There is a wide area network in which a special route was selected. Propagation

Question

There is a wide area network in which a special route was selected. Propagation delay is so small that it could be neglected. Traffic is light – thus, there are no queuing delays. The length of this route is k node-to-node links. Transmission speed of each link is N bps. There is a need to transmit m packets. The length of each packet is l bit. Find the time needed to transmit the file from the source to the destination in the following networks.

a) Suppose the network is packet-switched virtual circuit network. Denote the VC set-up time by ts seconds. Suppose the sending layers add a total of h bits of header to each packet.

b) Suppose the network is packet-switched datagram network and a connectionless service is used. Now suppose each packet has 2h bits of header.

c) Repeat b), however assume that message switching is used (that is, 2h bits are added to the message, and the message is not segmented).

d) Suppose that the network is circuit-switched network. Further suppose that the transmission rate of the circuit between source and destination is N bps. Assume ts is set- up time and h bits of header are appended to the entire file.

Explanation / Answer

Hi,

Answers to the above question:

Question a:

Since it is a packet switched virtual circuit network path is established between the source and the final destination through which all the packets will be routed during a call.only one path will be established.

No of packets to be transfered=m

Length of each packet is =I bit

Therefore total length to be transfered =m*I bits(i.e if there are 10 packets and length of each packet is 2 bits the total length to be transfered is 2*10=20 bits)

No of node to node links =k

Transmission speed of each link =N bps

Now the transmission speed of all links=K*N bps(i.e if there are 10 links and transmission speed of each link is 10bps then each link transmission speed 10*10bps=100bps)

No of packets to be transfered =m

Length of each packet =I bit

Length of all the packets =m*I(i.e if there are 10 packets and length of each packet is 1 bit then length os 10 packets put together =10*1 bit=10 bits in total)

Now in case of virtual circuit network first time taken to setup virtual circuit is ts seconds.

Transmission of m packets =ts(initial time taken to setup VC)+Nbps(Transmission speed of this VC link)

Now since there is addition of a header filed to m packets i.e h bits of header to m packets.As above m packets take ts+N,then m packets sixe now increases from I bit to (I+H) bit,if m packets each of length I bit take ts+N time then m packets of (I+h) length will take ts+Nbps+H(addition length added to the packet)

Therefore time taken =ts+N+H sec

Question b:

Now if the network is assumed to be packet switched datagram network  each packet, now called a datagram, is treated as a separate entity. Each packet is routed independently through the network. Therefore packets contain a header with the full information about the destination. The individual packets which form a data stream may follow different paths between the source and the destination.Because each packet is switched independently, there is no need for connection setup and no need to dedicate bandwidth in the form of a circuit.

So here all the communication links i.e 'k'node to node links can be used to transfer 'm' packets each of length 'I' bits.

Each communication link has transmission speed of 'Nbps' therefore combining all communication links together will have k*N bps(i.e if nodes=5 and speed of each node is 5bps then together 5 nodes will have speed of 5*5bps=25bps)

Here the length of the packet is increased to '2h' bit

Transmission of m packets =(K*N)bps(Transmission speed of this VC link)

Now since there is addition of a header filed to m packets i.e 2h bits of header to m packets.As above m packets take K*N,then m packets size now increases from I bit to (I+2H) bit,if m packets each of length I bit take K*N time then m packets of (I+2h) length will take (N*K)bps+2H(addition length added to the packet) and this time is much lesser than virtual -circuit since there is combined network and packets can be sent parallely.

Question c:

If we are using a message switching a mode of data transmission in which a message is sent as a complete unit and routed via a number of intermediate nodes at which it is stored and then forwarded and packet switched datagram network is used.we cannot fragment the entire mesasage and the message must thus be sent sequentially.

Now since there is addition of a header filed to m packets i.e 2h bits of header to m packets.As above m packets take K*N,then m packets size now increases from I bit to (I+2H) bit,if m packets each of length I bit take K*N time then m packets of (I+2h) length will take (N*K)bps+2h(addition length added to the packet) .

Question d:

Considering circuit switched network  two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session.

Assuming transmission rate of the circuit now between source and destination is N bps

Time taken to set-up =ts

No of packets =m

Size of each packet is =I bits and now if the packet size is increased from I+h bits

Transmission speed of sending m packets each of size I+h bits=N+ts(set-up time)+h(increased size of file).

Hope that helps.HAPPY ANSWERING!!!!!!!!!!!!!!!!!!!!!!

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