lec06b - Network layer ! ! ! ! ! transport segment from...

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Network Layer 4-4 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
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Network Layer 4-5 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. " routing algorithms analogy: ! routing: process of planning trip from source to dest ! forwarding : process of getting through single interchange
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Network Layer 4-6 1 2 3 0111 value in arriving packet ` s header routing algorithm local forwarding table header value output link 0100 0101 1001 3 2 2 1 Interplay between routing and forwarding
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Network Layer 4-9 Network layer service models: Network Architecture Internet ATM ATM Service Model best effort CBR VBR ABR UBR Bandwidth none constant rate guaranteed rate guaranteed minimum none Loss no yes yes no no Order no yes yes yes yes Timing no yes yes no no Congestion feedback no (inferred via loss) no congestion no congestion yes no Guarantees ?
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Network Layer 4-16 Datagram networks ! no call setup at network layer ! routers: no state about end-to-end connections " no network-level concept of l connection z ! packets forwarded using destination host address " packets between same source-dest pair may take different paths application transport network data link physical network physical 1. Send data 2. Receive data
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Network Layer 4-17 Datagram Forwarding table 1 2 3 IP destination address in arriving packet ` s header routing algorithm local forwarding table dest address output link address-range 1 address-range 2 address-range 3 address-range 4 3 2 2 1 4 billion IP addresses, so rather than list individual destination address list range of addresses (aggregate table entries)
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Network Layer 4-18 Datagram Forwarding table Destination Address Range 11001000 00010111 00010000 00000000 through 11001000 00010111 00010111 11111111 11001000 00010111 00011000 00000000 through 11001000 00010111 00011000 11111111 11001000 00010111 00011001 00000000 through 11001000 00010111 00011111 11111111 otherwise Link Interface 0 1 2 3 Q: but what happens if ranges don ` t divide up so nicely?
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Network Layer 4-19 Longest prefix matching Destination Address Range 11001000 00010111 00010*** ********* 11001000 00010111 00011000 ********* 11001000 00010111 00011*** ********* otherwise DA: 11001000 00010111 00011000 10101010 Examples: DA: 11001000 00010111 00010110 10100001 Which interface?
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This note was uploaded on 02/28/2011 for the course CS 436 taught by Professor Dr.reidholmes during the Winter '11 term at Waterloo.

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lec06b - Network layer ! ! ! ! ! transport segment from...

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