Introduction to IT and Communications Technology Justin Champion C208 – 3292 Ethernet Fundamentals CE

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 cable  The 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 BCD

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  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 Ethernet  IEEE 1284 – Parallel Port  IEEE b – Wireless LAN  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 Ethernet

Ethernet II frame format

Ethernet and IEEE 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