The Network Layer

Network Performance Measures Two Performance Measures Quantity of Service (Throughput) How much data travels across the net? How long does it take to transfer long files? Quality of Service (Average packet delay) How long does it take for a packet to arrive at its destination? How responsive is the system to user commands? Can the network support real-time delivery such as audio and video?

Types of Routing Algorithms Nonadaptive (static) Do not use measurements of current conditions Static routes are downloaded at boot time Adaptive Algorithms Change routes dynamically Gather information at runtime locally from adjacent routers from all other routers Change routes Every delta T seconds When load changes When topology changes

Network Layer Design Issues Store-and-forward packet switching Services provided to transport layer Implementation of connectionless service Implementation of connection-oriented service Comparison of virtual-circuit and datagram networks

Store-and-Forward Packet Switching ISP’s equipment The environment of the network layer protocols.

Services Provided to the Transport Layer Services independent of router technology. Transport layer shielded from number, type, topology of routers. Network addresses available to transport layer use uniform numbering plan even across LANs and WANs

Implementation of Connectionless Service ISP’s equipment A’s table (initially) A’s table (later) C’s Table E’s Table Routing within a datagram network

Implementation of Connection-Oriented Service ISP’s equipment A’s table C’s Table E’s Table Routing within a virtual-circuit network

Comparison of datagram and virtual-circuit networks

1.Distance Vector Routing 2.Link State Routing Routing Algorithms 1.Distance Vector Routing 2.Link State Routing

The Concept of Distance Vector Routing

Distance Vector Routing Table

Routing Table Distribution

Updating Routing Table for Router A

Final Routing Tables

Example 21.1

Concept of Link State Routing

Cost in Link State Routing

Link State Packet

Flooding of A’s LSP

Link State Database

Dijkstra algorithm

Shortest Path Algorithm (1) The first five steps used in computing the shortest path from A to D. The arrows indicate the working node

Hierarchical Routing Hierarchical routing.

Broadcast Routing Reverse path forwarding. (a) A network. (b) A sink tree. (c) The tree built by reverse path forwarding.

Flooding Flooding is a simple routing algorithm in which every incoming packet is sent through every outgoing link except the one it arrived on. Algorithm Each node acts as both a transmitter and a receiver. Each node tries to forward every message to every one of its neighbors except the source node.

Flooding Advantages: If a packet can be delivered, it will (probably multiple times). Since flooding naturally utilizes every path through the network, it will also use the shortest path. This algorithm is very simple to implement

Flooding