Networks Network:end-node and router C 2 B 1 3 D 5 A 4 6 E 7 Router F link Network:end-node and router

Network Topology: Physical & Logical The topology of a network defines how the nodes of a network are connected. A network is defined by a physical topology and a logical topology. Physical topology defines how the nodes of the network are physically connected . Logical topology dedicated connections between certain selected source-destination pairs using the underlying physical topology.

Multi-hop Network T T T T 1 w w w w 1, 2 4, 6 w 1 w 7, w 8 w 1, w 7 1 Star coupler 4 w T 2 4 w T 3, w 5 w 3, w 4 w w 2 T 7 w w 3 6 w 5, w 6 w 2, w 8 3 4 w 5 3 w 8 Physical Topology Logical Topology

Communication Networks Network topologies: The Bus Network Hub/Tree Network Star Network 4 Ring Network

A bus network topology Use: This topology is useful in LANs. It does not rely on central host.This network can still function if one of the computers malfunctions. Other advantages: easy to wire, quick response, less expensive C 1 C 3 C 2 C 6 C 5 C 4 Problem: The main disadvantage is bad connection to the cable can bring down the entire network. Another problem: collision occurs when 2 nodes send messages simultaneously.

A Hub/Tree Network Hub End node Hub Hub Hub Hub A Hub / Tree Network

A ring network topology Use: This topology is useful in LANs. It does not rely on central host.This network can still function if one of the computers malfunctions. C 1 C 6 C 2 Problems: The connecting wire, cable, or optical fiber forms a closed loop. Data are passed along the ring from one computer to another and always flow in one direction C 3 C 5 C 4

A star network topology Use: This topology is useful for applications where processing must be centralized and some can be performed locally. Host CPU C 1 C 2 C 3 C 4 C 5 C 6 Problems: All communication pass through the central computer. The communications in the network will stop if the host computer stops functioning.

Complex Networks: De Bruijn graphs 001 010 011 110 101 111 100 000 no. of nodes = 2 ^ 3 = 8 Advantages: diameter = max hop no. = 3

Complex Networks:ShuffleNet A ( 2, 2 ) Shuffle Net. 1 2 3 4 5 6 7

Complex Networks: Manhattan Street Network A 4 x 4 Manhattan Street Network 0,0 0,1 0,2 0,3 1,0 1,1 1,2 1,3 2,0 2,1 2,2 2,3 3,0 3,1 3,2 3,3

Complex Networks:Binary Hypercube 010 011 000 001 110 111 100 101 An 8-node binary hypercube

Fault-tolerant network reliable operation in faulty networks. alternate ways of communication. faults in optical networks channel fault link fault node fault

Channel fault Why and when it occurs? A channel fault occurs when a single wavelength channel on a link between two nodes has failed due to the failure of the laser or receiver for that wavelength channel, or due to cable disconnections. How to manage? Thus fault can be managed by routing the traffic to a spare channel on the same physical link and bypassing the faulty channel.

Link fault Why and when it occurs? A link fault occurs due to fiber cut or due to noise (particularly those running over long distance). How to manage? It can be managed by using a bundle of protection fibers in addition to the working fiber. The performance or survivability is limited by the number of links in each bundle. Another way of solving this problem is by providing a “loopback” mechanism within each node on the same working fiber.

Node fault Why and when it occurs? A node fault occurs due to power outages or catastrophic failure in an entire WADM node failure. How to handle? It is complicated to handle since when this fault occurs, a part of the conversion capability of the network as a whole is lost and leaves an open circuit and can result in deadlock of all routing networks. One solution is to introduce redundancy in the internal connections of the networks rather than in the connections of the nodes. In case of multiple failures, the solution is a “firewall” that can prevent deadlock spreading in the network. This can be achieved by a simple device that tomes out if a packet passing through it stay longer than a specified time.

Survivable route graph F E G D A C B E F G A C B D A Network. Survival route graph.