Module A -

Module A -

10Base-T Ethernet LAN Copyright 1998 Panko 1 LANs Local Area Networks Limited Geographical Area Single office Single building University campus or industrial park Generally, high speeds Now, most operate at around 10 Mbps 100 Mbps is emerging as the new base speed

Most Data Traffic is Local 2 Standards Setting LANs are Subnets (single networks) Subnet technology is Dominated by OSI Standards (true for LANs) IEEE Creates most LAN Standards Institute for Electrical and Electronic Engineers Submits its standards to ISO and ITU-T for ratification IEEE 802 Committee

LAN standards are set by the IEEE 802 Standards Committee. 802.3 for Ethernet Standards 802.5 for Token-Ring LAN Standards 802.11 for Radio and Infrared Wireless LANs 3 LANs and OSI Architecture OSI is a 7-layer architecture LAN transmission only uses Layers 1 and 2 Layer 1: Physical Layer Connectors, Media, Electrical signaling Layer 2: Data Link Layer Packaging data into frames

Managing transmission over link (error handling, etc.) Access control: when each station may transmit 4 OSI Physical and Data Link Layers Physical Layer (OSI Layer 1) Physical (plugs, media, etc.); Electrical (voltages, timing, etc.) Electrical Signal Station Station AA Connector Plug F4-1 Station Station BB Transmission Medium (telephone wire, etc.) Connector Plug

5 OSI Physical and Data Link Layers Data Link Layer (OSI Layer 2) Frame Frame22 Station Station AA Frame Frame11 Station Station BB 6 Data Link Layer For point-to-point transmission A point-to-point connection is a data link

So is a transmission system shared by multiple devices, only one of which can transmit at a time because of collisions Transmission 7 Data Link Layer First function: Packaging of Data (1s and 0s) PDU at Data Link Layer is called a frame Second Function: Access Control Only one station can transmit at any time If another transmitted, their signals would scramble one another Must control access to (transmission into) the transmission medium 8 Data Link Layer

OSI Data Link Layer (Layer 2) OSI Physical Layer (Layer 1) Logical LogicalLink LinkControl ControlLayer Layer Media MediaAccess AccessControl Control(MAC) (MAC)Layer Layer 802.3 802.3 802.3 802.3 Other 802.3

802.3 Other 10Base-T 10Base-T 10Base-5 10Base-5 Physical Physical Layer Layer 802.5 802.5 Physical Physical Layer Layer 44Mbps Mbps 802.5 802.5 Physical Physical Layer Layer 16 16Mbps

Mbps Other Other Physical Physical Layer Layer OSI OSIData DataLink LinkLayer Layerisissubdivided subdividedinto intotwo twolayers layers Media Mediaaccess accesscontrol control Logical Logicallink linkcontrol control

9 MAC Layer Media Access Control OSI Physical (Layer 1) Media MediaAccess AccessControl Control(MAC) (MAC)Layer Layer 802.3 802.3 802.3 802.3 Other 802.3 802.3 Other

10Base-T 10Base-T 10Base-5 10Base-5 Physical Physical Layer Layer 802.5 802.5 Physical Physical Layer Layer 44Mbps Mbps 802.5 802.5 Physical Physical Layer Layer 16 16Mbps Mbps

Other Other Physical Physical Layer Layer MAC MAClayer layerimplements implementsmedia mediaaccess accesscontrol: control: When Whenaastation stationmay maytransmit transmit Controls Controlsthe theframing framingof ofdata dataalong alongthe

thewire wire 10 Logical Link Control Layer LLC OSI Physical (Layer 1) 802.2 802.2Logical LogicalLink LinkControl ControlLayer Layer 802.3 802.3Media MediaAccess AccessControl Control (MAC Layer) (MAC Layer)

802.5 802.5 MAC MAC 44Mbps Mbps 802.5 802.5 MAC MAC 16 16Mbps Mbps Other Other MAC MAC 802.3 802.3 802.3 802.3 Other

802.3 802.3 Other 10Base-T 10Base-T 10Base-5 10Base-5 Physical Physical Layer Layer 802.5 802.5 Physical Physical Layer Layer 44Mbps Mbps 802.5 802.5 Physical Physical Layer Layer 16

16Mbps Mbps Other Other Physical Physical Layer Layer Provides ProvidesControl ControlFunction Function Begin/end Begin/endconnections connectionsbetween betweenstations stations Error Errorcorrection correction(optional) (optional) 11

Simple LAN Using Ethernet 10Base-T 10Base-T Hub (Multiport Repeater) Unshielded Twisted Pair (UTP) Wiring (4-Pair Bundle) PC NIC RJ-45 Jack RJ-45 jacks 10Base-T UTP Wiring Bundles: 4 Pairs EIA Category 3, 4, or 5 Network Interface Card

12 Ethernet 10Base-T (802.3u) Physical Layer Standard 10 Mbps (10 in 10Base-T) Baseband signaling: Injects voltage changes directly into the wires (Base in 10Base-T) Hubs (Multiport Repeaters) Connect the stations together 10Base-T Hub 13 NICs Network Interface Cards Implement Physical Layer Plug and Electrical Signaling

Implements the Data Link Layer (data packaging, access control, etc.) LLC (802.2) MAC (802.3 MAC) 14 Wiring Unshielded Twisted Pair (UTP) Twisted several times per foot to reduce interference, T in 10Base- and Unshielded No protection except for plastic coating Distance limitation: 100 meters (attenuation, distortion, noise and

interference, crosstalk) -- propagation Categories of UTP Wiring Category 5: The best. Good for 100 Mbps Category 3 and 4: lower. May be OK for 100 Mbps Wiring Plugs: RJ-45 Standard Similar to home (RJ-11) jacks, but wider 15 Attenuation As signal travels, gets weaker If too weak, cannot tell 1s and 0s Distance 16 Distortion As signal travels, it become distorted

Changes shape Successive bits may merge, making reception difficult Distance 17 Noise Unwanted energy on line. Always present Noise floor is average level Noise spikes will cause problems Signal Strength Signal Noise Spike Noise Floor Time 18

Signal to Noise Ratio (SNR) Ratio of Signal Power to Noise Power If SNR is high, few noise errors 100% Error Rate 0% 1 SNR 19 Interference Unwanted signal from outside sources Often intermittent, difficult to diagnose Signal Strength Signal

Interference 20 Physical Layer Transmission in 10Base-T 10Base-T Hub Step Step11 Station StationAA Transmits Transmitson on Upstream Upstream Pair Pair (Wires (Wires1&2) 1&2) Station A

F4-4 Station B Station C 21 Physical Layer Transmission in 10Base-T 10Base-T Hub Step Step22 Hub HubRepeats Repeats (Broadcasts) (Broadcasts) The TheMessage Message To ToAll All Stations

Stations On OnDownstream Downstream Pairs Pairs (Wires (Wires3&6) 3&6) Station A Station B Station C Bus transmission means broadcasting 22 Manchester Encoding

Inefficient Transmits 10 million bits per second Must change line state 20 million times per second 20 Mbaud (baud is a change in the line state) Technology limits the baud rate Only 10 Mbps for 20 Mbaud Bit rate is less than the baud rate (opposite in modems) 23 MAC Layer CSMA/CD Media Access Control Controls when stations may transmit If two transmit at once, signals will be scrambled X

Collision Collisions will grow rapidly above 30% of line utilization. Keep traffic moderate, or throughput will be affected. 24 CSMA/CD Media Access Control CS: Carrier Sense Each NIC always listens for traffic on the line This lets it recognize messages sent to its address This also lets it know if the line is free CSMA: Carrier Sense Media Access A station may transmit if it hears no traffic on the network 25 CSMA/CD Media Access Control in Ethernet 10Base-T Hub Station StationAA

isisTransmitting Transmitting Station StationBB must mustwait wait Must Wait Station A Station B Station C 26 CSMA/CD Media Access Control CD: Collision Detection If two stations transmit at once .

Their signals collide, scrambling one another Because each sender listens (senses the carrier), both know that there has been a collision Both stop and wait a random amount of time. 101010 X 001110 Collision 27 802.3 MAC Layer Frame Preamble Preamble Start Startof ofFrame FrameDelimiter Delimiter In asynchronous transmission, each byte is sent separately, in a 10-bit frame.

Destination DestinationAddress Address In 802.3 MAC Layer frames, transmission is synchronous. Source SourceAddress Address Many data bytes are sent in each frame of variable length. Length Length Data Data Pad Pad Frame FrameCheck CheckSequence Sequence

Frames must be between 64 octets and 1518 octets long, divided into groups of bits called fields. Field lengths are measured in octets, eight bits. Octet is a synonym for byte 28 Error Detection MAC Layer Process Provides error detection Determines that an error exists Does not provide error correction Merely discards the frame No request for retransmission if there is an error Logical Link Control Layer may do error correction Receiving LLC process detects discarded frames

Receiving LLC process asks for retransmissions 29 Logical Link Control (LLC) Layer Next NextHigher HigherLayer Layer (Usually (UsuallyInternet) Internet) LLC LLCLayer Layer Process Process MAC MACLayer Layer Process Process Station A 802.2 can ask

for retransmission of lost MAC frames. Optional. LLC Frame LLC frame placed within MAC frame MAC Frame Next NextHigher HigherLayer Layer (Usually (UsuallyInternet) Internet) LLC LLCLayer Layer Process Process MAC MACLayer Layer Process

Process Station B 30 Ethernet 10Base-T Network with Two Hubs Hub 1 Station A Transmits to Hub 1 100 m Segment Maximum Hub 2 100 m Segment Maximum Hub 1 Transmits Out All Ports, Including the Port to Hub 2

100 m Segment Maximum Hub 2 Broadcasts the Message Out All of Its Ports Station C Receives the Message Station A Station B Station C 31 Ethernet 10Base-T LAN with Multiple Hubs Hub 2

Hub 3 Hub 1 UTP Wire UTP Wire Station A Station B UTP Wire UTP Wire Daisy Daisychain, chain, no noLoops Loops

allowed! allowed! Maximum distance between farthest Stations is 4 Hubs/5 100 meter segments Hub 4 Station C UTP Wire Station D 32 Speed and Distance Transmission speed worsens problems Error rates increase because bit periods are smaller and are more likely to be damaged by brief noise spikes and interference High speeds create high-frequency components in the signal that attenuate more rapidly than lower-frequency

components In general, as speed increases, maximum distance decreases, although improving technology can lessen the decrease 33 Dealing with Propagation Effects Use High-Quality, High-Cost Media Use media designed for long-distance propagation Optical fiber, coaxial cable Too expensive for runs to many desktops, good for hubto-hub Use Inexpensive Media to the Desktop Improve the technology (allows 100 Mbps+ on UTP) Accept distance limitations (100 meters for UTP) More popular alternative to desktop because of low cost 34 Other Ethernet Physical Layer Standards

100Base-X 100 Mbps 100Base-TX uses Cat 5 UTP to desktop 1000Base-X Gigabit Ethernet Traditional Ethernet (before 10Base-T) 10Base5 10Base2 35 10Base5 Original Ethernet with slight changes Thick coaxial cables

No hubs Drop Cable 10Base5 Trunk Cable Segment Drop cables from stations to trunk cable 500 Meters maximum per segment Maximum 5 segments between farthest stations So maximum distance is 2500 meters 36

10Base5 15-pin DIX Connector AUI Drop Cable (Attachment Unit Interface) 50 meters maximum distance 10Base5 Trunk Cable 500 meters maximum distance Transceiver (Medium Attachment Unit or MAU) 37 10Base5 Segments Runs of trunk cable 500 meters per segment (the 5 in 10Base5)

Repeaters Connect trunk cable segments Up to 5 segments between farthest two stations 2500 meters maximum distance 38 Coax (Coaxial Cable) Signal is trapped between the two conductors Signals travel far Interference from outside signals is low Problem: Being squeezed out of the market Cheaper UTP can now go almost as fast Optical fiber is faster, only slightly more expensive 39 Coax (Coaxial Cable) Widely used in

Cable television service To connect VCRs to televisions Two conductors Inner wire Outer cylinder Inner Wire Outer Cylinder 40 Co-Axial Cable Outer Conductor (cylinder) Inner Conductor (wire)

Insulation Insulation 41 Linking 10Base-T Hubs with 10Base5 Hub 10Base5 AUI Connector Hub 10Base5 Segment 500 meters maximum 42 Ethernet Multiport Repeater (Hub) with 10Base-T and 10Base5 Ports 10B ase5 D IX C o n n e c to r fo r A U I

T o T r a n s c e iv e r ( M A U ) o n 1 0 B a s e 5 T r u n k C a b le 1 0 B a s e -T M u lt ip le R J - 4 5 J a c k s fo r U T P W ir e s T o S t a t io n s a n d O t h e r H u b s 43 10Base2 Uses less expensive thin coaxial cable (Cheapernet or Thinnet) Segment can connect up to 30 stations 185 Meters/segment (the 2 in 10Base2)

With repeaters, 5 segments maximum between distant stations Daisy Chain Layout Segment with 3 PCs 44 10Base2 NIC has BNC Connector T-Connector attaches to NIC BNC connector Cable segments attach to tops of T Dont forget terminator Segment to Next PC T-Connector Segment to Next PC

BNC Connector NIC 45 10Base2 Connection BNC T-Connector NIC Thin Ethernet (10Base2) Coaxial Cable 185m Maximum Per Segment 30 Stations Per Segment Maximum NIC BNC T-Connector NIC 46 Linking Hubs with 10Base2

Hub 10Base2 BNC Connector Hub 10Base2 Segment 185 meters maximum 47 Optical Fiber Very thin glass Core is where signal travels Cladding is ring of glass around core Core and cladding have different indices of refraction Cladding Light Source Core

48 Single Mode Optical Fiber Core and cladding are very thin All parts of a bits wavefront travel the same distance Arrive with little distortion Can propagate long distances Used in telephone company long-distance links Too expensive, difficult to install for LAN use Wavefront Light Source Cladding Core

49 Multimode Optical Fiber Thick (usually around 62.5 micron core): easy to join Different parts of wavefront travel different paths: limits distance before successive wavefronts overlap Multimode is most common type in LANs Step Index: core index of refraction is constant across core Cladding Light Source Core 50

Multimode Optical Fiber Graded Index Index of refraction varies along core Rays at different angles travel similar distances Signals travel longer distances before distortion is bad Multimode graded index fiber is dominant today C la d d in g L ig h t S o u r c e C o re 51 10Base-F Standard for connecting hubs

Can carry signals for 2,000 meters (2Km =~ 1.2 miles) much farther and faster than 10Base5 52 Stackable Hubs Physically Stacked Can mix hubs of various types Easy to add capacity

High-speed backplane or 10Base2 connectors link the stacked hubs (switch next class meeting) Visit 3Com for a view of actual products. 53 Chassis Hubs Chassis provides slots for expansion boards Expansion boards are hubs of different types Very high-speed backplane bus to link hubs 54

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