1. Advanced Networking Lecture for September 17 X.25, Frame and ATM Many of these figures were adapted from Tanenbaum (Computer Networks) and from Forouzan (Data Communications and Networking)

2. Shared medium drawbacks Shared-medium networks do not scale –Simple hub sends incoming frames to all output ports – (a layer 1 hub) –As more nodes are added, congestion becomes a problem >> it’s a shared medium A B C D E F G 10Base2 10BaseT

3. Layer 2 Switching Layer 2 switch is used to interconnect LAN segments –Usually Ethernet Types of layer 2 switches –Simple Bridge –Multiport Bridge –Transparent Bridge –Remote Bridge –Possibly others??

4. Hub and Spoke (cont) Filtering alleviates this problem –Why not just send the frames to the destination port and not the others? –This requires processing the destination fields in the frame Drawbacks: –Requires the switching fabric to be much faster than before 10 users all transmitting at 100Mbps >>> 1Gbps –Hub must be able to “Learn” the proper destination i.e. How does the hub know to selectively forward frames?

5. Bridges Bridges forward at Layer2 based on destination MAC address in Ethernet frame –When Ethernet frame comes in, sent out only on port corresponding to MAC address in table Port #MAC address 02b:6:8:f:1e:5b 1f:1e:5b:2b:6:8 22b:6:8:f:1e:51 Problem: How is this table built???

6. Learning Bridges Bridges are Hubs that filter and forward selected layer 2 frames. A B C D E F G H I J K L M N Bridging Switch

7. Learning Bridge (cont) Old bridges required these tables to be built by hand. The learning bridge builds and maintains a map of the physical port and the MAC address. It does this by watching source MAC address of frames and from what physical port they come. Problem: What if we have multiple bridges connecting networks???

8. Spanning Tree Bridges Two parallel transparent bridges. These can create multiple copies of the frame. Can also cause forwarding loops.

9. Spanning tree (cont) Often multiple bridges are used for redundancy. Spanning tree algorithm is used to eliminate forwarding loops and multiple copies of frames. Routes and bridges with lower numbers become primary elements of the spanning tree. Other routes and bridges are used in the event of a failure Exact algorithm is detailed but straightforward. Algorithm also used at layer 3 for multicast IP and other applications.

10. Spanning Tree Bridges (2) (a) Interconnected LANs. (b) A spanning tree covering the LANs. The dotted lines are not part of the spanning tree.

11. Bridges from 802.x to 802.y Operation of a LAN bridge from 802.11 to 802.3. MAC layers are different for.11 and.3, LLC the same

12. Bridges from 802.x to 802.y (2) The IEEE 802 frame formats.

13. Remote Bridges Remote bridges can be used to interconnect distant LANs.

14. Repeaters, Hubs, Bridges, Switches, Routers and Gateways (a) Which device is in which layer. (b) Frames, packets, and headers.

15. Figure 17-1 X.25

16. Was the first popular packet switched network Allowed for the setup of data connections at speeds between 300bps to about 56kbps. Uses the “Virtual Circuit” concept. –Connection oriented packet switch. Still used for low bandwidth transactions –credit cards / Point-of-Sale (POS) transactions. –Telemetry networks.

17. Figure 17-2 X.25 Layers in Relation to the OSI Layers

18. Figure 17-3 Format of a Frame

19. Figure 17-6 Frame Layer and Packet Layer Domains

20. Figure 17-7 Virtual Circuits in X.25 Virtual circuits allow “meshy” network with fewer physical links.

21. Figure 17-8 LCNs in X.25 LCN: Logical Channel Number, identifies the VC at different sections of the network.

22. Figure 17-10 PLP Packet Format Note the LCN is in the Layer 3 portion of the protocol. GFI: General Format Identifier-- defines which device should acknowledge the packet PTI: Packet Type Identifier – The type of packet

23. Figure 17-11 Categories of PLP Packets RR: Receive Ready RNR: Receive not ready REJ: Reject

24. Figure 17-12 Data Packets in the PLP Layer

25. Figure 17-13 RR, RNR, and REJ Packets

26. Figure 17-14 Other Control Packets

27. Figure 17-15 Control Packet Formats

28. Figure 17-17 Triple-X Protocols

29. Key points on X.25 Was developed as a packet switching protocol. Standard includes Layer 1,2,3 Incorporates SVCs and PVCs Limited in bandwidth Not optimized for high quality links –Too much error checking for “good” networks Not optimized for TCP / IP transport –Already has PLP defined at Layer 3

30. Chapter 18 Frame Relay

31. Figure 18-1 Frame Relay versus Pure Mesh T-Line Network

32. Figure 18-2 Fixed-Rate versus Bursty Data

33. Figure 18-3 X.25 Traffic

34. Figure 18-4 Frame Relay Traffic

35. Figure 18-5 Frame Relay Network

36. Figure 18-6 DLCIs: Data Link Connection Identifier

37. Figure 18-7 PVC DLCIs

38. Figure 18-8 SVC Setup and Release

39. Figure 18-9 SVC DLCIs

40. Figure 18-10 DLCIs Inside a Network Note that the overall connection is a mixture of different interfaces and DLCIs This allows DLCIs to be re-used on different interfaces

41. Figure 18-11 Frame Relay Switch

42. Figure 18-12 Frame Relay Layers

43. Figure 18-13 Comparing Layers in Frame Relay and X.25

44. Figure 18-14 Frame Relay Frame

45. Figure 18-15 BECN BECN assumes the source can reduce congestion by slowing down the transmission of data.

46. Figure 18-16 FECN FECN notifies the receiver that congestion is occurring. It can then be more patient and not request so much data.

47. Figure 18-17 Four Cases of Congestion

48. Frame Relay bandwidth management Frame customers typically connect at T1 or T3 line rate. –They can “burst” up to this speed They pay for something less –Normally pay based on CIR: Committed Information Rate When Customers exceed CIR for an extended period, their traffic is subject to being discarded Allows service providers to “oversubscribe” the network, but prevent individual users from “hogging” the resources.

49. Figure 18-18 Leaky Bucket

50. Figure 18-19 A Switch Controlling the Output Rate

51. Figure 18-20 Flowchart for Leaky Bucket Algorithm

52. Figure 18-21 Example of Leaky Bucket Algorithm

53. Figure 18-22 Relationship between Traffic Control Attributes

54. Figure 18-23 User Rate in Relation to B c and B c + B e

55. Figure 18-25 FRAD

56. Chapter 19 ATM

57. ATM in context Development of ATM began prior to the WWW and TCP/IP explosion- early nineties. There was a desire for a packet switched protocol that was faster than X.25 and Frame and could support multiple classes of service –Video, Voice, Data ATM was selected as the technology of choice for BISDN –The plan was to allow “fast” phone calls all over the place. These could support differing levels of bandwidth and QoS.

58. Figure 19-1 Multiplexing Using Different Packet Sizes 53 byte “cell” allowed for higher levels of QoS with minimal cell-tax – the ratio of overhead to payload in the cell.

59. Figure 19-2 Multiplexing Using Cells

60. Figure 19-3 ATM Multiplexing

61. Figure 19-4 Architecture of an ATM Network UNI – User to Network Interface NNI – Network to Network Interface

62. Figure 19-5 TP, VPs, and VCs TP: Transmission path – link between two switches VP: Virtual Path – Contains several VCs VC: Virtual Circuit

63. Figure 19-6 Example of VPs and VCs VPs originally conceived to simplify management of VC bundles

64. Figure 19-7 Connection Identifiers

65. Figure 19-8 Virtual Connection Identifiers in UNIs and NNIs

66. Figure 19-9 An ATM Cell

67. Figure 19-10 SVC Setup

68. Figure 19-11 Routing with a VP Switch

69. Figure 19-12 A Conceptual View of a VP Switch In theory, a VP switch is simpler because it just switches based on the VPI. Fewer entries to be maintained.

70. Figure 19-13 Routing with a VPC Switch

71. Figure 19-14 A Conceptual View of a VPC Switch

72. Figure 19-15 Crossbar Switch

73. Figure 19-16 Knockout Switch Output queuing reduces lost cells. Introduces some jitter.

74. Figure 19-17 A Banyan Switch Self routing switch, minimizes control hardware required. A multi-stage switch

75. Figure 19-18-Part I Example of Routing in a Banyan Switch (a)

76. Figure 19-18-Part II Example of Routing in a Banyan Switch (b)

77. Figure 19-19 Batcher-Banyan Switch Cells are reordered at input port so they don’t block each other as they go through the fabric

78. Figure 19-20 ATM Layers

79. Figure 19-21 ATM Layers in End-Point Devices and Switches

80. Figure 19-27 ATM Layer

81. ATM Adaption Layers These allow other protocols to mapped into cells. AAL1: Good for Constant Bit Rate (CBR) AAL2 –Variable Bit Rate Services – Particularly Video AAL3/4 AAL5 –Ethernet and IP – Data oriented protocols Lots of references available on these

82. Figure 19-28 ATM Header

83. Figure 19-29 PT Fields

84. Figure 19-30 Service Classes

85. QoS Constant Bit Rate (CBR) used for carrying DS1 and DS3 or other traffic requiring a constant guaranteed QoS VBR (Real Time and Non Real Time) used for data that is bursty but need QoS –Especially for Video UBR/ABR lower QoS for Data similar to Frame Relay level of QoS

86. Figure 19-31 Service Classes and Capacity of Network

87. Figure 19-32 QoS Lots of parameters for QoS. Homework: Go look these up and also understand the concept of CAC.

88. Figure 19-33 ATM WAN

89. Figure 19-34 Ethernet Switch and ATM Switch ATM hasn’t really taken hold in the Enterprise. Much more expensive than Ethernet switches.

90. Figure 19-35 LANE Approach