Chapter4 - Chapter 4 Network Layer Chapter 4: Network Layer...

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1 Network Layer 4-1 Chapter 4 Network Layer Al material copyright 1996-2007 J.F Kurose and K.W. Ross, Al Rights Reserved Network Layer 4-2 Chapter 4: Network Layer Chapter goals: ± understand principles behind network layer services: ² network layer service models ² forwarding versus routing ² how a router works ² routing (path selection) ² dealing with scale ² advanced topics: IPv6, mobility ± instantiation, implementation in the Internet Network Layer 4-3 Network layer ± transport segment from sending to receiving host ± on sending side encapsulates segments into datagrams ± on rcving side, delivers segments to transport layer ± network layer protocols in every host, router ± router examines header fields in all IP datagrams passing through it application transport data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical Network Layer 4-4 Two Key Network-Layer Functions ± forwarding: move packets from router’s input to appropriate router output ± routing: determine route taken by packets from source to dest. ² routing algorithms analogy: ± routing: process of planning trip from source to dest ± forwarding: process of getting through single interchange Network Layer 4-5 1 2 3 0111 value in arriving packet’s header routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 Interplay between routing and forwarding Network Layer 4-6 Virtual circuits: signaling protocols ± used to setup, maintain teardown VC ± used in ATM, frame-relay, X.25 ± not used in today’s Internet application transport network data link physical application transport network data link physical 1. Initiate call 2. incoming call 3. Accept call 4. Call connected 5. Data flow begins 6. Receive data
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2 Network Layer 4-7 Datagram networks ± no call setup at network layer ± routers: no state about end-to-end connections ² no network-level concept of “connection” ± packets forwarded using destination host address ² packets between same source-dest pair may take different paths application transport network data link physical application transport network data link physical 1. Send data 2. Receive data Network Layer 4-8 Router Architecture Overview Two key router functions: ± run routing algorithms/protocol (RIP, OSPF, BGP) ± forwarding datagrams from incoming to outgoing link Network Layer 4-9 Input Port Functions Decentralized switching : ± given datagram dest., lookup output port using forwarding table in input port memory ± goal: complete input port processing at ‘line speed’ ± queuing: if datagrams arrive faster than forwarding rate into switch fabric Physical layer: bit-level reception Data link layer: e.g., Ethernet see chapter 5 Network Layer 4-10 Output Ports ±
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Chapter4 - Chapter 4 Network Layer Chapter 4: Network Layer...

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