Computer Networks

Computer Networks

Computer Networks
| Computer Networks |
Q.1
In the following pairs of OSI protocol layer/sub-layer and its functionality, the INCORRECT pair is
A. Network layer and Routing
B. Data Link Layer and Bit synchronization
C. Transport layer and End-to-end process communication
D. Medium Access Control sub-layer and Channel sharing
Answer : Option B
Explaination / Solution:

(a) One of the main functionality of Network Layer is Routing. So Option (a) is CORRECT. (b) Bit Synchronization is always handled by Physical Layer of OSI model but not Data Link Layer. So Option (b) is INCORRECT. (c) End – to – End Process Communication is handled by Transport Layer. So Option (c) is CORRECT. (d) MAC sub layer have 3 types of protocols (Random, Controlled and Channelized Access).

Workspace
Report
Q.2
A bit-stuffing based framing protocol uses an 8-bit delimiter pattern of 01111110. If the output bit-string after stuffing is 01111100101, then the input bit-string is
A. 0111110100
B. 0111110101
C. 0111111101
D. 0111111111
Answer : Option B
Explaination / Solution:

Given 8 – bit delimiter pattern of 01111110.
Output Bit string after stuffing is 01111100101
                                                              ⇓
                                                       StuffedBit
Now, Input String is 0111110101 

Workspace
Report
Q.3
Given the following state table of an FSM with two states A and B, one input and one output: 

If the initial state is A = 0, B = 0, what is the minimum length of an input string which will take the machine to the state A = 0, B = 1 with Output = 1?
A. 3
B. 4
C. 5
D. 6
Answer : Option A
Explaination / Solution:
No Explaination.


Workspace
Report
Q.4
Host A (on TCP/IP v4 network A) sends an IP datagram D to host B (also on TCP/IP V4 network B). Assume that no error occurred during the transmission of D. When D reaches B, which of the following IP header field(s) may be different from that of the original datagram D? (i) TTL (ii) Checksum (iii) Fragment Offset
A. (i) only
B. (i) and (ii) only
C. (ii) and (iii) only
D. (i), (ii) and (iii)
Answer : Option D
Explaination / Solution:

While an IP Datagram is transferring from one host to another host, TTL, Checksum and Fragmentation Offset will be changed.

Workspace
Report
Q.5
An IP router with a Maximum Transmission Unit (MTU) of 1500 bytes has received an IP packet of size 4404 bytes with an IP header of length 20 bytes. The values of the relevant fields in the header of the third IP fragment generated by the router for this packet are
A. MF bit: 0, Datagram Length: 1444; Offset: 370
B. MF bit: 1, Datagram Length: 1424; Offset: 185
C. MF bit: 1, Datagram Length: 1500; Offset: 370
D. MF bit: 0, Datagram Length: 1424; Offset: 2960
Answer : Option A
Explaination / Solution:



Workspace
Report
Q.6
A layer-4 firewall (a device that can look at all protocol headers up to the transport layer) CANNOT
A. block entire HTTP traffic during 9:00PM and 5:00AM
B. block all ICMP traffic
C. stop incoming traffic from a specific IP address but allow outgoing traffic to the same IP address
D. block TCP traffic from a specific user on a multi-user system during 9:00PM and 5:00AM
Answer : Option A
Explaination / Solution:

Since it is a layer 4 firewall it cannot block application layer protocol like HTTP.

Workspace
Report
Q.7
Consider different activities related to email. m1: Send an email from a mail client to a mail server m2: Download an email from mailbox server to a mail client m3: Checking email in a web browser Which is the application level protocol used in each activity?
A. m1:HTTP m2:SMTP m3:POP
B. m1:SMTP m2:FTP m3:HTTP
C. m1: SMTP m2: POP m3: HTTP
D. m1: POP m2: SMTP m3:IMAP
Answer : Option C
Explaination / Solution:

Sending an email will be done through user agent and message transfer agent by SMTP, downloading an email from mail box is done through POP, checking email in a web browser is done through HTTP

Workspace
Report
Q.8
Consider a simple checkpointing protocol and the following set of operations in the log.
(Start, T4); (write, T4,y,2,3); (Start, T1); (commit,T4); (write, T1,z,5,7);
(checkpoint);
(Start,T2); (write, T2,x,1,9); (commit,T2); (start,T3), (write,T3,z,7,2);
If a crash happens now and the system tries to recover using both undo and redo operations, what are the contents of the undo lists and the redo list? 
A. Undo T3,T1; Redo T2
B. Undo T3,T1; Redo T2,T4
C. Undo: none; redo:T2,T4,T3,T1
D. Undo T3,T1; T4; Redo:T2
Answer : Option A
Explaination / Solution:

As T1 & T3are not yet committed they must be undone. The transactions which are after the latest checkpoint must be redone. So T2 must be redone. No need to redo the records which are before last checkpoint, so T4 need not be redone.

Workspace
Report
Q.9
Which one of the following hash functions on integers will distribute keys most uniformly over 10 buckets numbered 0 to 9 for i ranging from 0 to 2020?
A. h(i) = i2 mod 10
B. h(i) = i3 mod 10
C. h(i) = (11*i2) mod 10
D. h(i) = (12*i) mod 10
Answer : Option B
Explaination / Solution:

If we take first 10 elements, number of collisions taken by the hash function given by option (B) is less when compared to others.

Workspace
Report
Q.10
HTML (Hyper Text Markup Language) has language elements which permit certain actions other than describing the structure of the web document. Which one of the following actions is NOT supported by pure HTML (without any server or client side scripting) pages?
A. Embed web objects from different sites into the same page
B. Refresh the page automatically after a specified interval
C. Automatically redirect to another page upon download
D. Display the client time as part of the page
Answer : Option D
Explaination / Solution:
No Explaination.


Workspace
Report