There are 3 terms.
1. Circuit Switched N/w
2. Datagram N/w
3. Virtual Circuit N/w.
All the 3 types of network can be established by using same infrastructure. but in each case, every node behaves differently. Lets see what each type of network does.
1. Circuit Switched N/w :
Infrastructure is considered to be consisting of many physical links which are connected using switches. Each link is divided into channels.
So, the link is like a road on high way. And the channels are lane on the road. this analogy is sufficient to understand the meaning of channel and its significance also.
In Circuit Switched N/w before the call is established or before the data transmission, intermediate route is determined and is reserved for the same purpose. So, link x's channel y is reserved for a particular duration of time for a specific data transfer. Before the time ends even if channel is idle, it is considered as busy and no one else can access it.
This gives the guarantee regarding QoS of the data. As far as reliability is concerned, it depends on whether the intermediate links are active during entire session. Even if one channel fails or one link fails the entire set up fails and need to be closed. And here the links are truly dedicated to particular connection.
Hence it is considered as fully dedicated. So the major disadvantage of the system is that resource utilization is poor, as can be seen from the idea of protocol itself. Connection establishment and teardown both requires certain amount of time.
2. Datagram N/w:
As the above mentioned protocol is very very poor in terms of resource utilization, another better technique is decided i.e. Datagram n/w. In this technique, the entire n/w is considered to be same as above, set of physical links and nodes. Each node has its routing table. Now, when the request is sent, it can go from anywhere, it just has to reach the desitnation. Each node can see where to route the packet and can forward them accordingly.
The end user is expected to have a high buffer size so that incoming packets if reached in any order can be assembled. Hence, generally a minimum and maximum allowed time for the packet is always decided so that it goes to destination without buffer overflow.
The major advantage of the system is that, Resource utilization is very high. And the reliability is maximum as the packet will reach destinaiton as long as there is at least one path possible. The major disadvantage of the system is that QoS cannot be guaranteed. Infact it may vary over a period of time. So, for initial 3 minutes you may get very clear sound quality and after that the sound is not even audible. So, for certain important data transmission, where QoS is very important , it cannot be used much. No time is required for Connection establishment and teardown.
3. Virtual Circuit N/w:
Virtual Circuit is the combination of above 2 in one. So, like the Circuit switched a virtual circuit is set up but the same circuit can be shared among many types of data transmission. So, all the pkts going from source to destination goes through same set of nodes. But different set of packets may go through same set of nodes if desired. Also if certain link fails then packet stram can be forwarded to another node and the node can be changed accordingly.
This makes it possible to give very high Reliability and optimum uses of resources is possible. QoS, if desired can be provided for the data transmission. Connection establishment and teardown both requires certain amount of time.
If you want to share something more about the same, please do add more to it. !!!
