Ethernet & IEEE 802.3

1. Ethernet & IEEE 802.3 What the IEEE standard covers- Physical layer and interface to the link layer. IEEE 802.2 is the Link layer standard. History- DEC/Intel/Xerox came up with it, then submitted to IEEE for standardization. Some changes were made so Ethernet 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, 802.3 uses LENGTH. SInce the frame is limited in size, the two coexist. Most people use the DIX format.

2. IEEE & OSI LLC 2 MAC 1 PHY LLC = Logical Link Control MAC = Media Access Control PHY = Physical

3. 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.

4. B C Address mismatch packet discarded Address mismatch packet discarded Send data to node D Address match packet processed Transmitted packet seen by all stations on the LAN (broadcast medium) A D Data Normal Ethernet Operation

5. Ethernet Collisions B C Collision Data transmission for C Data transmission for A A D

6. CSMA/CD "Carrier Sense/Multiple Access with Collision Detection" "Driving in Boston" BUS! 51.2 microseconds "Many stations; Listen before talking; listen while talking; if a collision, backoff and try again"

7. 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.

8. 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.

9. 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.

10. Ethernet Cable Names Name Thick coaxial Thin coaxial Unshielded Twisted Pair Fiber RG-8 Wire Type 22 - 26 AWG 62.5/125 micron RG-58 10BASE5 10BASE2 10BASEF 10BASET IEEE Name N/A Standard Number IEEE 802.3 IEEE 802.3a IEEE 802.3i Other names Thick net Thin net UTP

11. Thick braid for EMI Foil Thin braid for EMI Thin foil bonded to insulation Jacket of PVC or Teflon Thick Coax Makeup Center conductor of tin plated solid copper conductor Teflon is used for fire code regulations

12. 500 meter maximum cable run Black marks every 2.5 meters to show transceiver placement Transceiver cable Transceiver Thick Coaxial Connection Pierce clamp

13. 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.)

14. Thin Coaxial Cable Makeup Polyethylene foam Tinned copper wire Jacket made of PVC or Teflon EMI braided shielding

15. Thin Coaxial Connection Concatenation of network attachments Direct connection to card T connector BNC connector at each cable end

16. On-board transceiver logic ASIC 02608C Thin Coaxial Connection (cont.) AUI connector T connector for connection to cable plant BNC connector Interface to computer bus

17. 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.

18. Unshielded Twisted Pair Unshielded twisted pair cable Repeater unit required 100m max cable run Straight through pins 1, 2, 3 and 6 Unshielded twisted pair atleast two (2) twists per foot RJ-45 connector RJ-45 Connector 8 pin 8 pin

19. 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.

20. 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).

21. IEEE802.3 Efficiency "WARNING: Opinion" % Utilization Status 0 - 10 Great! 10 - 40 OK 40 - 60 Performance Problems -- look at it 60+ "Utilization" Signal On Time