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  1. Homework • Chapter 12: p 404 1-21

  2. Chapter 12Local Area Networks • Project 802 • Ethernet • Token Ring • Token Bus • FDDI

  3. Local Area Networks • A computer network concentrated in a small area. • Ethernet LANs ( random access based) • Token Ring LANs

  4. Scope of Project 802 • Sets standards for intercommunications between equipment from various manufacturers in LAN environment. • It is concerned with the lower layers of the OSI model and part of the network layer. • The data link layer is divided into two sublayer: • LLC Independent of network architecture • MAC Dependent on network architecture

  5. OSI Model and Project 802

  6. Project 802

  7. Protocol Data Unit (PDU) • Data unit in the LLC sublayer is called PDU. • It contains 4 fields. • DSAP • Identifies the protocol stack on the receiving device. • SSAP • Identifies the protocol stack on the transmitting device • Control • Information

  8. PDU Format

  9. Characteristics of Baseband Transmission • 100 % of bandwidth n% of time • Digital signaling • Entire bandwidth used by the signal • FDM is not possible • Bidirectional • Distances of up to few kilometers

  10. Characteristics of Broadband Transmission • N% of bandwidth 100% of time • Analog signaling • Unidirectional • FDM is possible • TDM is not possible • Distances of up to tens of kilometers

  11. Local Area Networks • A computer network concentrated in a small area. • Ethernet LANs ( random access based) • Token Ring LANs

  12. Medium Access • Centralized • Offers greater control, providing priorities, overrides, guaranteed capacity • Simple implementation at stations • It may create single point of failure • It may become a bottleneck, reducing performance • Decentralized

  13. Medium Access Control Methods • Synchronous • A specific capacity is dedicated to a connection. • Asynchronous • Round Robin Token Bus, Token Ring • Reservation DQDB (802.6) • Contention Bus

  14. Evolution of CSMA/CD

  15. IEEE 802.3 Medium Access Control • ALOHA • Suitable in Small networks • Slotted ALOHA • Carrier-sense media access (CSMA) • CSMA/CD

  16. CSMA/CD Bus Operation • A node will "listen" to the bus to discover the status of the line. • If the bus is not in use, the node will try to transmit its frame and will continue to "listen" to the bus to see if a collision occurs. • A collision is detected when a node "hears" something different from what it is sending. This is called collision detection. • If no collision occurs, the frame is successfully broadcast over the bus and its header is read by all nodes. It is accepted by the node with the correct destination address. • If a collision occurs, the colliding frames are garbled and each of the sending nodes will detect this and will attempt retransmission after a random delay period.

  17. MAC Frame

  18. IEEE 802.3 Medium Access Control (continued) • Frame must be long enough to allow collision detection prior to the end of transmission. (min. requirement for frame length) • Padding is used to accomplish this.

  19. Ethernet Segments

  20. 10BASE5

  21. Transceiver

  22. 10BASE2

  23. IEEE 802.3 Spec. for 10-Mbps baseband coaxial cable bus LANs

  24. 10 BASE T

  25. Developed by AT&T Uses star topology Rarely used Very low speed

  26. 1 BASE 5

  27. 100 BASE-T4 • Both category 3 and category 5 UTP can be used. • When using CAT3 UTP: • Data stream is split up into three separate data streams. • Four TP cables are used. • Data are transmitted using three pairs and received using three pairs. • Two of the pairs must be configured for bidirectional transmission.

  28. 100BASE-T4 33.3 Mbps each Bidirectional