Media, Connections & Collisions – 1
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Transcript of Media, Connections & Collisions – 1
Media, Connections &Collisions – 1
Andres, Wen-Yuan Liao
Department of Computer Science and Engineering
De Lin Institute of Technology
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