1. 1 Ethernet & IEEE 802.3 Cisco Section 7.3 Stephanie Hutter October 2000

2. 2 Ethernet Commonly used to refer to all carrier sense multiple access collision detection (CSMA/CD) LANS that generally conform to Ethernet specifications, including IEEE 802.3

3. 3 History of Ethernet 1960’s –CSMA/CD developed at the University of Hawaii 1970’s –First experimental Ethernet system at Xerox PARC 1980’s –IEEE 802.3 released –Digital Equipment, Intel, and Xerox jointly develop & release Ethernet Version 2.0 DIX standard Substantially compatible with IEEE 802.3

4. 4 CSMA/CD MAC Stations can access the network at any time Stations listen to the network before transmitting If no signal on the wire, the station sends If two stations send at the same time, a collision occurs –Both transmissions are damaged –Both stations must retransmit –Backoff algorithms determine when each station can retransmit

5. 5 Broadcast Networks All stations see all transmissions Each station must examine each frame to determine if they are the destination –If yes, the frame is passed to upper layers for processing Ethernet & IEEE 802.3 are both broadcast networks

6. 6 Differences between Ethernet and IEEE 802.3 Ethernet provides services to all of OSI Layer 1 & Layer 2 IEEE 802.3 specifies the physical layer and the MAC sublayer of the data link layer. –Does not define a Logical Link Control sublayer protocol Both are implemented through hardware –Typically an interface card or circuitry on a primary circuit board

7. 7 Ethernet Family Tree “Ethernet” is a vague term Includes 18 varieties –Already specified –In the works Legacy networks –10Base2 –10Base5 (Coax)

8. 8 Ethernet Family Tree Current installed base –10Base-T 10 Mbps Cat 5 UTP –100Base-TX Fast Ethernet –100Base-FX 100 Mbps fiber Future Growth –1000Base-T Gigabit over UTP –1000Base-SX Gigabit over fiber Short wavelength laser source –1000Base-LX Gigabit over fiber Long wavelength laser source

9. 9 Ethernet Frame Format Preamble –Alternating patterns of 1s and 0s –Tells receiving stations whether frame is Ethernet or IEEE 802.3 Ethernet frame contains an additional byte –Equivalent to the Start of Frame (SOF) field specified in 802.3

10. 10 Ethernet Frame Format Start of Frame –SOF –802.3 delimiter byte ends with 2 consecutive 1 bits Synchronize the frame-reception –Explicitly specified in Ethernet

11. 11 Ethernet Frame Format Destination and source addresses –1 st 3 bytes are vendor-specific Specified by IEE –Last 3 bytes are specified by vendor Ethernet or IEEE –Source address is always unicast –Destination can be unicast, multicast, or broadcast

12. 12 Ethernet Frame Format Type –Ethernet only –Specifies the upper-layer protocol to receive the data Length –IEEE 802.3 only –Number of data bytes in the frame

13. 13 Ethernet Frame Format Data—Ethernet –At least 46 bytes of data –Padding bytes inserted as needed

14. 14 Ethernet Frame Format Data—IEEE 802.3 –Upper-layer protocol destination is defined within the data portion of the frame –At least 64 bytes –Padding bytes inserted as needed Frame Check Sequence –4 byte CRC value

15. 15 Ethernet MAC

16. 16 Ethernet MAC Connectionless network architecture –Source device is not notified of successful delivery of data packet –“Best-effort” delivery system

17. 17 Signaling Most common varieties use Manchester encoding Newer, faster varieties use more complex encoding schemes

18. 18 Half Duplex Ethernet Design 10Base-T Transceivers –Built on to NIC –Use 4 wires –1 pair transmits –1 pair receives

19. 19 10Base-T Media & Topologies Why 10Base-T? –Commonly installed –Basic configuration –Not always applicable

20. 20 Star Topology Media runs from a central hub out to each device Central point of control All communication is via the hub

21. 21 Hubs Receive data on one port, broadcast it to all other ports Active or passive –Active Connection and regeneration Extends networking distances Sometimes called concentrators –Passive Connection only

22. 22 Advantages of star topology Easy to design and install Ease of maintenance –Only area of concentration is at the hub –Layout is easy to modify and troubleshoot Easy to add workstations Limited network effect if a device or cable goes down –Increased reliability

23. 23 Disadvantages of star topology Lots of media needed –Increases setup costs Hub represents single point of failure

24. 24 Horizontal Cabling TIA/EIA 568-A –Horizontal cabling must be star topology Mechanical termination for each jack is located at the patch panel in the wiring closet

25. 25 Horizontal cabling UTP –Horizontal cable 90m maximum –Patch cables 3m maximum –Horizontal cross-connect (Wiring closet) 6m maximum –Total 100m (approx)

26. 26 Network Area Cable length limitations limit the size of a star topology network Sneakernet outside the 200m 2 area

27. 27 Extending the network Repeaters regenerate and retime signals Attenuation is “repaired” Cable length specification “restarts”