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Wednesday, September 18, 2013

What are the advantages and disadvantages of datagram approach?

- Today’s packet switching networks make use of a basic transfer unit commonly known as the datagram. 
- In such packet switched networks, the order of the data packets arrival, time of arrival and delivery comes with no guarantee. 
- The first packet switching network to use the datagrams was CYCLADES. 
Datagrams are known by different names at different levels of the OSI model. 
- For example, at layer 1 we call it Chip, at layer 2 it is called Frame or cell, data packet at layer 3 and data segment at layer 4. 
- The major characteristic of a datagram is that it is independent i.e., it does not rely on any other thing for the information required for exchange.
- The duration of a connection between any two points is not fixed such as in telephone conversations. 
- Virtual circuits are just the opposite of the datagrams. 
- Thus, a datagram can be called as a self containing entity. 
- It consists of information sufficient for routing it from the source to the destination without depending up on the exchanges made earlier. 
- Often, a comparison is drawn between the mail delivery service and the datagram service. 
- The user’s work is to just provide the address of the destination. 
- But he/she is not guaranteed the delivery of the datagram and if the datagram is successfully delivered, no confirmation is sent to the user. 
- The data gram are routed to some destination without help of a predetermined path. 
- The order in which the data has to be sent or received is given no consideration. 
- It is because of this that the datagrams belonging to a single group might travel over different routes before they reach their common destination. 

Advantages of Datagram Approach
  1. Datagrams can contain the full destination address rather than using some number.
  2. There is no set up phase required for the datagram circuits. This means that no resources are consumed.
  3. If it happens during a transmission that one router goes down, the datagrams that will suffer will include only those routers which would have been queued up in that specific router. The other datagrams will not suffer.
  4. If any fault or loss occurs on a communication line, the datagrams circuits are capable of compensating for it.
  5. Datagrams play an important role in the balancing of the traffic in the subnet. This is so because halfway the router can be changed.
Disadvantages of Datagram Approach

  1. Since the datagrams consist of the full destination address, they generate more overhead and thus lead to wastage of the bandwidth. This in turn makes using datagram approach quite costly.
  2. A complicated procedure has to be followed for datagram circuits for determining the destination of the packet.
  3. In a subnet using the datagram approach, it is very difficult to keep congestion problems at bay.
  4. The any-to-any communication is one of the key disadvantages of the datagram subnets. This means that if a system can communicate with any device, any of the devices can communicate with this system. This can lead to various security issues.
  5. Datagram subnets are prone to losing or re - sequencing the data packets during the transition. This puts a great burden on the end systems for monitoring, recovering, and reordering the packets as they were originally.
  6. Datagram subnets have less capability of dealing with congestion control as well as flow control. This happens because the direction of the incoming traffic is not specified. In the virtual circuit subnets, the flow of the packets is directed only along the virtual circuits thus making it comparatively easy for controlling it.
  7. The unpredictable nature of the flow of the traffic makes it difficult to design the datagram networks

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