Routing
requires the use of routing algorithms for the construction of the routing
tables.

**A number of routing algorithms are today available with us such as:**

1.
Distance vector algorithm (bellman ford algorithm)

2.
Link state algorithm

3.
Optimized link state routing algorithm (OLSR)

- In a
number of web applications, there are a number of nodes which require communicating
with each other via communication channels.

- Few examples of such applications
are telecommunication networks (such as POTS/ PSTN, internet, mobile phone
networks, and local area networks), distributed applications, multiprocessor
computers etc.

- All nodes cannot be connected to each other since doing so will
require many high powered transceivers, wires and cables.

- Therefore, the
implementation is such that the transmissions of nodes are forwarded by the
other nodes till the data or info reaches its correct destination.

- Thus, routing
is the process of determining where the packets have to be forwarded and doing
so.

__Properties of Routing Algorithm__- The packets must reach their destination if there are no factors preventing this such as congestion.

- The
transmission of data should be quick.

- There
should be high efficiency in the data transfer.

- All
the computations involved must not be long. They should be as easy and quick as
possible.

- The
routing algorithm must be capable of adapting to the two factors i.e., changing
load and changes in topology (this includes the channels that are new and the
deleted ones.)

- All
the different users must be treated fairly by the routing algorithm.

**The second and the third properties can be achieved using fastest or the shortest route algorithms.**

- Graphical representation of the network is a crucial part of
the routing process.

- Each network node is represented by a vertex in the graph
whereas an edge represents a connection or a link between the two nodes.

- The
cost of each link is represented as the weight of the edge in the graph.

**- There are 3 typical weight functions as mentioned below:**

**1.**

**Minimum hops:**The weight of all the edges in the graph is same.

**2.**

**Shortest path:**The weight of all the edges is a constant non – negative value.

**3.**

**Minimum delay:**The weight of every edge depends up on the traffic on its link and is a non – negative value.

However
in real networks, the weights are always positive.

__Goals of Routing Algorithms__
- The goal
of these routing algorithms is to find the shortest path based up on some
specified relationships that if used will result in the maximum routing
efficiency.

- Another point is to use as minimum information as possible.

- Goal of
the routing algorithm is also to keep the routing tables update with all
alternative paths so that if one fails, the other one can be used.

- The channel
or the path that fails is removed from the table.

- The routing algorithms need
to be stable in order to provide meaningful results but at the same time is
quite difficult to detect the stable state of an algorithm.

- Choosing a routing
algorithm is like choosing different horses for different courses.

- The
frequency of the changes in the network is one thing to be considered.

- Other
things to be considered include the cost function that is needed to be
minimized and the calculation of the routing tables in a centralized fashion.

- For
static networks the routing tables are fixed and therefore they require only
simple routing algorithms for calculation.

- On the other hand, the networks that
are dynamic nature require distributed routing algorithms which are of course
complex.

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