Chapter 4 physical layer

Coaxial cable (two conductors that share the same axis)

-A copper conductor used to transmit the electronic signals. -The copper conductor is surrounded by a layer of flexible plastic insulation. -The insulating material is surrounded in a woven copper braid, or metallic foil, that acts as the second wire in the circuit and as a shield for the inner conductor. This second layer, or shield, also reduces the amount of outside electromagnetic interference. -The entire cable is covered with a cable jacket to protect it from minor physical damage. Coaxial cable was traditionally used in cable television capable of transmitting in one direction. It was also used extensively in early Ethernet installations

Cable categories

-CAT3(UTP) -CAT7(ScTP) -CAT6(UTP) -CAT5 & 5e(UTP) As new gigabit speed Ethernet technologies are being developed and adopted, Cat5e is now the minimally acceptable cable type, with Cat6 being the recommended type for new building installations.

Physical layer media

-Copper cable: The signals are patterns of electrical pulses. -Fiber-optic cable: The signals are patterns of light. -Wireless: The signals are patterns of microwave transmissions.

Fiber vs Copper

-Fiber has longer distance than UTP -Fiber has high immunity to EMI and RFI compared to UTP with low immunity -Fiber has high immunity to electrical hazards whereas UTP has low immunity -Fiber has highest cost -Highest installation skills are required for fiber -Fiber requires highest safety precautions -Fiber supports 10 Mb/s-100 Gb/s whereas UTP supports 10 Mb/s-10 Gb/s of bandwidth

Types of UTP cables

-T568A -T568B

UTP cable test parameters:

-Wire map -Cable length -Signal loss due to -attenuation -Crosstalk

Physical layer

Accepts a complete frame from the data link layer Encodes it as a series of signals that are transmitted onto the local media

Ethernet straight-through

Both ends type A or both ends type B connects a network host to a network device such as a switch or a hub

Copper cabling

Characteristics of Copper Cabling -Inexpensive, easy to install, low resistance to electric current -Distance and signal interference Copper Media -Unshielded Twisted-Pair Cable -Shielded Twisted-Pair Cable -Coaxial Cable Copper Media Safety -Fire and electrical hazards

Crosstalk

Crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire to the signal in an adjacent wire. In telephone circuits, crosstalk can result in hearing part of another voice conversation from an adjacent circuit.

Cancellation

Designers now pair wires in a circuit. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other. Therefore, the two magnetic fields cancel each other out and also cancel out any outside EMI and RFI signals.

Electromagnetic interference (EMI) or radio frequency interference (RFI)

EMI and RFI signals can distort and corrupt the data signals being carried by copper media. Potential sources of EMI and RFI include radio waves and electromagnetic devices such as fluorescent lights or electric motors.

Encoding

Encoding or line encoding is a method of converting a stream of data bits into a predefined "code". Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the receiver.

Enterprise networks

Fiber is used for backbone cabling applications and interconnecting infrastructure devices

FTTH and access networks

Fiber-to-the-home (FTTH) is used to provide always-on broadband services to homes and small businesses. FTTH supports affordable high-speed Internet access, as well as telecommuting, telemedicine, and video on demand.

Physical layer characteristics

Functions -Physical components -Encoding -Signaling Data Transfer Bandwidth - capacity to a medium to carry data, usually expressed in bit per second or bps Throughput - measure of the transfer of bits across the media

Characteristics of copper media

Networks use copper media because it is inexpensive, easy to install, and has low resistance to electrical current. However, copper media is limited by distance and signal interference Data is transmitted on copper cables as electrical pulses. However, the longer the signal travels, the more it deteriorates in a phenomenon referred to as signal attenuation. For this reason, all copper media must follow strict distance limitations as specified by the guiding standards The timing and voltage values of the electrical pulses are also susceptible to interference

Fiber-optic cabling

Properties of Fiber-Optic Cabling -Transmits data over longer distances -Flexible, but thin strands of glass -Transmits with less attenuation -Immune to EMI and RFI Fiber Media Cable Design Types of Fiber Media -Single mode and multimode Fiber-Optic Connectors Testing Fiber Cables

Wireless media

Properties of Wireless Media -Data communications using radio or microwave frequencies Types of Wireless Media -Wi-Fi, Bluetooth, WiMax Wireless LAN -Wireless Access Point -Wireless NIC adapters

Fiber connectors

SC, ST, and LC + duplex multimode LC connectors

Long-haul networks

Service providers use long-haul terrestrial optical fiber networks to connect countries and cities. Networks typically range from a few dozen to a few thousand kilometers and use up to 10 Gb/s-based systems

shielded twisted pair (STP) cable

Shielded twisted-pair (STP) provides better noise protection than UTP cabling. However, compared to UTP cable, STP cable is significantly more expensive and difficult to install. Like UTP cable, STP uses an RJ-45 connector STP cable combines the techniques of shielding to counter EMI and RFI and wire twisting to counter crosstalk To gain the full benefit of the shielding, STP cables are terminated with special shielded STP data connectors. If the cable is improperly grounded, the shield may act like an antenna and pick up unwanted signals. STP cable shields the entire bundle of wires with foil eliminating virtually all interference (more common). STP cable shields the entire bundle of wires as well as the individual wire pairs with foil eliminating all interference.

Submarine network

Special fiber cables are used to provide reliable high-speed, high-capacity solutions capable of or surviving in harsh undersea environments up to transoceanic distances.

Testing fiber cables (using Optical Time Domain Reflectometer/OTDR)

Terminating and splicing fiber-optic cabling requires special training and equipment. Incorrect termination of fiber-optic media will result in diminished signaling distances or complete transmission failure common errors: -Misalignment: The fiber-optic media are not precisely aligned to one another when joined. -End gap: The media does not completely touch at the splice or connection. -End finish: The media ends are not well polished or dirt is present at the termination

Purpose of the physical layer

The OSI physical layer provides the means to transport the bits that make up a data link layer frame across the network media. This layer accepts a complete frame from the data link layer and encodes it as a series of signals that are transmitted onto the local media. The encoded bits that comprise a frame are received by either an end device or an intermediate device. The process that data undergoes from a source node to a destination node is: -The user data is segmented by the transport layer, placed into packets by the network layer, and further encapsulated as frames by the data link layer. -The physical layer encodes the frames and creates the electrical, optical, or radio wave signals that represent the bits in each frame. -These signals are then sent on the media one at a time. -The destination node physical layer retrieves these individual signals from the media, restores them to their bit representations, and passes the bits up to the data link layer as a complete frame.

Varying number of twists per wire pair

To further enhance the cancellation effect of paired circuit wires designers vary the number of twists of each wire pair in a cable. UTP cable must follow precise specifications governing how many twists or braids are permitted per meter (3.28 feet) of cable.

Physical components

The physical components are the electronic hardware devices, media, and other connectors that transmit and carry the signals to represent the bits. Hardware components such as NICs, interfaces and connectors, cable materials, and cable designs are all specified in standards associated with the physical layer

Signaling

The physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media. The method of representing the bits is called the signaling method.

Summary part 1

The physical layer standards address three functional areas: physical components, frame encoding technique, and signaling method. Using the proper media is an important part of network communications. Without the proper physical connection, either wired or wireless, communications between any two devices will not occur. Wired communication consists of copper media and fiber cable. There are three main types of copper media used in networking: unshielded-twisted pair (UTP), shielded-twisted pair (STP), and coaxial cable. UTP cabling is the most common copper networking media. Optical fiber cable has become very popular for interconnecting infrastructure network devices. It permits the transmission of data over longer distances and at higher bandwidths (data rates) than any other networking media.

Types of copper media used in networking: -Unshielded Twisted-Pair (UTP) -Shielded Twisted-Pair (STP) -Coaxial

These cables are used to interconnect nodes on a LAN and infrastructure devices such as switches, routers, and wireless access points. Each type of connection and the accompanying devices have cabling requirements stipulated by physical layer standards. Different physical layer standards specify the use of different connectors. These standards specify the mechanical dimensions of the connectors and the acceptable electrical properties of each type.

Properties of UTP cabling

UTP cable does not use shielding to counter the effects of EMI and RFI. Instead, cable designers have discovered that they can limit the negative effect of crosstalk by: -cancellation -varying the number of twists per wire pair

UTP Connectors

UTP plugs(RJ-45) UTP socket(RJ-45)

Unshielded Twisted Pair (UTP)

Unshielded twisted-pair (UTP) cabling is the most common networking media. UTP cabling, terminated with RJ-45 connectors, is used for interconnecting network hosts with intermediate networking devices, such as switches and routers. In LANs, UTP cable consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath which protects from minor physical damage. The twisting of wires helps protect against signal interference from other wires.

Physical layer connection

Whether connecting to a local printer in the home or to a web site in another country, before any network communications can occur, a physical connection to a local network must be established first. A physical connection can be a wired connection using a cable or a wireless connection using radio waves. The type of physical connection used is totally dependent upon the setup of the network

Summary part 2

Wireless media carry electromagnetic signals that represent the binary digits of data communications using radio or microwave frequencies. The actual media access control method used depends on the topology and media sharing. LAN and WAN topologies can be physical or logical. WANs are commonly interconnected using the point-to-point, hub and spoke, or mesh physical topologies. In shared media LANs, end devices can be interconnected using the star, bus, ring, or extended star (hybrid) physical topologies.

Wireless network

With wireless devices, data is transmitted using radio waves. The use of wireless connectivity is becoming more common as individuals, and businesses alike, discover the advantages of offering wireless services. In order to offer wireless capability, a network must incorporate a wireless access point (WAP) for devices to connect to.

Rollover(cross cable)

cisco propriety connects a workstation serial port to a router console port using an adapter

Wired network

data is transmitted across a physical cable

UTP cabling standards: (UTP cabling conforms to the standards established jointly by the TIA/EIA)

elements defined: -Cable types -Cable lengths -Connectors -Cable termination -Methods of testing cable The electrical characteristics of copper cabling are defined by the Institute of Electrical and Electronics Engineers (IEEE). IEEE rates UTP cabling according to its performance. Cables are placed into categories according to their ability to carry higher bandwidth rates Cables in higher categories are designed and constructed to support higher data rates

Ethernet crossover

one end type A one end type B connects two network hosts connects two network intermediary devices(switch to switch,router to router) (connects similar devices eg.router to pc,router has an OS)

Properties of fiber optic cabling

permits the transmission of data over longer distances and at higher bandwidths (data rates) than any other networking media,making it popular for interconnecting infrastructure network devices Optical fiber is a flexible but extremely thin transparent strand of very pure glass (silica).Bits are encoded on the fiber as light impulses. The fiber-optic cable acts as a waveguide, or "light pipe," to transmit light between the two ends with minimal loss of signal. Unlike copper wires, fiber-optic cable can transmit signals with less attenuation and is completely immune to EMI and RFI