4network - Network Layer C5(5.1-5.4 • Overview of...

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Unformatted text preview: Network Layer: C5 (5.1-5.4) • Overview of Functions • Comparison of circuit-switched, virtual circuit, and datagram • Datagram routing • Fragmentation • Virtual circuits: X.25 • Congestion Control 1 Network Layer Design Issues • Store-and-Forward Packet Switching • Services Provided to the Transport Layer • Implementation of Connectionless Service • Implementation of Connection-Oriented Service • Comparison of Virtual-Circuit and Datagram Subnets 2 Store-and-Forward Packet Switching The environment of the network layer protocols. fig 5-1 3 Datagram • Each packet treated independently • Packets can take any practical route • Packets may arrive out of order • Packets may go missing • Up to receiver to re-order packets and recover from missing packets 4 Implementation of Connectionless Service Routing within a diagram subnet. 5 Implementation of Connection-Oriented Service Routing within a virtual-circuit subnet. 6 Virtual Circuit • Preplanned route established before any packets sent • Call request and call accept packets establish connection (handshake) • Each packet contains a virtual circuit identifier instead of destination address • No routing decisions required for each packet • Clear request to drop circuit • Not a dedicated path 7 Virtual Circuits v Datagram • Virtual circuits – Network can provide sequencing and error control – Packets are forwarded more quickly • No routing decisions to make – Less reliable • Loss of a node looses all circuits through that node • Datagram – No call setup phase • Better if few packets – More flexible • Routing can be used to avoid congested parts of the network 8 Comparison of Virtual-Circuit and Datagram Subnets 5-4 9 Routing Algorithms • The Optimality Principle • Shortest Path Routing • Flooding...
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4network - Network Layer C5(5.1-5.4 • Overview of...

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