Chapters 3 and 4

SSID broadcasts

SSID broadcasts are a continuous announcement by a wireless access point that transmits its name, or SSID, so that it is discoverable by wireless devices searching for a network connection. An SSID broadcast is sometimes referred to as a beacon. When a WAP is secured with a password, devices might see the SSID but be unable to connect to it.

Physical vs. Logical Topologies

A physical topology describes a network's physical wiring layout or shape, whereas a logical topology describes the paths through which data moves. The physical and logical topologies can be different for a network. Common physical topologies include a bus, ring, star, and mesh.

Broadcast radio

Broadcast radio is a form of RF networking that is non-directional, uses a single frequency for transmission, and comes in low- and high-power versions. Low-power RF transmissions travel a short distance, often no more than 70 meters, but are inexpensive and relatively easy to install. High- power RF transmissions travel longer distances; however, specially trained technicians are often required to install this more expensive type of system.

Spread spectrum

Spread spectrum is a form of radio transmission in which the signal is sent over more than one frequency. Because signals are transmitted over different frequencies, it is more difficult to eavesdrop and capture the signals. Additionally, distinguishing between the signal and background noise is more difficult.

Wireless bridges

A wireless bridge can be used to connect two wired networks by using a wireless connection. A wireless bridge receives the signal from a wireless router and sends it out to other wired devices. The wireless bridge needs to be within range of the wireless router's signal and also within cable length of the other wired devices

Wireless controllers

Wireless controllers provide wireless LAN management for multiple access points. The network administrator uses a wireless controller in combination with the Lightweight Access Point Protocol (LWAPP) to manage lightweight access points. The wireless controller automatically handles the configuration of wireless access points. A wireless controller can be a physical device or a software application. LWAPP is a protocol that controls multiple Wi-Fi wireless access points. This can reduce the amount of time spent on configuring, monitoring, or troubleshooting a large network.

Spanning tree protocol (STP) IEEE 802.1d

The Spanning Tree Protocol (STP) is a Layer 2 protocol used to prevent switching loops. Whenever there are redundant paths between switches, where either two switches are connected using two different links or a ring of switches is connected to each other, a switching loop will occur. Because switches, by their nature, flood broadcasts and multicasts out all ports, the first Address Resolution Protocol (ARP) frame sent by a client trying to find a neighbor or a router will cause a Layer 2 broadcast storm. The ARP broadcast will go down one link to the next switch, which will send the broadcast back up the redundant link. This feedback loop will continue indefinitely until there is manual intervention by an administrator. It will cause network utilization to go to near maximum capacity, and the CPU utilization of the switches to jump to 80 percent. This makes the switched segment effectively unusable until the broadcast storm stops. STP prevents switching loops and broadcast storms because switches use it to determine if there are any redundant links that may cause a loop. During the STP process, all switches in the same broadcast domain elect among them a root bridge (switch), which acts as a reference point for all of the other switches. A switch will then listen for special frames coming from the root to determine if those frames are coming into different ports. If the frames are coming into different ports, then there is a redundant link. The switch will then temporarily block its redundant link, thus eliminating the possibility of a loop. Should the first link fail for some reason, the switch will then unblock the redundant link so that there is connectivity on the network. STP is an old protocol. Its full process to determine redundancy actually takes 50 seconds, which is considered too long by modern standards. It has since been replaced by the Rapid Spanning Tree Protocol (RSTP), IEEE 802.1w, which takes only 20 seconds to identify and rectify loops. There is also Shortest Path Bridging (SPB), which is another replacement for STP. It is intended to simplify the creation and configuration of networks, while enabling multipath routing. Switches on which the STP is enabled can be in one of five port states. The switches use Bridge Protocol Data Units (BPDUs) to exchange data between bridges and calculate route costs. State What Happens in This State Blocking User data is not sent or received. BPDU data is received, but the port only goes into another state if other links are unavailable and the spanning tree algorithm determines that the port should change to the forwarding state. Listening BPDUs are processed by the switch. It does not forward frames. It waits for information to determine if it should return to the blocked state. It does not update the MAC tables. Learning Learns source addresses from received frames. Addresses are added to the switching database. MAC address table is updated. No frames are forwarded. Forwarding Data is sent and received on a port in this state. BPDUs are monitored to determine if the port should return to the blocked state. Disabled A port that has been manually disabled.

Microwave transmission

Microwave transmission is a form of point-to-point wireless transmission in which signals are sent via pulses of electromagnetic energy in the microwave region of the electromagnetic spectrum. It transmits signals at a frequency range of 1 GHz to 300 GHz. Receivers need an unobstructed view of the sender to successfully receive the signal, and depending on the frequency in use, transmission can be affected by environmental conditions such as fog, birds, and so on. Signals can be reflected off satellites to increase the transmission distance. Microwave transmission technologies are often used in WANs and MANs. Mobile carriers often use point-to-point microwave connections as part of their backhaul network. A backhaul is the connection between the provider's core network and its smaller distribution-level (regional) subnetworks. Microwave is also used by wireless Internet service providers (WISPs) to provide broadband Internet access to customers in areas where wired connections are not practical. Examples include rural areas, or developing nations that lack the infrastructure for copper or fiber connections. Microwave transmissions are used in the great plains areas to connect locations that are miles away. Transmitting towers or satellites are used to beam two-way microwave signals to the customer's dish antenna.

10 gigabit ethernet

10 Gigabit Ethernet is currently the highest speed at which Ethernet operates. It can achieve speeds of 10 Gbps, which is 10 times faster than Gigabit Ethernet. There are several standards and specifications for 10 Gbps or 10 Gigabit Ethernet, the most common of which are described in the following table. Standard IEEE Specification Medium and Characteristics Speed (in Gbps) Distance (m) 10GBase-X 802.3ae Multimode fiber Wavelength: 850 nm 9.9 65 10GBase-SR 802.3ae Multimode fiber Wavelength: 850 nm 10.3 300 10GBase-SW 802.3ae Multimode fiber Wavelength: 850 nm 9.9 300 Standard IEEE Specification Medium and Characteristics Speed (in Gbps) Distance (m) 10GBase-LR 802.3ae Single mode fiber Wavelength: 1,310 nm Dark fiber 10.3 10,000 10GBase-LW 802.3ae Single mode fiber Wavelength: 1,310 nm Synchronous Optical Network (SONET) 9.9 10,000 10GBase-ER 802.3ae Single mode fiber Wavelength: 1,550 nm Dark fiber 10.3 40,000 10GBase-EW 802.3a Single mode fiber Wavelength: 1,550 nm SONET 9.9 40,000 10GBase-T 802.3an CAT5e, 6, or 7 UTP 10 100 10GBase-CX4 802.3ak Four thin twin-axial cables 4 × 2.5 25 Note: SONET is described in detail later in the course. Note: A nanometer (nm) is one trillionth of a meter (10 -9 )

Firewalls

A firewall is a software program or a hardware device or a combination of both that protects a device or network from unauthorized data by blocking unsolicited traffic. Firewalls generally are configured to block suspicious or unsolicited incoming traffic, but allow incoming traffic sent as a response to requests from internal hosts.

Switches

A switch is a network device that acts as a common connecting point for various nodes or segments. Working at Layer 2 of the OSI model, switches make forwarding decisions based on Layer 2 (MAC) addresses. A switch listens for the MAC addresses of all the nodes plugged into it, and builds a table in memory that maps each MAC address with its associated port. When an Ethernet frame comes into the switch, the switch reads the destination MAC address from the header and consults its table to determine which port to repeat the frame out of. In this way, switches can keep conversations limited to only the nodes that are involved. Thus, a 24-port switch can have 12 pairs of conversations going on at the same time. In order to perform switch management, you will need to supply the appropriate user name and password. This can be configured through the AAA configuration services. This sets up the authentication (identify user through login and password), authorization (access control), and accounting (logging information and forwarding it to a AAA server for auditing and reporting). Configuration of the switch can be performed using a management console or a virtual terminal. Multiple administrators can be connected and configure the switch management features. In-band management requires that software be loaded and in-band connectivity between the managed system and the device. It is less expensive to implement than out-of-band management, but is not as robust as it does not allow you to access the firmware or deal with boot problems. Out- of-band management uses a dedicated channel or port to manage the device. Out-of-band management enables you to access firmware and diagnose and correct boot issues. You can assign the switch IP address through the switch setup program, or DHCP. Switches can be configured with the IP address of the next-hop router interface that is directly connected to the switch where a default gateway is being configured. The default gateway receives IP packets with unresolved destination IP addresses from the switch. Unmanaged vs. Managed Switches Unmanaged switches are devices that perform switching without user intervention. In other words, the functions of an unmanaged switch cannot be controlled. On the other hand, a managed switch provides complete control over how the device functions. It is typically assigned its own IP address and can be managed either directly through the use of a console cable, a Telnet or as a Secure Shell (SSH) connection, or a web browser. Managed switches allow administrators to create virtual local area networks (VLANs) within the network.

Logical ring topology

A logical ring topology is a network topology in which each node receives data only from its upstream neighbor and retransmits data only to its downstream neighbor, regardless of the physical layout of the network. In a LAN, the logical ring topology has generally been implemented as a physical star (physical star-logical ring). In the days of token ring, a central hub (multistation access unit or MSAU) would connect the devices in a star shape, but the wiring was such that the electrical path was actually a never-ending loop, passing from the hub to a node, back to the hub, to another node, back to the hub, and so forth. In today's networks, a logical ring is typically not implemented in LANs.

Transceiver

A transceiver is a device that has both a transmitter and a receiver integrated into it and, as a result, can both send and receive data. Most modern transceivers are built into the network card. In networking, the transceiver supports the NIC in allowing data transmission through the medium. A gigabit interface converter (GBIC) is a transceiver used to convert electrical signals into optical signals and vice versa. It is used as an interface for high-speed networking and to upgrade the network, without needing to replace all components in the motherboards. For instance, if different optical technologies are used, GBICs can be used to specifically configure that link on the network. Based on the wavelength of laser light generated within the GBIC generator, GBICs can be categorized into short-wave GBICs and long-wave GBICs. The short-wave GBIC is used for connecting devices that are between 0.5 meters and 500 meters apart. Meanwhile, the long-wave GBIC is used for connecting devices that are between 2 meters and 6 miles apart. A small form factor pluggable (SFP) transceiver is most commonly used in 2 Gbps and 4 Gbps Fibre Channel components to interconvert electrical signals and optical signals. SFPs are similar to GBICs in their architecture, but they allow higher port density than GBICs. A MAC transceiver, also known as an Ethernet transceiver or AUI-to-Ethernet transceiver, is a passive device that connects a 15-pin AUI Ethernet connector to an RJ-45 Ethernet connector. It was used as an adapter to connect twisted pair to the old attachment unit interface (AUI) Ethernet ports. This transceiver helped extend the life of the popular Cisco 2500 series router that had only an AUI Ethernet port

Ethernet frames

An Ethernet frame is a data packet that has been encoded at the Data Link layer (Layer 2) for transmission from one node to another on an Ethernet network. The basic Ethernet frame contains seven fields. Preamble (PRE) (7 bytes) A pattern of ones and zeros used to signal the start of the frame and provide synchronization and timing information. The preamble notifies all nodes that there is data to follow. Start-of-Frame Delimiter (SFD) (1 byte) The SFD identifies the beginning of the data field. Destination Address (DA) (6 bytes) This is the MAC address of the computer to which the frame is being transmitted; it can be a unicast, multicast, or broadcast address. Source Address (SA) (6 bytes) This is the MAC address of the computer transmitting data—the SA is always a unicast address. Frame type (2 bytes) This is the length of the entire Ethernet frame in bytes, or the frame type ID of the frame. This field can hold a value between 0 and 65,534, but the maximum value is usually less than 1,500. Data (n bytes) The payload of the frame (or the information being sent). It must be a minimum of 46 bytes long and can be a maximum of 1,500 bytes. If the length of data is less than 46 bytes, the data field must be extended by adding a filler to increase the length to a minimum of 46 bytes. Frame Check Sequence (FCS) (4 bytes) The FCS checks the frame by using a 32-bit cyclic redundancy check (CRC) value. The FCS allows the receiving device to detect errors in the Ethernet frame and reject it if it appears damaged.

IEEE 802.1q

Because trunk links carry all VLAN traffic, there must be some mechanism for identifying which frame belongs to which VLAN as it moves from switch to switch. IEEE 802.1q is the most commonly used trunk link protocol to address this issue. 802.1q inserts a special tag in the Ethernet header identifying the VLAN for that frame. The switch at the other end of the trunk link will read that tag and forward the frame to the appropriate VLAN. A competitor to 802.1q is Cisco's inter-switch link (ISL). This protocol encapsulates an Ethernet frame into a proprietary format that identifies the VLAN. ISL is an older protocol. Most Cisco switches now use 802.1q.

Fast ethernet

Fast Ethernet is an Ethernet technology that can transmit data at speeds of 100 Mbps. It can use either coaxial cables or optical fibers. It is used as a backbone network to interconnect several LANs. There are several standards and specifications for 100 Mbps or Fast Ethernet, the most common of which are described in the following table. Standard IEEE Specification Medium Distance (m) 100Base-T 802.3u CAT5 UTP 100 100Base-T4 802.3u CAT3, 4, or 5 UTP 100 100Base-TX 802.3u CAT5 UTP or STP 100 100Base-FX 802.3u Multimode or single mode fiber 412 (half duplex), 2,000 (full duplex), 15,000-20,000 (full duplex)

Mobile devices

More and more mobile devices, such as cell phones, tablets, and laptops, are connecting to wireless networks. Connecting these devices is similar to connecting a desktop computer that has a wireless network interface card (NIC). Mobile phone Mobile phones range from simple mobile phones to smartphones. Connecting a mobile phone requires locating where in the interface to select the wireless network and input the security key. Laptop Laptops are connected in the same manner as desktop computers. Tablet Tablets are computing devices that contain a touchscreen display for input. Connecting a tablet requires locating where in the interface to select the wireless network and input the security key. Gaming device Gaming devices come in many different forms and are primarily used for playing games. Depending on the environment, these may not be appropriate to connect to the network. Connecting a gaming device requires locating where in the interface to select the wireless network and input the security key. Media device Media devices allow access to a particular form of media such as music, movies, and more. Examples of media players are MP3 players and Internet TV devices. Connecting a media device requires locating where in the interface to select the wireless network and input the security key.

Guidelines for implementing a basic wireless network

Note: All of the Guidelines for this lesson are available as checklists from the Checklist tile on the CHOICE Home screen. By considering several key factors of wireless network installation along with the cost of implementing and maintaining a secure wireless network, a network professional both demonstrates the proper installation methods and ensures maximum network functionality. Implement a Wireless Network To implement a basic wireless network, follow these guidelines: •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, and more. • Consider the devices you will need and any requirements they have. • Consider the environmental limitations such as the amount of ventilation for a network closet or access to power that can affect your network. • 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. • Choose the appropriate 802.11 technology for your needs, such as 802.11a, ac, b, g, or n. • Choose the appropriate AP placement locations for your network. • Obtain a scale drawing of the building. This will assist you in all areas of AP placement. • Determine the range of the AP for the wireless technology you have chosen. This will help you to better determine how many APs you will need to ensure adequate coverage for the space. • Balance the number of users who will have access to the AP, and ensure that the AP can cover all employees in the range of the AP. More employees in a given area means more APs. •Tour the area in the range of the AP and check to see if there are any devices that will interfere with the wireless network. This can include devices such as microwave ovens, Bluetooth-enabled devices, or an existing wireless network—whether from a community network, a neighboring building, or another floor of your company's building. These devices or networks can possibly interfere with your new implementation. • Consider whether the AP will be exposed or concealed in the ceiling or placed in a secure room. • Ensure that there are no obstacles in the path of the AP, such as doors, closed windows, walls, and furniture, that the wireless signal will need to pass through on its way to a client. If there are too many obstacles in the path, adjust the placement of your AP accordingly. • Consider bringing in a consultant to help with the site survey, especially if you do not have access to someone who has good knowledge of wireless networks. The survey may include a heat map. • Install the APs. The specific steps for installing the AP will vary by vendor, but the common steps may include: • Connecting the AP to a router. • Configuring the DHCP service as appropriate. • Configuring the appropriate encryption schemes. • Configuring channels and frequencies. • Setting the SSID/ESSID and an 802.11 beacon. • If necessary, creating an access control list (ACL). The ACL contains a list of users who have access to the wireless network. • Configuring the network adapters of the devices that will connect to the AP. • Test to ensure that the installation is appropriately sized, secure, and operational. Make sure these tests are done under real world conditions so that you have an accurate test. • Document the steps and establish a baseline for future installations. Wireless Access Point Placement While deciding on placement of WAPs, you need to consider several important factors. •Building layout: The building layout is a very important factor when deciding on the positions at which to place WAPs. A scaled building layout of the coverage area will help in deciding on the areas where you require wireless access. Use the layout to identify locations of possible interference and obstacles. Also, the layout helps in locating strategic spots where you can place the WAPs. •Coverage area: The area covered by an access point is called a cell. If the cell area is large, then you need to consider increasing the number of WAPs. Overlapping cells with multiple access points provide continuous access for devices. •Clients: The number of clients accessing the WAP plays a major role in deciding on the placement of the WAP. Depending on the number of clients, you need to decide on the number of WAPs to install. •Obstacles: Obstacles in the path of transmission of RF waves sometimes absorb the signals when they pass through, whereas others might reflect the signals, resulting in signal loss. Avoiding obstacles such as doors, walls, and windows between access points and devices can considerably reduce signal loss. •Interference: Radio frequency interference from other devices such as mobile phones and microwave ovens can affect signals from WAPs. Removing other devices that can cause radio frequency interference will significantly reduce signal interference.

Port mirroring

Port mirroring is the practice of duplicating all traffic on one port in a switch to a second port, effectively sending a copy of all the data to the node connected to the second port. This is known as local port mirroring. Remote port mirroring implements port mirroring between multiple devices. In this case, the source port is on one device and the destination port is located on a different device. Port mirroring is useful as a diagnostic tool when you need to monitor all traffic going to a particular port or node with minimal impact on the network performance.

VLAN trunking protocol (VTP)

The VLAN Trunking Protocol (VTP) is the messaging protocol that switches use to update each other's VLAN databases. Developed by Cisco, it allows switches to quickly advertise to each other when a VLAN is created or deleted. This saves an administrator some manual labor. If the administrator wishes to extend a VLAN across several switches, he or she would have to manually configure each switch with the same VLANs. With VTP, this is done automatically. There are three VTP modes that a switch can use: server, client, and transparent. • Server mode: This is the default mode for VTP on a switch. In the server mode, a switch can modify VLANs. This information is then transmitted to all the other switches that are configured to the same group using VTP. • Client mode: In the client mode, a switch cannot modify VLANs but will receive configuration information from other switches. • Transparent mode: In the transparent mode, a switch receives configuration messages from other switches but does not process them. Configuration changes to the VLAN are not transmitted to other switches in the group.

802.11 modes

The 802.11 standard supports two modes: the infrastructure mode and the ad-hoc mode. Infrastructure mode The infrastructure mode utilizes one or more WAPs to connect workstations to the cable backbone. Infrastructure mode wireless networks use either BSS or ESS. Infrastructure mode uses the hub-and-spoke topology. Ad-hoc mode The ad-hoc mode, also referred to as IBSS, utilizes a peer-to-peer configuration in which each wireless workstation talks directly to other workstations. Ad-hoc mode uses the mesh topology

IEEE 802.x standards

The 802.x standards are a family of networking standards developed by the IEEE in 1980 to address the rapid developments in networking technology. The 802.x standards are divided into subcategories to address different networking requirements. The more popular groups of standards are described in the following table. IEEE Standard 802.2 The 802.2 standard was developed to address the need for MAC-sub-layer addressing in switches. The 802.2 standard specifies the frame size and transmission rate. Frames can be sent over Ethernet and Token ring networks by using either copper or fiber media. 802.3 The original Ethernet network implementation was developed by Xerox® in the 1970s. The IEEE issued the 802.3 standard to standardize Ethernet and expand it to include a wide range of cable media. In addition to the media type, 802.3 also specifies transmission speeds and the signaling method. This type of network is most efficient in a physical star-logical bus topology. 802.3af The 802.3af standard describes Power over Ethernet (PoE) technology, which enables networks to deliver electrical power and standard data over Ethernet cabling. Up to 15.4 W of DC power can be supplied to each powered device, with 12.95 W being ensured to the powered device due to power dissipation during delivery. 802.3at The 802.3at standard is an update to 802.3af and describes Power over Ethernet Plus (PoE+) technology, which enables networks to deliver electrical power and standard data over Ethernet cabling. With PoE+, up to 30 W of power can be supplied to each powered device, with 25.5 W being assured to the powered device. 802.11 The 802.11 standard describes Layer 1 and Layer 2 specifications for wireless LANs in the 2.4-, 3.6- , 5-, and 60-GHz frequency bands. Numerous amendments to the standards have been adopted as Wi-Fi technology has evolved.

Gateways

The word gateway is a generic term for any device or software that translates one network protocol to another. Working at OSI Layer 3 or above, gateways connect incompatible systems by taking an incoming packet, stripping off the lower-level encapsulation of the original protocol, and re- encapsulating the packet with a new protocol. For example, a router can translate between Ethernet and token ring by stripping off the Layer 2 Ethernet encapsulation and replacing it with token ring encapsulation (also at Layer 2). Some gateways can strip off entire protocol stacks, leaving only the data payload, re-inserting the data into an entirely new packet. For example, a gateway could connect an IP network to an IPX network, stripping off the entire Transmission Control Protocol/Internet Protocol (TCP/IP) stack and replacing it with Internetwork Packet eXchange/Sequenced Packet eXchange (IPX/SPX). Note: It is important not to confuse a gateway with the default gateway in TCP/IP, which just forwards IP data packets.

Wireless communication

Wireless communication is a type of communication in which signals are transmitted over a distance without the use of a physical medium. Information, data or voice, is transmitted as electromagnetic waves, such as radio and microwaves, or as light pulses. Wireless communication enables users to move around while remaining connected to the network. Wireless media are also referred to as unbounded network media, where data signals are transmitted through the air instead of cables. Wireless communication permits connections between areas where it would be difficult or impossible to connect using wires, such as in hazardous areas, across long distances, or inside historic buildings. Wireless connections can be point-to-point, multipoint, or broadcast. • Point-to-point communication is a direct connection between two nodes. Data transmitted by one node goes directly to the other. Cellular communications are point-to-point communications. Typically, point-to-point wireless connections are used to link distant buildings or networks as part of a campus area network (CAN), a metropolitan area network (MAN), or a wide area network (WAN). • Multipoint communication involves connections between many nodes. Each multipoint connection has more than two endpoints. A signal transmitted by any device through a medium is not private. All devices that share the medium can detect the signal but cannot receive it. Wireless networks are an example of multipoint communication. Licensed For Use Only By: Joshua Ross [email protected] Apr 3 2018 8:57AM • Broadcast communication is a communication method in which data goes from a source node to all other nodes on a network. Each node receives and acts on the data. Radio communication is an example of broadcast communication.

Infrared transmission

Infrared transmission is a form of wireless transmission in which signals are sent as pulses of infrared light. Infrared signals transmit at frequencies between 300 GHz and 300,000 GHz and in the range just below visible light in the electromagnetic spectrum. Receivers need an unobstructed view of the sender to successfully receive the signal, though the signal can reflect off hard surfaces to reach the recipient. Many infrared-compatible devices follow the standards set forth by the Infrared Data Association (IrDA). Infrared transmissions are still used in legacy remote control systems, security sensors that can be wired to the network, and manufacturing plants in which sensors are wired to the network.

Radio networking

Radio networking is a form of wireless communications in which signals are sent via radio frequency (RF) waves in the 10 KHz to 1 GHz range. Radio networking is subject to electrical interference from power lines, a building's metal structural components, and atmospheric conditions. Note: U.S. regulatory agencies define the limits on which frequencies and how much power can be used to transmit radio signals. In the United States, the Federal Communications Commission (FCC) regulates radio transmission.

Network controllers

Network controllers support large-scale interactive networks and communication between set-tops and application servers. A set-top is an information appliance device that contains a television-tuner input and displays output to a television set. They are used in cable television, satellite television, and over-the-air television systems. Network controllers are used in digital cable networks and enable such services as video-on-demand (VOD), catalog shopping, web browsing, and email. Network controllers act as a gateway between the IP network, which connects application servers, and the digital cable network, which connects set-tops.

Frequencies and overlap of wireless channels

The 802.11b and g specifications define 14 channels within the Industrial, Scientific, and Medical (ISM) 2.4 GHz band. Each channel is composed of a range of frequencies transmitting at low power, rather than a single frequency transmitting at high power. The data from a single transmitting node is spread across all frequencies in the channel. Because the overall frequency range of the ISM band is limited, the channels have been implemented with substantial overlap. Special codes embedded in the signal give each transmitting node a distinguishing pattern, so that several nodes can share the same channel at once. At some point, however, the channel becomes saturated with too many nodes sharing not only the frequencies from their own channel, but also portions of adjacent channels. The only three channels that have no overlap with each other are 1, 6, and 11. Nonetheless, they still have overlap with the other channels. In addition, most wireless access points come configured out of the box with one of these channels. Because of their popularity, these channels may in practice be busier than some of the others. You should use a wireless spectrum analyzer such as InSSIDer to find which channels in your area are actually the least busy. Newer access points will auto-negotiate their channel.

Logical star topology

The implementation of a logical star topology on a different physical topology is less common than a logical ring or a logical bus, but the logical star topology running on a physical star topology is the single most common implementation in modern LANs. After that, logical star topologies are often implemented on a physical bus topology (physical bus-logical star). In a physical bus-logical star topology, although all nodes are wired onto the same bus cable, a central device polls each node to see if it needs to transmit data. The central device also controls how long a node has access to the cable. A multiplexer (mux) manages individual signals and enables them to share the media.

Gigabit ethernet

Gigabit Ethernet is an Ethernet technology that can transmit data at speeds of 1,000 Mbps and primarily uses optical fibers for transmission. It can be used for distances ranging from 500 to 5,000 meters depending on the type of optical fiber used. The hardware required for Gigabit Ethernet is very expensive when compared with other types of Ethernet. There are several standards and specifications for 1,000 Mbps or Gigabit Ethernet, the most common of which are described in the following table. Standard IEEE Specification Medium Distance (m) 1000Base-T 802.3ab CAT5 CAT6 UTP 100 1000Base-TX 802.3ab CAT6 UTP CAT7 UTP 100 1000Base-X 802.3z Shielded Balanced coax 25 to 5,000 1000Base-CX 802.3z Shielded Balanced coax 25 1000Base-SX 802.3z Multimode fiber Wavelength: 850 nm 550 in practice (220 per specification) 1000Base-LX 802.3z Single-mode fiber Wavelength: 1,300 nm 5,000 1000Base-LX 802.3z Multimode fiber Wavelength: 1,300 nm 550 1000Base-LH 802.3z Single-mode fiber Wavelength: 1,300 nm 10,000 1000Base-LH 802.3z Multimode fiber Wavelength: 1,300 nm 550

MAC addresses

A MAC address , also called a physical address, is a unique, hardware-level address assigned to every networking device by its manufacturer. MAC addresses are 6 bytes long. The first 3 bytes uniquely identify the manufacturer and are referred to as the organizationally unique identifier (OUI). The remaining 3 bytes identify the device itself and are known as the Universal LAN MAC address. MAC addresses can be assigned manually. MAC addresses use hexadecimal numeral system, a positional numeral system with a base of 16. It uses 16 distinct symbols, 0 through 9 to represent values 0 to 9, and A, B, C, D, E, F to represent values 10 to 15. On a local network it is often necessary for one host to send messages to all the other hosts at the same time. This can be done by using broadcast messaging. A message can contain only one destination MAC address, but there is a unique MAC address that is recognized by all hosts. The broadcast MAC address is a 48-bit address made up of all ones. Because MAC addresses are in hexadecimal form, the broadcast MAC address notation is FF:FF:FF:FF:FF:FF. Each F in the hexadecimal notation represents four ones (1s) in the binary address.

Collision and broadcast domains

A collision domain is a network segment in which a collision can happen. In a collision domain, nodes contend for access to the same physical medium. This occurs on a logical bus, where the transmission of a single node is heard by all nodes. A single hub creates a single collision domain, because all nodes hear all transmissions from all other nodes. Likewise, a coax bus (which is both a physical and logical bus) is a single collision domain because the transmission of one node fills the entire medium, potentially colliding with other nodes that try to transmit. A switch, because of its microsegmentation, effectively eliminates collisions. Each port on the switch becomes its own collision domain because it will forward traffic to only the one recipient that is connected to it. A 24-port switch will effectively have 24 collision domains. And, if the switch ports are placed in full duplex mode, there will be no collisions of any sort because one pair of wires will be used for transmitting and another pair for receiving. Should a user plug a hub into a switch port, that port becomes a collision domain for all of the nodes plugged into the hub. A broadcast domain is a network segment on which broadcasts occur. Microsegmentation will not stop broadcasts. Because switches flood broadcasts out all ports by default, a single switch, or any number of switches connected together, comprise a single broadcast domain. Routers block broadcasts by default, so they become the point at which the broadcast domain ends. If a router has two Ethernet interfaces, the network has two broadcast domains, one on either side of the router.

Routers

A router is a networking device that connects multiple networks. Operating at Layer 3 of the OSI model, it makes forwarding decisions based on Layer 3 addresses, such as Internet Protocol (IP) addresses. When a packet comes in one of the router's interfaces, the router reads the destination IP address and forwards the packet out the appropriate interface. If necessary, it will strip off the packet's Layer 2 encapsulation and replace it with encapsulation that is appropriate for the outgoing transmission medium; for example, replacing Ethernet with Point-to-Point Protocol (PPP). Routers can work only with routable protocols, which are network protocols that provide separate network and node addresses. Examples of routable protocols include IP, Internetwork Packet eXchange (IPX), and AppleTalk. A rollover cable is often used to initially configure a network device such as a router or switch. Used most notably by Cisco Systems, the rollover cable connects the device's console port to a PC's serial port, enabling the administrator to use a PC to access the device's configuration console. Using a PC is necessary because routers and switches do not have any ports to plug in a monitor or keyboard.

Virtual LAN (VLAN)

A virtual LAN (VLAN) is a logical grouping of ports on the switch. An administrator determines which ports are grouped together. Nodes that plug into those ports can communicate only with nodes that belong to the same VLAN. They cannot communicate with nodes that belong to other VLANs. This effectively divides a physical switch into multiple, smaller logical switches. When a VLAN port group is extended to another device, then tagging is used. Since communications between ports on two different switches travel via the uplink ports of each switch involved, every VLAN containing such ports must also contain the uplink port of each switch involved, and these ports must be tagged. This also applies to the default VLAN. The default VLAN is the default VLAN on a switch that is used unless another VLAN is created and specified. On a Cisco switch, that default VLAN is VLAN1, which cannot be removed or renamed. If the VLAN port group exists on only a single device, then those ports would be untagged. A Native VLAN is a VLAN that handles traffic that is not tagged. There are several common uses for VLANs, including: • Traffic management, especially to reduce the impact of broadcasting, which is a natural and unavoidable part of Ethernet networking. If a node transmits a Layer 2 broadcast, such as an ARP broadcast to discover some other node's MAC address, the switch will forward the frame only out the ports that belong to the same VLAN, rather than flood the broadcast out all ports. • Security. Instead of buying a separate switch to isolate a group of computers, the administrator can put them in their own VLAN. In this way, each department can have its own VLAN, and not interfere with the traffic of other departments. For example, it is very common to have a separate VLAN just for guests who connect to a guest wireless access point (WAP) in the office lobby. • To separate nodes based on traffic type and the need for Quality of Service. For example, it is commonplace to put all VoIP phones on their own VLAN, so there is no interference coming from nodes that are sending email or downloading large files on the same network. The switches and routers can then be configured to give the VoIP VLAN priority over other VLANs. A great convenience of VLANs is that they can be extended beyond a single switch. Switches can connect to each other using trunk links that will carry all VLAN traffic from one switch to the next. In this way, a single VLAN can extend across an entire campus and not be limited to one switch or one building. Ethernet-based MANs also use VLAN tagging to keep different customers' traffic separate.

Wireless Access Points

A wireless access point (WAP) , or access point (AP), is a device that provides a connection between wireless devices and can connect to wired networks. It has a network interface to connect to the wired network and an antenna or infrared receiver necessary to receive wireless signals. The WAP can be a wireless router in a large environment or in a small office/home office. The Service Set Identifier (SSID) is a 32-bit alphanumeric string that identifies a WAP and all devices attached to it. Wireless connectivity devices such as the WAP or wireless routers come with a default SSID. Many access points include security features that enable you to specify which wireless devices can make connections to the wired network Note: IEEE 802.11 does not specify how two WAPs should communicate. To ensure compatibility, it is best to use WAPs from the same manufacturer. A client device uses its SSID to identify itself to the wireless network. An SSID mismatch can occur when a device receives a packet that contains a different SSID than its own. Devices need to be configured with the same SSID as the WAP in order to communicate with it. A mismatch of SSIDs can block communication between the device and the WAP. Currently, there are fewer episodes of SSID mismatch, because the configuration is done automatically. When determining device density, you need to consider the number of users who will be accessing the WAPs, the number of access points available, and the square footage covered by the access points. Typically, consumer-based WAPs are hardware based to allow about 10 devices to connect. Enterprise WAPs use hardware and software to increase the number of concurrent wireless devices that can connect to the access point

Hybrid topologies

A hybrid topology is any topology that exhibits the characteristics of more than one standard topology. Each section of the network follows the rules of its own topology. Hybrid topologies can be complex to maintain because they typically incorporate a wide range of technologies. Most large networks consist of several smaller subnetworks, and each subnetwork may have a different topology. Note: Hybrid topologies are typically not designed as such. They usually arise when administrators connect existing network implementations independently by using different topologies. Common types of hybrid topologies are described in the following table. Star-bus Linking the central nodes of several star networks by using a common bus, or network backbone. Inside each subnetwork, data flows as it would on a star network, and each of these star networks is treated as a node on the larger bus network. To move data from one subnetwork to another, it must be placed on the common bus. Star-bus topologies are commonly found in local area networks (LANs). Extended-star (or star-of-stars) Connecting the central nodes of two or more star networks with a new common node. To move data from one subnetwork to another, it must be forwarded through the new common node. extended star topologies are commonly found in LANs. Star-ring Connecting the central nodes of multiple star networks in a ring. The data flow between different subnetworks is through this ring. Data is sent in a circular pattern around the star configuration. Star-ring topologies are commonly found in metropolitan area networks (MANs).

NICs

A network interface card (NIC), also called a network adapter or network card, is a device that serves as an interface between a network node and the network. To connect to a network, whether wired or wireless, a node must have a NIC installed. NICs can be: • Built into the motherboard of a computer or other network device. • Internally connected to a computer by using one of the expansion slots on the computer's motherboard. • Externally connected to a computer or other network device by using a USB, CompactFlash®, or FireWire® port. Most NICs can operate in full duplex or half duplex mode. There is also an auto negotiation feature, where devices perform self-configuration to achieve the best possible mode of operation across a link. •A full duplex NIC enables a device to send and receive data simultaneously using separate channels or wire pairs for transmitting and receiving. If the NIC is connected to a switch that is also in full duplex mode, it can transmit and receive at maximum speed. This means that a 100-MB full duplex connection can carry 200 MB of data at any time. In addition, because a switch forms a miniature network between a node and itself (with no other nodes involved), there is no chance of data collision. Note: While an eight-port 100-MB switch in full duplex mode can theoretically carry 1,600 MB of data, in reality only high-end switches can deliver full throughput. • A half duplex NIC can send or receive data, but not both, at any one time. In many cases, the NIC is configured to use auto negotiation by default, but there are times when this is not the optimal configuration. If a NIC is set to auto negotiate duplex, and it is connected to a full duplex-only switch or router, the auto-negotiate port will negotiate to half duplex because the full duplex port does not send any negotiation signals. This will cause a duplex mismatch, which can severely affect performance.

Logical bus topology

A ogical bus topology is a network topology in which nodes receive the data transmitted all at the same time, regardless of the physical wiring layout of the network. A common implementation is physical star-logical bus. In this topology, even though nodes connect to a central switch and resemble a star, data appears to flow in a single, continuous stream from the sending node to all other nodes through the switch. Because the transmission medium is shared, only one node can transmit at a time.

Physical Bus Topology

A physical bus topology is a network topology in which the nodes are arranged in a linear format, and a T-connector connects each node directly to the network cable. The cable is called the bus and serves as a single communication channel. Signals can reflect off the ends of the cable, so you must install 50 ohm terminators to prevent this reflection. Attaching a terminator at both ends of the network cable prevents a condition called signal bounce, in which signals endlessly move from one end of the wire to the other. Terminators impede or absorb signals so they cannot reflect onto the wire. Using 10BASE-2 coaxial cable (ThinNet) to connect computers is a classic example of a physical bus topology. The bus topology has a few disadvantages. A bus network: •Is easy to implement but can be unreliable, because the entire bus fails if there is a break in the network cable. • Transmits data more slowly than the other topologies, as only two nodes can communicate at any time. On a bus, as all communication takes place through the same path, only a single pair of terminals can communicate at a time. Data is transmitted on a bus in a sequence of steps: 1. Each node on a bus listens passively to the channel until it receives a signal. The data signal passes by every node, but not through the node. 2. The node transmits data when the bus is free, and the allocation of the channel to nodes is done on a first-come, first-served basis. 3. If two nodes try to transmit data at exactly the same time, a collision occurs on the wire. A 32-bit jam signal is sent to indicate that a collision has occurred. Each node then waits a random period of time before retransmission in order to avoid further collisions. 4. The transmission fills the entire media of the bus, moving nearly instantaneously along the entire pathway. It passes the network interface card of all nodes. Each node examines the destination MAC address to determine whether or not the transmission is intended for it, and whether or not it should process the transmission. 5. The destination node picks up the transmission. 6. If none of the nodes accept the transmitted data, such as in the case of the destination node being switched off, the data packet is absorbed by the terminator. Termination Termination is the application of a resistor or other device to the end of a cable. Adding a terminator ensures that the ends of the cable do not represent an abrupt change in impedance, causing signal reflections and noise. The electrical characteristics of a terminator must match those of the cable and other components. Note: In legacy networking equipment, you had to install terminators yourself. They are now typically built into the networking devices you use. Generally, you must match the impedance of all devices and cables to achieve proper signal flow. Signals can reflect off the points where impedance changes, such as at a connector between devices or cable segments of mismatched impedance. Signals flow smoothly across connections when impedances match. Note: A cable's impedance is typically marked on its outer jacket.

Physical mesh topology

A physical mesh topology is a network topology in which each node is directly connected to every other node, similar to the physical point-to-point topology. This configuration allows each node to communicate with multiple nodes at the same time. All nodes have dedicated links with other nodes, so there is no congestion on the network and data travels very fast. Because no node can be isolated from the network, this topology is extremely reliable. It is also difficult to implement and maintain because the number of connections increases exponentially with the number of nodes. Mesh topologies typically provide reliable communications between independent networks. When all nodes are connected to all nodes, this is referred to as full mesh. The partial mesh topology is a variation of the mesh topology in which only a few nodes have direct links with all the other nodes. This differentiates it from the full mesh topology where all nodes have direct links with others. It is less complex, less expensive, and contains fewer redundancies than a full mesh topology. A partial mesh topology is also sometimes referred to as a redundant star. The connections between major divisions of the Internet use a mesh topology, making the Internet the largest partial mesh network in the world. A wireless ad-hoc network between multiple laptops is also an example of a physical mesh. In addition, a frame relay or asynchronous transfer mode (ATM) cloud may also have a physical full mesh or partial mesh topology.

Physical ring topology

A physical ring topology is a network topology in which each node is connected to the two nearest nodes: the upstream and downstream neighbors. The flow of data in a ring network is unidirectional to avoid collisions. All nodes in the network are connected to form a circle. There is no central connecting device to control network traffic, and each node handles all data packets that pass through it. Data moves in one direction through each node that scans data packets, accepts packets destined for it, and forwards packets destined for another node. Each node in the ring topology acts as a repeater and boosts the signal when it retransmits the data packet. This boost in the signal ensures that the signal quality is high. Ring topologies are potentially unreliable, as the failure of a single node can bring down the entire network. A variant of the ring topology is the dual ring topology, which allows the use of two counter-rotating rings, in which each ring carries data in the opposite direction. Dual ring configurations are faster, as data can be sent through the shortest path between a sender and the receiver. It is a more reliable topology because in case of a breakage in the inner or outer ring, the two nodes on either side of the break connect the two rings together, essentially closing the loop into a single ring. The topology is thus automatically reconfigured to a single-ring data flow, reducing downtime on the network.

Physical star topology

A physical star topology is a network topology that uses a central connectivity device, such as a switch, with individual physical connections to each node. The individual nodes send data to the connectivity device, and the device then forwards data to the appropriate destination node. In legacy implementations, hubs were also used in physical star topologies, where nodes sent data to the hub, which simply passed it through to all attached nodes. Star topologies are reliable and easy to maintain, as a single failed node does not bring down the whole network. However, if the central connectivity device fails, the entire network fails. Although star topologies are extremely common in client/server networks, a mainframe-based computing system is also a classic example of a physical star topology. Each node has a connection to the mainframe computer and is not aware of other nodes on the network.

WLAN overview

A wireless LAN (WLAN) is a self-contained network of two or more devices connected by using a wireless connection. A WLAN spans a small area, such as a small building, floor, or room. A typical WLAN consists of client systems such as desktops, laptops, smartphones, or tablets, and wireless connectivity devices such as access points. The access points interconnect these client systems in a wireless mode, or they can connect them to a wired network. WLANs enable users to connect to the local network or the Internet, even on the move. A physical location that enables users to access the Internet over a WLAN is referred to as a hotspot. This can be created from a hardware device designed specifically to be a hotspot, or you can enable a hotspot on a computer or mobile phone to allow Internet access. Devices can have simultaneous wired and wireless connections to a network. In these cases, one will be used over the other. If that connection is lost then it will switch over to the other connection after a brief interruption in connection. When you are examining the throughput of your wireless network, you should also consider the goodput. Goodput is the data exchanged at the application level, without considering the additional packet information needed to transfer data over the network

Wireless antennas

A wireless antenna is a device that converts high frequency signals on a cable into electromagnetic waves and vice versa. In wireless communication, an antenna is used to receive or transmit radio waves. The frequency at which an antenna can send or receive radio waves depends on the physical dimensions of the antenna. The higher the frequency, the shorter the wavelength of the signal, and the shorter the antenna will be. You can choose different antenna types to use in different wireless networking situations. Different styles of antennas vary in their gain or signal strength, and the shape or the radiation pattern of the transmission beam. Gain is an increase in the amplitude of a radio wave. Gain can occur due to the use of external sources such as amplifiers that amplify a radio signal. It has both positive and negative effects. Typically, high gain is advantageous, but there may be situations in which the amplitude of a radio wave is already very close to the legal value and added power could be a serious problem. You also need to be aware of the FCC's rules for unlisted wireless equipment and make sure wireless signals stay within the established limits. Wireless signals are not bound by the same physical limitations of wired media. Wireless signals that travel where they are not intended is known as bleed. For example, the wireless signal in an office is not restricted to that office, and someone outside might also use the signal. Some antennas and access points allow administrators to restrict the range of a wireless signal by reducing the strength of the wireless signal output. Antenna polarization is a very important consideration when selecting an antenna. Most communications systems use vertical, horizontal, or circular polarization. Knowing the difference between polarizations and how to maximize their benefit is very important to the antenna user. Most antennas radiate either linear or circular polarization. A linear polarized antenna radiates wholly in one plane containing the direction of propagation. In a circular polarized antenna, the plane of polarization rotates in a circle making one complete revolution during one period of the wave. A vertically polarized (linear) antenna has its electric field perpendicular to the Earth's surface. Horizontally polarized (linear) antennas have their electric field parallel to the Earth's surface. A circular polarized wave radiates energy in both the horizontal and vertical planes and all planes in between. The default antennas on APs are typically omnidirectional, covering an area that is mostly circular except for areas where the signal is impacted by things like walls, motors, and other RF obstacles. Placing the antenna in a central location and then allowing AP coverage areas to overlap is one way to ensure coverage, but not likely the best choice. APs that use MIMO antennas do not provide circular coverage. These MIMO antennas take advantage of multiple path signal reflections to extend coverage areas; however, you still might have gaps in coverage. Purchasing additional APs is often the way administrators cover the gaps, but you should consider using directional antennas instead.

Analog modems

An analog modem is a device that modulates signals to encode digital information and demodulates signals to decode the transmitted information. A common type of modem is one that takes the digital data of a device and turns it into modulated electrical signal for transmission over telephone lines, which is then demodulated by another modem at the receiver side to recover the digital data. Though modems are not used much anymore, they can be used in locations where you have no other options for connections. Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second (bps). Modems can also be classified by their symbol rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. Carrier detect is used by a modem to let the computer know that a carrier is available to send and receive data. It is a control signal on an RS-232 serial cable between the computer and the modem. Carrier sense uses a handshake signal to let the computer know a carrier is available. It can be used to alert a UNIX host that a terminal is on before the host sends the logon screen to the terminal.

Wireless antenna types

Antennas can be grouped into one of two broad categories. Directional antenna A type of antenna that concentrates the signal beam in a single direction, sometimes referred to as a unidirectional antenna. . They have a relatively narrow, focused transmission beam and a relatively high gain. Because they transmit primarily in a single direction, the sending and receiving stations must be precisely aligned. The high gain provides for good signal quality and the narrow beam ensures that only a narrow transmission area needs to be clear of interference. Directional antennas are used in a point-to-point network to connect one station to another. Directional antennas include the parabolic dish antenna, backfire antenna, yagi antenna, and panel antenna. Some of these antennas can be semi-directional, which are designed to provide specific, directed signal coverage over large areas. Others can be bidirectional, which have two high-gain directions, usually oriented opposite to each other in space. Other antennas can provide 180-degree coverage in a single direction. Omni-directional antenna A type of antenna that radiates the signal beam out in all directions and has lower gain but a wider coverage area. The transmission radiates from the antenna in all directions, generally in a single horizontal or vertical plane, so that the sending and receiving stations do not need to be as precisely aligned. However, a wider coverage zone means there are more potential sources of interference, and there is lower gain because the signal power is not as focused. Omni-directional antennas are used in multipoint and distributed networks. Omni-directional antennas include the ceiling dome or "blister" antenna, blade antenna, and various rod-shaped antennas. Note: The wireless antenna in a laptop typically runs along the lid of the display.

Bluetooth

Bluetooth 4.1 is a wireless technology that facilitates short-range wireless communication between devices such as personal computers, laptops, cellular phones, tablets, and gaming consoles, thus creating a wireless personal area network (WPAN). Up to eight Bluetooth devices, usually less than 30 meters apart, can be connected to each other at a point in time. Bluetooth establishes a link using an RF-based media and does not need line-of-sight to make connections. Note: The "Bluetooth" technology is named in memory of a Danish king named Harald Bluetooth. Bluetooth uses the 2.4 GHz spectrum to communicate a 24 Mbps connection between two devices as far as 100 meters apart, but in most cases only 30 meters. Examples include Bluetooth wireless keyboards, mice, headsets, and recent-model cars. Bluetooth is also used (in conjunction with near field communications, or NFC ) as the back-end transport mechanism for when you tap your smartphone to a point of sale machine such as an ATM card reader in a market.

Legacy network connectivity devices

Due to technological advancements in the field of networking, some of the network connectivity devices have become outdated. Although some of them are no longer available as separate devices, their functionality is built into devices such as routers and switches. Network Device Description Repeater A repeater is a device that regenerates a signal to improve signal strength over transmission distances. By using repeaters, you can exceed the normal limitations on segment lengths imposed by various networking technologies. Repeaters are used frequently with coax media, such as cable TV, and were also deployed in networks that used coax cabling. On today's networks, repeaters are not commonly needed because other devices perform that function, but they are sometimes used in fiber networks. Wireless network repeaters and bridges are frequently used to extend the range of a wireless access point (WAP). Repeaters are not needed when you are using twisted pair because other devices act as repeaters. Hub A hub , or multiport repeater , is a networking device used to connect the nodes in a physical star topology network into a logical bus topology. A hub contains multiple ports to which the devices can be connected. When a data packet from the transmitting device arrives at a port, it is copied and transmitted to all other ports so that all other nodes receive the packets. However, only the node to which it is addressed reads and processes the data while all other nodes ignore it. Two common types of hubs used were passive and active. • A passive hub simply has its ports wired together physically. It connects devices plugged into it without the use of power. Acting like a patch panel, it merely makes the electrical connection without repeating or transmitting any frames. A token ring MSAU is an example of a passive hub. • An active hub is a true multiport repeater. It receives incoming frames and retransmits those frames out all ports. An Ethernet hub is an example of an active hub. In today's networks, hubs have been replaced by switches. Bridge A bridge is an older version of a switch. It has the same basic functionality of a switch, but it has fewer ports and is software based, rather than hardware based (like a modern switch).

Ethernet (IEEE 802.3)

Ethernet is a set of networking technologies and media access methods specified for LANs. IEEE has defined the 802.3 specifications and standards for Ethernet implementations. Ethernet enables computers to communicate over small distances using a wired medium. Ethernet has evolved as the most widespread technology for wired LANs. Most Ethernet networks use twisted pair cables at the access layer (where computers plug in) and either high-speed twisted pair or fiber optic cable for the network backbone. The original 802.3 specification for Ethernet included both OSI Layer 1 and Layer 2 protocols. In today's networks, however, we tend to associate Ethernet only with Layer 2, because Ethernet can now be carried on a variety of physical media and is not restricted to only thick or thin coaxial cable. Traditional Ethernet networks used a shared medium, as they were all connected to the same bus and competed for bandwidth by using the CSMA/CD media access control (MAC) method. Modern Ethernet implementations are considered to be switched Ethernet, where there are one or more direct point-to-point connections between hosts or network segments. The switch enables each device to use the full bandwidth of the medium. In switched Ethernet, switches read the destination Layer 2 (MAC) address and forward the frame only to the destination node. A 24-port switch can, in theory, handle 12 pairs of conversations simultaneously. ThinNet and ThickNet Although today's networks commonly use twisted pair cabling in their Ethernet implementations, you might still encounter some coaxial cables. The following table describes the most common coaxial cables used in Ethernet networking. ThinNet ThinNet is the name given to Ethernet networking that uses RG58/U or RG58A/U cabling. ThinNet is wired in a bus configuration where segments can be up to 185 meters (607 feet) long. ThinNet connections are made with a BNC connector. Devices connect to the network with T-connectors, and each end of the cable must be terminated with a 50-ohm resistor. ThickNet ThickNet is the name given to Ethernet networking that uses RG8 cabling. ThickNet is not commonly used today, but was popular as a network backbone because ThickNet segments can be up to 500 meters (or 1,640 feet) long. Networking devices are not directly connected to the ThickNet cable. Instead, transceivers are connected to the cable with a vampire tap, which is a clamshell-like device that pierces an RG8 cable, to make contact with its conductors. This permits a networking device to connect to the ThickNet segment. Transceivers can be installed as needed at intervals of 2.5 meters along the length of the cable. The networking device connects to the transceiver via 15-pin AUI connector and a short section of cable called a drop cable. An AUI connector is also known as a DIX connector, which gets its name from the three companies that invented it: Digital Equipment Corporation (DEC), Intel, and Xerox. Connections between ThickNet segments are made with a screw-type connector called an N-connector. ThickNet segments must be terminated with a 50-ohm resistor.

Wireless antenna performance factors

It is important to consider various performance factors before installing antennas for infrared, radio, or microwave wireless technologies. Wireless Technology Type Performance Factors Infrared The maximum transmitting distance of an infrared wireless installation is affected by these factors: • Sunlight. • Obstacles. • Smoke, dust, or fog. Radio The maximum transmitting distance of a radio wireless installation is affected by all of these factors: • Signal characteristics of the antenna. • Environment conditions such as wire mesh in wall construction, thick walls, and so on. • Ambient electrical noise. • Conductive obstacles in the path. • Presence of other electrical equipment. • Data transmission rate. Microwave The maximum transmitting distance of a microwave wireless installation is affected by all of these factors: • Weather. • Signal characteristics of the antenna. • Line of sight. • Distance between transmitting stations. Note: Although there are a few exceptions, most notably in developing nations, most radio- based wireless is in the microwave frequency range.

PoE

Power over Ethernet (PoE) uses the IEEE 802.3af standard for transferring both electrical power and data to remote devices over twisted-pair cable in an Ethernet network. This technology allows you to place devices such as network switches, Voice over IP (VoIP) phones, wireless access points, and cameras in locations where it would be inconvenient or impossible to run electrical power for the device. PoE provides up to 15.4 W of power and requires CAT5 or higher copper cable. The updated IEEE 802.3at standard, also known as Power over Ethernet+ (PoE+) , provides up to 25.5 W of power per port and is backward compatible with all existing IEEE 802.3af devices. PoE+ allows for a broader range of devices to be powered such as: • Cameras with pan/tilt/zoom capabilities • Door controllers • Point-of-sale terminals Many switches provide PoE directly from their switch ports. This is used to power VoIP phones that are plugged into the switch. Another common implementation is a small device that plugs into AC power at the wall. This device is a special power supply that is inserted between the switch and the device that needs power (such as a camera, access point, or radio transmitter). It applies the needed DC power onto the Ethernet cable that leads to the connected device. This allows the camera or access point to be mounted on a pole or under the eave of a roof, where power is not normally available.

Types of routers

Routers can be classified into three main categories: access, distribution, and core. Router Type Description Access routers Routers used in small office/home office (SOHO) networks. They are located at customer sites and are inexpensive. Distribution routers Routers that collect data from multiple access routers and redistribute them to an enterprise location such as a company's headquarters. The routing capabilities of a distribution router are greater than those of access routers. Core routers Core routers are located at the center of network backbones. They are used to connect multiple distribution routers located in different buildings to the backbone.

WLAN architecture

Several components comprise a WLAN architecture. WLAN Architecture Station (STA) A device that can use the IEEE 802.11 protocol. A wireless STA contains an adapter card, a PC card, or an embedded device to provide wireless connectivity. Access point (AP) A device or software that facilitates communication and provides enhanced security to wireless devices. It also extends the physical range of a WLAN. The AP functions as a bridge between wireless STAs and the existing network backbone for network access. Service sets The service set defines the way a WLAN is configured. There are three ways to configure a WLAN—BSS, IBSS, and ESS. Basic Service Set (BSS) and Basic Service Set Identifier (BSSID) A set of devices with an AP connected to a wired network and one or more wireless stations or clients. A BSS can effectively extend the distance between wireless endpoints by forwarding signals through the WAP. The BSSID is a unique address that identifies the BSS. Extended Service Set (ESS) and Extended Service Set Identifier (ESSID) A configuration of multiple BSSs used to handle mobility on a wireless network. BSSs are connected to a common distribution system such as a wired network. ESS enables users to move their mobile devices, such as laptop computers, outside of their home BSS while keeping their connection. It also enables data to be forwarded from one BSS to another through the network backbone. The ESSID identifies the extended service set. In most cases, the term service set identifier (SSID) is used. Independent Basic Service Set (IBSS) A peer-to-peer network where each wireless station acts as both a client and a wireless AP. Each wireless station can both transmit and receive data. Distribution System (DS) A wired connection between a BSS and a premise-wide network that enables mobility to devices and provides access to available network resources. DCF 802.11 defines distributed Coordination Function (DCF) as a collision avoidance method that controls access to the physical medium. Each station checks the status of the wireless medium before beginning transmission. If a station determines that the network is busy, the station must wait for a random backoff period before it can try to access the network again. In a network where many stations contend for the wireless medium, if multiple stations sense the channel busy and defer access, they will also virtually simultaneously discover that the channel is open and then try to transmit, possibly causing collisions. That is why a random backoff interval is used.

Signal distribution methods

Spread spectrum uses either frequency hopping or direct sequencing techniques to distribute the signal across the radio spectrum. Spread Spectrum Type Description Orthogonal Frequency Division Multiplex (OFDM) OFDM uses multiple frequencies simultaneously to send data. A high-speed data stream is converted into multiple low-speed data streams via Serial-to-Parallel (S/P) conversion. Each data stream is modulated by a subcarrier. This produces multiple flat-fading subchannels. It is used in applications such as digital television and audio broadcasting, digital subscriber line (DSL) Internet access, wireless networks, powerline networks, and 4G mobile communications. Direct Sequence Spread Spectrum (DSSS) DSSS uses multiple frequencies simultaneously to send data. Additionally, Error Detection and Correction (EDAC) techniques are used to reduce data transmission errors. In DSSS, a data signal is converted into multiple data signals called chips . The set of chips is sent across a wide band of adjacent frequencies. Upon receiving the data, the receiver combines and converts the signals back into the original. Because of the included EDAC information, the signal can often be reconstructed only if some of the frequencies are received clearly. It is used in satellite navigation systems such as GPS; cordless phones operating in the 900 MHz, 2.4 GHz, and 5.8 GHz bands; IEEE 802.11b 2.4 GHz Wi-Fi; and radio-controlled model automotive vehicles

Switches and network performance

Switches make forwarding decisions based on Layer 2 (MAC) addresses. They do this through a process called microsegmentation , in which all nodes are logically separated from each other until there is a need to connect them. A switch listens to the transmissions of all of the nodes plugged into its ports. It learns the MAC addresses of each of the nodes and puts those MAC addresses into a table in memory. The table associates each MAC address with the port that it is plugged into. This table is called a MAC table or content addressable memory (CAM) table. When a node sends a frame to another node, the switch examines the Ethernet header for the destination MAC address. It refers to its MAC table to see which port it must forward the frame out of. It does not repeat the frame out any other port except the one that is required. In this way, conversations are limited to the nodes involved. If the switch receives a frame that has an unknown unicast (the address is not in the MAC table), multicast, or a broadcast destination MAC address, the switch will flood the frame out all ports except for the port that it received the frame from. Switching offers a dramatic performance improvement over hubs, which simply flood all frames out all ports regardless of which port the intended recipient is plugged into. Most switches allow you to configure the port speed and duplex settings to allow for greater control of the switch performance. The speed and duplex options are similar to those used for NICs, as seen in the previous topic. A managed switch, also called an intelligent switch, is one that includes functions that enable you to monitor and configure its operation. Typically, you connect to the switch by using a web browser or via a dedicated management port.

The 10Base standards

The 10Base standards describe the media type and the speeds at which each type of media operates. The cable standard specification contains three components: • A number indicating media speed • The signal type (baseband or broadband) • A code for either copper or fiber media There are several standards and specifications for 10 Mbps Ethernet, the most common of which are described in the following table. Standard IEEE Specification Medium Distance (meters) 10Base-2 802.3a ThinNet coax 185 10Base-5 802.3 ThickNet coax 500 10Base-T 802.3i CAT5 UTP 100 10Base-F 802.3j Fiber 2,000 10Base-FB 802.3j Fiber 2,000 10Base-FL 802.3j Fiber 2,000 10Base-FP 802.3j Fiber 500

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.

VLAN assignment

The use of VLANs must be carefully planned. Because the switch will not forward frames between VLANs, the administrator must determine which nodes should be grouped together into the same VLAN. If a node in one VLAN needs to communicate with a node in another VLAN, some other mechanism must be used to allow that communication. The common practice is to assign each VLAN its own set of IP addresses (IP subnet) and to have a router route packets between the VLANs. Assigning ports to VLANs can be done in one of two ways: manually configuring each port on a switch to belong to a particular VLAN, or associating a VLAN with a node's MAC address. If the latter is done, a database must be configured ahead of time that maps the VLANs to the MAC addresses. The convenience of using this technique is that if a user moves freely between locations, plugging a device into different ports, the node always stays in the same VLAN. Generally, a single port on the switch can belong to only one VLAN at a time. The exceptions are ports that have been configured to be trunk ports to connect to other switches, or ports that are configured for port mirroring.

Switch types and operating modes

There are several types of switches available for your network. Switch Type Description Multilayer A multilayer switch performs both routing and switching. Also referred to as a Layer 3 switch or a Layer 2-3 switch, it can perform only limited routing functions and supports only Ethernet connections. Multilayer switches support the configuration of virtual local area networks (VLANs), which are discussed later in this topic. Content A content switch supports load balancing among server groups and firewalls, and web cache and application redirection, in addition to other server management functions. Content switches are often referred to as 4-7 switches as they primarily work on Layers 4 and 7 of the OSI model. They make intelligent decisions about data by analyzing data packets in real time, and understanding the criticality and type of the request. Content switching supports load balancing for servers by directing traffic to assigned server groups that perform the function. This increases the response time for requests on the network. Although complex to implement, a content switch can perform many critical functions on a network and increase throughput. Note: Basic or traditional switches operate at the Data Link layer of the OSI model (Layer 2). However, modern switches include more complex capabilities and can operate at the Network (Layer 3) and Transport layers (Layer 4). Higher layer switches are often called application or routing switches. There are also several different operating modes for switches. Switching Mode Description Cut-through In cut-through switching, the switch forwards a data packet as soon as it receives it; no error checking or processing of the packet is performed. The switch performs the address table lookup immediately upon receiving the Destination Address field in the packet header. The first bits in a packet are sent out of the outbound port on a switch immediately after it receives the bits. The switch does not discard packets that are corrupt and fail error checking. Fragment-free In fragment-free switching, the switch scans the first 64 bytes of each packet for evidence of damage by a collision. If no damage is found, it forwards the packet; otherwise, it discards it. Fragment-free switching reduces network congestion by discarding fragments. It is similar to the cut-through switching method, but the switch waits to receive 64 bytes before it forwards the first bytes of the outgoing packet. Store-and-forward In store-and-forward switching, the switch calculates the cyclic redundancy check (CRC) value for the packet's data and compares it to the value included in the packet. If they match, the packet is forwarded. Otherwise, it is discarded. This is the slowest type of switching mode. The switch receives the entire frame before the first bit of the frame is forwarded. This allows the switch to inspect the frame check sequence (FCS) before forwarding the frame. FCS performs error checking on the trailer of an Ethernet frame.

Trunking

Trunk links can be combined to increase bandwidth and reliability in a process called trunking. . This is also known as link aggregation, port bonding, port teaming, EtherChannel, and NIC bonding, among other names. Although a variety of manufacturer-implemented techniques exist, IEEE 802.1AX-2008 defines a standard for link aggregation. Within the IEEE specification, the Link Aggregation Control Protocol (LACP) provides a method to control the bundling of several physical ports together to form a single logical channel. LACP allows a network device to negotiate an automatic bundling of links by sending LACP packets to the peer. The primary purpose of link aggregation is to allow redundant links to combine their bandwidth together without causing spanning tree loops. Link aggregation is typically implemented between switches, although it can be implemented between a node and a switch. Linking two 1-Gbps ports on a server to two 1-Gbps ports on a switch can result in 2 Gbps aggregate throughput. Depending on the implementation, this can result in a redundant connection in case one of the cables or ports fails. However, this still leaves the possibility of the entire switch failing, so some hardware vendors provide proprietary methods for trunking ports across two physically separate switches. Trunking can be used to connect a variety of network hardware, including switch-to-switch, server-to-switch, server-to-server, or switch-to-router.

VLAN pooling

VLAN pooling is a mechanism whereby WAPs can choose among several different available VLANs to assign to incoming client connections. This strategy distributes and load-balances wireless client traffic among multiple VLANs so that no single network segment is overwhelmed by too many wireless client connections.