Monday, August 12, 2013
Without broadcasting, our information theory and telecommunications does not mean anything.
- It is broadcasting that actually makes the transfer of data possible from one point to another.
- Broadcasting can be defined as the method of transfer of a message to a number of recipients, all at the same time.
- Broadcasting is often considered to be a sort of high – level operation in some programs while low level operation in some other programs.
- For example, in message passing interface, broadcasting is a high level operation whereas in broadcasting on Ethernet, it is considered to be a low level operation in networking.
We have many kinds of routing schemes suiting for various kinds of broadcasting requirements:
- Broadcasting is transmission of a packet to each and every device that is attached to the network.
- However, the broadcasting is limited to transmission in the broadcast domain in practical applications.
- Broadcasting can be contrasted with uni cast routing scheme in the sense that in uni cast, the datagrams are transmitted by one host and are received by another single host only.
- This receiving host is identified with an IP address on the network that is unique to it.
- All the technologies used in networking are not capable of supporting broadcasting.
For example, the following do not have this capability:
Ø X.25 relay
Ø Frame relay
- The broadcast method cannot be implement with IPv6 i.e., the successor of the IPv4 (internet protocol version 4).
- This is for the avoidance of the disturbance to the nodes.
- Also, there does not exist anything such as the internet wide broadcast.
- Therefore, this limits the scope of the broadcasting to the LAN technologies such as token ring and Ethernet since here the impact of the broadcasting performance is small.
The broadcasting methods can be classified in to 4 major categories as per the IEEE 802.11 standard:
1. Simple flooding method:
- In this method the packets are rebroadcast-ed by each of the nodes.
- A message is disseminated to all the neighboring nodes by a source node in the MANET.
- If the neighboring nodes would have received this message already, then this time the message will be dropped.
- If not, they will re-disseminate the message to their neighbors simultaneously.
- This process continues until all the nodes have received this message.
- Only for a MANET this method proves to be reliable that too only if the nodes have low density as well as high mobility.
- This method has a good potential for harming the network and make it unproductive.
- This happens so because it will cause congestion in the network thereby exhausting the power of the battery.
2. Area based broadcasting method:
- Here, we assume a transmission distance.
- Only if sufficient coverage area is detected, the node can rebroadcast otherwise not.
- This method can be of two types namely location based scheme and the distance based scheme.
3. Probability tested:
- Rebroadcasting is done by the nodes depending up on the network’s topology and probabilities assigned to them.
- This somewhat resembles the flooding algorithm with the only exception that a predetermined probability is used for rebroadcasting by the nodes.
- The transmission coverage might be shared by the multiple nodes where the network is too dense.
4. Neighborhood based broadcasting method:
- Neighborhood method is used for maintaining a state in the neighborhood and rebroadcasting is done with the help of the info obtained from the nodes in this neighboring area.
- There are two types of this method namely self-pruning approach and ad hoc broadcasting approach.