Question 1 a. Increasing the router memory to infinite cannot control the conges

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Question 1

a. Increasing the router memory to infinite cannot control the congestion. Agree or disagree? Elaborate briefly (60-100 words)

b. Compare the following:

Flow Control vs Congestion Control

Open loop congestion control methods vs Closed Loop congestion control

Leaky Bucket Algorithm vs Token Bucket Algorithm

Warning Bit Method vs Random Early Detection Method

c. What do you mean by Load Shedding in congestion control?

d. Transport protocols resemble those you studied in Data Link Layer since both will have to deal with error control, sequencing, flow control etc. Still the two differ significantly. How? elaborate with at least 4 differences.

e. What is a 3 way hand shake? Is it better than 2 way hand shake?

f. When do we use Upward Multiplexing and Downward Multiplexing?

g. Suppose we design a reliable transport protocol that use only NAKs as feedback from receiver to sender:

If the data rate is low (sender sends packets infrequently),is a NAK-only protocol better than a ACK-based protocol? Why?

if the data rate is high and the network drops only a small number of packets is a NAK-only protocol better than a ACK-based protocol? Why?

g. What are the 3 transport layer servcies?

h. Compare the design issues of Transport Layer with those of Network Layer

i. What is fragmentation? Why is fragmentation important in Transport Layer?

Explanation / Answer

a)Answer:

When too many packets are present in (a part of) the subnet, performance degrades. This situation is called congestion.

When the number of packets dumped into the subnet by the hosts is within its carrying capacity, they are all delivered and the number delivered is proportional to the number sent.

- However, as traffic increases too far, the routers are no longer able to cope and they begin losing packets. This tends to make matters worse. At very high trafffic, performance collapses completely and almost no packets are delivered.

If there is insufficient memory to hold all of them, packets will be lost. But even if routers have aninfinite amount of memory, congestion gets worse, because by the time packets reach to the front of the queue, they have already timed out (repeatedly), and duplicates have been sent.

It has been found that networks withinnite-memory

that if routers have an infiniteamount of memory, congestion gets worse, not better.

All these packets will be dutifully forwarded to the next router.

b)Answer:

Flow Control vs Congestion Control:

->Flow control and congestion control are two network traffic control mechanisms used in computer networks, they have their key differences. Flow control is an end to end mechanism that controls the traffic between a sender and a receiver, when a fast sender is transmitting data to a slow receiver.

->On the other hand, congestion control is a mechanism that is used by a network to control congestion in the network. Congestion control prevents loss of packets and delay caused due to congestion in the network. Congestion control can be seen as a mechanism that makes sure that an entire network can handle the traffic that is coming to the network. But, flow control refers to mechanisms used to handle the transmission between a particular sender and a receiver.

->Congestion control basically states that a network device can transmit only a certain number of packets and can not add more packets to a network until an acknowledgement is received.

->Flow control works by refusing new connections until congestion is resolved. In serial transmissions, Xon/Xoff is used for flow control. It is a handshaking mechanism that will keep a sender from sending data faster than a receiver can receive it.

Open Loop Congestion Control:

->Open loop congestion control is based onprevention of congestion

->It prevents the congestion from happening.

->It do not need end-to-end feedback.

->Open loop control is exercised by usingthe tools such as deciding when to accept the newpackets, when to discardthe packets, which packets are to be discarded andmaking the schedulingdecisions at various points.

Closed Loop Congestion Control:

->Closed loop congestion control is basedon the solution for removing thecongestion

->It removes the congestion; after it tookplace

->It adjust its cell-rate depending on somekind of feedback

c)Answer:

Load shedding: This is what routers do when they run out of buffers. If they must throw away a packet then they can at least try to pick the best packets to pitch. This depends on the application and on the error strategy used in the data link layer.

e)Answer:

Three-way handshake:

A three-way handshake is a method used in a TCP/IP network to create a connection between a local host/client and server. It is a three-step method that requires both the client and server to exchange SYN and ACK (acknowledgment) packets before actual data communication begins.

A three-way handshake is also known as a TCP handshake.

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