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Semester 1 CHAPTER 7 Wael Yousif

Semester 1 CHAPTER 7 Wael Yousif. Connecting The Internet Generation. Content. Token-ring. FDDI LAN. Ethernet and IEEE 802.3. Layer 2 devices and effects on data flow. BASIC OF TOKEN-RING. Variants.

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Semester 1 CHAPTER 7 Wael Yousif

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  1. Semester 1CHAPTER 7Wael Yousif Connecting The Internet Generation

  2. Content • Token-ring. • FDDI LAN. • Ethernet and IEEE 802.3. • Layer 2 devices and effects on data flow.

  3. BASIC OF TOKEN-RING

  4. Variants IBM developed the first Token Ring network in the 1970s. It is still IBM's primary LAN technology, and is second only to Ethernet (IEEE 802.3) in terms of LAN implementation.

  5. Ring topology

  6. Data passing • When a station has information to transmit, it seizes the token and sends data frame to the next station. • When frame reaches the destination station, the data is copied for processing. • Frame continues to circle the ring until it returns to the sending station. • Sending station removes the frame from the ring, verifies receipt, and releases the token.

  7. Token-Ring frame format

  8. Start delimiter and End delimiter • Start delimiter. • Alert for the arrival of a token. • End Delimiter • Completes the token or data/command frame. • Contains damage indicator. • Last of logical sequence.

  9. P P P T M R R R Access control • P: Priority bits • T: Token bit • M: Monitor bit • R: Reservation bits

  10. Priority and reservation bits • B'000' Normal User Priority • B'001' Normal User Priority • B'010' Normal User Priority • B'011' Normal User priority • B'100' Bridge/Router • B'101' Reserved IBM • B'110' Reserved IBM • B'111' Station Management

  11. Priority management • Using the priority field and the reservation field. • Stations with a higher priority can reserve the token for the next network pass. • Stations that raise a token's priority level must reinstate the previous priority after their transmission has been completed.

  12. Frame control Only present in data/command frames. Indicates whether frame contains data or control information. If control, this byte specifies type of control information.

  13. Destination and Source addresses Universal Address. Local Administered Address. Broadcast Address Functional Address (0x0C0000 00XXXX)

  14. Data Length limited by the maximum time a station may hold the token.

  15. Frame checksum Frame Check Sequence. Source fills field with calculated value dependent on frame contents. Destination recalculates to check data integrity. Frame is discarded if damaged.

  16. Frame status Address recognized / frame copied indicator.

  17. Management mechanisms • Active Monitor • One station acts as centralized source of timing information for other stations. • Removes continuously circulating frames by set monitor bit to 1. • Start a token, when token have been lost. • Beaconing • Detects and repairs network faults. • Initiates auto-reconfiguration.

  18. Physical topology • Physical topology : Star. • Logical topology : Ring. • IBM Token Ring network stations are connected to MSAU (Multi-Station Access Unit). • Many MSAU can be wired together to form one large ring.

  19. Multi-MSAU

  20. Physical connection

  21. BASIC OF FDDI

  22. Characteristics • Fiber Distributed Data Interface. • FDDI is popular as a campus backbone technology. • 100 Mbps • Token passing • Dual-ring • Fiber Optic Cable • Total fiber length of 200Km

  23. FDDI dual-ring (PR and SR)

  24. Fiber-optic modes

  25. FDDI Connections • Class A: connect directly with PR – SR. • DAC: Dual Attachment Concentrator • DAS: Dual Attachment Station • Class B: connect via FDDI concentrator. • SAS: Single Attachment Station

  26. Operation mechanisms • Connection Establishment • Station connect to neighbors to form the ring. • Negotiate the length of the link. • Ring Initialization • Station claim the right to generate a token. • Steady-state Operation • Token passing • Ring Maintenance • Detects and repairs token or network faults.

  27. FDDI topology

  28. ETHERNET AND IEEE 802.3

  29. Ethernet introduction • Ethernet is the most widely used local area network (LAN) technology. • Ethernet was designed to carry data at high speeds for very limited distances. • Ethernet is well suited to applications where a local communication medium must carry sporadic, occasionally heavy traffic at high peak data rates.

  30. Datalink and Physical layers

  31. Comparing Ethernet and IEEE 802.3 • Specify similar technologies. • Broadcast network. • Using CSMA/CD algorithm. • Hardware implementation. • Differences: • Ethernet provides services corresponding to physical and datalink layer. • IEEE 802.3 specifies the physical layer and the channel-access portion of the data link layer but does not define a LLC protocol.

  32. Ethernet family: 1000Base-SX-LX

  33. Ethernet family: 1000Base-T

  34. Ethernet family: 100Base-TX

  35. Ethernet family: 10Base-T

  36. Ethernet family

  37. Ethernet frame format

  38. Preamble Note that a frame is Ethernet or IEEE 802.3.

  39. Start of frame delimiter (SOF) The IEEE 802.3: synchronize the frame-reception portions of all stations on the LAN. Be explicitly specified in Ethernet.

  40. Source and destination addresses MAC addresses. Unicast. Multicast (D) Broadcast (D)

  41. Type (Ethernet) Specifies the upper-layer protocol to receive the data after Ethernet processing is completed

  42. Length (IEEE 802.3) The length indicates the number of bytes of data that follows this field

  43. Data (Ethernet) the data contained in the frame is sent to an upper-layer protocol

  44. Data (IEEE 802.3) Data send to LLC layer, including LLC header and upper-layer data

  45. Frame check sequence (FCS) This sequence contains a 4 byte CRC value that is created by the sender and is recalculated by the receiver to check for damaged frames

  46. Media Access Control (MAC) • Shared-media broadcast technology. • Ethernet’s MAC performs three functions: • transmitting and receiving data packets • decoding data packets and checking them for valid addresses before passing them to the upper layers of the OSI model • detecting errors within data packets or on the network

  47. Broadcast technology MAC

  48. Broadcast address FF-FF-FF-FF-FF-FF

  49. CSMA/CD • When a station wishes to transmit, it checks the network to determine whether another station is transmitting. • If network is free, the station proceeds with the transmission. • While sending, the station monitors the network to ensure that no other station is transmitting. • If a transmitting node recognizes a collision, it transmits a jam signal so that all other nodes recognize collision. • All transmitting nodes then stop sending for a backoff time (randomly 0 .. 2n - 1 of 51.2ms).

  50. CSMA/CD (cont.)

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