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  • Chapter 7: Packet-Switching Networks

    School of Info. Sci. & Eng. Shandong Univ.

  • Outline ¸ 7.1 Network Services and Internal Network

    Operation ¸ 7.2 Packet Network Topology ¸ 7.3 Datagrams and Virtual Circuits l 7.4 Routing in Packet Networks l 7.5 Shortest Path Algorithms l 7.6 ATM Networks (Skip) l 7.7 Traffic Management and QOS l 7.8 Congestion Control

  • Figure 7.1

    t0 t1

    Network

    Top level view: a network transfers info among users

    The figure simply shows transmission of a single block or a stream of info

  • Figure 7.2

    Physical layer

    Data link layer

    Physical layer

    Data link layer

    End system α

    Network layer

    Network layer

    Physical layer

    Data link layer

    Network layer

    Physical layer

    Data link layer

    Network layer

    Transport layer

    Transport layer

    Messages Messages

    Segments

    End system β

    Network service

    Network service

    Peer-Peer Protocols Operating End-to-End Across Networks

    Protocol Stack View. In C7 we are mostly concerned with the network layer

  • 3 2 11 2 2

    1

    3 2 11 2 2

    1

    2 1

    Medium

    A B

    3 2 11 2 2

    1

    C

    2 1

    2 1

    2 134 1 2 3 4

    End system α

    End system β

    Network

    1

    2

    Physical layer entity

    Data link layer entity 3 Network layer entity

    3 Network layer entity

    Transport layer entity4

    Figure 7.3

    Layer 3 Entities work together to provide services to Layer 4 Entities

    Spatial view

  • Figure 7.4

    .

    .

    .MUX

    Network access

    Node

    Packet Network Topologies:

    How do users access a packet-switching network?

    One way is shown. Today the MUX might be a shared DSL or Cable Modem. More likely it would be a router that permits a LAN connection between the PCs.

  • LAN

    Bridge

    LAN 1

    LAN 2

    (a) (b)

    Figure 7.5

    Mostly users at one geographic site are connected with one or more Local Area Networks

    (a) Broadcasts frames to all PCs. (b) A bridge usually just connects LANs to make a larger broadcast segment, but a LAN switch isolates traffic to a particular LAN, unless it needs to be sent to another LAN

  • A large site usually sets up many LANs l LANs are connected usually connect by switches or routers to

    isolate traffic to a particular segment if possible l Such a network of LANs is called a campus network l The next slide shows a campus network with a backbone internal to

    the organization l It also has a gateway to connect to other networks, usually the

    Internet l A site with remote locations might lease lines or share frame relay

    interconnections. A multiplexer or router helps share the line by queueing packets to be sent

  • R R

    RR 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

    The s = LAN switch. The S is usually a router

  • More about the typical campus network l The campus backbone is usually a high speed LAN FDDI at

    100Mbps is common, or Gigabit Ethernet l The traffic within an extended LAN segment is delivered

    using 48-bit physical addresses; however applications use 36-bit IP addresses. The Address Resolution Protocol ARP automatically builds tables to relate the two.

    l To connect the campus network to the larger Internet, we go one more step up the hierarchy. The campus network is then called an autonomous system

  • Interdomain level

    Intradomain level

    LAN level

    Autonomous system or domain

    Border routers

    Border routers

    Figure 7.7

    Internet service provider

    The autonomous system connects to the rest of the internet via border routers at ISP Points of Presence

  • Role of the National Service Providers

    l About 20 in US l See Russ Haynal page on resources

    navigators.com/isp.html l Some of the largest are bankrupt l Connections at NAP and MAEs

  • RA

    RB

    RC

    Route server

    NAP

    National service provider A

    National service provider B

    National service provider C

    LAN

    NAP NAP

    (a)

    (b)

    Figure 7.8

    NSPs are connected at Network Access Points

    Details

  • Control

    1 2

    3

    N

    Line Card

    Line Card

    Line Card

    Line Card

    In te

    rc on

    ne ct

    io n

    Fa br

    ic

    Line Card

    Line Card

    Line Card

    Line Card

    1 2

    3

    N

    Figure 7.10

    …… ……

    Components of a Generic Switch/Router

  • CPU

    1 2

    3

    N

    NIC Card NIC Card NIC Card

    NIC Card M ai

    n M

    em or

    y

    I/O Bus

    Figure 7.11

    ……

    Building a router from a PC

  • 1

    2

    N

    1

    2

    N

    Figure 7.12

    ……

    Routers perform demultiplexing and multiplexing functions

  • Network nodes

    Message

    Subscriber B

    Subscriber A

    Message

    Message

    Message

    Figure 7.13

    Message switching

  • t

    t

    t

    t

    Delay

    Source

    Destination

    T

    p

    Minimum Delay = 3p + 3T

    Switch 1

    Switch 2

    Figure 7.14

    Delays in Message Switching

  • Packet 2

    Packet 1

    Packet 1

    Packet 2

    Packet 2

    Figure 7.15

    Datagram Packet Switching

  • t

    t

    t

    t

    31 2

    31 2

    321

    3p + 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

    p + P

    Source

    Destination

    Switch 1

    Switch 2

    Figure 7.16

    Delays in Packet Switching; note that pipelining can speed transfer vs. message switching

  • Destination address

    Output port

    1345 12

    2458

    70785

    6

    12

    1566

    Figure 7.16

    Routing table in connectionless packet switching

  • Packet

    Packet

    Figure 7.17

    Virtual Circuit Packet Switching

    A virtual connection is set up for the duration of the call, which simplifies routing. Other streams can use the same physical links, so we still have advantage of sharing resources.

  • t

    t

    t

    t

    31 2

    31 2

    321

    Release

    Connect request

    CR

    CR Connect confirm

    CC

    CC

    Delays in virtual-circuit packet switching

  • SW 1

    SW 2

    SW n

    Connect request

    Connect request

    Connect request

    Connect confirm

    Connect confirm

    Figure 7.20

    Signaling message exchanges in virtual circuit set up

  • Identifier Output port

    15 15

    58

    13

    13

    7

    27

    12

    Next identifier

    44

    23

    16

    34

    Entry for packets with identifier 15

    Figure 7.21

    Example of a virtual circuit routing table for an input port. ID is virtual circuit number. Abbreviated headers can be used.

  • 31 2

    31 2

    321

    Minimum Delay = 3p+T t

    t

    t

    t Source

    Destination

    Switch 1

    Switch 2

    Figure 7.22

    Standard virtual circuits have same delay to send k packets and the datagram variety, plus the set up phase

    "Cut through" packet switching speeds by starting output transmission as soon as header is decoded

  • Comparison of Virtual Circuit and Datagram Subnets

    Issue Datagram Subnet VC Subnet

    Addressing Each packet has source and dest address

    Packets contain short VC number

    State Info Subnet does not hold state info

    Each VC requires subnet table space

    Routing Packets routed independently

    Route chosen on set up. All packets follow this route

    Effect of Router Crashes

    None, except packets lost during crash

    All VCs that pass through this router are terminated

    Congestion Control Difficult Easy if enough buffers can be allocated for each VC

  • IP Internet Protocol (Network Layer)

    l Actually most information on IP is in Chapter 8 on TCP/IP l Here we should just know that IP is a datagram service,

    packets are routed independently of one another l It is not connection-oriented at the network layer, but can be

    at the transport layer above l The IP packet has a heade

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