Ethernet & IEEE 802.3

What the IEEE standard covers- Physical layer andinterface to the link layer. IEEE 802.2 is the Link layer standard.

History- DEC/Intel/Xerox came up with it, then submitted toIEEE for standardization. Some changes were made soEthernet is not identical to IEEE 802.3

Differences between Ethernet and 802.3

There are some electrical and connector differences; most equipment uses IEEE 802.3.There is difference in the header. DIX uses TYPE, 802.3uses LENGTH. SInce the frame is limited in size, the two coexist.Most people use the DIX format.

IEEE & OSI

PHY

MAC

LLC 2

1

LLC = Logical Link ControlMAC = Media Access ControlPHY = Physical

Ethernet• Work started back in 1973 by Bob Metcalfe and David Boggs from Xerox Palo Alto

Research Center (PARC).

–He studied the Aloha network and "fixed" the mathematics.

• Experimental Ethernet implemented in 1975.

• Cooperative effort between Digital, Intel, and Xerox produced Ethernet Version 1.0 in 1980. –This also became known as the Blue Book specification or DIX standard. Ethernet V2.0 adopted in 1982.

• Ethernet was adopted with modifications by the standards committees IEEE 802.3 and ANSI 8802/3.

• Ethernet allows for only connectionless communication.

Normal Ethernet Operation

A

B

D

Data

C

Address mismatchpacket discarded

Address mismatchpacket discarded

Address matchpacket processed

Send datato node D

Transmitted packet seenby all stations on the LAN

(broadcast medium)

Ethernet Collisions

A

B C

D

Collision

Data transmission for A Data transmission for C

CSMA/CD"Carrier Sense/Multiple Access with Collision Detection"

"Driving in Boston"

BUS!

"Many stations; Listen before talking; listen while talking; if a collision,backoff and try again"

51.2 microseconds

CSMA/CD - A Simple Definition• A network station wishing to transmit will first check the cable plant to ensure that

no other station is currently transmitting (CARRIER SENSE).

• The communications medium is one cable, therefore, it does allow multiple stations access to it with all being able to transmit and receive on the same cable (MULTIPLE ACCESS).

• Error detection is implemented throughout the use of a station "listening" while it is transmitting its data.

–Two or more stations transmitting causes a collision (COLLISION DETECTION)

–A jam signal is transmitted to network by the transmitting stations that detected the collision, to ensure that all stations know of the collision. All stations will "backoff" for a random time.

–Detection and retransmission is accomplished in microseconds.

Frame/Packet Format

Preamble SFD Dst Src Type Data/Pad FCS

Size 7 1 6 6 2 46-1500 4(octets)

In IEEE 802.3, the Type field is used as a Length field.

Addresses are generally (3) octets vendor code, (3) octets device number.

Ethernet Addressing

Each station recognizes three classes of addresses.• Own address• Broadcast address (all 1's)• Optionally, one or more multicast addresses

Major reason for broadcast is address discovery.Multicast addresses are used for specialized link layer functions.

Ethernet Cable Names

RG-8 RG-58 22 - 26 AWG 62.5/125 micron10BASE5 10BASE2 10BASET 10BASEF

IEEE 802.3 IEEE 802.3a IEEE 802.3i

Name

Wire Type

IEEE Name

Standard Number

Other names

FiberUnshielded Twisted PairThin coaxialThick coaxial

N/A

Thick net Thin net UTP

Thick Coax Makeup

Jacket of PVC or Teflon

Thick braid for EMI

FoilThin braid for EMI

Thin foil bonded to insulation

Center conductor of tin plated solid copper conductor

Teflon is used forfire code regulations

Thick Coaxial Connection

Pierce clamp

Transceiver

Transceiver cable

Black marksevery 2.5 meters

to show transceiverplacement

500 meter maximum cable run

Transceivers• Transmitter/Receiver: AUI on one side, media on the other

• Used on all Ethernet networks and is the device that allows data to flow between the controller card and the network.

• Detects errors on the bus cable plant and reports them to the station's controller card.

• For thick coaxial cable, the transceiver is external to the controller card and attaches directly to the thick coaxial cable via a special cable known as the transceiver cable.

• External transceivers have a SQE function that enables the controller to determine the status of the transceiver.

• Usually has status indicators (LEDs) physically located on it to indicate the state of the transceiver (transmitting, receiving, collision, and power.)

Thin Coaxial Cable Makeup

Jacket made of PVC or Teflon

Polyethylene foam

Tinned copper wire

EMI braided shielding

Thin Coaxial Connection

T connector

Directconnection

to card

BNC connector at each cable end

Concatenation of network attachments

Thin Coaxial Connection (cont.)

Interface to computer bus

T connector for connection to cable plant

transceiver logicOn-board

BNC connector

AUI connector

02608C

ASIC

UTP Makeup• UTP was standardized by the IEEE 802.3 committee in October of 1990.

• Standardized by the EIA under TIA 568A.

• UTP for LANs is now classified as:

–Category 3 - used for LANs up to 10 Mbps.–Category 4 - used for LANs up to 16 Mbps.–Category 5 - used for LANs up to 100 Mbps.

• Cable is made up of 8 strands of 24 AWG wire.–Only 2 pair are used for single 10BASET connection.

Unshielded Twisted Pair

Unshielded twisted pairatleast two (2) twists per foot

RJ-45Connector

RJ-45connector

100m max cable run

8 pin 8 pin

Unshielded twisted pair cable

Straight through pins 1, 2, 3 and 6

Repeater unit required

Concentrator (Hub) Management• With the concentration of the wiring into a common point, network managers can manage the hub with specialized

software.

• Network management software resides not only in the concentrator but on an external workstation’s device (a PC, for example).

– The workstation can query the concentrator for information.

• Concentrators also allow the control of individual ports.

• This software allows managers to extract information from each card that is inserted in the repeater. You could query the hub for statistics such as:

– number of packets (bytes),

– number of collisions (single and multiple),

– number of framing errors,

– number of time the particular card de-inserted itself from the network,

– ability to turn on/off any repeater card in the hub, and

– all information is time and date stamped.

• With 10BASET, all information is provided on an individual-connection basis, giving a manager information right from the desktop.

Ethernet Repeaters• Extend the network by interconnecting multiple segments

–Extend the physical domain of the network

• Governed by the IEEE 802.3c working group standard.

–This governs the electrical specifications of a repeater.–The physical configurations of a repeater varied from vendor to vendor.

• Some repeaters contain the intelligence to:

–detect collisions per cable plant (will not repeat collision fragments to other cable plants).

–de-insert themselves from a wiring concentrator (when there are excessive errors on the cable plant).

– submit network management information to a central controller.

• Repeaters have been transformed into wiring concentrators or hubs

• Repeaters can be used to interconnect different wiring types but not different access methods (i.e., not Token Ring to Ethernet).

IEEE802.3 Efficiency

"WARNING: Opinion"

% Utilization Status

0 - 10 Great!

10 - 40 OK

40 - 60 Performance Problems -- look at it

60+ RIP

Time

SignalOn

"Utilization"