1

LANs are Subnet Standards• Only Physical and Data Link Layer standards• Implemented by the NICs:

Application

Transport

Internet

LAN Subnet(NIC)

Application

Transport

Internet

LAN Subnet(NIC)

2

Subnets

GOLDMAN: DATACOMM FIG. 06-07

8 pin RJ-45 jack for 10Base-T

BNC connector for 10Base-2 (thin coax ethernet)

DB-15 AUI connector for 10Base-5 (thick coax ethernet)

Jumpers to enable/disable media interfaces

Transceiverthick coax ethernet

DB-15 AUI

AUI or transceiver cable

DB-15 AUI

3

CharacteristicsCharacteristicsCharacteristicsCharacteristics DescriptionDescriptionDescriptionDescription

Access MethodAccess Method CSMA/CDCSMA/CD

Transfer SpeedTransfer SpeedStandard Ethernet – 10 MbpsFast Ethernet – 100 MbpsGigabit Ethernet – 1 Gbps (1000 Mbps)

Standard Ethernet – 10 MbpsFast Ethernet – 100 MbpsGigabit Ethernet – 1 Gbps (1000 Mbps)

Collision DetectionCarrier Sense Multiple Access

Detects signalTransmits signal Collision detected

Ethernet (802.3)

4

Ethernet: CSMA/CD

CSMA/CD process

5

Sample Ethernet Frame

6

Ethernet

Ethernet frame

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Logical Topology

• Bus logical topology: signals travel from one network device to all other devices on network

– Broadcast

– Required by bus, star, star-wired physical topologies

8

Bus• Single cable connects all network nodes without

intervening connectivity devices• Devices share responsibility for getting data from one

point to another• Terminators stop signals after reaching end of wire

– Prevent signal bounce• Inexpensive, not very scalable• Difficult to troubleshoot, not fault-tolerant

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Bus

10

Star

A typical star topology network

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Star• Any single cable connects only two devices

– Cabling problems affect two nodes at most• Requires more cabling than ring or bus networks

– More fault-tolerant• Easily moved, isolated, or interconnected with other

networks– Scalable

• Supports max of 1024 addressable nodes on logical network

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Hybrid: Star-Wired Ring

A star-wired ring topology network

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Star-Wired Bus

A star-wired bus topology network

14

Network Cables

Coaxial ThinNetThickNet10Base2, 10Base5

Fiber-Optic

Twisted-PairUnshielded (UTP)Shielded (STP)10BaseT

15

10Base2 /Thinnet

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The 5-4-3 Rule• A thinnet network can combine as many as five cable

segments connected by four repeaters; but only three segments can have stations attache– " This is known as the 5-4-3 rule.

• repeaters can be used to join Ethernet segments and extend the network

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ThinNet 5-4-3 Rule

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10Base2 Standard• Coaxial cable, or thinnet,

which has a maximum segment length of 185 meters.

• Thinnet cabling components include:

• BNC barrel connectors.

• BNC T connectors.

• BNC terminators

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10Base-5 / Thicknet

20

Thicknet 5-4-3 rule

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10BaseT Standard• In 1990, the IEEE committee published the 802.3

specification for running Ethernet over twisted-pair wiring. – UTP

• Most networks of this type are configured in a star pattern, but internally they use a bus signalling system like other Ethernet configurations

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10BaseT Specifications Summary

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10BaseFL Standard• is an Ethernet network that typically uses fiber-optic

cable to connect computers and repeaters.• The maximum distance 2000 meters (about 6500

feet).