Chapter4-helmy-intro

Chapter4-helmy-intro - Network Layer 4-1 Chapter 4 Network Layer Computer Networking A Top Down Approach 4 th edition Jim Kurose Keith Ross

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Unformatted text preview: 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. 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 Network Layer 4-3 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 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 Network Layer 4-5 VC implementation a VC consists of: 1. path from source to destination 2. VC numbers, one number 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 be changed on each link. ❍ New VC number comes from forwarding table 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 table in northwest router: Routers maintain connection state information! 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. Initiate call 2. incoming call 3. Accept call 4. Call connected 5. Data flow begins 6. Receive data Network Layer 4-8 Datagram networks ❒ no call setup at network layer ❒ routers: no state about 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. Receive data 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...
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Chapter4-helmy-intro - Network Layer 4-1 Chapter 4 Network Layer Computer Networking A Top Down Approach 4 th edition Jim Kurose Keith Ross

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