CSC581 Communication Networks II Chapter 7a: Wide Area Network and Switching Techniques Dr. Cheer-Sun Yang

2 Topics Circuit switching (p ) Message switching (p. 25) Packet switching (p ) –Datagram –Virtual Circuit Example of Packet Switching Protocol: X. 25 (Section 7.3)

3 Network Layer Functions Switching (layer 3 switching): packet switching Routing Fragmentation and assembly Congestion Control Internetworking

4 WAN vs. LAN Wide area network (WAN) is the “cloud” that we’ve been ignoring. A WAN covers much larger areas for which LAN protocols are inappropriate. Routing in WAN is more complex than that in LAN. Switching is a main topic in the design of WAN (circuit, message, packet switching).

5 WAN vs. LAN(cont’d) Error recovery at the network layer is needed. Internetworking may require protocol conversion performed by a protocol converter, including bridges and routers, or gateways. Packet fragmentation and assembly Quality of Service (QoS) and Internet Management are important. Let’s start with another look of the big picture.

6 Simple Switched Network

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 7 Figure 7.1 t0t0 t1t1 Network

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 8 Figure 7.2 Physical layer Data link layer Physical layer Data link layer End system  Network layer Network layer Physical layer Data link layer Network layer Physical layer Data link layer Network layer Transport layer Transport layer Messages Segments End system  Network service Network service

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks Medium A B C End system  End system  Network 1 2 Physical layer entity Data link layer entity 3 Network layer entity 3 Transport layer entity 4 Figure 7.3

10 Switching Networks Category of switching functions within a switch: space division switching, time division switching Category of switching techniques: –layer 1: circuit switching –layer 2: cell switching (ATM), frame switching (frame ralay) –layer 3: packet switching

11 Space Division Switching Developed for analog environment Separate physical paths Crossbar switch –Number of crosspoints grows as square of number of stations –Loss of crosspoint prevents connection –Inefficient use of crosspoints All stations connected, only a few crosspoints in use –Non-blocking

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 12 User 1 Switch Link User n User n-1 (a) Network (b) Switch Control N N Connection of inputs to outputs Figure 4.21

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 13 N N 2  N-1 Figure 4.22

14 Crossbar Matrix

15 Multistage Switch Reduced number of crosspoints More than one path through network –Increased reliability More complex control May be blocking

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 16 nxknxk nxknxk nxknxk nxknxk N/n x N/n kxnkxn 1 2 N/n N inputs N/n N outputs 1 2 k 2(N/n)nk + k (N/n) 2 crosspoints kxnkxn kxnkxn kxnkxn Figure 4.23

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 17 nxknxk nxknxk nxknxk N/n x N/n kxnkxn 1 N/n Desired input 1 j m N/n Desired output 1 2n-1 kxnkxn kxnkxn n-1 N/n x N/n n+1 N/n x N/n 2n-2 free pathfree path n-1 busy n-1 busy Figure 4.24

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks From TDM DeMUX To TDM MUX Read slots in permuted order Figure 4.25

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 19 nxknxk nxknxk nxknxk nxknxk N/n x N/n kxnkxn 1 2 N/n N inputs n input TDM frame with n slots output TDM frame with k slots Figure 4.26

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 20 nxknxk N/n x N/n kxnkxn N/n 1 2 k kxnkxn kxnkxn nxknxk 2 nxknxk N/n first slot kth slot first slot kth slot Figure 4.27

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 21 nxknxk nxknxk nxknxk nxknxk N/n x N/n Time-Shared Space Switch kxnkxn 1 2 N/n N inputs N/n N outputs TDM n slots kxnkxn kxnkxn kxnkxn TDM k slots TDM k slots TSI Stage Space Stage Figure 4.28

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 22 2x3 3x D1D1 B1B1 A1A1 B2B2 A2A2 C1C1 D2D2 C2C2 B1B1 A1A1 C1C1 D1D1 A1A1 B1B1 C1C1 D1D1 A1A1 C1C1 B1B1 D1D1 Figure 4.29

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 23 Figure 4.30

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 24 Signal Source Signal Release Signal Destination Go Ahead Message Figure 4.31

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 25 (a) Routing in a typical metropolitan area (b) Routing between two LATAs LATA 1 LATA 2 net 1 net 2 A B C D Figure 4.32

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 26 local telephone office Distribution Frame Serving Area I/f Pedestal feeder cable Switch distribution cable Figure 4.33

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 27 Original signal Hybrid transformer Received signal Echoed signal Receive pair Transmit pair Figure 4.34

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 28 Local analog Local digital Digital trunks Local Switch Tie lines Foreign exchange Channel-switched traffic (digital leased lines) Circuit- switched traffic Digital cross-connect System Figure 4.35

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 29 Physical SONET Topology using ADMs and DCCs Logical Topology Switches see this topology DCC Figure 4.36 ADM

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 30 Basic Rate Interface (BRI): 2B+D Primary Rate Interface (PRI): 23B+D BRI PRI BRI PRI Circuit Switched Network Channel Switched Network Private Signaling Network Packet Switched Networks Figure 4.37

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 31 SPC Control Signaling Message Figure 4.39

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 32 Switch Processor Office B Switch Office A Processor Signaling Modem Trunks Figure 4.39

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 33 STP SSP Transport Network Signaling Network SSP = Service switching point (signal to message) STP = Signal transfer point (message transfer) SCP = Service control point (processing) SCP Figure 4.40

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 34 SSP Transport Network External Database Signaling Network Intelligent Peripheral Figure 4.40

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 35 Application Layer Transport Layer Network Layer Data Link Layer Physical Layer Presentation Layer Session Layer SCCP MTP Level 3 MTP Level 2 MTP Level 1 ISUPTCAPTUP Figure 4.42

36 Time Division Switching Partition low speed bit stream into pieces that share higher speed stream e.g. TDM bus switching –based on synchronous time division multiplexing –Each station connects through controlled gates to high speed bus –Time slot allows small amount of data onto bus –Another line’s gate is enabled for output at the same time

37 Control Signaling Functions Audible communication with subscriber Transmission of dialed number Call can not be completed indication Call ended indication Signal to ring phone Billing info Equipment and trunk status info Diagnostic info Control of specialist equipment

38 Control Signal Sequence Both phones on hook Subscriber lifts receiver (off hook) End office switch signaled Switch responds with dial tone Caller dials number If target not busy, send ringer signal to target subscriber Feedback to caller –Ringing tone, engaged tone, unobtainable Target accepts call by lifting receiver Switch terminates ringing signal and ringing tone Switch establishes connection Connection release when Source subscriber hangs up

39 Switch to Switch Signaling Subscribers connected to different switches Originating switch seizes interswitch trunk Send off hook signal on trunk, requesting digit register at target switch (for address) Terminating switch sends off hook followed by on hook (wink) to show register ready Originating switch sends address

40 Control Signals

41 Location of Signaling Subscriber to network –Depends on subscriber device and switch Within network –Management of subscriber calls and network –ore complex

42 In Channel Signaling Use same channel for signaling and call –Requires no additional transmission facilities Inband –Uses same frequencies as voice signal –Can go anywhere a voice signal can –Impossible to set up a call on a faulty speech path Out of band –Voice signals do not use full 4kHz bandwidth –Narrow signal band within 4kHz used for control –Can be sent whether or not voice signals are present –Need extra electronics –Slower signal rate (narrow bandwidth)

43 Drawbacks of In Channel Signaling Limited transfer rate Delay between entering address (dialing) and connection Overcome by use of common channel signaling

44 Common Channel Signaling Control signals carried over paths independent of voice channel One control signal channel can carry signals for a number of subscriber channels Common control channel for these subscriber lines Associated Mode –Common channel closely tracks interswitch trunks Disassociated Mode –Additional nodes (signal transfer points) –Effectively two separate networks

45 Common v. In Channel Signaling

46 Signaling Modes

47 Signaling System Number 7 SS7 Common channel signaling scheme ISDN Optimized for 64k digital channel network Call control, remote control, management and maintenance Reliable means of transfer of info in sequence Will operate over analog and below 64k Point to point terrestrial and satellite links

48 SS7 Signaling Network Elements Signaling point (SP) –Any point in the network capable of handling SS7 control message Signal transfer point (STP) –A signaling point capable of routing control messages Control plane –Responsible for establishing and managing connections Information plane –Once a connection is set up, info is transferred in the information plane

49 Transfer Points

50 Signaling Network Structures STP capacities –Number of signaling links that can be handled –Message transfer time –Throughput capacity Network performance –Number of SPs –Signaling delays Availability and reliability –Ability of network to provide services in the face of STP failures

51 Circuit Switching Routing Many connections will need paths through more than one switch Need to find a route –Efficiency –Resilience Public telephone switches are a tree structure –Static routing uses the same approach all the time Dynamic routing allows for changes in routing depending on traffic –Uses a peer structure for nodes

52 Alternate Routing Possible routes between end offices predefined Originating switch selects appropriate route Routes listed in preference order Different sets of routes may be used at different times

53 Alternate Routing Diagram

54 Problems RE Circuit Switching Circuit switching designed for voice –Resources dedicated to a particular call –Much of the time a data connection is idle –Data rate is fixed Both ends must operate at the same rate

55 Message Switching A message is broken into smaller data units, called messages. Each message is sent to the destination via different paths. At each node, the message is stored temporarily prior to retransmission. This concept is called store-and-forward.

56 Message Switching (cont’d) In circuit switching, a single route is dedicated to the exchange of all messages. In message switching, different message data units can be transmitted via different routes.

57 Message Switching (cont’d) In circuit switching, a connection between the two parties is required, whereas in message switching, a message can be sent and stored for later retrieval. However, since the size of each message data unit is quite large, error recovery is costly. The message data unit is broken into a smaller chunkm called packet. Packet switching is more realistic.

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 58 Network nodes Message Subscriber B Subscriber A Message Figure 7.13

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 59 t t t t Delay Source Destination T p Minimum Delay = 3p + 3T Switch 1 Switch 2 Figure 7.14

60

61 Packet Switching The size of a packet is design dependent. Each packet contains the destination address or some other designator indicating where it should go. When the packets all arrive, they are reassembled. Network Layer protocol is responsible for routing, fragmentation/reassembly.

62 Basic Operation Data transmitted in small packets –Typically 1000 octets –Longer messages split into series of packets –Each packet contains a portion of user data plus some control info Control info –Routing (addressing) info Packets are received, stored briefly (buffered) and past on to the next node –Store and forward

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 63 Figure MUX Network access Node

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 64 LAN Bridge LAN 1 LAN 2 (a) (b) Figure 7.5

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 65 R R R R S SS s s s s ss s ss s R s R Backbone To internet or wide area network Organization Servers Gateway Departmental Server Figure 7.6

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 66 Interdomain level Intradomain level LAN level Autonomous system or domain Border routers Figure 7.7 Internet service provider

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 67 RARA RBRB RCRC Route server NAP National service provider A National service provider B National service provider C LAN NAP (a) (b) Figure 7.8

68 Advantages Line efficiency –Single node to node link can be shared by many packets over time –Packets queued and transmitted as fast as possible Data rate conversion –Each station connects to the local node at its own speed –Nodes buffer data if required to equalize rates Packets are accepted even when network is busy –Delivery may slow down Priorities can be used

69 Switching Technique Station breaks long message into packets Packets sent one at a time to the network Packets handled in two ways –Datagram –Virtual circuit

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 70 Network Packet switch Transmission link Figure 7.9

71 Structure of Switch/Router Line card Interconnection Fabric Control Input ports Output ports

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 72 Control N Line Card Interconnection Fabric Line Card N Figure 7.10 … … … …

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 73 CPU N NIC Card Main Memory I/O Bus Figure 7.11 … …

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks N 1 2 N Figure 7.12 … …

75 Datagram Each packet treated independently Packets can take any practical route Packets may arrive out of order Packets may go missing Up to receiver to re-order packets and recover from missing packets

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 76 Packet 2 Packet 1 Packet 2 Figure 7.15

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 77 t t t t p + 2(T/3) first bit received 3p + 3(T/3) first bit released 3p + 5 (T/3) last bit released Lp + (L-1)P first bit received Lp + LP first bit released Lp + LP + (k-1)P last bit released where T = k P 3 hops L hops p p + P Source Destination Switch 1 Switch 2 Figure 7.16

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 78 Destination address Output port Figure 7.16

79 Virtual Circuit Preplanned route established before any packets sent Call request and call accept packets establish connection (handshake) Each packet contains a virtual circuit identifier instead of destination address No routing decisions required for each packet Clear request to drop circuit Not a dedicated path

80 Virtual Circuits vs Datagram Virtual circuits –Network can provide sequencing and error control –Packets are forwarded more quickly No routing decisions to make –Less reliable Loss of a node looses all circuits through that node Datagram –No call setup phase Better if few packets –More flexible Routing can be used to avoid congested parts of the network

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 81 Packet Figure 7.17

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 82 t t t t Release Connect request CR Connect confirm CC Figure 7.19

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 83 SW 1 SW 2 SW n Connect request Connect confirm Figure 7.20 …

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 84 Identifier Output port Next identifier Entry for packets with identifier 15 Figure 7.21

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks Minimum Delay = 3p+T t t t t Source Destination Switch 1 Switch 2 Figure 7.22

86 ATM Networks and Layer 2 Packet Switching-Cell Switching Asynchronous Transfer Mode (ATM)

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 87 MUX ` Wasted bandwidth ATM TDM Voice Data packets Images Figure 7.37

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks N 1 Switch N 1 … 5 6 video 25 video voice data N video75 voice67 data 39 video 67 Figure 7.38 … …

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 89 c ATM Sw 1 ATM Sw 4 ATM Sw 2 ATM Sw 3 ATM DCC a b d e VP3 VP5 VP2 VP1 a b c d e Sw = switch Figure 7.39

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 90 Physical Link Virtual Paths Virtual Channels Figure 7.40

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks NN-1 Figure 7.41 …

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 92 Packet buffer Transmission link Arriving packets Packet discard when full Packet buffer Transmission link Arriving packets Class 1 discard when full Class 2 discard when threshold exceeded (a) (b) Figure 7.42

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 93 Transmission link Packet discard when full High-priority packets Low-priority packets Packet discard when full When high-priority queue empty Figure 7.43

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 94 Sorted packet buffer Transmission link Arriving packets Packet discard when full Tagging unit Figure 7.44

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 95 Transmission link Packet flow 1 Packet flow 2 Packet flow n C bits/second Approximated bit-level round robin service Figure 7.45

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 96 Queue t=0 Queue t=0 1 t 1 2 Fluid-flow system: both packets served at rate 1/2 Both packets complete service at t=2 0 1 t 1 2 Packet-by-packet system: queue 1 served first at rate 1; then queue 2 served at rate 1. Packet from queue 2 being served Packet from queue 1 being served Packet from queue 2 waiting 0 Figure 7.46

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 97 Rounds Generalize so R(t) is continuous, not discrete R(t) grows at rate inversely proportional to n active (t) Figure 7.47

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 98 Queue t=0 Queue t=0 2 1 t 3 Fluid-flow system: both packets served at rate 1/2 Packet from queue s served at rate t 1 2 Packet-by-packet fair queueing: queue 2 served at rate 1 Packet from queue 1 being served at rate 1 Packet from queue 2 waiting 0 3 Figure 7.48

Copyright 2000 McGraw-Hill Leon- Garcia and Widjaja Communication Networks 99 Queue t=0 Queue t=0 1 t 1 2 Fluid-flow system: packet from queue 1 served at rate 1/4; Packet from queue 1 served at rate 1 Packet from queue 2 served at rate 3/4 0 1 t 1 2 Packet-by-packet weighted fair queueing: queue 2 served first at rate 1; then queue 1 served at rate 1. Packet from queue 1 being served Packet from queue 2 being served Packet from queue 1 waiting 0 Figure 7.49

100 Reading Assignment 7.1 Network Services 4.4 Layer 1 switching: Circuit Switching 7.2 Packet Networks 7.3 Layer 3 Switching: Message Switching, Virtual Circuit Packet Switching, Datagram Packet Switching 7.6 Layer 2 Switching: ATM Cell Switching