1. Routing

2. Routing
 Routing is the process of selecting
paths in a network along which to send
network traffic
 Process of relaying packets among
multiple interconnected networks

3. Least Cost Routing
 Based on efficiency
 Which of the available paths is cheapest
 A value is assigned to each link; length
of the particular route is equal to the
total no of the values of the component
links.
 Shortest means the route requiring the
smallest no of relays

4. Non adaptive and Adaptive routing
 Non Adaptive
 Once the pathway to destination has
been selected, the router sends all
packets for that destination along that
route
 Adaptive
 Router may select a new route for each
packet

5. Routing Algorithms
 Shortest Path Routing
 Flooding
 Flow Based Routing
 Distance Vector Routing
 Link State Routing
 Hierarchical Routing
 Broadcast Routing
 Multicast routing

6. Shortest Path Routing
 A graph of subnet is built.
 Each node represents a router
 Each arc of graph represents a
communication link.
 To choose a route algorithm just finds
the shortest path between them on the
graph

7. Flooding
 Every incoming packet is sent out on every outgoing
line except the one it arrived on.
 So it generates vast no. of duplicate packets.
 A hop counter is maintained in header of each packet
 Hop counter is decremented at each hop
 Packet is discarded when the counter reaches zero
 Ideally hop counter is initialized to the length of the
path from source to destination
 Selective flooding- incoming packets are sent on lines
that are going approximately in the right direction

8. Flow Based Routing
 Used when data flow between each pair of nodes is relatively
stable and predictable
 Considers the flow in the network; mean consider the amount
of traffic in the network before deciding on which outgoing line
to place the packet.
 The key here is to be able to characterize the nature of the
traffic flows over time.
 The basic idea behind the algorithm, is that any given line, if
the capacity and average flow are known, it is possible to
compute the mean packet delay on that line from queuing
theory.
 The routing problem thus reduces to finding the routing
algorithm that produces the minimum average delay for the
subnet.

9. Distance Vector Routing
 Each router maintains a table giving the
best known distance to each destination
and which line to use to get there
 These tables are updated by
exchanging info from neighbors.

10. Distance Vector Routing-
Mechanism
 Each router maintains a table indexed by and
containing one entry for each router in the subnet.
 The entry has two parts
 Preferred outgoing line
 Estimate of time or distance to that destination
 The router is assumed to know the “distance” to
each of its neighbors.
 if metrics is hops , distance is one hops
 If metrics is queue length, the route simply examines each
queue
 If metrics is delay, the router can measure it directly with
the special echo packets that the receiver just timestamps
and send back as fast it can

11. TO A I H K Line
A 0 24 20 21 8 A
B 12 36 31 28 20 A New
estimated
C 25 18 19 36 28 I delay from J
D 40 27 8 24 20 H
E 14 7 30 22 17 I
A B C D F 23 20 19 40 30 I
G 18 31 6 31 18 H
H 17 20 0 19 12 H
I 21 0 14 22 10 I
F G
E H J 9 11 7 10 0 -
K 24 22 22 0 6 K
L 29 33 9 9 15 K
L
K
I J J computes its new route J to H=12 msec
to router G H to G =6 msec
JA Delay=8 J to A=8 msec Total=18 msec
JI Delay=10 A to g=18 msec
J to K =6 msec
Total=26 msec K To G=31 msec
JH Delay=12
Total=37 msec
JK Delay=6 J to I=10 msec
I to G=31 msec Best : 18 i.e via H
Total=41 msec

12. Link State Routing
 Each router must
 Discover its neighbour and learn their network
address by sending Hello packet
 Measure the delay or cost to each of the
neighbours by sending echo packet
 Construct a packet telling all it has learned
 Send this packet to all other routers
 Compute the shortest path to every other router.
 In effect, the complete topology and all delays are
experimentally measured and distributed to every
router.

13. Hierarchical Routing
 As network grow, routing tables increase in size
consuming router memory
 It is not feasible for every router to have an entry for
every other router
 Routing is done hierarchically
 Routers are divided into regions
 Each router knows all details of router within its own
region.
 In very large networks
 regions -> clusters
 Clusters->zones
 Zones->groups

14. Hierarchical Routing
Region1 Region 2
Region 4
Region 3

15. Routing for mobile hosts
 When a new user enters an area it must register
itself with the foreign agent here
 Each foreign agent broadcasts a packet announcing
its existence and address
 A newly arrived mobile host broadcasts a packet
inquiring any foreign agents
 Mobile hosts registers with the foreign agent giving
its home address, DL layer Address and security info
 Foreign agent contacts mobile host’s home address
 Home agent checks info sent by foreign agent, if ok,
informs foreign agent to proceed
 Foreign agent the makes an entry in tables and
informs mobile hosts that it is registered

16. Broadcast Routing
 Send messages to many or all hosts simultaneously
 Each packet contains a list of destinations
 Router examines this list to determine set of output
lines that will be needed
 It generates a new copy of packet for each output
line to be used and include in each packet only those
destination that are to use the line
 Destination set is partitioned amount output lines
 Each packet will carry only one destination

17. Multicast Routing
 Sending messages to well defined network
groups
 With a multicast design, applications can send
one copy of each packet and address it to the
group of computers that want to receive it.
 This technique addresses packets to a group
of receivers rather than to a single receiver
 It depends on the network to forward the
packets to only the networks that need to
receive them.