1. ECE537/8 #1Spring 2009 © 2000-2009, Richard A. Stanley ECE537 Advanced and High Performance Networks 8: Frame Relay, ATM, and Other High-Speed Networks Professor Richard A. Stanley, P.E.

2. ECE537/8 #2 Overview of Tonight’s Class Student presentations/discussions on TEMPEST Review of last time Overview of frame relay, ATM, and other networking protocols of interest

3. ECE537/8 #3 Last time While TEMPEST is a uniquely government program, the issue of compromising emanations is not; it affects all systems Sensitive information is not limited to government systems Networks exacerbate the compromising emanations problem, and they must be considered in network design

4. ECE537/8 #4 Packet-Switching Networks Basic technology the same as in the 1970s One of the few effective technologies for long distance data communications Frame relay and ATM are variants of packet- switching Advantages: –flexibility, resource sharing, robust, responsive Disadvantages: –Time delays in distributed network, overhead penalties –Need for routing and congestion control

5. ECE537/8 #5 Circuit-Switching Long-haul telecom network designed for voice Network resources dedicated to one call Shortcomings when used for data: –Inefficient (high idle time) –Constant data rate

6. ECE537/8 #6 Packet-Switching Data transmitted in short blocks, or packets Packet length < 1000 octets Each packet contains user data plus control info (routing) Store and forward

7. ECE537/8 #7 Figure 4.1 The Use of Packets

8. ECE537/8 #8 Figure 4.2 Packet Switching: Datagram Approach

9. ECE537/8 #9 Advantages over Circuit-Switching Greater line efficiency (many packets can go over shared link) Data rate conversions Non-blocking under heavy traffic (but increased delays)

10. ECE537/8 #10 Disadvantages relative to Circuit- Switching Packets incur additional delay with every node they pass through Jitter: variation in packet delay Data overhead in every packet for routing information, etc Processing overhead for every packet at every node traversed

11. ECE537/8 #11 Figure 4.3 Simple Switching Network

12. ECE537/8 #12 Switching Technique Large messages broken up into smaller packets Datagram –Each packet sent independently of the others –No call setup –More reliable (can route around failed nodes or congestion) Virtual circuit –Fixed route established before any packets sent –No need for routing decision for each packet at each node

13. ECE537/8 #13 Figure 4.4 Packet Switching: Virtual- Circuit Approach

14. ECE537/8 #14 Routing Adaptive routing Node/trunk failure Congestion

15. ECE537/8 #15 X.25 3 levels Physical level (X.21) Link level (LAPB, a subset of HDLC) Packet level (provides virtual circuit service)

16. ECE537/8 #16 Figure 4.5 The Use of Virtual Circuits

17. ECE537/8 #17 Figure 4.6 User Data and X.25 Protocol Control Information

18. ECE537/8 #18 Frame Relay Networks Designed to eliminate much of the overhead in X.25 Call control signaling on separate logical connection from user data Multiplexing/switching of logical connections at layer 2 (not layer 3) No hop-by-hop flow control and error control Throughput an order of magnitude higher than X.25

19. ECE537/8 #19 Figure 4.7 Comparison of X.25 and Frame Relay Protocol Stacks

20. ECE537/8 #20 Figure 4.8 Virtual Circuits and Frame Relay Virtual Connections

21. ECE537/8 #21 Frame Relay Architecture X.25 has 3 layers: physical, link, network Frame Relay has 2 layers: physical and data link (or LAPF) LAPF core: minimal data link control –Preservation of order for frames –Small probability of frame loss LAPF control: additional data link or network layer end-to-end functions

22. ECE537/8 #22 LAPF Core Frame delimiting, alignment and transparency Frame multiplexing/demultiplexing Inspection of frame for length constraints Detection of transmission errors Congestion control

23. ECE537/8 #23 LAPF-core Formats

24. ECE537/8 #24 User Data Transfer No control field, which is normally used for: –Identify frame type (data or control) –Sequence numbers Implication: –Connection setup/teardown carried on separate channel –Cannot do flow and error control

25. ECE537/8 #25 Frame Relay Call Control Data transfer involves: –Establish logical connection and DLCI –Exchange data frames –Release logical connection

26. ECE537/8 #26 Frame Relay Call Control 4 message types needed SETUP CONNECT RELEASE RELEASE COMPLETE

27. ECE537/8 #27 ATM Protocol Architecture Fixed-size packets called cells Streamlined: minimal error and flow control 2 protocol layers relate to ATM functions: –Common layer providing packet transfers –Service dependent ATM adaptation layer (AAL) AAL maps other protocols to ATM

28. ECE537/8 #28 Protocol Model has 3 planes User Control management

29. ECE537/8 #29 ATM Protocol Architecture

30. ECE537/8 #30 Logical Connections VCC (Virtual Channel Connection): a logical connection analogous to virtual circuit in X.25 VPC (Virtual Path Connection): a bundle of VCCs with same endpoints

31. ECE537/8 #31 ATM Connection Relationships

32. ECE537/8 #32 Advantages of Virtual Paths Simplified network architecture Increased network performance and reliability Reduced processing and short connection setup time Enhanced network services

33. ECE537/8 #33 Table 5.1

34. ECE537/8 #34 VCC Uses Between end users Between an end user and a network entity Between 2 network entities

35. ECE537/8 #35 Figure 5.3

36. ECE537/8 #36 VPC/VCC Characteristics Quality of Service (QoS) Switched and semi-permanent virtual channel connections Cell sequence integrity Traffic parameter negotiation and usage monitoring (VPC only) virtual channel identifier restriction within a VPC

37. ECE537/8 #37 Control Signaling A mechanism to establish and release VPCs and VCCs 4 methods for VCCs: –Semi-permanent VCCs –Meta-signaling channel –User-to-network signaling virtual channel –User-to-user signaling virtual channel

38. ECE537/8 #38 Control Signaling 3 methods for VPCs –Semi-permanent –Customer controlled –Network controlled

39. ECE537/8 #39 ATM Cells Fixed size 5-octet header 48-octet information field Small cells reduce delay for high-priority cells Fixed size facilitate switching in hardware

40. ECE537/8 #40 Header Format Generic flow control Virtual path identifier (VPI) Virtual channel identifier (VCI) Payload type Cell loss priority Header error control

41. ECE537/8 #41 Figure 5.4

42. ECE537/8 #42 Generic Flow Control Control traffic flow at user-network interface (UNI) to alleviate short-term overload conditions When GFC enabled at UNI, 2 procedures used: –Uncontrolled transmission –Controlled transmission

43. ECE537/8 #43 Table 5.3

44. ECE537/8 #44 Header Error Control 8-bit field calculated based on remaining 32 bits of header error detection in some cases, error correction of single-bit errors in header 2 modes: –error detection –Error correction

45. ECE537/8 #45 Figure 5.5

46. ECE537/8 #46 Figure 5.6

47. ECE537/8 #47 Figure 5.7

48. ECE537/8 #48 Service Categories Real-time service –Constant bit rate (CBR) –Real-time variable bit rate (rt-VBR) Non-real-time service –Non-real-time variable bit rate (nrt-VBR) –Available bit rate (ABR) –Unspecified bit rate (UBR) –Guaranteed frame rate (GFR)

49. ECE537/8 #49 Figure 5.8

50. ECE537/8 #50 ATM Adaptation Layer (AAL) Support non-ATM protocols –e.g., PCM voice, LAPF AAL Services –Handle transmission errors –Segmentation/reassembly (SAR) –Handle lost and misinserted cell conditions –Flow control and timing control

51. ECE537/8 #51 Applications of AAL and ATM Circuit emulation (e.g., T-1 synchronous TDM circuits) VBR voice and video General data services IP over ATM Multiprotocol encapsulation over ATM (MPOA) LAN emulation (LANE)

52. ECE537/8 #52 AAL Protocols AAL layer has 2 sublayers: –Convergence Sublayer (CS) Supports specific applications using AAL –Segmentation and Reassembly Layer (SAR) Packages data from CS into cells and unpacks at other end

53. ECE537/8 #53 Figure 5.9

54. ECE537/8 #54 Figure 5.10

55. ECE537/8 #55 AAL Type 1 Constant-bit-rate source SAR simply packs bits into cells and unpacks them at destination One-octet header contains 3-bit SC field to provide an 8-cell frame structure No CS PDU since CS sublayer primarily for clocking and synchronization

56. ECE537/8 #56 AAL Type 2 Variable bitrate, connection-oriented, low latency (delay) service –Takes advantage of existing SDH/PDH transport bandwidth by multiplexing small (voice and control) packets into standard ATM cells which would otherwise be largely unfilled Basic component is the CPS packet –Unanchored unit of data that can cross ATM cells, and starts from any location within the payload of the ATM cell, other than the STF

57. ECE537/8 #57 AAL Type 3/4 May be connectionless or connection oriented May be message mode or streaming mode

58. ECE537/8 #58 Figure 5.11

59. ECE537/8 #59 AAL Type 5 Streamlined transport for connection oriented protocols –Reduce protocol processing overhead –Reduce transmission overhead –Ensure adaptability to existing transport protocols

60. ECE537/8 #60 Figure 5.13

61. ECE537/8 #61 Emergence of High-Speed LANs 2 Significant trends –Computing power of PCs continues to grow rapidly –Network computing Examples of requirements –Centralized server farms –Power workgroups –High-speed local backbone

62. ECE537/8 #62 Classical Ethernet Bus topology LAN 10 Mbps CSMA/CD medium access control protocol 2 problems: –A transmission from any station can be received by all stations –How to regulate transmission

63. ECE537/8 #63 Solution to First Problem Data transmitted in blocks called frames: –User data –Frame header containing unique address of destination station

64. ECE537/8 #64 Figure 6.1

65. ECE537/8 #65 CSMA/CD Carrier Sense Multiple Access/ Carrier Detection 1.If the medium is idle, transmit. 2.If the medium is busy, continue to listen until the channel is idle, then transmit immediately. 3.If a collision is detected during transmission, immediately cease transmitting. 4.After a collision, wait a random amount of time, then attempt to transmit again (repeat from step 1).

66. ECE537/8 #66 Figure 6.2

67. ECE537/8 #67 Figure 6.3

68. ECE537/8 #68 Medium Options at 10Mbps 10Base5 –10 Mbps –50-ohm coaxial cable bus –Maximum segment length 500 meters 10Base-T –Twisted pair, maximum length 100 meters –Star topology (hub or multipoint repeater at central point)

69. ECE537/8 #69 Figure 6.4

70. ECE537/8 #70 Hubs and Switches Hub Transmission from a station received by central hub and retransmitted on all outgoing lines Only one transmission at a time Layer 2 Switch Incoming frame switched to one outgoing line Many transmissions at same time

71. ECE537/8 #71 Figure 6.5

72. ECE537/8 #72 Bridge Frame handling done in software Analyze and forward one frame at a time Store-and-forward Layer 2 Switch Frame handling done in hardware Multiple data paths and can handle multiple frames at a time Can do cut-through

73. ECE537/8 #73 Layer 2 Switches Flat address space Broadcast storm Only one path between any 2 devices Solution 1: subnetworks connected by routers Solution 2: layer 3 switching, packet-forwarding logic in hardware

74. ECE537/8 #74 Figure 6.6

75. ECE537/8 #75 Figure 6.7

76. ECE537/8 #76 Figure 6.8

77. ECE537/8 #77 Figure 6.9

78. ECE537/8 #78 Figure 6.10

79. ECE537/8 #79 Figure 6.11

80. ECE537/8 #80 10 Gbps Ethernet Benefits over ATM No expensive, bandwidth consuming conversion between Ethernet packets and ATM cells Network is Ethernet, end to end IP plus Ethernet offers QoS and traffic policing capabilities approach that of ATM Wide variety of standard optical interfaces for 10 Gbps Ethernet

81. ECE537/8 #81 Fibre Channel 2 methods of communication with processor: –I/O channel –Network communications Fibre channel combines both –Simplicity and speed of channel communications –Flexibility and interconnectivity of network communications

82. ECE537/8 #82 Figure 6.12

83. ECE537/8 #83 I/O channel Hardware based, high-speed, short distance Direct point-to-point or multipoint communications link Data type qualifiers for routing payload Link-level constructs for individual I/O operations Protocol specific specifications to support e.g. SCSI

84. ECE537/8 #84 Fibre Channel Network-Oriented Facilities Full multiplexing between multiple destinations Peer-to-peer connectivity between any pair of ports Internetworking with other connection technologies

85. ECE537/8 #85 Fibre Channel Requirements Full duplex links with 2 fibres/link 100 Mbps – 800 Mbps Distances up to 10 km Small connectors High-capacity Greater connectivity than existing multidrop channels Broad availability Support for multiple cost/performance levels Support for multiple existing interface command sets

86. ECE537/8 #86 Figure 6.13

87. ECE537/8 #87 Fibre Channel Protocol Architecture FC-0 Physical Media FC-1 Transmission Protocol FC-2 Framing Protocol FC-3 Common Services FC-4 Mapping

88. ECE537/8 #88 Summary There are many networking protocols other than IP, and each is suited to one or more particular needs Because of the proliferation of IP at the desktop, viable networking protocols must support encapsulation of virtually any sort of end protocol Efficiency is important

89. ECE537/8 #89Spring 2009 © 2000-2009, Richard A. Stanley Homework You must interconnect two tactical networks, separated by from 15 to 100 kM. IP is used for services at the user desktop, and is 100Base-T extended by a combination of WiFi and WiMAX links, but IP is not deemed suitable for backbone use. What protocol would you select for backbone trunking? Why? Would you argue for IP backbone despite the first direction not to use it? Why? What problems do you anticipate? Why? Be prepared to discuss your findings with the class for 5- 10 minutes next week. You may use slides if you desire.

90. ECE537/8 #90Spring 2009 © 2000-2009, Richard A. Stanley Disclaimer Parts of the lecture slides contain original work of William Stallings and Prentice-Hall, and remain copyrighted materials by the original owner(s). The slides are intended for the sole purpose of instruction in computer networks at Worcester Polytechnic Institute.