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ECE544: Communication Networks-II, Spring 2010

ECE544: Communication Networks-II, Spring 2010. D. Raychaudhuri Lecture 3. Includes tutorial materials from the ATM Forum & U VA. Today’s Lecture. Switched Networks Switched Ethernet Concepts Learning bridge, spanning tree ATM networks Overview Signaling PNNI Routing (basics).

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ECE544: Communication Networks-II, Spring 2010

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  1. ECE544: Communication Networks-II, Spring 2010 D. Raychaudhuri Lecture 3 Includes tutorial materials from the ATM Forum & U VA

  2. Today’s Lecture • Switched Networks • Switched Ethernet • Concepts • Learning bridge, spanning tree • ATM networks • Overview • Signaling • PNNI Routing (basics)

  3. Ethernet Hub • Used to connect hosts to Ethernet LAN and to connect multiple Ethernet LANs • Collisions are propagated

  4. Bridges/LAN switches • We will use the terms bridge and LAN switch (or Ethernet switch in the context of Ethernet) interchangeably. Interconnect multiple LAN, possibly with different type • Bridges operate at the Data Link Layer (Layer 2)

  5. Ethernet Hubs vs. Ethernet Switches • An Ethernet switch is a packet switch for Ethernet frames • Buffering of frames prevents collisions. • Each port is isolated and builds its own collision domain • An Ethernet Hub does not perform buffering: • Collisions occur if two frames arrive at the same time. Hub Switch

  6. Internet A Switched Enterprise Network Router Switch

  7. What do bridges do if some LANs are reachable only in multiple hops ? What do bridges do if the path between two LANs is not unique ? Need for Routing

  8. Transparent Bridges • Three principal approaches can be found: • Fixed Routing • Source Routing • Spanning Tree Routing (IEEE 802.1d) • We only discuss the last one in detail. • Bridges that execute the spanning tree algorithm are called transparent bridges

  9. Transparent Bridges • Three parts to transparent bridges: • (1) Forwarding of Frames • (2) Learning of Addresses • (3) Spanning Tree Algorithm

  10. (1) Frame Forwarding • Each bridge maintains a forwarding database with entries < MAC address, port, age> MAC address:host name or group address port:port number of bridge age:aging time of entry with interpretation: • a machine with MAC address lies in direction of the port number from the bridge. The entry is age time units old.

  11. Src=x, Dest=y Src=x, Dest=y (2) Address Learning (Learning Bridges) • Routing tables entries are set automatically with a simple heuristic: The source field of a frame that arrives on a port tells which hosts are reachable from this port. Port 1 Port 4 x is at Port 1 y is at Port 5 Port 2 Port 5 Port 3 Port 6

  12. Example • Consider the following packets: (Src=A, Dest=F), (Src=C, Dest=A), (Src=E, Dest=C) • What have the bridges learned?

  13. F F F F F F Danger of Loops • Consider the two LANs that are connected by two bridges. • Assume host n is transmitting a frame F with unknown destination. What is happening? • Bridges A and B flood the frame to LAN 2. • Bridge B sees F on LAN 2 (with unknown destination), and copies the frame back to LAN 1 • Bridge A does the same. • The copying continues F

  14. Spanning Trees / Transparent Bridges • A solution is to prevent loops in the topology • IEEE 802.1d has an algorithm that organizes the bridges as spanning tree in a dynamic environment • Note: Trees don’t have loops • Bridges that run 802.1d are called transparent bridges • Bridges exchange messages to configure the bridge (Configuration Bridge Protocol Data Unit, Configuration BPDUs) to build the tree.

  15. ATM Overview • Introduction • Physical Layers • ATM Layer • ATM Adaptation Layer • Interfaces • Management

  16. ATM Basic Concepts • Negotiated Service Connection • End-to-end connections, called virtual circuits • Traffic contract • Switched Based • Dedicated capacity • Cell Based • Small, fixed length A

  17. Negotiated Service Connection Traffic Contract • Parameters • Traffic Characteristics • Peak Cell Rate • SustainableCell Rate • Quality of Service • Delay • Cell Loss Virtual Connection 1-QOS A Virtual Connection 1-QOS B Virtual Connection 1-QOS b

  18. The ATM Cell Header Payload • Small Size • 5 Byte Header • 48 Byte Payload • Fixed Size • Header contains virtual circuit information • Payload can be voice, video or other data types 5 Bytes 48 Bytes A

  19. Voice Voice ATMNetwork Data Voice Video Data Data Video Video ATM Vision The Ultimate Integrated Services Network • ATM network moves cells (fixed length packets) with low delay and low delay variation at high speeds • Devices at ends translate (e.g., segment and reassemble) between cells and original traffic

  20. Video Cell Data Cell Voice Cell ATM System Architecture A

  21. ATM Adaptation Layer AAL Types 1 Circuit Emulation -Constant Bit Rate (CBR) Low Bit Rate Voice (Real Time) -Variable Bit Rate (VBR) Time Invariant Data “Simple” Data • Provides Mapping Of Applications To ATM Service Of The Same Type • Segments/Reassembles Into 48 Payloads • Hands 48 Byte Payloads To ATM Layer 48 Bytes 2 3/4 5 A

  22. ATM Layer 48-Byte Payloads From AAL 5-Byte Header } • Adds/Removes Header To 48 Byte Payload • Header Contains Connection Identifier • Multiplexes 53 Byte Cells Into Virtual Connections • Sequential Delivery Within A Virtual Connection 53-Byte Cell To Physical Layer Header Contains Virtual Path and Channel Identifiers A

  23. Physical Layer Cable Plants Speed Matching and Framing Uses Existing Media Twisted Pair Coax Fiber -Multimode -Single Mode Wide Range of Speeds LAN, MAN, WAN Compatibility Transmission Frame A

  24. ATM System Architecture ATM Cell Creation Transmission Forward Cell Through Network Add 5-Byte Header Conversion to ATM Data Types, 48-Byte Length Convert To Correct Electrical Or Optical Format Video Cell Data Cell Voice Cell Services ATM Layer Physical Layer Adaptation Layer A

  25. Private UNI PHY ATM Forum Physical Layer UNI Interfaces Frame Format Bit Rate/Line Rate Transmission Media 25.6 Mb/s / 32 Mbaud UTP-3 Cell Stream STS-1 51.84 Mb/s UTP-3 FDDI 100 Mb/s / 125 Mbaud MMF STS-3c, STM-1 155.52 Mb/s UTP-5, STP 155.52 Mb/s SMF, MMF, Coax pair STS-3c, STM-1 Cell Stream 155.52 Mb/s / 194.4 Mbaud MMF/STP STS-3c, STM-1 155.52 Mb/s UTP-3 STS-12, STM-4 622.08 Mb/s SMF, MMF STS-48, STM-16* 2,488.32 Mb/s SMF *-Under Development SMF-Single Mode Fiber MMF-Multimode Fiber UTP-Unshielded Twisted Pair STP-Shielded Twisted Pair DS1 and DS3-Also Private Speeds B

  26. Public UNI PHY ATM Forum Physical Layer UNI Interfaces Frame Format Bit Rate Transmission Media DS1 Twisted Pair 1.544 Mb/s Coax Pair DS3 44.736 Mb/s STS-3c, STM-1 SMF 155.520 Mb/s E1 Twisted Pair, Coax Pair 2.048 Mb/s Coax pair E3 34.368 Mb/s Coax pair J2 6.312 Mb/s N X T1 Twisted pair N X 1.544 Mb/s Twisted pair N X E1 N X 2.048Mb/s *-Under Development SMF-Single Mode Fiber PLCP-Physical Layer Convergence Protocol B

  27. Transmission Convergence Sublayer Physical Layer Medium Dependent Sublayer ATM PHY: Two Sublayers • PMD: • Medium, line code, connectors • Probably use existing standards and technology • TCS: • Specific to the PMD • Cell delineation • Cell rate decoupling (inserting empty cells during idle periods)

  28. 155 Mbps, SONET STS-3c/SDH STM-1 270 columns • 9 ´ 260 ´ 8/125 msec = 149.76 Mbps payload 9 R o w s . . . Maintenance and operations 1 Synchronous Payload Envelope (1 column of overhead) 125msec 9 bytes A

  29. HEC Cell Delineation (For SONET, etc...) Peek ahead at the cell format HEC (Header Error Check) Header Payload Coverage of the 1 byte HEC • Receiver locks on 5 byte blocks that • Satisfy the HEC calculation • Are separated by 48 bytes • HEC includes coset so that empty cell (first 4 bytes of header = 0) does not make HEC = 0 A

  30. 1.5 Mbps, DS1 125 msec • (24 bytes x 8 bits/byte)/125 msec=1.536 Mbps of payload • Cell delineation by HEC detection as with SONET • Cell payload=1.536 Mbps x (48/53)=1.391 Mbps . . . F B B . . . B F B . . . B F . . . 24 bytes Framing Bit

  31. 25.6 Mbps UTP-3 • Based on IEEE 802.5 physical layer with 4B/5B coding plus scrambling • 32 Mbaud x 4/5 = 25.6 Mbps • Cells delineated by special symbol pairs x Cell x x Cell 4 or Reset Scramble No Scramble Reset A

  32. ATM UNI Cell 7 6 5 4 3 2 1 0 Generic Flow Control Virtual Path Identifier Virtual Path Identifier Virtual Channel Identifier Virtual ChannelIdentifier 5 Bytes Virtual ChannelIdentifier Virtual Channel Identifier Payload Type Identifier CLP Header ErrorCheck 48 Bytes Payload(48 bytes) CLP = Cell Loss Priority

  33. Why 53 Bytes? • Compromise reached in ITU-TS Study Group XVIII in June 1989 64 + 5 32 + 4 48 + 5

  34. Percent Overhead and Packetization Delay for 64 Kbps Voice Packetization Delay Advantage of Small Cells 100 10 Delay 80 8 Overhead 60 6 % Overhead Delay (ms) 40 4 20 2 0 0 0 20 40 60 80 Payload (Bytes)

  35. Queuing Advantage of Small Cells 100 byte message Delay and delay variation are small for small messages e.g., a digitized voice sample 100 other active connections 45 Mbps • • • 12 High overhead Wait for other cells 10 Max 8 Just fits in one cell Delay 6 4 (ms) 2 0 1 50 100 150 200 250 300 Payload (bytes) A

  36. 7 6 5 4 3 2 1 0 Generic Flow Control Virtual Path Identifier Virtual Channel Identifier Virtual Path Identifier Virtual ChannelIdentifier Payload Type Identifier Virtual Channel Identifier CLP Header ErrorCheck Payload(48 bytes) Virtual Connections 76 Video 3 88 Voice 4 37 42 Video Data 1 37 78 52 Data Voice 5 Video 2 6 22 Video Connection Table Port VPI/VCI Port VPI/VCI 1 0/37 3 0/76 1 0/42 5 0/52 2 0/37 6 0/22 2 0/78 4 0/88 Video Data Video Voice

  37. 7 6 5 4 3 2 1 0 Generic Flow Control Virtual Path Identifier Virtual Channel Identifier Virtual Path Identifier Virtual ChannelIdentifier Payload Type Identifier Virtual Channel Identifier CLP Header ErrorCheck Payload(48 bytes) Virtual Paths and Virtual Channels Physical Link Virtual Path Virtual Channel

  38. 7 6 5 4 3 2 1 0 Generic Flow Control Virtual Path Identifier Virtual Channel Identifier Virtual Path Identifier Virtual ChannelIdentifier Payload Type Identifier Virtual Channel Identifier CLP Header ErrorCheck Payload(48 bytes) Virtual Paths and Virtual Channels ATM Switch or Network • Bundles of Virtual Channels are switched via Virtual Paths • Virtual Path service from a carrier allows reconfiguration of Virtual Channels without service orders to carrier VPI = 1 VPI = 4 VCI = 31 VCI = 55 VCI = 32 VCI = 57 VPI = 2 VPI = 5 VCI = 31 VCI = 99 VCI = 40 VCI = 32 VPI = 3 VPI = 6 VCI = 96 VCI = 96 VCI = 97 VCI = 97

  39. 7 6 5 4 3 2 1 0 Generic Flow Control Virtual Path Identifier Virtual Channel Identifier Virtual Path Identifier Virtual ChannelIdentifier Payload Type Identifier Virtual Channel Identifier CLP Header ErrorCheck Payload(48 bytes) Cell Loss Priority • Cells with bit set should be discarded before those with bit not set • Can be set by the terminal • Can be set by ATM switches for internal network control • Virtual channels/paths with low quality of service • Cells that violate traffic management contract • Key to ATM Traffic Management

  40. 7 6 5 4 3 2 1 0 Generic Flow Control Virtual Path Identifier Virtual Channel Identifier Virtual Path Identifier Virtual ChannelIdentifier Payload Type Identifier Virtual Channel Identifier CLP Header ErrorCheck Payload(48 bytes) Generic Flow Control • Used for UNI only - Not NNI • Currently undefined • Set to 0000B • Proposed future uses • Flow control • Shared media multiple access B

  41. 7 6 5 4 3 2 1 0 Generic Flow Control Virtual Path Identifier Virtual Channel Identifier Virtual Path Identifier Header Error Check Virtual ChannelIdentifier Payload Type Identifier Virtual Channel Identifier CLP Header ErrorCheck Payload(48 bytes) • Header error control • Detection mode: • Protects header only (all five bytes) • Discards cell when header error • Correction mode (optional): Correct 1 bit errors else discard when error detected • Reduced cell loss in face of single bit errors • Reduced error detection for multiple bit errors • Cell delineation for SONET, SDH, etc... • Recalculated link-by-link because of VPI/VCI value changes B

  42. Permanent Virtual Circuits • Long setup time (especially with human intervention) means that connections are left active for long periods of time e.g., days, weeks • VPI/VCI tables setup in terminals and switches VPI/VCI VPI/VCI VPI/VCI VPI/VCI NetworkManagementSystem B

  43. Switched Virtual Circuits Signalling Channel(VPI/VCI = 0/5) Signalling Channel(VPI/VCI = 0/5) • Switch and terminal exchange signalling messages using the predefined signalling channel, VPI/VCI = 0/5 CallProcessing ATM Switch B

  44. Point-to-Point Connection • Data may flow in one or both directions (unidirectional or bidirectional) • Bandwidth may be: • Same in both directions (symmetric), or • Different in each direction (asymmetric)

  45. Point-to-Multipoint Connection • Data are replicated by the network • Data flow only from Root to Leaves “Root” “Leaves”

  46. Why SVCs? • Universal connectivity • More efficient resource utilization A

  47. Call Control Signalling Call control protocol is used to establish, maintain, and clear virtual channel connections between a user and network UNI or NNI User Network UNI Call Control Signalling Call Control Signalling Virtual Channel Connections Interface UNI or NNI

  48. Signalling 4.0 • Delta from Q.2931 etc. • Extensions for parameterized QoS, ABR, LIJ • Some restrictions

  49. Signalling Protocol Stack UNI 4.0 Q.931 Q.2931 SSCOP Q.921 LAPD ATM I.430/431 SONET/DS3 ISDN UNI ATM UNI

  50. Setting Up a Call - 1 A wants to communicate with B A B • Setup message • Call reference • Called party address • Calling party address • Traffic characteristics • Quality of service • Call proceeding message • Call reference • VPI/VCI Setup CallProceeding B

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