Computer Network GATE previous year questions with answer
Ques 40 Gate 2016 Set-1
A sender uses the Stop-and-Wait ARQ protocol for reliable transmission of frames. Frames are of size 1000 bytes and the transmission rate at the sender is 80 Kbps (1Kbps = 1000 bits/second). Size of an acknowledgement is 100 bytes and the transmission rate at the receiver is 8 Kbps. The one-way propagation delay is 100 milliseconds. Assuming no frame is lost, the sender throughput is __________ bytes/second.
Ques 41 Gate 2016 Set-1
An IP datagram of size 1000 bytes arrives at a router. The router has to forward this packet on a link whose MTU (maximum transmission unit) is 100 bytes. Assume that the size of the IP header is 20 bytes. The number of fragments that the IP datagram will be divided into for transmission is________
Ques 42 Gate 2016 Set-1
For a host machine that uses the token bucket algorithm for congestion control, the token bucket has a capacity of 1 megabyte and the maximum output rate is 20 megabytes per second. Tokens arrive at a rate to sustain output at a rate of 10 megabytes per second. The token bucket is currently full and the machine needs to send 12 megabytes of data. The minimum time required to transmit the data is _________________ seconds.
Ques 43 Gate 2016 Set-1
Consider that B wants to send a message m that is digitally signed to A. Let the pair of private
and public keys for A and B be denoted by K-x
and K+x
for x = A,B, respectively. Let Kx(m)
represent the operation of encrypting m with a key Kx and H(m) represent the message digest.
Which one of the following indicates the CORRECT way of sending the message m along
with the digital signature to A?
Given:
Sender: B
Receiver: A
Message to be sent: m
Message digest: H(m)
Private key of x: K-x
Public key of x: K+x (where x ∈ {A, B})
Encryption of message m with key Kx: Kx(m)
To find:
The correct way of sending message m along with the digital signature from B to A.
Solution:
First, let me recall how a digital signature works.
To create a digital signature, the sender computes the hash of the message, which is the message digest H(m).
Now, to prove authenticity and provide non-repudiation, the sender must encrypt this digest using their own private key.
Here, the sender is B, so B must encrypt H(m) using B's private key K-B.
So, the digital signature generated by B is K-B(H(m)).
Now, B sends the original message m along with this digital signature to A.
Therefore, the package sent to A is {m, K-B(H(m))}.
Let me just verify the options to make sure.
Option A uses B's public key, which makes no sense because anyone could have made it.
Option C uses A's private key, which B does not even have access to.
Option D uses A's public key, which is for confidentiality, not a signature by B.
Hence, Option B is definitely the correct one.
Answer:
(B) {m,K-B (H(m))}
Ques 44 Gate 2016 Set-1
Which of the following is/are example(s) of stateful application layer protocols?
(i) HTTP
(ii) FTP
(iii) TCP
(iv) POP3
Given:
Protocols to check: (i) HTTP, (ii) FTP, (iii) TCP, (iv) POP3.
Condition: Stateful protocol at the application layer.
To find:
Which of the given protocols are stateful application layer protocols.
Solution:
Let me check each protocol one by one for two things: layer of operation and whether it is stateful.
First, check (i) HTTP:
HTTP works at the application layer, but by default it is stateless because the server does not retain any information about previous client requests.
So, HTTP is not stateful.
Next, check (ii) FTP:
FTP operates at the application layer and maintains state information (like current directory and user login state) throughout the control connection session.
So, FTP is a stateful application layer protocol.
Next, check (iii) TCP:
TCP is indeed stateful (maintains connection state, sequence numbers, etc.), but it operates at the transport layer, not the application layer.
So, TCP is ruled out.
Finally, check (iv) POP3:
POP3 works at the application layer and maintains state across the session (like authorization, transaction, and update states to keep track of emails marked for deletion).
So, POP3 is also a stateful application layer protocol.
Combining the valid ones, we have (ii) and (iv).
Answer:
(C) (ii) and (iv) only
Ques 45 Gate 2016 Set-1
Which one of the following protocols is NOT used to resolve one form of address to another one?
Given:
Protocols: DNS, ARP, DHCP, RARP.
To find:
The protocol that is NOT used to resolve one form of address to another.
Solution:
Let me check what each protocol does one by one.
First, looking at DNS (Domain Name System):
It resolves a domain name (like www.google.com) to an IP address, so it maps one address format to another.
Now, looking at ARP (Address Resolution Protocol):
It resolves a logical IP address to a physical MAC address on a local network.
Next, looking at RARP (Reverse Address Resolution Protocol):
It does the reverse of ARP, resolving a physical MAC address to an IP address.
Finally, looking at DHCP (Dynamic Host Configuration Protocol):
It is used for dynamic configuration of IP addresses and other network parameters to hosts from a server.
It allocates IP addresses dynamically rather than resolving or mapping one address form to another.
Therefore, DHCP is not an address resolution protocol.
Answer: (C) DHCP
Ques 46 Gate 2016 Set-1
Which one of the following protocols is NOT used to resolve one form of address to another one?
Given:
Four network protocols: DNS, ARP, DHCP, and RARP.
To find:
The protocol that is NOT used to resolve one form of address to another.
Solution:
Let me check what each protocol does one by one.
First, let's look at DNS (Domain Name System).
DNS maps/resolves a host domain name to an IP address (e.g., www.google.com to an IP). So it does resolve one form of address/name to another.
Next, checking ARP (Address Resolution Protocol).
ARP resolves a logical IP address to a physical MAC address on a local network. So it definitely does address resolution.
Next, checking RARP (Reverse Address Resolution Protocol).
RARP resolves a physical MAC address to an IP address. So it also performs address resolution.
Now looking at DHCP (Dynamic Host Configuration Protocol).
DHCP is used to dynamically allocate/assign IP addresses, subnet masks, default gateways, and DNS server IPs to client hosts automatically from a pool.
DHCP doesn't map or resolve one existing address into another form; it simply assigns configuration parameters to a device.
Therefore, DHCP is not an address resolution protocol.
Answer:
(C) DHCP
Ques 47 Gate 2015 Set-3
Consider a network connecting two systems located 8000 kilometers apart. The bandwidth of the network is 500 × 106 bits per second. The propagation speed of the media is 4 × 106 meters per second. It is needed to design a Go-Back-N sliding window protocol for this network. The average packet size is 107 bits. The network is to be used to its full capacity. Assume that processing delays at nodes are negligible. Then, the minimum size in bits of he sequence number field has to be ________.
Ques 48 Gate 2015 Set-3
Consider the following statements.
I. TCP connections are full duplex.
II. TCP has no option for selective acknowledgment
III. TCP connections are message streams.
PROCESSED
Ques 49 Gate 2015 Set-3
Consider a CSMA/CD network that transmits data at a rate of 100 Mbps (108 bits per second) over a 1 km (kilometre) cable with no repeaters. If the minimum frame size required for this network is 1250 bytes, what is the signal speed (km/sec) in the cable?
PROCESSED
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