Network Service Types

There are two types of Network Services one is known as Connectionless (or Datagram) and the other is Connection-Oriented (or Virtual Circuit).

Connectionless Service

In connectionless service the endnode transmits with every piece of data the address to which the data should be delivered. Every piece of data called packet is independently routed,so the network can't guarantee that all the packets will reach the destination in the transmitting order since the packets can be delivered through more then one path.

Connection-Oriented Service

In connection-oriented service the endnode first informs the network it wishes to start a conversation with another endnode,the network sends it's request to the destination that accepts or rejects the request.
If the destination refuses, connection fails, otherwise connection is established.

Connection-Oriented service usually has the following characteristics:

• The network guarantees that all packets will be delivered in order without loss or duplication of data.
• Only a single path is established for the call, and all the data follows that path.
• The network guarantees a minimal amount of bandwidth and this bandwidth is reserved for the duration of the call.
• If the network becomes overly utilized, future call requests are refused.

Is one type of service is better than the other?
The answer is not conclusive and depends on several considerations.
Here are two examples for such considerations:

• Different kind of services type are required by different applications.
• 1. File transfer and remote terminal protocols will not tolerate loss of data, and require the packets to remain ordered. This kind of application dictates a connection-oriented service.
  2. Electronic mail do not requires that packets remain ordered. Speech conveying systems can tolerate a modest percentage of lost packets. In packet voice, receiving delayed packets is actually useless. This kind of application dictates connectionless service.
• What are the requirements from the network.
• 1. When a network accepts a call it has to provide reasonable bandwidth for the call even if it has to lock out other calls.
  2. All the users have to be able to use the network (even if it causes the service to degrade equally for every one.).

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