Unit4_Net - Unit 4 Network Layer After studying this unit,...

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Network Layer 4-1 Unit 4 Network Layer After studying this unit, you will be able to 1. describe how internetworking works 2. explain the principles of packet forwarding by routers.
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Network Layer 4-2 Unit 4: Outline ± 4. 1 Introduction ± 4.2 Virtual circuit and datagram networks ± 4.3 IP: Internet Protocol ² Datagram format ² IPv4 addressing ² DHCP ² NAT ² ICMP ² ARP ² IPv6
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Network Layer 4-3 Unit 4.1 Introduction
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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 everyhost, router ± Router examines header fields in all IP datagrams passing through it 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 application transport network data link physical application transport network data link physical
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Network Layer 4-5 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
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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 0111 1001 3 2 2 1 Interplay between routing and forwarding
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Network Layer 4-7 Connection setup ± The 3 rd important function in some network architectures: ² ATM, frame relay, X.25 ± Before datagrams flow, two hosts and intervening routers establish virtual connection ² Routers get involved • A fixed route is determined ± Remark: there is no connection setup in the Internet.
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Network Layer 4-8 Unit 4.2 Virtual Circuit and Datagram Networks
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Network Layer 4-9 Network Architectures Two classes: ± Datagram network: ² Each packet carries a destination address. ² A router determines next hop according to the address. ² Routes may change during a session. ² Provides connectionless service. ± Virtual circuit network: ² Each packet carries a tag ( virtual circuit number ). ² A router determines next hop according to the tag. ² A fixed path is determined at call setup time, and remains fixed throughout the call. ² Provides connection service.
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Network Layer 4-10 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 • that’s why packets in the Internet may arrive out of order.
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This note was uploaded on 05/01/2011 for the course ELECTRICAL EE3015 taught by Professor Albertsun during the Spring '11 term at City University of Hong Kong.

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Unit4_Net - Unit 4 Network Layer After studying this unit,...

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