Computer Networks | Set 8

Following questions have been asked in GATE CS 2008 exam.

1) What is the maximum size of data that the application layer can pass on to the TCP layer below?
(A) Any size
(B) 2^16 bytes-size of TCP header
(C) 2^16 bytes
(D) 1500 bytes

Answer (A)
Application layer can send any size of data. There is no limit defined by standards. The lower layers divides the data if needed.

2) A client process P needs to make a TCP connection to a server process S. Consider the following situation: the server process S executes a socket(), a bind() and a listen() system call in that order, following which it is preempted. Subsequently, the client process P executes a socket() system call followed by connect() system call to connect to the server process S. The server process has not executed any accept() system call. Which one of the following events could take place?
(A) connect () system call returns successfully
(B) connect () system call blocks
(C) connect () system call returns an error
(D) connect () system call results in a core dump

Answer (C)
Since accept() call is not executed then connect () gets no response for a time stamp to wait & then return no response server error.

3) A computer on a 10Mbps network is regulated by a token bucket. The token bucket is filled at a rate of 2Mbps. It is initially filled to capacity with 16Megabits. What is the maximum duration for which the computer can transmit at the full 10Mbps?
(A) 1.6 seconds
(B) 2 seconds
(C) 5 seconds
(D) 8 seconds

Answer (B)

New tokens are added at the rate of r bytes/sec which is 
2Mbps in the given question. 

Capacity of the token bucket (b) = 16 Mbits
Maximum possible transmission rate (M) = 10Mbps
So the maximum burst time = b/(M-r) = 16/(10-2) = 2 seconds

In the above formula, r is subtracted from M to calculate the maximum burst time. The reason for this subtraction is, new tokens are added at the rate of r while transmission happens at maximum transmission rate M.

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