Introduction to IT and Communications Technology

Justin Champion

C208 – 3292

Ethernet FundamentalsCE00378-1

Content What we are looking at

Ethernet technology How did it develop How and why it works Features of the Technology

Evolution of Ethernet The most widely used technology LAN

based network technology is Ethernet (IEEE 802.2)This technology is based on broadcast radio,

used within a cableThe technology is widely used due

Cheapness of installation Reliability Ease of expansion and extension of the networks Ability to adapt to multi types of usage

Evolution of Ethernet

One part of Ethernet is an extension of the Alohanet which was developed in the 1960’s This was a radio technique which was used to allow

multiple people on a network, using radio technology to access computer systems

The access techniques used for this network was used for Ethernet

Evolution of Ethernet

Ethernet is a broadcast medium The only change to this is with various new pieces of kit,

which will be covered later in the course Switch Router Bridge

If a device send a message from device A to D, device B and C will also receive it

They recognise it is not for them due to the MAC address and ignore it A B C D

MAC addresses

Media Access Control (MAC) address Are a unique address which is assigned to a network

card when manufactured This address can NOT be changed and is based on a

48bit sequence Made up of a 24 bit OUI and a vendor assigned 24 bits

http://idogan.istanbul.edu.tr/oui.html list of OUI’s

Ethernet technologies: 3 part names

The names used in Ethernet tell you about the technology i.e. 10BaseT

10 Mbps, BaseBand using Unshielded Twisted pair cabling

802.3 Ethernet in relation to the OSI model

Ethernet as with all other network communications Integrates with the OSI model Ethernet standards are concerned with layers 1 and 2

1 – Physical Transfer of the signal across the medium

2 – Data Link Allowing access to layer 1 Formatting the data correctly Addressing the data

IEEE ?

Institute of Electrical and Electronic Engineers (IEEE) These are not for profit group with a worldwide base They develop standards for electrical and electronic products

The standards are based on the input of the members of the IEEE, to agree on the best standards

Currently there are 900 IEEE standards with many more being developed

IEEE 802.3 - Ethernet IEEE 1284 – Parallel Port IEEE 802.11b – Wireless LAN http://wally.rit.edu/pubs/guides/ieeestds.html list of standard groups

The peer review methods allow for standards to be developed that take account of worldwide concerns for a technology

IEEE 802.x standards

OSI Layer 1 Vs layer 2

Frames to bits Ethernet Frame

This is how Ethernet combines the bits to transfer the data Additional information is added to the data by layer 2

Generic frame format Ethernet Frame

By putting the data into a known sequence i.e. the frame Each part of the frame can be known If data was “Just” transferred how would the recipients

know when the data started and ended The frame fields are usually measure in Octets for brevity

8 Bits = 1 Octet

IEEE 802.3 Ethernet

Ethernet II frame format

Ethernet and IEEE 802.3 formats Ethernet Types

There is the small 1 octet difference between the formats Both can be used interchangeably without concern

Common LAN technologies A number of different physical topologies exist for

LANs Ethernet

Uses a shared medium with devices communicating when silence is detected

Token Ring Devices can only communicate when they control of the token

Fibre Distributed Data Interface (FDDI) High speed fibre optic data transfer using token technology

Ethernet – Collisions ! Ethernet is a shared broadcast

technology Transmitting when silence is

detected on the cable This becomes a issue if multiple

devices want to communicate They will both detect silence and

start transmitting Causing a collision and corrupting

the data which is on the cable The method of dealing with this is

CSMA/CD Carrier Sense Multiple Access /

Collision Detection This is the same method as used

for Alohanet, discussed earlier

CSMA/CD process

Bit time Bit Times

These times are the transmission times for a single bit of data

So 10 bits can be transferred in the time that a single 10 Mbps version of Ethernet can send a bit

Slot time parameter

Interframe spacing

This is the delay time between sending successful frames, the value is fixed at 96 bits, but the rate of transmitting bits varies between technologies

Slot time only applies to half-duplex Ethernet links

In the event of a collision the slot time is used in increments to back off before attempting retransmission

Routine error handling in a 10Mbps collision domain

Summary of collision types: local, remote and late

10Base2/10Base5 local collision

Long frame

Short frame

FCS errors

NLP Vs FLP timing

Actual FLP auto-negotiation burst

Transmission priority rank

Summary of Today's lecture What was looked at today

Ethernet technology How did it develop How and why it works Features of the Technology