Chapter 7—packet-switchingTwo views of networksComparisons of two views by examplesWhat we will discussSlide 5Services provided by network layerSlide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Packet-switching topologySlide 16Brief discussion of switchesSlide 18Slide 19Three basic resources and bottlenecks in switchesSlide 21Slide 22BackSlide 24Slide 25Slide 26Delay comparison of message switch vs. packet switchSlide 28Example –IP internetworksVirtual-circuit packet switchingbackSlide 32Slide 33Slide 34Pro and con about virtual-circuit switchingSlide 36Slide 37Example –ATM networks1Chapter 7—packet-switching•Chapter 5: data-link layer protocols (some protocols are nearly same for transport layer)•Chapter 6: MAC sublayer (for broadcast networks).•This chapter: network layer–Telephony networks (i.e., circuit-switching) for stream of real time voice–Packet-switching networks for short messages, burst information, as well as real-time applications.2Two views of networks•External view: what services provided to transport layer by a network (i.e. network layer)–Need connection setup or not–What QoSs are provided–Services should be independent from underlying networks so that transport layer can run over any networks as long as the networks provide the services•Internal view: –physical topology,– datagram message transfer or virtual circuit information transfer, –addressing and routing, congestion control.•In this chapter, networks indicate systems to transfer information from one end to the other. It is reasonable to consider networks to be network layer here.3Comparisons of two views by examples•Broadcast networks and packet-switched networks•From external view, both networks provides transfer of information between users, not too much different•But from internal view, very different:–A broadcast network (such as LANs) is small, addressing is simple, frame transferred in one hop so no routing is needed–In a packet-switching network, addressing must accommodate large-scale networks and routing is necessary.4What we will discuss•Network services and internal network operations•Physical view of networks,•Datagram and virtual circuit•Routing•Shortest path algorithms•ATM networks•Traffic management and congestion control (if have time)5Figure 7.1t0t1NetworkTransfer of a block of info. VS. a sequence of blocks6Services provided by network layer•Two basic kinds of services–One view: Transfer of a block of information VS. a sequence of blocks –Second view: connectionless VS. connection-oriented.–IP provides connectionless service VS. ATM provides connection-oriented service•Other services such as:–Best-offer connectionless services–Low-delay connectionless service–Connection-oriented reliable stream service–Connection-oriented transfer of packets with delay and bandwidth guarantees•End-to-end argument:–Functions should be placed as close as possible to the application since the application is in best position to determine whether a function is being carried out completely and correctly,–Therefore, network layer should provide minimum functions required to meet application requirements and performance. Leave more functions to upper layers such as transport layer.7Figure 7.2PhysicallayerData linklayerPhysicallayerData linklayerEnd systemNetworklayerNetworklayerPhysicallayerData linklayerNetworklayerPhysicallayerData linklayerNetworklayerTransportlayerTransportlayerMessagesMessagesSegmentsEnd systemNetworkserviceNetworkservice protocol stack: network provides minimum required services to transport layer8Discussion of connectionless vs. connection-oriented Both connection-oriented and connectionless services in the upper layer can be implemented over a connectionless network (layer) (such as IP), similarly, can be implemented over a connection-oriented network (layer) (such as ATM). In network layer, connectionless service is also called datagram service, connection-oriented service called virtual-circuit service.Which is preferred?From end-to-end argument, connectionless network (IP) is preferred becauseIP makes intermediate nodes as simple as possible and put the burden on endsystems. Moreover, it makes the network grow easily (more scalable).Why ATM which is connection-oriented?Main reason is QoS because connection-oriented network can easily guarantee bandwidth, delay, etc. Detail motivation behind ATM will be discussed later.Network layer: connectionless(IP) connection-oriented (ATM)Transport layer: connectionless connection-oriented Thinking: differences (or implications) of connection-oriented in transport layer and in network layer. What the connection between two ends in transport layer means?9Most basic functions of a network (layer)Routing and forwarding. Priority and scheduling (to provide QoS)Congestion control (also in transport layer)Segmentation (to deal with different frame sizes of underlying systems)Alternatively, network (layer) sends error message to let edge system to do segmentation.Addressing 1. to deal with different address formats when interconnecting networks. 2. Hierarchical address for scalability.10Figure 7.4 ...MUXNetwork accessNodePacket network topology --Access multiplexerMultiplexer combines multiple bursty flowsinto one aggregated flow.Access node forwardspackets into backbonepacket networks.11LANBridgeLAN 1LAN 2(a)(b)Figure 7.5Packet network topology --LAN Now nearly every LAN is connected to packet-switching network (the Internet) to share information globally and to make the Internet extremely large. LANs were introduced for sharing of resources in a organization.They are basic building components for Wide Area Networks.12RRRRSSSs s s s ssssss R sRBackboneTo internet or wide area networkOrganization ServersGatewayDepartmental ServerFigure 7.6Campus networkLANsextended LANs subnetworks (by backbone networks) campus network university network, finally connect to Internet, bridges, routers and gateway,… play key-role in networksBacknone network may be connected by links, LAN, or ATMs. Servers provide various services.13Interdomain levelIntradomain levelLAN levelAutonomous systemor domainBorder routersBorder routersFigure 7.7Internet service providerIntradomain and interdomain levelsDomain: indicate the routers run the same routing