CHAPTER 4ETHERNET BASICS

Ethernet HistoryDeveloped to replace “Sneakernet"Originally developed in 1973 by Xerox Corp. for internal computer networksStayed an internal technology until 1979IEEE 802.3

Coaxial10Mbps

Ethernet Basic Concept

Ethernet quirks due to early design decisions:

“Shared Cable” conceptData frames with MAC addressCSMA/CD

The Ethernet Topology

Early Ethernet based on bus topology

The Ethernet Topology

Ethernet still operates in a logical bus topology regardless of physical topologyIn the early 1990s the bus gave way to the hubHub is multi-port repeater

“Bus in a box”

Ethernet FramesRecall from chapter 2 that frames are packages of data defined in the datalink layer of the OSI modelEthernet frame:

CSMA/CD

Carrier Sense Multiple Access (with) Collision Detection

Carrier SenseMultiple AccessCollision Detection

Collision Domain

Early Ethernet Networks:A History Lesson

IEEE 802.3 “Ethernet” standard:10baseT

10MbpsbasebandTwisted pair

Physical vs. Logical Topology

Physical:

How the cables are connectedLogical:

How the data flowsEthernet is now a Logical bus and a physical starWas it always like this? How was it different?

Physical components of Ethernet

UTP (Unshielded Twisted Pair)Ethernet requires CAT3 or higher & RJ-45 ConnectorCabling made up of 4 pairsEach Pair has a color & color with white stripe

Orange, Green, Blue, BrownWrapped in an outer sheath that has NO shielding (unshielded)

Cable Termination4 Pairs, but what order?Where the cable meets the connector is explicitly defined by:

TIA/EIA 568A & 568B

Transmission ModesHalf Duplex

NIC can only transmit OR receive at one timeThink of a walkie talkie

Full Duplex

NIC can transmit AND receive at the same timeThink of a telephone

Fiber-optic Ethernet

10baseFL10Mbpsbasebandfiber-optic

Fiber vs. Copper Comparison

10BaseT 10BaseFL

Speed 10Mbps 10Mbps

Signal Type Baseband Baseband

Max. Distance 100 Meters 2000 Meters

Node Limit 1024 Nodes 1024 Nodes

Topology Star-Bus Star-Bus

Cable Type CAT3 UTP Multimode Fiber

Fiber vs. Copper Comparison

10BaseT 10BaseFL

Speed 10Mbps 10Mbps

Signal Type Baseband Baseband

Max. Distance 100 Meters 2000 Meters

Node Limit 1024 Nodes 1024 Nodes

Topology Star-Bus Star-Bus

Cable Type CAT3 UTP Multimode Fiber

Connecting Ethernet Segments

Hubs replace the bus cable very early onHubs have limited port counts

That’s a good thing2 types of ports on a hub

RegularUplink(usually only one)

Crossing OverTIA 568B specifies how to terminate both ends of a cable to make a “straight-through” cableTIA 568B on one end and 568A on the other makes a “crossover” cable

Reverses the send/receive pairs to allow direct connection between to devicesCan take the place of the uplink port on hubs

The Path to SwitchingRepeaters

Extend the range of the networkHubs

Think of them as “multi-port repeaters”Bridges

Think of them as “filtering repeaters”Switches

A whole other level of networking

SwitchesThe problem with hubs

They have no intelligenceShared bandwidth10Mbps / 10 clients = 1Mbps

Switches offer intelligence and thus more bandwidth

SwitchesSwitches look like hubs but that’s where the similarities end.Hub: repeats all traffic to all portsSwitch: only sends traffic to the port connecting to the recipient’s NIC

SAT (Source Address Table)Directory of who is connected to what port

SwitchesProblems with SAT and connecting switchesNetwork “Loops” can bring down the networkSpanning tree was developed to solve this

Spanning Tree Protocol

Spanning tree directs switch to shut down (block) the duplicate path