GATE CS Computer Networks questions

Let

G(x)

be the generator polynomial used for CRC checking. What is the condition that should be satisfied by

G(x)

to detect odd number of bits in error?

In the RSA public key cryptosystem, the private and public keys are

(e, n)

and

(d, n)

respectively, where

n=p \times q

and

p

and

q

are large primes. Besides,

n

is public and

p

and

q

are private. Let

M

be an integer such that

0<M<n

and

\phi(n) = (p-1)(q-1)

. Now consider the following equations. …

While opening a

TCP

connection, the initial sequence number is to be derived using a time-of-day (ToD) clock that keeps running even when the host is down. The low order

32

bits of the counter of the ToD clock is to be used for the initial sequence numbers. The clock counter increments once per milliseconds. The maximum packet lifetime is given to be …

A computer on a

10\text{Mbps}

network is regulated by a token bucket. The token bucket is filled at a rate of

2\text{Mbps}

. It is initially filled to capacity with

16\text{Megabits}

. What is the maximum duration for which the computer can transmit at the full

10\text{Mbps}

?

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

\text{socket()}

, a

\text{bind()}

and a

\text{listen()}

system call in that order, following which it is preempted. Subsequently, the client process P executes a

\text{socket()}

system call followed by …

If a class

B

network on the Internet has a subnet mask of

255.255.248.0

, what is the maximum number of hosts per subnet?

In the slow start phase of the TCP congestion algorithm, the size of the congestion window:

Which of the following system calls results in the sending of SYN packets?

What is the maximum size of data that the application layer can pass on to the TCP layer below?

Match the following: …

The distance between two stations

M

and

N

is

L

kilometers. All frames are

K

bits long. The propagation delay per kilometer is

t

seconds. Let

R

bits/second be the channel capacity. Assuming that the processing delay is negligible, the

\text{minimum}

number of bits for the sequence number field in a frame for maximum utilization, …

The message

11001001

is to be transmitted using the CRC polynomial

x^3 +1

to protect it from errors. The message that should be transmitted is:

The address of a class

\text{B}

host is to be split into subnets with a

6\;\text{-bit}

subnet number. What is the maximum number of subnets and the maximum number of hosts in each subnet?

In a token ring network the transmission speed is

10^7

bps and the propagation speed is

200\;\text{meters}/\mu \text{s}.

The

1

-bit delay in this network is equivalent to:

There are

n

stations in slotted LAN. Each station attempts to transmit with a probability

p

in each time slot. What is the probability that ONLY one station transmits in a given time slot?

Which one of the following uses UDP as the transport protocol?

In Ethernet when Manchester encoding is used, the bit rate is:

Consider the diagram shown below where a number of LANs are connected by (transparent) bridges. In order to avoid packets looping through circuits in the graph, the bridges organize themselves in a spanning tree. First, the root bridge is identified as the bridge with the least serial number. Next, the root sends out (one or more) data units to enable the …

Station

A

needs to send a message consisting of

9

packets to Station

B

using a sliding window (window size

3

) and go-back-

n

error control strategy. All packets are ready and immediately available for transmission. If every

5

th packet that

A

transmits gets lost (but no acks from

B

ever get lost), then what is the number of …