Networking Classes

Virtual Circuit Packet Switching

In this a single route is choose between sender and receive at the beginning of the session.When the data are sent , all packets of the transmission travel one after another along that route.

Today virtual circuit transmission is implemented in two formats:

✔ Switched Virtual Circuit (SVC)

✔ Permanent Virtual Circuit (PVC)

1. Switched Virtual Circuit (SVC):

The switched virtual circuit (SVC) format is comparable conceptually to dial-up lines in circuit switching.

In this method a virtual circuit is made whenever it is needed and exist upto duration of message transmission.

Example:

Suppose A wants to send four packet to station (X). First a A request is establish connection to X. Once the connection is establish the packet are send one after another and in sequential order.

When the last packed has been received and if necessary acknowledged , the connection is released and virtual circuit causes to exist. Only one single path will exist for duration of transmission.

2. Permanent Virtual Circuit (PVC):

PVC is comparable to leased line in circuit switching. In this method , the same virtual circuit is provided between two user on a continues basis.The circuit is dedicated to the specific user. No one can else use it.It can be used without connection establishment and connection termination.When as one SVC user may get a different route , every time they request for connection , two PVC user always get the same route.

Note:

In virtual switching when we want to establish a connection than we first send Connection Request Packet (CR) which contain :

When route is create between two points than create an entry in Routing Table Such as:

The above figure explain the communication between A to B .When A will send packet to B , It will send Connection Request (CR) packet to B for establishing connection.In this case each router maintain Routing Decision Table which contain four fields.

Than B will send packet connection Confirm (CC) packet for confirming B is ready to receive data or packet to A.

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✔ Switching

Datagram Packet Switching

In previous post we already discuss about Packet Switching.

Now we will discuss about Datagram Packet Switching. It is one of the type of packet switching. In Datagram Packet Switching connection less scheme is used. In this scheme different packet can send through different path , So sequencing is necessary. When the packets are send through different path than it is duty of transport layer to rearrange the packets before reaching at destination.

In this scheme packets are known as Datagram.

The link joining each pair of node can contain multiple channels , each of these channel is capable of carrying datagram either from several different sources or from one sources.Multiplexing can be done using TDM (Time Division Muntiplexing) or FDM (Frequency Division Multiplexing).

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✔ Switching

Concept of Packet Switching

It is a Store and Forward type of switching. In this scheme message or data are divided into packets.This scheme is connection less that mean there is no need to establish connection before transferring message.

Each packet contains not only data but also a header with control information ( such as priority code, source address and destination address ) .The packets are sent over node to node over the network.

At each node or router there is a buffer which store those packets and than router takes decision about path or rout. Here the problem will arise that what will be the size of buffer that store the packets ?

For removing the problem of buffer.We consider a constant size of packet.If the size of packet is constant than we consider the size of buffer according to packet size.

Suppose the packet size is 1KB than the buffer size is also 1KB.

This scheme is not connection oriented so we send different packet through different path.In this scheme utilisation of channel is good.

Advantages of circuit switching over packet switching:

✔ In circuit switching it is guarantee to transfer message or data from some of destination in few seconds.

✔ But in packet switching it is not guarantee to transfer data / message to destination with in few seconds at minimum because here it will wait until the line is not free.

Example:

There are two popular approach for packet switching is:

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✔ Circuit Switching

Thursday, August 6, 2020

Concept of Circuit Switching

Circuit Switching is a connection oriented technique for establishing the connection. Suppose A first make connection request packet called control packet (CP), which contain following.

Circuit switching was designed for voice communication. In telephone conversation for example, once a circuit is established it remain connected for duration of the session. Circuit switching creates temporary (dialled) or permanent (leased) dedicated link that are well suited to this type of communication.

Explanation:

Suppose A make connection with following path like A--V--W--X--Y--B decision is taken place at each router, that decision is routing decision when (CP) is reached at that router.

When the connection is established then the whole path is reserved for that particular transmission. This path is reserved until the whole transmission is not completed.

After that B make a connection confirm packet (CC) and send to A. (CC) does not contain any source address and destination address because path is already establish and (CC) packet will follow that path to reach A.

When A receive (CC) packet than it confirm that B is ready to receive data.

The time which is used to make circuit or connection is called circuit setup.

In circuit switching before sending message connection is establish. Handshaking is done before message sending.

Drawback of Circuit Switching:

✔ When circuit switching link are used for data transmission therefore the line is often ideal and its facilities wasted.

✔ A second weakness of circuit switched connection for data transmission is in its data rate. A circuit switched link creates the equivalent of a single cable between two device and there by assume a single data rate for both device. This assumption limits the flexibility and usefulness of a circuit switched connection for network interconnecting a variety of digital device.

✔ Third circuit switching is inflexible once a circuit has been established that circuit is the path which is reserved until all the message are not transferred.

✔ Utilisation of channel is poor.

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