transmission request as high priority. This is done by ensuring that each node has an equal opportunity to transmit, and a node is not allowed a second normal transmission unless all nodes have completed their first normal transmission. Note: The IEEE has not standardized polling in general. However, the IEEE 802.12 standard defines 100VG-AnyLAN, which uses a specific polling technique called demand priority to control media access.

The network backbone

The network backbone is a very-high-speed transmission path that carries the majority of network data. It connects either small networks into a larger structure or server nodes to a network where the majority of client devices are attached. Network backbones can take many different forms, such as a bus, cloud, or mesh. The technology in use on a backbone network can be different from that used on client network sections. Since the backbone cabling connects switches and routers on a network, it can carry more traffic than other types of cabling on the network. In a local area network (LAN), a typical network backbone is one or more core level switches, or several switches connected together by trunk links. In a wide area network (WAN), a typical backbone is an asynchronous transfer mode (ATM) or frame relay cloud.

Network coverage areas

There are other network categories based on the geographical areas they cover. Network Category Description MAN A metropolitan area network (MAN) covers an area equivalent to a city or a municipality. CAN A campus area network (CAN) covers an area equivalent to an academic campus or business park. A CAN is typically owned or used exclusively by an entity. PAN A personal area network (PAN) connects two to three devices with cables and is most often seen in small or home offices. A wireless personal area network (WPAN) is a variation of a PAN that connects wireless devices in close proximity but not through a Wireless Access Point (WAP) or access point (AP). Infrared and Bluetooth are technologies used for connecting devices in a WPAN.

The IEEE 802.11 standard

The 802.11 standard is a family of specifications developed by the Institute of Electrical and Electronics Engineers (IEEE) for the wireless LAN technology. 802.11 specifies an over-the-air interface between a wireless client and a base station or between two wireless clients. 802.11 defines the access method as Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). It specifies spread spectrum radio devices in the 2.4 GHz band for reliability. The 802.11b standard also defines a multichannel roaming mode and automatic data rate selection. The 802.11ac standard provides faster wireless connections, better range, improved reliability, and improved power consumption than previous wireless standards. 802.11ac routers can also have up to eight antennas. Latency is the time taken by a data packet sent through a wireless connection from a requesting device to the receiving device and back. Latency includes the time taken for checking the data packets, correcting errors, and resending data lost in transit. Some of the wireless technologies based on the 802.11 specifications are more prone to latency and interference than Gigabit Ethernet. Multiple input, multiple output (MIMO) uses multiplexing to increase wireless network range and bandwidth. MIMO uses algorithms to send and receive data using multiple antennas, using multiple antenna pathways to send additional data. It can also recombine signals it receives to increase capacity and provide more reliable connections. Multi-user MIMO (MUMIMO) allows multiple independent radio antennas to access a system. Using MUMIMO, multiple users can access the same channel. It uses spatial degrees of freedom to allow multiple user access to receive data from the access point to the wireless devices. The 802.11 standards provide specifications for different wireless technologies. Standard Transmission Speed (Mbps) Frequency (GHz) Geographic Range (meters) MIMO Streams 802.11a 54 5 20 1 802.11ac 433 per channel 5 35 8 802.11b 11 2.4 100 1 802.11g 54 2.4 100 1 802.11n 150 2.4 or 5 70 4 Note: The 802.11a standard is not cross-compatible with 802.11b and g. There are also the 802.11a-ht and 802.11g-ht standards. These are the same as the base standard but they have high throughput (ht), making the transmission speed the same as 802.11n.

Mulitplexing

The modulation technique multiplexing is a controlled media access method in which a central device combines signals from multiple nodes and transmits the combined signal across a medium. To carry multiple signals, the medium or channel is separated logically into multiple, smaller channels. Signals can be multiplexed using Time-Division Multiplexing (TDM) or Frequency-Division Multiplexing (FDM) . Both multiplexing techniques rely on a central device, called a multiplexer, or mux , to manage multiplexing from the sending end. At the receiving end, a demultiplexer, or demux, separates the signals. De-multiplexing is done on the receiving end of a multiplexing transmission. The data is gathered, examined, and passed to the Application layer of the OSI model. In TDM, a communication channel is divided into discrete time slots. Each node on a network is assigned a time slot, and each sender is given exclusive access to the medium for a specific period of time. Nodes have exclusive access to the connection between themselves and a mux for that period of time. The mux combines each node's signal, and in turn, sends the resulting combined signal over the primary network medium. Using TDM, multiple baseband signals can be combined and sent over a single medium. In FDM, data from multiple nodes is sent over multiple frequencies, or channels, using a network medium. Nodes have exclusive access to the connection between themselves and a mux. The mux includes each node's signal onto its own channel, sending the resulting combined signal over the primary network medium. Using FDM, multiple broadband signals can be combined and sent over a single medium. There are three commonly used connection modes for multiplexing. Connection Mode Description Simplex The simplex mode of communication is the one-way transmission of information. There is no return path. Because the transmission operates in only one direction, simplex mode can use the full bandwidth of the medium for transmission. Radio and television broadcasts are simplex mode transmissions. Half duplex The half duplex mode of communication permits two-way communications, but in only one direction at a time. When one device sends, the other must receive; then they can switch roles to transfer information in the other direction. Half duplex mode can use the full bandwidth of the medium because the transmission takes place in only one direction at a time. Full duplex The full duplex mode of communication permits simultaneous two-way communications. A device can both send and receive data simultaneously. Sending and receiving can occur over different channels or on the same channel. Generally, neither the sender nor the receiver can use the full bandwidth for their individual transmission because transmissions are allowed in both directions simultaneously. Full duplex mode also may be called a bidirectional transmission. If someone speaks about "duplex" transmissions, they likely are referring to full duplex mode. Telephone systems are full duplex devices—all persons involved can talk simultaneously. Many modern networking cards support full duplex mode

Numbering systems

Various numbering systems are used in networking. Typically, in day-to-day use, decimal numbering, or base 10, is used. Most are familiar with the place values of ones, tens, hundreds, thousands, and so on. Place values can also be expressed as 10 0 , 10 1 , 10 2 , and so on. Values in each place value can be between 0 and 9. If you get to 9 in a place value, the next number starts with 1 in the next place value and zero in the current place value. Binary is used whenever an on/off state is needed and when IP addresses are being calculated. Binary is also referred to as base 2 numbering. There are only two numbers used: 0 and 1. The place values are expressed as 2 0 , 2 1 , 2 2 , 2 3 , and so on. If you get to 1 in a place value, the next number starts with 1 in the next place value and zero in the current place value. Hexadecimal numbers are base 16 numbers. The values in each place can be between 0 and F; numbers above 9 are expressed with letters A through F. As with the other numbering systems, place values are used with the first place value being 16 0 , followed by 16 1 , 16 2 , and so on. You are most likely to encounter these types of numbers in MAC addresses. Octal numbers are base 8 numbers and use the numbers 0 to 7. These are more often used by programmers and are not typically used when viewing networking addresses or routes.

Clients

A client is a computer or process running on a device that initiates a connection to a server. The client contacts the server attempting to make the connection. The server may or may not accept the connection. The client device has its own processor, memory, and storage, and can maintain its own resources and perform its own tasks and processing. Any type of device on a network can function as a client of another device, when needed. The term "client" most often refers to workstation or desktop computers employed by end users. Any device on the network can function as a client when it uses other computers' resources, such as a Windows Server computer accessing resources on another server. There are also thin clients , which are devices that depend on a server to fulfill their computational needs to some degree. They can range from a terminal that has no computing abilities to a normal client device that relies on a server to perform its main functions. Client Operating Systems There are many different types of operating systems for client devices, including: • Microsoft ® Windows ® : Microsoft Windows features an enhanced graphical user interface (GUI), support for a wide range of applications and devices, a minimum of 32-bit processing, native networking support, and a large suite of built-in applications and accessories such as the Internet Explorer ® browser. Windows is often factory-installed on new personal computers that are designed for retail sale. • Apple ® OS X ® : OS X is a GUI-based operating system developed by Apple Inc. for their Macintosh ® line of computer systems. It features an enhanced GUI, enhanced support and compatibility with iOS devices, native networking support, and a large suite of built-in applications and accessories such as the Safari ® browser. OS X is factory-installed on new Macintosh computers that are designed for retail sale. • Linux operating systems: Linux OS is a freely distributable open-source, cross-platform operating system based on UNIX ® that can be installed on different hardware devices such as PCs, laptops, mobile and tablet devices, video game consoles, servers, etc. No single official Linux desktop exists; rather, desktop environments and Linux distributions select components from a pool of free and open-source software with which they construct a GUI implementing some more or less strict design guide. • Android operating systems: Android ™ is a mobile OS based on the Linux kernel and is developed by Google. The Android OS is designed primarily for touchscreen mobile devices such as smartphones and tablet computers. • iOS operating systems: iOS is a mobile OS developed by Apple Inc. and distributed exclusively for Apple ® hardware such as their iDevices. The user interface is based on the concept of direct manipulation using multi-touch gestures

Fiber optic cables

A fiber optic cable is a network cable that has a core surrounded by one or more glass or plastic strands. In addition, it contains extra fiber strands or wraps, which are surrounded by a protective outer jacket. The core is the thin glass center through which light travels transmitting data. The core is between 5 and 100 microns thick with cladding made from optical materials such as silica. Figure 2-6: Layers in a fiber optic cable. The cladding reflects light back to the core in patterns determined by the transmission mode. A buffer, often made of plastic, surrounds the cladding and core. To add strength to the cable, strands of synthetic fiber surround the buffer. An outer jacket, sometimes called an armor, wraps and protects the whole assembly. Light pulses from a laser or high intensity LED are passed through the core to carry the signal. The cladding reflects the light back into the core, increasing the distance the signal can travel without a need for regeneration.

Local area network (LAN)

A local area network (LAN) is a self-contained network that spans a small area, such as a single building, floor, or room. In a LAN, all nodes and segments are directly connected with cables or short-range wireless technologies. It does not require a leased telecommunication system to function. Due to their smaller size and fewer number of nodes, LANs provide faster data transfers than other network types. Different technologies can be implemented on a LAN depending on the configuration needs and functionality of the network. Ethernet is the most commonly implemented LAN technology. Other LAN technologies such as token ring, token bus, and Fiber Distributed Data Interface (FDDI) can also be used on LANs. A LAN can be extended or replaced by a Wireless LAN (WLAN) , which is a self-contained network of two or more devices connected using a wireless connection. A WLAN spans a small area, such as a small building, floor, or room. LAN Administration LAN administration encompasses tasks for managing and maintaining the local network. LAN administration includes the following duties: • Maintaining devices and cabling. • Maintaining network software. • Performing the installation and deployment, upgrades, and troubleshooting for different applications. • Maintaining a broad range of skills and knowledge about network applications and hardware.

Mixed mode networks

A mixed mode network incorporates elements from more than one of the three standard network configurations. Some mixed mode networks consist of a client/server network combined with a centralized mainframe. An end user's device functions as a client to the network directory server and employs terminal emulation software to authenticate to the mainframe system. A common example of a mixed mode network is a workgroup created to share local resources within a client/server network. For example, you might share one client's local printer with just a few other users. The client sharing the printer on the network does not use the client/server network's directory structure to authenticate and authorize access to the printer.

Nodes

A node is any device or computer that can connect to a network and generate, process, or transfer data. Every node has addressing information to enable other devices to communicate with it. Network nodes can either be endpoints or redistribution points. Endpoints are nodes that function as a source or destination for data transfer. Redistribution points are nodes that transfer data, such as a network switch or a router. Note: This is a common definition of a node. Some people may refer to a node as a workstation, client, host, etc. Computers and devices that are connected via network media require a method for communicating with other computers and devices on the network. For communication to occur, there must be a set of rules or protocols . Network communication protocols establish the rules and formats that must be followed for effective communication between networks, as well as from one network node to another.

Peer devices

A peer is a self-sufficient computer that acts as both a server and a client to other computers on a network. Peer computing is most often used in smaller networks with no dedicated central server, but both clients and servers in other types of networks can share resources with peer devices

Peer-to-peer networks

A peer-to-peer network is a network in which resource sharing, processing, and communications control are completely decentralized. All clients on the network are equal in terms of providing and using resources, and each individual device authenticates its users. Peer-to-peer networks are easy and inexpensive to implement. However, they are only practical in very small organizations due to the lack of centralized data storage and administration. A peer-to-peer network is more commonly referred to as a workgroup . In a peer-to-peer network, user accounts must be duplicated on every device from which a user accesses resources. Such distribution of user information makes maintaining a peer-to-peer network difficult, especially as the network grows.

Plenum and PVC Cables

A plenum cable is a network cable that is jacketed tightly around conductors so that fire cannot travel within the cable. The jacket of the plenum cable does not emanate poisonous gases when it burns. Fire codes require that you install this special grade cabling in the plenum , an air handling space, including ducts and other parts of the heating, ventilating, and air conditioning (HVAC) system in a building, between the structural and suspended ceilings, and under raised floors, as well as in firebreak walls. Unlike non-plenum cables, plenum cables can run through the plenum and firebreak walls. Polyvinyl chloride (PVC) -jacketed cabling is inexpensive and flexible. The PVC cable is also referred to as the non-plenum cable. However, when PVC burns, it gives off noxious or poisonous gases. Additionally, PVC jacketing is not formed tightly to the conductors it contains. Tests show that fire can travel within a PVC cable, passing through firebreaks. Note: For additional information, check out the LearnTO Implement Best Practices for Cabling in the LearnTOs for this course on your CHOICE Course screen.

Wide area network (WAN)

A wide area network (WAN) is a network that spans a large area, often across multiple geographical locations. WANs typically connect multiple LANs and other networks using long-range transmission media. Such a network scheme facilitates communication among users and devices in different locations. WANs can be private, such as those built and maintained by large, multinational corporations, or they can be public, such as the Internet. When a WAN includes sites and networks around the world, it is considered a global area network (GAN) . WAN Administration WAN administration typically includes more complex technical issues than LAN administration, and focuses on resolving network issues rather than user issues. WAN administration includes the following duties: • Designing and maintaining the connection scheme between remote segments of a network. • Developing and troubleshooting routing structures. • Working with both voice and data systems. • Developing scripts to automate complex network administrative tasks. • Working on security issues and helping to implement recovery schemes. • Planning, testing, and implementing hardware and software upgrades.

Servers

A server can be a computer or a process running on a device that listens for incoming connection requests from clients. It will accept or reject those incoming connection attempts based on whether or not it provides the service the client is requesting. It can also reject or accept a connection attempt based on security settings configured by the administrator. Microsoft Windows Server Microsoft's network operating system is called Microsoft ® Windows Server ® . The networking features of Windows Server include, but are not limited to: • The Active Directory service (ADS). • Integrated network services such as the Domain Name System (DNS) and the Dynamic Host Configuration Protocol (DHCP) . • Advanced services such as clustering, public key infrastructure (PKI), routing, and web services. • User and group security on the file and object levels. • Advanced security features such as a built-in firewall, file encryption, and Internet Protocol Security (IPSec). Linux Servers There are several open-source network operating systems based on the Linux ® operating system. Two of the more popular distributions are Red Hat ® Enterprise Linux ® (RHEL) and SUSE LINUX Enterprise Server ® (SLES). Common features of Linux servers include, but are not limited to: • Lightweight Directory Access Protocol (LDAP)-compliant directory services. • Network services such as DNS and DHCP. • Advanced services such as clustering, PKI, routing, and web services. • User and group security on the file and object levels. • Advanced security features such as a built-in firewall, file and disk encryption, and IPSece

Twisted pair cable types

A twisted pair cable can be of two types: unshielded twisted pair (UTP) or shielded twisted pair (STP) . • UTP: • Does not include shielding around its conductors. • Typically contains four pairs of stranded or solid conductors. • Is inexpensive and reliable. • STP: • Includes foil wrapper shielding around its conductors to improve the cable's resistance to interference and noise. • Typically contains four pairs of stranded or solid conductors. • Is more expensive than UTP. Note: Twisted pair cables are available in 2-pair, 4-pair, 6-pair, 25-pair, 100-pair, and larger bundles. Note: A variation of STP, known as screen twisted pair (ScTP) or foil twisted pair (FTP), uses only the overall shield and provides more protection than UTP, but not as much as STP. Wire colors are standardized. The industry standard for twisted pair is one solid color and the same color with white. The first four standard color pairs are listed in the following table. Primary Wire Secondary Wire White/blue Blue White/orange Orange White/green Green White/brown Brown

Sources of electrical noise

A variety of sources contribute to electrical noise. Noise Source Description Ambient noise Ambient noise can come from many sources, including solar disturbances that affect the Earth's magnetosphere, or nearby radio broadcasting towers. These forms of noise affect both bounded and unbounded media, with longer network segments being affected more than shorter ones. Power wires High-tension power lines or a building's own electrical wiring can create electrical noise. Network cables that run parallel to electric wires are more susceptible to electrical noise than those that run perpendicular. Metal-based network transmission media Network wiring, particularly unshielded twisted pair, will also generate its own electrical noise. Any time a current flows through a metal conductor, a magnetic field is generated around that conductor. If the magnetic field is close enough to cut across neighboring wires, it will induce a voltage in those wires, thus creating an unwanted signal. This is known as crosstalk. Electric motors Electric motors, such as those used in elevators, refrigerators, water fountains, and HVAC equipment, create noise while running, but this is more when they start up. Motors require a huge amount of electricity to start up, causing a burst of noise. These bursts can create temporary outages that resolve themselves when the motor reaches full speed or stops. Electrical heat- generating devices Like electric motors, electric heating elements use a lot of electricity and cause a significant amount of electrical noise while running. Fluorescent, neon, and HID lights Fluorescent, neon, and high-intensity discharge (HID) lighting devices produce a large amount of electrical noise, generally due to the transformers and ballasts required to make these lights work. Interior overhead lights, building security lights, and decorative lighting can create enough noise during operation to interfere with networking signals traveling over either bounded or unbounded media. Other Effects of Noise In addition to the noise that affects data networking media, noise can affect the electricity that powers computing devices. Surges or dips can result in the electric current, which can damage equipment, and cause application or operating system software crashes, or even system restarts. Electric motors, heating elements, solar disturbances, or natural disasters can cause transient power problems. Most devices include power conditioning components that handle at least some of these power fluctuations. However, sensitive equipment should be protected through the use of specialized power conditioning devices, such as an uninterruptible power supply (UPS) or a surge protector

Broadband transmission

Broadband transmission uses a single medium to carry multiple channels of data, usually through modulation. Multiple carrier signals, usually at different frequencies, act as different channels, each carrying their own data on the same transmission line. An example of this is broadband Internet access via cable modem. The cable provider assigns each customer two premium TV channels for their Internet data: one for transmit and one for receive. All of the cable TV channels, including those used for data, travel on different carrier frequencies on the same coaxial cable. DOCSIS, the Data Over Cable Service Interface Specification, is the standard used by cable companies to provide high-speed data communication using the existing cable TV system. DOCSIS 3.1 was released in 2013 with specifications to support at least 10 Gigabits per second downstream and 1 Gigabit per second upstream.

Coaxial connector types

Connectors are metal devices that are located at the end of a wire. Coaxial connectors are used to connect video equipment and network nodes in a LAN. Signals flow from the wire to network devices through connectors. All connectors are metal plated and some of the metals used are gold, silver, rhodium, nickel, or tin. Coax network segments must be terminated to prevent signal reflections off the ends of the cable. Cables are terminated by installing a resistor of an appropriate rating, typically 50 ohms, at either end of the cable. Two broad categories of connectors are typically used in coax cables: F and BNC connectors. Connector Type Characteristics F A coax connector type used with a 75-ohm cable to connect cable TV and FM antenna cables. It comes in a secure screw-on form or as a non- threaded slip-on connector. BNC A cable connector used to terminate a coaxial cable. It is usually used with the RG58/U cable. A Bayonet-Neill-Concelman (BNC) connector has a center pin connected to the center cable conductor and a metal tube connected to the shield of the cable. A rotating ring outside the metal tube locks the cable to the connector. The types of BNC connectors include: • T-connectors • Barrel connectors You can also connect two BNC cables together by using a BNC coupler .

Cable management

If not managed properly, cables can become tangled, making them difficult to work with. Cable management is the means of neatly securing electrical, data, and other cables. Cable management is focused on supporting the cables as they are routed through the building from point A to B, and to make any future management of the cables after installation easier. Cable trays , cable ladders , and cable baskets can be used to support a cable through cabling routes. Buildings and office furniture are often designed with cable management in mind. Buildings may have dropped ceilings and raised floors to provide easy access and desks may have holes for cables to pass through. Patch panels are used to connect circuits to the network. Messy patch panels can make finding the correct cable difficult when you need to add, remove, or replace a cable. Remove unused cables from the patch panel not only to make it neater, but also to prevent unauthorized network access. Consider purchasing patch panels with locking covers to prevent unauthorized access to add or remove cables. Make cables the right length: too short cables can pull on connectors and too long cables can make cable management difficult. Labeling cables is another important aspect of cable management. Labels should help you accelerate tracing a cable to see where it runs to. This can be achieved by numbering the cables and labeling each end of the cable with the same number. Labeling can also be used to identify the properties of the cable, such as the length, type, and so on. Labeling of equipment, ports, and cables is so important, that TIA created a standard for labeling items. TIA-606B specifies standards for labeling and record keeping. All changes should be managed through Move/Add/Change (MAC) documents. Labels need to be printed (not handwritten) and securely attached to the port, cable, system, circuit, or patch panel. The standard specifies how port labeling, system labeling, circuit labeling, and patch panel labeling should be structured. Cables should be labeled within 12 inches of each end of the cable. Patch panel ports should be labeled above the port. Circuits should be individually labeled with the FS-AN. The identifier on the label should confirm to the FS-AN naming convention: FS-AN character(s) Description F The floor number and telecommunications space. S A letter that identifies the telecommunications space within the "F" area. A One or two characters (letters or numbers) corresponding to a patch panel that makes up the horizontal cross-connect. N Two to four numbers corresponding to the patch panel port where the cable connects to the patch panel.

Network media

Network media, the conduit through which signals flow, can be either bounded or unbounded. Bounded media use a physical conductor. This conductor can be a metal wire through which electricity flows, or a glass or plastic strand through which pulses of light flow. Unbounded media do not need a physical connection between devices, and can transmit electromagnetic signals through air using radio waves , microwaves , or infrared radiation .

Noise reduction considerations

The installation techniques you follow can affect the amount of noise introduced into a network cable. There are several considerations that you can use to limit the impact of noise on your network. Consideration Description Separate data and electric cables Do not run data and electricity cables in the same trays, raceways, and conduits. Avoid running network cables parallel to each other when you can, because crosstalk is worst when cables run in parallel. Make sure to comply with any building codes. Fluorescent lights Keep network cables at least 20 inches from fluorescent lights as they can cause electromagnetic interference. If you must run data cables across or near these lights, do so in such a way that exposes the smallest length of cable to the light. Power ground Ground all equipment and electrical circuits according to the manufacturer's instructions and local building codes. Connector installation Follow standards, specifications, and manufacturer's directions when installing network cables. Do not unwind conductor pairs any more than required or allowed. Make sure connectors are firmly attached and connected to the appropriate jacks. Use of other media Consider using fiber optic cabling in environments where the noise is unmanageable. As a general rule, consult local building codes any time you are working with power and ground issues.

Noise control with twisted pair

The twists in the twisted pair cable determine how resistant the cable will be to noise, and in particular, to crosstalk. When data wires lie next to each other, they generate crosstalk in each other. This effect accumulates over distance. Twists effectively move adjacent wires away from each other on a regular interval, providing less opportunity for crosstalk to occur. The more twists, the more the crosstalk is disrupted. Note: The tightness of the twists in twisted pair is called the "twist ratio." The primary difference between twisted pair cable categories is the number of twists per inch. However, to fully support the network speeds for which they are rated, you must take care when adding connectors to these cables. You should not unwind the pairs too much or you will eliminate the noise-canceling benefits of the twists. The more twists per foot and the more consistently the twists are arranged, the more resistant to noise a cable will be. As a rule, you should not unwind to more than 3/8 of an inch (about 10 mm) for a Category 5 cable. A Category 3 cable is more tolerant to unwinding of twists. A Category 6 cable requires special connectors that maintain the twists inside the connector. Note: Twisted pair is effective in office environments in which the amount of electromagnetic interference (EMI) and radio frequency interference (RFI) are relatively low. In high-noise environments such as machine shops and hospital radiology departments, consider using fiber optic cabling, which is immune to EMI/RFI.

Types of network backbones

There are several types of network backbones that you may encounter. Network Backbone Type Description Serial Consists of multiple switches connected by one backbone cable. Typically not scaled for enterprise-wide use. Distributed/ hierarchical Consists of multiple switches connected serially to hubs or routers. Due to their hierarchical structure, these networks can be easily expanded without a significant cost impact. Serves well as one-site enterprise-wide networks; their switch layers can be configured by geography (such as a floor in a building) or function (such as a workgroup). Distributed backbone networks enable an administrator to segregate workgroups, simplifying their management. Collapsed Uses a router or switch as the nexus for several subnetworks. The router or switch must have multiprocessors to bear the frequently high level of network traffic. Router or switch failures in a collapsed backbone can bring down the entire network. Depending on the routers' processing capabilities, data transmission can also be slow. Parallel Suits enterprise-wide applications. Like the collapsed backbone network, the parallel backbone network uses a central router or switch but augments the dependent switches with multiple cable connections. These multiple links ensure connectivity to the whole enterprise.

Fiber optic cable modes

There are two modes of fiber optic cables available: multimode and singlemode . Both modes have an outer diameter of 125 microns; that is, 125 millionths of a meter or 5 thousandths of an inch, which is just larger than a single human hair. • Multimode fiber allows light to travel through its core in multiple rays or modes. Its core of 50 or 62.5 microns works with LED sources for slower networks and with laser for faster networks. Multimode fiber is used mostly for short distances (up to 500 m). • At only 9 microns, the core of a singlemode fiber is much smaller in diameter than multimode fiber. Within a singlemode fiber, light travels unidirectionally. Singlemode fiber is used with laser to process telephony and cable TV transmissions. Singlemode fiber has a higher transmission rate and up to 50 times more potential distance than multimode fiber. Singlemode and multimode fibers have different characteristics. Fiber Optic Cable Mode Description Singlemode fiber Carries an optical signal through a small core, which allows only a single beam of light to pass. A laser, usually operating in the infrared portion of the spectrum, is modulated in intensity to transmit the signal through the fiber. It provides a bandwidth of up to 30 MHz. Multimode fiber There are two subtypes of multimode fiber: • Step-index multimode fiber contains a core surrounded by cladding, each with its own uniform index of refraction . When light from the core enters the cladding, a "step down" occurs due to the difference in the refractive indices. Step-index fiber uses total internal reflection to trap light. • Graded-index multimode fiber possesses variations in the core glass to compensate for differences in the mode path length. Provides up to 2 GHz of bandwidth, which is significantly more than step-index fiber. Refraction Refraction occurs when a light ray, passing from one transparent medium to another, bends due to a change in velocity. The change in velocity occurs due to the differences in the density of the two media. The angle of incidence is the same as in reflection. The angle between the normal and the light ray as light enters the second medium is called the angle of refraction. Color Coding The color code standard for fiber optic cable is TIA-598C, and it recommends the following colors and labeling be used on fiber optic cables. Type of Fiber Optic Cable Application and Color Suggested Labeling Multimode (50/125) • Military application: Orange • Nonmilitary application: Orange 50/125 Multimode (50/125), 850 nm laser-optimized • Military application: Not defined • Nonmilitary application: Aqua 850 LO 50/125 Multimode (62.5/125) • Military application: Slate • Nonmilitary application: Orange 62.5/125 Multimode (100/140) • Military application: Green • Nonmilitary application: Orange 100/140 Singlemode • Military application: Yellow • Nonmilitary application: Yellow SM/NZDS or SM Polarization maintaining singlemode • Military application: Not defined • Nonmilitary application: Blue Not defined

Cable properties comparison

Twisted pair, coaxial, and fiber optic cables have different properties with regard to transmission speed, distance, duplex, noise immunity, and frequency. Cable Type Properties Twisted pair Transmission Speed: • CAT3: UTP at 10 Mbps. CAT3 cable might still be found in legacy installations that use 10 Mbps hubs or switches. • CAT5: Up to 100 Mbps. CAT5 cable is most commonly found in office installations connecting computers to network drops in wall or floor jacks. It is rapidly being replaced by CAT5e. • CAT5e: Up to 1 Gbps. Category 5e cable is the current de facto standard for Ethernet cabling, and will be found in most new office and home installations. It is less expensive and easier to work with than CAT6, but it has less resistance to EMI and RFI. • CAT6: Up to 1 Gbps. CAT6 cable may be found where higher immunity to EMI/RFI noise is desired than what CAT5e can provide. • CAT6a: Up to 10 Gbps. CAT6a is primarily found in network backbones and data centers. Distance: 100 meters per network segment Duplex: Supports full-duplex transmission Noise Immunity (security, EMI): up to 30 MHz Frequency: Up to 600 MHz Coaxial Transmission Speed: 10 Mbps Distance: 500 meters per network segment Duplex: Supports both half-duplex and full-duplex transmission Noise Immunity (security, EMI): High Frequency: 1 GHz to 10 GHz Fiber optic Transmission Speed: 40,000 Mbps Distance: Multimode fiber is typically used for shorter runs of up to 500 meters, and singlemode for longer runs. The ultra high quality of some fiber cables allows runs of 62 miles or more between repeaters, which are rarely used now. Duplex: Supports full-duplex transmission as it consists of two fibers that can be used for simultaneous, bidirectional data transfer. Noise Immunity (security, EMI): High Frequency: Normally the frequency is very high and its range depends on the bandwidth and the device that you use.

Serial data transmission

With serial data transmission, the transmission of bits occurs as one per clock cycle across a single transmission medium. The transmission of synchronization, start/stop, and error correction bits occurs along with data bits, thus limiting the overall throughput of data. Serial data transmission does not use direct current (DC) pulses for transmission. Serial transmission can delineate bytes by using either synchronous or asynchronous techniques. Many common networking systems, such as Ethernet, use serial data transmission. Keyboards, mice, modems, and other devices can connect to your PC over a serial transmission port. Note: A clock cycle refers to a signal that synchronizes different parts of a circuit by oscillating between low and high states. Synchronous and Asynchronous Communications The receiver of an analog signal must have a way of delineating between bytes in a stream of data. This can be done using either asynchronous or synchronous techniques. • With asynchronous communications, a sender inserts special start and stop bit patterns between each byte of data. By watching for these bit patterns, the receiver can distinguish between the bytes in the data stream. • With synchronous communications, a byte is sent after a standardized time interval. The receiver assumes that one byte is transmitted every interval. However, the two devices must start and stop their reckoning of these intervals at precisely the same time. Synchronous devices include a clock chip. A special bit pattern is inserted at specific intervals in the data stream, enabling the receiving device to synchronize its clock with the sender. After synchronizing the clocks, a receiver can use the predetermined time interval as a means to distinguish between bytes in the data stream. In asynchronous communications, the two sides negotiate a sustainable speed. In synchronous communications, one side sets the clock rate and the other side slaves to that rate.

Fiber connector ferrule polish

With fiber connectors, there will be some loss in the lightwave transmission. This is caused by the light being reflected directly back down the fiber and disrupting the transmitted signal. To reduce these back reflections, the connector ferrules can be polished to different finishes. Fiber Connector Ferrule Polish Description Physical Contact (PC) In the PC connector, the end faces are polished to be slightly curved or spherical. This eliminates any air gap and forces the fibers into contact. The back reflection is only about -40 dB. This connector is used in most applications. Ultra Physical Contact (UPC) The UPC connector is an improvement to the PC connector. The end faces are given an extended polishing for a better surface finish, which reduces the back reflection to about -55 dB. These connectors are often used in digital, cable television (CATV), and telephony systems. Angled Physical Contact (APC) In the APC connector, the end faces are still curved but are angled at an industry-standard 8 degrees. This maintains a tight connection and reduces back reflection to about -70 dB. These connectors are preferred for CATV and analog systems.

Specialized network types

You might also encounter some specialized networks, such as Industrial Control Systems (ICSs) and medianets. Industrial Control Systems (ICSs) are networks and systems used to support municipal services and industrial processes such as power generation and distribution, water treatment and distribution, wastewater collection and treatment, oil and natural gas collection and production, chemical synthesis and other production processes, as well as in transportation systems. The two main types of ICSs are Supervisory Control and Data Acquisition (SCADA) systems and Distributed Control Systems (DCSs). • Supervisory Control and Data Acquisition (SCADA) systems are used in situations where sites are at great geographical distances from one another, and where centralized data collection and management is critical to the industrial operation. Examples of industries where SCADA systems are common include systems like water distribution systems, wastewater collection systems, oil or natural gas pipelines, electrical power grids, and railway transportation systems. A SCADA control center monitors and manages remote sites by collecting and processing data and then sending supervisory commands to the remote station's control devices. Remote control devices, or field devices, are responsible for controlling operations like opening and closing valves, collecting data from sensor systems, and monitoring the environment for alarm conditions. • Distributed Control Systems (DCSs) are used in process-based industries such as electric power generation; oil refining; water treatment; wastewater treatment; and chemical, food, and automotive production. In most instances, each main process is broken down into a series of sub-processes, each of which is assigned an acceptable tolerance level. Programmable Logic Controllers (PLCs) provide control over these sub-processes by using control loops, and the DCS manages the PLCs. DCSs are used primarily in industries where the parts of the manufacturing system are in close geographic proximity, and where feedback and feed-forward loops are used to create a closed-loop or closed network system. The ICS server contains the DCS or PLC control software that communicates with subordinate control devices on an ICS network. A remote terminal unit (RTU) connects physical objects to an ICS or SCADA system. The connection established via a microprocessor-controlled device transmits telemetry data to the master system. Data and messages from the master system or server are used to control the objects that are connected. Note: Do not confuse ICSs with Microsoft's Internet Connection Sharing, which is a way for Microsoft devices to share an Internet connection with other computers. A medianet is a network optimized for rich media, such as voice and video, and is designed to transport a mixture of rich media and other content, such as text. The coordination of multiple types of video, audio, and written documents into a single experience is a critical aspect of a medianet. A medianet does not replace existing network architectures, and is an evolutionary extension in the multimedia space of these existing network architectures. One of the uses for a medianet is to support video teleconferencing (VTC), which is also referred to as video conferencing.