1. 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

2. 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.

3. 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

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

5. 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.

6. A Hub/Tree Network
Hub
End node
Hub
Hub
Hub
Hub
A Hub / Tree Network

7. 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

8. 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.

9. 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

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

11. 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

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

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

14. 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.

15. 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.

16. 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.

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