# Recent questions and answers in Computer Networks

1
Consider a situation in which a cyberterrorist makes all the DNS servers in the world crash simultaneously. How does this change one’s ability to use the Internet?
2
Many business Computers have three distinct world wide unique identifiers. what are they?
3
Consider sliding window protocol for a 10 MBps point to point link with propagation delay of 2 sec. If frame size is of 4kB then what wil be the minimum number of bits number required for the sequence number? Which approach to take and why? Notice the difference in frame numbers, why does this arise and which one is correct. The answer is not affected in this question.
4
Suppose an IP packet has been fragmented. Then which of the following is a set of fragments?   A) 128, 56, 84, 42 B) 372, 408, 12, 56 C) 248, 72, 120, 18 D) 48, 88, 70, 52
5
In stop and wait protocol , every 4th packet is lost.If 8 packets are being sent, Find number of packets ? Answer given is : 10 Shouldn't Acknowledgements considered as well , in such case answer should be 18 , Right ?
6
For a communication session between a pair of processes, which process is the client and which is the server?
7
8
The maximum data rate of a channel of $3000$-Hz bandwidth and SNR of $30$ db is $60000$ $15000$ $30000$ $3000$
9
An IP packet to be transmitted by Ethernet is 60 bytes long, including all its headers. If LLC is not in use, is padding needed in the Ethernet frame, and if so, how many bytes?
10
A router has two full-duplex Ethernet interfaces each operating at $100$ $\text{Mb/s}$. Ethernet frames are at least $84$ $\text{bytes}$ long (including the Preamble and the Inter-Packet-Gap). The maximum packet processing time at the router for wirespeed forwarding to be possible is (in micro­seconds) $0.01$ $3.36$ $6.72$ $8$
11
Every host in an IPv4 network has a $1-second$ resolution real-time clock with battery backup. Each host needs to generate up to $1000$ unique identifiers per second. Assume that each host has a globally unique IPv4 address. Design a $50-bit$ globally unique ID for this purpose. After what period (in seconds) will the identifiers generated by a host wrap around?
1 vote
12
If the TCP round-trip time, RTT, is currently 30 msec and the following acknowledgements come in after 26, 32, and 24 msec, respectively, what is the new RTT estimate using the Jacobson algorithm? Use α = 0.9.
1 vote
13
Consider a TCP connection between two machines (A and B) in an environment with 0% packet loss. Assume the round trip time (RTT) between the two machines is 4 [seconds], and the segment size is 3 [Kbytes]. The bandwidth of the connection is 500 [kbps]. What is the ... buffer close to zero. I.e., TCP packets are continuously, back-to-back, sent out of the sender before the first ack arrives back.)
1 vote
14
Consider a scnario of CSMA/CD network. Suppose A & B attempt to transmit a frame simultaneously and collide. Using exponential backoff algorithm A chooses K=0 and B chooses K=1. Again they collide and after the 2nd collision both A & B will choose K with equal probability from set: For A {0,1} and for B {0,1} For ... for B {0,1} For A {0,1} and for B {0,1,2,3} For A {0,1,2,3} and for B {0,1,2,3}
15
Determine the maximum length of the cable (in km) for transmitting data at a rate of $500$ Mbps in an Ethernet LAN with frames of size $10,000$ bits. Assume the signal speed in the cable to be $2,00,000$ km/s. $1$ $2$ $2.5$ $5$
16
Consider a $128 \times 10^3$ bits/second satellite communication link with one way propagation delay of $150$ milliseconds. Selective retransmission (repeat) protocol is used on this link to send data with a frame size of $1$ kilobyte. Neglect the transmission time of acknowledgement. The minimum number of bits required for the sequence number field to achieve $100 \%$ utilization is ________.
17
In CRC, if the degree of Generator polynomial is n, then the number of bits in divisor is?
1 vote
18
Given a mask, M=255.255.255.248. How many subnet bits are required for given mask M? (A) 2 (B) 3 (C) 4 (D)5
19
Start and stop bits are used in serial communication for error detection error correction synchronization slowing down the communication
20
Repeaters function in Physical layer Data link layer Network layer Both (A) and (B)
21
What are the primary characteristics that distinguish a cell from a packet? cells are generally smaller that packets cells do not incorporate physical address all cells have the same fixed length packet cannot be switched
22
In networking terminology UTP means Unshielded Twisted pair Ubiquitious Teflon port Uniformly Terminating port Unshielded T- connector port
23
How many bits are required to encode all twenty six letters, ten symbols, and ten numerals? $5$ $6$ $7$ $46$
24
Bit stuffing refers to Inserting a $’0’$ in user data stream to differentiate it with a flag Inserting a $’0’$ in flag stream to avoid ambiguity Appending a nibble to the flag sequence Appending a nibble to the user data stream
25
The address of a class $B$ Host is to be split into subnets with a $3$-bit subnet number. What is the maximum number of subnets and maximum number of hosts in each subnet? $8$ subnets and $262142$ hosts $6$ subnets and $262142$ hosts $6$ subnets and $1022$ hosts $8$ subnets and $1024$ hosts
26
Which of the following is minimum error code? Octal Code Binary Code Gray Code Excess-$3$ Code
27
If the original size of data is $40$ then after adding error detection redundancy bit the size of data length is $26$ $36$ $46$ $56$
28
Which of the following would not be specified in a communication protocol? Header contents Trailer contents Error Checking Data content of message
29
Bit stuffing refers to Inserting a $’0’$ in user data stream to differentiate it with a flag Inserting a $’0’$ in flag stream to avoid ambiguity Appending a nibble to the flag sequence Appending a nibble to the user data stream
30
If the channel is band limited to $6\;kHz$ and signal to noise ratio is $16,$ what would be the capacity of channel? $16.15$ kbps $23.24$ kbps $40.12$ kbps $24.74$ kbps
31
Correct expression tor UDP user datagram length is length of UDP = length of IP- length of IP header's length of UDP= length of UDP-length of UDP header's length of UDP = length of IP+length of IP header's length of UDP = length of UDP+length of UDP header's
32
Closed - Loop control mechanism try to : Remove congestion after it occurs Remove congestion after sometime Prevent congestion before it occurs Prevent congestion before sending packets
33
In classless addressing, there are no classes but addresses are still granted in : Codes Blocks IPs Sizes
34
Which multiple access technique is used by $\text{IEEE } 802.11$ standard for wireless $\text{LAN}$ ? $\text{CDMA}$ $\text{CSMA/CA}$ $\text{ALOHA}$ None of the options
35
$PGP$ encrypts data by using a block cipher called : international data encryption algorithm private data encryption algorithm internet data encryption algorithm none of the options
36
A subnet mask in class $C$ can have _____________ $1$’s with the remaining bits $0$’s. $10$ $24$ $12$ $7$
37
What is the value of acknowledgement field in a segment Number of previous bytes to receive Total number of bytes to receive Number of next bytes to receive Sequence of zero's and one's
Which of the following is a class $B$ host address ? $230.0.0.0$ $130.4.5.6$ $230.7.6.5$ $30.4.5.6$
There is a need to create a network that has $5$ subnets, each with at least $16$ hosts. Which one is used as classful subnet mask ? $255.255.255.192$ $255.255.255.248$ $255.255.255.240$ $255.255.255.224$
Which NetWare protocol provides link - state routing ? $NLSP$ $RIP$ $SAP$ $NCP$