Chapter 18. Virtual-Circuit Networks: Frame Relay and ATM

1. Chapter 18. Virtual-Circuit Networks:Frame Relay and ATM 18.1 Frame Relay 18.2 ATM 18.3 ATM LANs Computer Networks

2. Wide area network and switching methods Computer Networks

3. Circuit switching • Create a real circuit (dedicated line) between source and destination • Physical layer technology Computer Networks

4. Packet Switching: Datagram Approach • Mostly used in the network layer • Routing (selecting the best route for a packet) is performed at each router Computer Networks

5. Packet Switching: Virtual Circuit Approach • Packets (frames) are switched along a pre-determined path from source to destination • Virtual circuit network has two addresses • Global address which is unique in the WAN • Virtual circuit identifier which is actually used for data transfer • VCI has switch scope; it is used between two switches • Each switch can use its own unique set of VCIs Computer Networks

6. VCI Phases • Two approaches for the VC setup • Permanent virtual circuit (PVC): • Switched virtual circuit (SVC): setup, data transfer, teardown Computer Networks

7. Data Transfer Phase • All switches need to have a table entry for the virtual circuit Computer Networks

8. Data Transfer using VCI Computer Networks

9. SVC Setup: Request and Acknowledgment Computer Networks

10. Frame Relay • Frame Relay is a virtual circuit wide area network • VCIs in Frame Relay are called DLCIs(Data Link Connection Identifier) Computer Networks

11. Frame Relay Features • Frame relay operates at a higher speed. It can easily be used instead of a mesh of T-1 or T-3 lines (1.544 Mbps or 44.376 Mbps) • Frame relay operates just the physical and data link layers. It is good as a backbone to provide services to protocols that already have a network layer protocol, such as Internet • It allows bursty data • It allows a frame size of 9000 bytes accommodating all LAN frame sizes • It is less expensive than other traditional WANs • It has error detection at the data link layer only. There is no flow control pr error control • X.25  Leased Lines  Frame Relay Computer Networks

12. Frame Relay vs. T-line Network Computer Networks

13. Frame Relay vs. X.25 Network Computer Networks

14. Frame Relay Layers • Frame relay operates only at the physical and data link layers Computer Networks

15. Comparing Layers: X.25 & Frame Relay Computer Networks

16. Frame Relay Frame Computer Networks

17. Congestion Control • Frame relay requires congestion control, because • Frame Relay does not have a network layer • No flow control at the data link layer • Frame Relay allows the user to transmit bursty data • Congestion avoidance • Two bits in the frame are used • BECN(Backward Explicit Congestion Notification) • FECN(Forward Explicit Congestion Notification) • Discard eligibility(DE): • Priority level of the frame for traffic control • Discarding frame to avoid the congestion or collapsing Computer Networks

18. BECN Computer Networks

19. FECN Computer Networks

20. Four Cases of Congestion Computer Networks

21. Extended Address: Three Address Formats FRAD Computer Networks

22. ATM • Asynchronous Transfer Mode • ATM is the cell relay protocol designed by ATM forum and adopted by ITU-T • ATM uses asynchronous TDM • Cells are transmitted along virtual circuits • Design Goals • Large bandwidth and less susceptible to noise degradation • Interface with existing systems without lowering their effectiveness • Inexpensive implementation • Support the existing telecommunications hierarchies • Connection-oriented to ensure accurate and predictable delivery • Many functions are hardware implementable Computer Networks

23. Multiplexing using Cells • The variety of packet sizes makes traffic unpredictable • A cell network uses the cell as the basic unit of data exchange • A cell is defined as a small, fixed sized block of information • Cells are interleaved so that non suffers a long delay • A cell network can handle real-time transmissions • Network operation is more efficient and cheaper Computer Networks

24. Synchronous vs. Asynchronous TDM Computer Networks

25. ATM Architecture • UNI: user-to-network interface • NNI: network-to-network interface Computer Networks

26. Virtual Connection • Connection between two endpoints is accomplished through • Transmission path (TP) • Virtual path (VP) • Virtual circuit (VC) • A virtual connection is defined by a pair of numbers: VPI and VCI Computer Networks

27. VPI and VCI: Hierarchical Switching Computer Networks

28. Identifiers and Cells Computer Networks

29. VP Switch and VPC Switch Computer Networks

30. ATM Layers Computer Networks

31. ATM Layer and Headers Computer Networks

32. Application Adaptation Layer (AAL) • Convert data from upper-layer into 48-byte data units for the ATM cells • AAL1 – constant bit rate (CBR) video and voice • AAL2 – variable bit rate (VBR) stream  low-bit-rate traffic an short-frame traffic such as audio (ex: mobile phone) • AAL3/4 – connection-oriented/connectionless data • AAL5 – SEAL (Simple and Efficient Adaptation Layer) No sequencing and error control mechanisms Computer Networks

33. AAL1 Computer Networks

34. AAL2 Computer Networks

35. AAL3/4 Computer Networks

36. AAL5 Computer Networks

37. ATM LAN • ATM is mainly a wide-area network (WAN ATM); however, the technology can be adapted to local-area networks (ATM LANs). The high data rate of the technology has attracted the attention of designers who are looking for greater and greater speeds in LANs. Computer Networks

38. Pure and Legacy ATM LAN Computer Networks

39. Mixed Architecture ATM LAN Computer Networks

40. LAN Emulation (LANE) • Connectionless versus connection-oriented • Physical addresses versus virtual-circuit identifiers • Multicasting and broadcasting delivery • Interoperability • Client/Server model in a LANE • LANE Configuration Server (LECS), LANE Server (LES), LANE Client (LEC) • Broadcast/Unknown Server (BUS) Computer Networks

41. Mixed Architecture Using LANE Computer Networks