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Chapter4-helmy-intro - C hapte 4 r Ne twork Laye r C pute...

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Network Layer 4-1 Chapter 4 Network Layer Computer Networking: A Top Down Approach 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007.
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Network Layer 4-2 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 network 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 4-3 Two Key Network-Layer Functions forwarding: movepackets fromrouter’s input to appropriaterouter output routing: determineroute taken by packets fromsource to dest. routing algorithms analogy: routing: process of planning trip fromsourceto dest forwarding: process of getting through single interchange
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Network Layer 4-4 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
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Network Layer 4-5 VC implementation a VC consists of: 1. path from sourceto destination 2. VC numbers, onenumber for each link along path 3. entries in forwarding tables in routers along path packet belonging to VC carries VC number (rather than dest address) VC number can bechanged on each link. New VC number comes from forwarding table
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Network Layer 4-6 Forwarding table 12 22 32 1 2 3 VC number interface number Incoming interface Incoming VC # Outgoing interface Outgoing VC # 1 12 3 22 2 63 1 18 3 7 2 17 1 97 3 87 Forwarding tablein northwest router: Routers maintain connection stateinformation!
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Network Layer 4-7 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. Initiatecall 2. incoming call 3. Accept call 4. Call connected 5. Data flow begins 6. Receivedata
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Network Layer 4-8 Datagram networks no call setup at network layer routers: no stateabout end-to-end connections no network-level concept of “connection” packets forwarded using destination host address 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. Receivedata
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Network Layer 4-9 Forwarding table Destination Address Range Link Interface 11001000 00010111 00010000 00000000 through 0 11001000 00010111 00010111 11111111 11001000 00010111 00011000 00000000 through 1 11001000 00010111 00011000 11111111 11001000 00010111 00011001 00000000 through 2 11001000 00010111 00011111 11111111 otherwise 3 4 billion possible entries
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Network Layer 4-10 Longest prefix matching Prefix Match
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