1. Prof. John Nestor ECE Department Lafayette College Easton, Pennsylvania 18042 nestorj@lafayette.edu ECE 491 - Senior Design I Lecture 16 - Ethernet Fall 2006

2. ECE 491 Fall 2006Lecture 16 - Ethernet2 Where we are  Last Time:  Data Communication Manchester Transmission  ASM Diagrams  Handshaking  Today:  Ethernet (Handout: Metcalfe & Boggs paper)

3. ECE 491 Fall 2006Lecture 16 - Ethernet3 Review: OSI Reference Model Physical Data Link Network Transport Session Host-Router Protocol Presentation Application Physical Data Link Network Transport Session Presentation Application Transport Protocol Session Protocol Presentation Protocol Application Protocol Physical Data Link Network Physical Data Link Network Internal Subnet Protocol

4. ECE 491 Fall 2006Lecture 16 - Ethernet4 Review: Comparing OSI to TCP/IP Physical Data Link Network Transport Session OSI Presentation Application Host-to- network Internet Transport TCP/IP Application Ethernet

5. ECE 491 Fall 2006Lecture 16 - Ethernet5 Ethernet  Connects computers in a local area network  Computers communicate on shared wires (ether)  Each computer has a unique address (MAC address)  Distributed control  Information passed as packets or frames

6. ECE 491 Fall 2006Lecture 16 - Ethernet6 Brief Ethernet History 1973First developed by R. Metcalfe at Xerox PARC - 3Mb “experimental ethernet” using CATV coax* 1976Boggs/Metcalfe paper published in CACM 1979Metcalfe leaves Xerox to form 3Com 1980Digital, Intel, & Xerox (DIX) form 10Mb standard 1985DIX standard becomes IEEE 802.3 1989IEEE 802.3a - “thin ethernet” (10B2) 1990IEEE 802.3i - twisted cable / star topology 1995IEEE 802.3u - Fast ethernet (100Mbs) 1998Gigabit Ethernet *this is what the paper describes

7. ECE 491 Fall 2006Lecture 16 - Ethernet7 Ethernet Background  Developed and refined at Xerox PARC during 1970s  Xerox Alto: Pioneering “personal computer”  Bitmapped graphical display  Mouse  Ethernet  Laser Printer

8. ECE 491 Fall 2006Lecture 16 - Ethernet8 Xerox Alto - Network Games trek MazeWar

9. ECE 491 Fall 2006Lecture 16 - Ethernet9 Design Principles  Network should be:  Scaleable - should grow smoothly to accommodate “several buildings full of personal computers”  Inexpensive - use inexpensive components, distributed control  Based on transmission of packets containing  Destination address  Source address  Data  Key ideas: packet collision and retransmission  Packet transmission is not guaranteed!

10. ECE 491 Fall 2006Lecture 16 - Ethernet10 Frame Format  Preamble/Start Frame Delimiter (SFD) - used to synchronize receiver  Addresses: destination, source  8-bit address in experimental ethernet  48-bit hardwired “MAC address” in standard ethernet  Data  Error checking - CRC code Preamble/SFDDest AddrSrc AddrDataCRC Accessible to Software

11. ECE 491 Fall 2006Lecture 16 - Ethernet11 Mechanisms  Carrier detection - detects when data is being sent  Deference - wait until  Interference detection - detects collisions  Packet error detection - CRC check  Truncated packet filtering  Collision consensus enforcement - jamming  Exponential backoff

12. ECE 491 Fall 2006Lecture 16 - Ethernet12 Ethernet Operation  Carrier Sense Multiple Access / Collision Detection (CSMA/CD) 1.Start - if wire is idle, start transmitting, else go to 4. 2. Transmitting - If collision detected, continue transmitting (jam) for minimum packet time, then go to 4. 3. End successful transmission - Report success, exit. 4.Wire busy - wait until wire becomes idle 5. Wire just became idle - wait random time, then go to 1 (except when max attempts reached) 6. Max attempts exceeded - Report failure, exit.

13. ECE 491 Fall 2006Lecture 16 - Ethernet13 Internet Protocol (IPv4)  Higher level protocol - IP packets are embedded within each Ethernet frame 0-34-78-1516-1819-31 VersionHdr LenType of Serv.Total Length IdentificationFlagsFragment Offset Time to LiveProtocalHeader Checksum Source Address Destination Address Options Data

14. ECE 491 Fall 2006Lecture 16 - Ethernet14 Where We’re Going - WimpNet  Scaled-down Ethernet interface  Medium: twisted pair  Encoding: Manchester  Details to follow, but based on the “experimental ethernet” described in the Metcalfe & Boggs paper