Ethernet 802.3.pptx

Computer Networks

1. Ethernet 802.3

2. What is Ethernet ? Ethernet is a certain type of a local area network (LAN) which was developed in 1972 in the renowned PARC-research facility of Xerox in Palo Alto by Robert Metcalfe. In the meantime the companies Intel, DEC and Xerox have specified a common standard that has been established in the IEEE-standard 802.3. Ethernet: It is a LAN protocol that is used in Bus and Star topologies and implements CSMA/CD as the medium access method

3. History 1969 student Robert Metcalfe (founder of 3Com in 1979) develops a Host Interface Controller for DARPA (Defense Advanced Research Projects Agency) in the company DEC. 1970 the ALOHA-Net (multiple access protocol) is developed and tested at the university of Hawaii 1972 the idea is picked up by the XEROX Palo Alto Research Center (Metcalfe works there by then). The project goal is: experimental Ethernet

4. History 1976 the results of the project are published. The companies DEC, Intel and Xerox join in the company DIX and complete Ethernet to the market entry stage. 1980 Ethernet version 1.0 is passed. 1981 IEEE starts standardization efforts. The Ethernet specification is accepted without major modifications. 1982 Publication of Ethernet version 2.0 1985 worldwide recognition of the Ethernet standard as ISO/DIS 8802/3

5. History 1986 Publication of the 10Base2- and 10BroadT standards 1987 Standardization of the 10BaseT spezification 1991 Publication of the 10BaseF standard 1994 more than 10.000 suppliers support the Ethernet globally 1995 Standardization of the 100 Mbit/s Ethernet 1997 Standardization efforts for the Gigabit Ethernet and presentation of first products prior to the completion of the standard

6. Ethernet TCP/IP Ethernet- Header Ethernet-DATA FCS IP- Header IP-DATA IP-frame TCP- Header TCP-DATA TCP-frame Ethernet-frame LAYER 7 Modbus etc.

7. Access method: CSMA/CD Station is ready to send check “Ether” Sending of data and checking the “Ether” Waiting according to back-off algorithm Medium occupied Discovered collision medium available send jam signal No collision New attempt

8. Back-Off Algorithm If a collision has occurred, the stations try to send again after a certain period of time. After the first collision there a two different back-off times available, from which one is chosen at random. Transmission probability is 50% After the second consecutive collision there are four different back-off times available, from which one is chosen at random. The transmission probability now is 75%

9. Delay depending on the network load delay 20 % 40 % 30 % 10 % 50 % 60 % 70 % 80 % Network load low high High throughput Beginning problems Overload

10. Ethernet address Also called "MAC address" Globally unique ID for each device Burnt into ROM, cannot be modified Six Bytes in which manufacturer, device model and serial number are coded Readable with many auxiliary tools e.g. WINIPCFG

11. Ethernet frame Preamble SFD DA SA LEN FCS Pad Data 7 1 6 6 2 >=46 4 Preamble DA SA Type FCS Pad Data 8 6 6 2 >=46 4 Ethernet II DIX Frame: IEEE 802.3 Frame: Frame formats. (a) DIX Ethernet (b) IEEE 802.3.

12. 802.3 MAC Frame

13. Ethernet frame Preamble Trailer consisting of the bit sequence “0101010101...” serving the bit synchronization of the receiver. SFD (Start Frame Delimiter) Start character consisting of the bit pattern “10101011” showing the recipient that the actual information will follow now. DA (Destination Address) Evaluated by the recipient‘s address filter; only data frames destined for this recipient will be passed on to the communication software. SA (Source Address) Sender‘s address LEN (Length) Indicates the length of the subsequent data field in Bytes according to IEEE 802.3.

14. Ethernet frame Data and Pad The data field may contain 46 to 1500 user data bytes. Are there less than 46 bytes the Ethernet controller independently adds padding bytes, until the total amount (data + pad) is 46. This miminum length is crucial for the CSMA/CD procedure to work faultlessly. The data field can be used at will, it only has to contain complete bytes. FCS (Frame Check Sequence) A check character. It is obtained by taking the rest of the division operation from the formula representing the wide-spread cyclic- redundancy-check procedure. This formula is applied to the bit sequence including the address field through to the padding field. In case of en error the whole frame is ignored, i.e. not passed on to the application program.

15. Ethernet Address WIN-NT: ipconfig /all

16. Ethernet Media Twisted Pair FO Coaxial cable Wireless transmission

17. Naming of the cable types Example: 10base5 10 Transmission rate in Mbytes/s base Base or Broadband ( data is sent as digital signals through the media as a single channel that uses the entire  bandwidth ) 5 Segment length in 100 meters UTP unshielded twisted pair STP shielded twisted pair S/STP screened shielded twisted pair

18. Ethernet evolution through four generations

19. <data rate><Signaling method><Max segment length or cable type>

20. 10Base5 Implementation

21. Connection of stations to the medium using 10Base2

22. 10BaseT • Uses twisted pair Cat3 cable Star -wire topology • A hub functions as a repeater with additional functions • Fewer cable problems, easier to troubleshoot than coax • Cable length at most 100 meters

23. Figure: 10Base-T implementation

24. Figure: 10Base-F implementation

25. 13.4 Fast Ethernet 100 Mbps transmission rate same frame format, media access, and collision detection rules as 10 Mbps Ethernet can combine 10 Mbps Ethernet and Fast Ethernet on same network using a switch media: twisted pair (CAT 5) or fiber optic cable (no coax) Star -wire topology Similar to 10BASE-T CAT 3 CAT 5

26. Figure 13.19 Fast Ethernet topology

27. Figure Full-duplex switched Ethernet

28. Figure Switched Ethernet

29. Gigabit Ethernet Speed 1Gpbs Minimum frame length is 512 bytes Operates in full/half duplex modes mostly full duplex

30. IEEE 802.3 Cable Types Name Cable Max. Max Cable Segment Length Nodes /segment 10Base5 thick coax 500 meters 100 10Base2 thin coax 185 meters 30 10BaseT twisted pair 100 meters 1 10BaseF Fiber Optic 2Km 1 Toplogy Bus Bus Star Star

31. IEEE Standard for LANs

32. Ethernet address Six bytes = 48 bits Flat address not hierarchical Burned into the NIC ROM First three bytes from left specify the vendor. Cisco 00-00-0C, 3Com 02-60-8C and the last 24 bit should be created uniquely by the company Destination Address can be: Unicast: second digit from left is even (one recipient) Multicast: Second digit from left is odd (group of stations to receive the frame – conferencing applications) Broadcast (ALL ones) (all stations receive the frame) Source address is always Unicast

33. The least significant bit of the first byte defines the type of address. If the bit is , the address is unicast; otherwise, it is multicast. Note

34. The broadcast destination address is a special case of the multicast address in which all bits are 1s. Note

35. Unicast and Multicast Address

36. Frame length: Minimum: 64 bytes (512 bits) Maximum: 1518 bytes (12,144 bits) Note

37. Ethernet topologies Bus Star Ring

38. Figure: Topologies of Gigabit Ethernet

39. Repeater / Hub Repeater Hub

40. Bridge Bridge A B C D E F

41. Switch = Multiport Bridge Bridge Switch

42. Characteristics of the switches Cut-Trough Switch noc cheking of the data frames Store-and-Forward checking of the data frames Frames with same destination kept in internal short term memory thus queueing them discard them or create collision Broadcast messages go to all stations anyway (z.B. ARP) so switches are of no advantage here there are specific approaches of different switch manufacturers to reduce broadcast data traffic

43. Typical office wiring Hub/Switch Hub/Switch Patch field Patch field Network socket Patch cable „normal“ Cat 5 cable RJ 45