Modern Ethernet

Chapter 6

Contents

• Define the characteristics, cabling, and connectors used in 10BaseT and 10BaseFL

• Explain how to connect multiple Ethernet segments

• Define the characteristics, cabling, and connectors used in 100Base and Gigabit Ethernet

Historical

• Early Ethernet using a bus topology was very popular– However, a break or bad connection anywhere on the

network would bring the entire network down

• IBM unveiled a competing technology called Token Ring in the mid 1980s– Used a physical star topology

– Any single break only affected a single station

– Substantial market share was being taken away from Ethernet in the second half of the 1980s

Ethernet’s Response

• Ethernet manufacturers countered with an improved Ethernet– Physical star for robustness

– Adopt inexpensive UTP cabling instead of the more expensive coax

– Same frame type of earlier versions for compatibility

• The new and improved Ethernet is called 10BaseT

10BaseT

10BaseT

10BaseTSpeed

10 MbpsSignal TypeBaseband

A single signalon the cable

Type of cableTwisted Pair

10BaseT Topology

• 10BaseT uses a physical star topology with each node connected to a central hub

10BaseT Topology

• The single segment is still there – having been shrunk to the inside of the hub

• The hub is a multiport repeater operating at the Physical layer

Broken Cables

• If a cable running to a specific node breaks, it affects only that computer

Broken Hub

• If the segment inside the hub breaks, then the entire segment fails

Hub Sizes

• The main difference between hubs is the number of ports

UTP

• Unshielded Twisted Pair (UTP)

• 10BaseT requires CAT 3 (or higher), two-pair, UTP cable– Installers usually install four-pair cable

• One pair sends data and one pair receives data

RJ-45 Connectors

• RJ-45 connectors are used on the ends of the cable

• Each pin in the connector connects to a different wire– 8 pins numbered 1 through 8

– Pins 1 & 2 send data; 3 & 6 receive data

Crimping

• A crimper is a tool used to secure an RJ-45 connector to the end of the cable

• Each wire must connect to the proper pin

• Color-coded wires are used

• Each pair has a solid and a striped wire

Wiring Standards

• Defined by the Telecommunications Industry Association/Electronics Industries Alliance (TIA/EIA)

• Two standards exist for four-pair UTP for 10BaseT networks– T-568A

– T-568B

Wiring Standards

EIA/TIA 568A standard

EIA/TIA 568B standard

Brown

Brown/WhiteOrange

Blue/WhiteBlue

Orange/WhiteGreen

Green/White

BrownBrown/White

Blue/WhiteBlue

Green

Green/WhiteOrange

Orange/White

1

2

3

4

5

67

8

1

2

3

4

5

6

7

8

Split Pairs

• Two pairs of wires are used in 10BaseT– 1 & 2

– 3 & 6

• Why split the second pair (3 & 6)?– This is to provide backward compatibility with

telephone wiring

– Telephone cables use RJ-11 connectors• A single line is wired using 2 & 3

• A second line is wired using 1 & 4

• An RJ-11 may be plugged into an RJ-45 outlet

Which Standard?

• Both 568A and 568B see wide spread usage

• The important thing is to be consistent within your organization

10BaseT Limitations

• Distance between hub and computer may not exceed 100 meters

• The maximum number of computers connected to a hub (or bank of hubs) is 1024

10BaseT Summary

• Speed: 10 Mbps

• Signal type: Baseband

• Distance: 100 meters between the hub and the node

• No more than 1024 nodes per hub

• Star bus topology: physical star, logical bus

• Uses CAT3 or better UTP cabling with RJ-45 connectors

10BaseFL

• 10BaseFL is a fiber-optic version of 10BaseT

• Uses pulses of light instead of electricity

• Longer distances – up to 2 kilometers

• Immune to electrical interference

• More secure – harder to tap into

10BaseFL Cable

• Uses fiber optic cable called multimode

10BaseFL Card

10BaseFL Summary

• Speed: 10 Mbps

• Signal type: Baseband

• Distance: 2000 meters between the hub and the node

• No more than 1024 nodes per hub

• Star bus topology: physical star, logical bus

• Uses multimode fiber optic cabling with ST or SC connectors

Connecting Ethernet Segments

Expanding the Network

• Additional hubs may be necessary– When all the ports are used up on a hub

– To provide fault tolerance

• Hubs may connected using coaxial cable or crossover cables

10BaseT hub with BNC connector used to connect

to another hub

Populated Segment

• A segment connecting two hubs may be populated by having one or more nodes connected to it

Crossover Cables

• Hubs may be connected using crossover cables

• In a crossover cable the send and receive pairs are reversed– One end uses 568A and the other 568B

Crossover Ports

• To avoid rewiring some hubs have special ports that switch the wires inside the hub

Uplink, crossover, in port, or out port all refer to a port where the

wires have been reversed

Connecting Hubs

• When connecting two hubs together, use a crossover cable between two regular ports

• Or use a straight-through (normal) cable between a regular port on one hub and a crossover port on the other hub– Some hubs have a button that switches a port between

normal and crossover

Two PCs may be connected by using a crossover cable from one NIC to the other NIC.

Hubs Connected by 10Base2

Broken Cables

• Segment C’s failure prevents communication between segments A and B, but does not affect communication within segments A and B

5-4-3 Rule

• Multiple Ethernet segments connected together with hubs and repeaters form one large collision domain

• The 5-4-3 rule limits the size of a collision domain

5-4-3 Rule

• In a collision domain no two nodes may be separated by more than– 5 segments

– 4 repeaters

– 3 populated segments• Populated segments have nodes

attached

• Unpopulated segments, or link segments, connect other segments

5-4-3 Rule

• Here’s a network with 6 segments that complies with the 5-4-3 rule

High-Speed Ethernet

100Base Ethernet

• Fast Ethernet refers to any of several Ethernet flavors that operate at 100 Mbps

100BaseT

• IEEE supports two variations: 100BaseTX and 100BaseT4– 100 means a speed of 100 Mbps

– Star bus topology

– UTP cabling and hubs

• 100BaseTX uses CAT 5e or better cabling and two pairs of wires

• 100BaseT4 uses four pairs of wires over CAT 3 or better cabling

Upgrading a Network

• The existing wiring (if it meets the CAT 3 or CAT 5e standard) may be used to upgrade a network– Just change the NICs and hubs

– Networks may be upgraded gradually by using 10/100BaseT devices that may operate at either 10 or 100 Mbps

• 100BaseTX is often referred to as 100BaseT (since 100BaseT4 is rarely used)

Limitations of UTP

• Distance is a limiting factor for large campuses

• Lack of electrical shielding is a problem in locations with lots of electrical interference

• UTP cabling can be easily tapped into

100BaseFX

• 100BaseFX uses multimode fiber optic cable with SC or ST connectors

• Maximum cable length is 400 meters

Gigabit Ethernet

• Gigabit Ethernet is also called 1000BaseX

• Several standards have been defined– 1000BaseSX, 1000BaseLX, 1000BaseT

• 1000BaseT, the dominant standard– Uses four-pair CAT 5e or CAT 6 cable

– Maximum cable length is 100 meters

• Gigabit Ethernet usually means 1000BaseT

Ethernet Switches

• An Ethernet switch is a hub with a bridge built in– Often called a layer 2 switch

Switched Ethernet

• Ethernet switches may be used to replace hubs for improved performance – resulting in switched Ethernet– Creates point-to-point links between devices to form

single two-node collision domains – essentially eliminating collisions

– Devices get full dedicated bandwidth

Backbone

• A backbone is a segment that connects other segments

• Backbones usually run at higher speeds than other segments

Full-Duplex Ethernet

• Full-duplex means that a device can send and receive data simultaneously

• Ethernet transmissions are half-duplex– At any given time a machine can either send or receive

data but not both

• Switched Ethernet uses different pairs of wires for sending and receiving – allowing for full-duplex communication– Essentially doubles the bandwidth

Full Duplex

• If a card supports full-duplex, its setup program will have an option to switch between half- and full-duplex