Media, Connections &Collisions – 1

Andres, Wen-Yuan Liao

Department of Computer Science and Engineering

De Lin Institute of Technology

andres@dlit.edu.tw

http://www.cse.dlit.edu.tw/~andres

Overview

Defines the electrical, mechanical, procedural, and functional specificationsNetworking media Network devices, cable specifications, network topologies, collisions and collision domains

Most Common LAN Media

STP and ScTP

UTP

Coaxial cable

Optical fiber

Wireless communication

STP

The techniques of shielding, cancellation, and twisting of wires

Each pair of wires is wrapped in metallic foil

The 4 pairs of wires are wrapped in an overall metallic braid or foil.

150 Ohm cable

STPSTP reduces electrical noiseWithin the cable: crosstalkFrom outside the cable: EMI and RFI

Greater protection from all types of external interferenceMore expensiveDifficult to install

ScTPA new hybrid of UTP with traditional STP Foil Twisted Pair (FTP) Essentially UTP wrapped in a metallic foil shield, or "screen“100 or 120 Ohm cable

STP & ScTPWorks both ways (inside, outside)

Need to be grounded at both ends

Increase the size, weight, and cost of the cable

Shielding materials make terminations more difficult

UTP

Unshielded twisted-pair cable A four-pair wire medium

Each pair of wires are twisted around each other

Limit signal degradation caused by EMI and RFI

UTP

22 or 24 gauge copper wire 100 ohms External diameter of approximately .43 cm Most of the major networking architectures

UTP

AdvantagesEasy to installCosts less Small external diameter

Disadvantages More prone to electrical noise and

interference Distance between signal boosts is shorter

Coaxial cable

Consists of a hollow outer cylindrical conductor that surrounds a single inner wire AdvantagesLonger distances Less expensive than fiber-optic cable The technology is well known

Coaxial Cable

Thicknet:largest diameter Ethernet backbone cable More expensive to install

Thinnet: cheapernet An outside diameter of only .35 cm Useful for cable installationsTaken to ensure that it is properly ground

ed

Optical fiber

A networking medium capable of conducting modulated light transmissionsMore expensiveIs not susceptible to electromagnetic interferenceIs capable of higher data rates

Optical Fiber

The light-guiding parts: the core and the cladding

The core: very pure glass High index of refraction Is surrounded by a cladding layer

A cladding layer: glass or plasticLow index of refraction

Wireless communication

Wireless signals are electromagnetic wavesTravel through the vacuum of

outer space and through media such as air

No physical medium is necessary

The speed of light, c = 299, 792, 458 meters per second

(frequency) x (wavelength) = c

The primary difference between the different electromagnetic waves is their frequency

Application of wireless

Mobile use

WLAN: Wireless LANs The IEEE 802.11 standards Radio waves (for example, 902 MHz),

microwaves (for example, 2.4 GHz), and Infrared waves (for example, 820 nanometers) for communication

Cable Specification and Termination

Purpose of LAN media specifications

TIA/EIA standards

Explain the details of TIA/EIA-568-A

Networking media and terminations

Purpose of LAN media specifications

Work compatibly and interoperably IEEE - Institute of Electrical and Electronics Engineers UL - Underwriters Laboratories EIA/TIAEIA - Electronic Industries Alliance TIA - Telecommunications Industry Associa

tion

IEEE

Has outlined cabling requirements 802.3 and 802.5 specifications

for Ethernet and Token Ring systems

The standards for FDDI

Underwriters Laboratories

Issues cabling specifications that are primarily concerned with safety standards

TIA/EIA standards

The greatest impact on networking media standards

Specify the minimum requirements for multi-product and multi-vendor environments

TIA/EIA-568-A and TIA/EIA-569-AThe most widely used standards for

technical performance of networking media

Details of TIA/EIA-568-A

Six elements of the LAN cabling processHorizontal cabling Telecommunications closets Backbone cabling Equipment rooms Work areas Entrance facilities

Horizontal Cabling

Cabling that runs from a telecommunications outlet to a horizontal cross-connectNetworking mediaThe maximum distance for cable runs in horizontal cabling is 90 meters (m)

Two Telecom Outlets

The first is a four-pair 100 ohm CAT 3 or higher UTP cableThe second can be any one of the following: Four-pair 100 ohm UTP 150 ohm STP Coaxial cableTwo-fiber 62.5/125 µ optical fiber

cable

Networking Media

Shielded twisted-pair Two pair 150 ohm cable

Unshielded twisted-pair four pair 100 ohm cable

Fiber-optic cable two fibers of 62.5/125  multi-mode cable

Coaxial cable 50 ohm coaxial cable

rollover or console cable

Layer 1 Components & Devices

Ethernet 10BASE-T

Connectors, Cabling, Jacks

Patch panels

Transceivers, Repeaters

OSI Layer 1 components and devices

Ethernet 10BASE-T Ethernet : LAN technologies Carry sporadic, occasionally heavy,

traffic at high-peak data rates

Four passive components Patch panels Plugs Cabling Jacks

Ethernet 10BASE-T

Three active componentsTransceivers Repeaters Hubs

Connectors

The standard 10BASE-T termination is the registered jack-45 connector (RJ-45)

Jacks RJ-45 plugs fit into RJ-45 jacks or receptacles

Eight conductors

On the other side of the RJ-45 jack is a punch down block where wires are separated out and forced into slots with a fork-like tool called a punch-down tool

Patch panels

Patch panels are convenient groupings of RJ-45 jacks

They come in 12, 24, and 48 ports, and are typically rack-mounted

The front sides are RJ-45 jacks

The back sides are punch-down blocks

Transceivers A combination of transmitter & receiver

Convert one form of signal to another form

The conversion of AUI ports to RJ-45 ports

Transceivers on NICs: signaling componentsEncode signals onto the physical medium

RepeatersRegenerate, and retime signals, which then enables cables to extend farther to reach longer distancesThe disadvantage They cannot filter network trafficData (bits) that arrive at one port of a

repeater are sent out on all other ports

Multiport repeaters (hubs)

The devices that serve as the center of a star topology network

OSI Layer 1 components and devices

They recognize no information patterns in the bits, no addresses, and no data

Their function is simply to move bits around

Collisions and Collision Domains in Shared Layer

Environments Shared Layer Environments

Collisions and Collision Domains

Shared Layer Environments

directly-connected all hosts share Layer 1

shared media environment occurs when multiple hosts have access to the

same medium

extended shared media environment

point-to-point network environment device is connected to only one other device via a

link

Shared Layer Environments

indirectly-connected some higher layer networking devices and/or

some geographical distance is between the two communicating hosts

circuit-switched actual electrical circuits are maintained for the

duration of the communication. packet-switched rather than dedicating a link as an exclusive

circuit connection between two communicating hosts, the source sends messages in packets

Collisions and collision domains

when two bits propagate at the same time on the same network, is a collision

The area within the network, where the data packets originated and collided, is called a collision domain

Repeaters and collision domains

Repeaters regenerate and retime bits, but they cannot filter the flow of traffic that pass through them

Using a repeater extends the collision domain

The four repeater rule

5-4-3-2-1 rule Five sections four repeaters or hubs three sections of the network are "mixing" s

ections (with hosts) two sections are link sections (for link purp

oses)one large collision domain