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Ethernet (IEEE 802.3)Ethernet (IEEE 802.3) Developed in 1973 by David Boggs and Bob

Metcalfe of Xerox Corporation Xerox, DEC, and Intel worked jointly to

establish the Ethernet standard 70 % of the Worldwide base of LANs uses

Ethernet technology Formalized as the IEEE 802.3 LAN standard

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First Ethernet System DrawingFirst Ethernet System Drawing

By Bob Metcalfe: http://wwwhost.ots.utexas.edu/ethernet

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TopologyTopology

Topology is the basic geometric layout of the network -- the way in which the computers on the network are interconnected.

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IEEE 802.3 Logical TopologyIEEE 802.3 Logical Topology

T-terminator

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IEEE 802.3 Physical TopologyIEEE 802.3 Physical Topology

HUB (MAU)

Bus cable

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CSMA/CD -1CSMA/CD -1

Carrier Sense (CS) Any node can detect

the presence of a carrier signal on the cable

If no signal is present, any node having data to send may access the cable

This gives rise to the term Multiple Access (MA)

Y N

N Y

CS?

Send Data

Send Jam

Random#Generated

Wait

CD?

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CSMA/CD -2CSMA/CD -2

Collision Detect (CD) Added so that

collisions could be detected

When a collision is detected, a JAM signal is sent out telling all stations to ignore the garbled transmission

Y N

N Y

CS?

Send Data

Send Jam

Random#Generated

Wait

CD?

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CSMA/CD -3 CSMA/CD -3

Backoff The transmitting

stations involved in the collision generate random numbers and wait that amount of time before trying again

Y N

N Y

CS?

Send Data

Send Jam

Random#Generated

Wait

CD?

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Ethernet CablesEthernet Cables

Called “10Base5” meaning 10 Mbps, baseband transmission, maximum distance of 500 meters between hubs

Using heavy, thick coax cable, it is often called “Thick Ethernet”

Difficult/expensive to install

10Base5 10Base2 10BaseT 10Broad36

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Uses a smaller coaxial cable Often called “Thin Ethernet” or “Cheapernet” Makes use of a T-connector mounted directly

into the NIC Real problems if something happens to one

system in the line


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The most common type of Ethernet The “T” means twisted-pair wiring Unshielded twisted Pair (UTP) Very low cost Also uses the T-connector


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Called “10Broad36” meaning 10 Mbps, broadband transmission, maximum distance of 3600 meters between hubs

Most commonly used in BN Allows an intermix of voice, data, and images


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Ethernet (IEEE 802.3)Ethernet (IEEE 802.3) Uses bus topology Computers receive messages intended for all

computers Bus - high speed circuit/limited distance Requires repeaters & terminators Carrier Sense Multiple Access with Collision

Detection (CSMA/CD) Baseband (digital) or Broadband (analog) 10Base5 (thick) 10Base2 (thin) 10BaseT

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Token Ring (IEEE 802.5)Token Ring (IEEE 802.5) This is the second most popular type of LAN,

25% worldwide installations Originally developed by IBM in 1985 and

known as the IBM Token Ring LAN Exists in both 4 Mbps and 16 Mbps versions Normally uses twisted-pair, either STP or UTP All wiring is done at a HUB

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IEEE 802.5 Logical TopologyIEEE 802.5 Logical Topology

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IEEE 802.5 Physical TopologyIEEE 802.5 Physical Topology

HUB (MAU)

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Token Passing Access Token Passing Access

Access Method The sending station

waits for a “free” token.

1

S

D

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Access Method Adds data,

addresses, and sets token as “busy”.

2

S

D

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Access Method Receiving station

copies data, adds the ACK, and sets “copied bit” on the token. 3

S

D

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Access Method Sending station

verifies the acknowledgement and generates “free” token. 4

S

D

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Problems One station in the ring

is designated as “token monitor” to deal with lost tokens.

The free token moves between the computers in a predetermined sequence.

Maximum number of messages that a computer can send before issuing a free token.

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Token Ring (IEEE 802.5)Token Ring (IEEE 802.5) Uses ring topology Messages pass to each computer in turn Token passing (short electronic message)

turn taken when has possession of free token changes free token to busy token and attaches

message token passed up the line to receiving computer

Requires a token monitor for lost tokens Token-ring-4 and Token-ring-16 (TR-100)

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Token Bus (IEEE 802.4)Token Bus (IEEE 802.4) May be either baseband or broadband in its

architecture baseband bus has only one token on the network

at any given time broadband bus has multiple tokens, one for each

channel, using FDM

MAP (Manufacturing Automation Protocol) uses IEEE 802.4 Token Bus

Supports factory automation where real-time, guaranteed response is a necessity (robotics)

Exists in 1, 5, 10 and 20 Mbps

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IEEE 802.4 Token BusIEEE 802.4 Token Bus The network maintains a table of addresses

for each node Addresses indicate the order in which nodes

receive the token Any node requiring priority is simply listed

more frequently in the table

A B C D E

1 2 345

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Arcnet - Attached Resource Arcnet - Attached Resource Computing Network Computing Network

Developed by Datapoint Corporation in 1977 Peer-to-Peer Low-cost PC LAN Baseband Token-passing Bus or star architecture ANSI 878.1 Coaxial cable 2.5 Mbps/Arcnet Plus 20Mbps 1000 feet between computers

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Apple TalkApple Talk Macintosh computers w/built-in network

hardware Apple cabling system (LocalTalk) 230 Kbps 32 computers / 1000 feet between computers Carrier Sense Multiple Access/Collision

Avoidance (CSMA/CA) LLAP - LocalTalk Link Access Protocol Slow data transmission rate Non-standard

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Wireless LANs (IEEE 802.11)Wireless LANs (IEEE 802.11) Transmit through the air rather than by cable Useful in old building where wiring is difficult

and costly NICs installed in the computer are attached to

external infrared or radio transmitters Increasingly used by laptop computers to

provide mobile workgroup computing

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Wireless LANs (IEEE 802.11)Wireless LANs (IEEE 802.11) There are three commonly used types of

wireless LANs: Infrared Direct-sequence spread spectrum radio Frequency hopping spread spectrum radio.

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Infrared Wireless LANsInfrared Wireless LANs Most require direct-line-of-sight Diffuse infrared -- bounces light around the

room Extremely short range (50-75 feet) Operate only within a room

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Radio Wireless LANsRadio Wireless LANs Travel in all directions and penetrates non-

metallic objects Larger range - 100 to 500 feet DSSS (Direct Spread Spectrum System)

transmit signals through a wide spectrum of radio frequencies simultaneously

FHSS (Frequency Hopping Spread Spectrum) minimizes eavesdropping by changing quickly from

one frequency to another

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Wireless LANs (IEEE 802.11)Wireless LANs (IEEE 802.11) Transmit through the air rather than by cable Use same protocols as other LANs NIC is connected to an external infrared or

radio transmitter low cost - no or little wiring noise disrupts transmissions slower data transmission rates lack of security

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LAN PerformanceLAN Performance

Throughput and Bottlenecks Software

NOS disk caching - storing commonly used data in memory disk elevatoring - order data is accessed

Hardware Server CPU Server memory Number and speed of hard disks NIC Cards

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Improving LAN PerformanceImproving LAN PerformancePerformance Checklist

Increase Server Performance Software

Upgrade to a faster network operating system Fine-tune the network operating system settings

Hardware Add more servers and spread the network applications across the servers

to balance the load Upgrade to a faster computer Increase the server’s memory Increase the number and speed of the server’s hard disk(s) Upgrade to a faster NIC

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Improving Server PerformanceImproving Server Performance

Software: Faster NOS Disk caching Disk elevatoring NOS software settings

Hardware Second server Upgrade server (CPU

speed, Memory) Number and speed of hard

drives in the server. NIC

Improving server performance can be approached from two directions simultaneously:

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Improving LAN Performance Improving LAN Performance

Performance Checklist (cont’d.)

Increase Circuit Capacity Upgrade to a faster circuit Change protocols Segment the network

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Circuit CapacityCircuit Capacity Increase capacity

4 Mbps --> 16Mbps --> 100Mbps

LAN Protocol Ethernet -vs- TokenRing

TokenRing supports higher data transmission CSMA/CD faster than token passing on smaller networks Token passing faster on larger networks Token ring response time more consistent Ethernet allows one computer to monopolize network

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Network SegmentationNetwork Segmentation Increasing circuit capacity by network

segmentation Breaking up the network into smaller

segments The more computers and NICs on the

segment the slower the performance

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Improving LAN Performance Improving LAN Performance

Performance Checklist (cont’d.)

Reduce Network Demand Move files from the server to the client computers Increase the use of disk caching on client computers Change user behavior

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Reducing Network DemandReducing Network Demand

Performance can also be improved by reducing network demand: Moving files from the server to clients. Using disk caching software on the client

machines, to reduce the client’s need for to access disk files stored on the server.

Attempting to move user demands from peak times to off-peak times.

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Selecting a LANSelecting a LAN

Start with basic questions: How many users are expected? How much data will be stored and

transmitted? How easy will it be to add workstations? What cabling is needed? Whose software should be selected? How much security is needed?

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LAN Selection ChecklistLAN Selection Checklist

Network Needs Number of client computers Number of dedicated servers Distance between computers Internetworking requirements Specific application needs User training, documentation, and network policies Future growth

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LAN Selection ChecklistLAN Selection ChecklistTechnology

Protocols Cabling/Wireless Network Operating System

Reliability Ease of use Performance

LAN management software LAN backup software and hardware

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LAN Selection ChecklistLAN Selection ChecklistVendor

Experience with network hardware and software Experience with your network application Vendor service and support

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Selecting a LAN Selecting a LAN

expected usage what cabling is required token ring or ethernet baseband or broadband NOS configuration topology vendor support print features

number of computers expected growth type of server distance (LAN or WAN) NIC cards backup and recovery legal issues privacy and security expertise

Chapter 7B PP

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