GATE-CS-2014-(Set-3)

Question 31

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

• 0111110100
• 0111110101
• 0111111101
• 0111111111

Question 32

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

• (i) only
• (i) and (ii) only
• (ii) and (iii) only
• (i), (ii) and (iii)

Question 33

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?

• 128
• 64
• 256
• 512

Question 34

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

• MF bit: 0, Datagram Length: 1444; Offset: 370
• MF bit: 1, Datagram Length: 1424; Offset: 185
• MF bit: 1, Datagram Length: 1500; Offset: 37
• MF bit: 0, Datagram Length: 1424; Offset: 2960

Question 35

Consider the transactions T1, T2, and T3 and the schedules S1 and S2 given below.

T1: r1(X); r1(Z); w1(X); w1(Z)
T2: r2(Y); r2(Z); w2(Z)
T3: r3(Y); r3(X); w3(Y)
S1: r1(X); r3(Y); r3(X); r2(Y); r2(Z);
    w3(Y); w2(Z); r1(Z); w1(X); w1(Z)
S2: r1(X); r3(Y); r2(Y); r3(X); r1(Z);
    r2(Z); w3(Y); w1(X); w2(Z); w1(Z) 

Which one of the following statements about the schedules is TRUE?

• Only S1 is conflict-serializable.
• Only S2 is conflict-serializable.
• Both S1 and S2 are conflict-serializable.
• Neither S1 nor S2 is conflict-serializable.

Question 36

Consider the relational schema given below, where eId of the relation dependent is a foreign key referring to empId of the relation employee. Assume that every employee has at least one associated dependent in the dependent relation.

employee (empId, empName, empAge)
dependent(depId, eId, depName, depAge) 

Consider the following relational algebra query: The above query evaluates to the set of empIds of employees whose age is greater than that of

• some dependent.
• all dependents.
• some of his/her dependents
• all of his/her dependents.

Question 37

An operating system uses shortest remaining time first scheduling algorithm for pre-emptive scheduling of processes. Consider the following set of processes with their arrival times and CPU burst times (in milliseconds):

Process      Arrival Time    Burst Time
  P1           0               12
  P2           2               4
  P3           3               6
  P4           8               5

The average waiting time (in milliseconds) of the processes is _________.

• 4.5
• 5.0
• 5.5
• 6.5

Question 38

Consider a paging hardware with a TLB. Assume that the entire page table and all the pages are in the physical memory. It takes 10 milliseconds to search the TLB and 80 milliseconds to access the physical memory. If the TLB hit ratio is 0.6, the effective memory access time (in milliseconds) is _________.

• 120
• 122
• 124
• 118

Question 39

Consider the basic block given below.

  a = b + c
  c = a + d
  d = b + c
  e = d - b
  a = e + b 

The minimum number of nodes and edges present in the DAG representation of the above basic block respectively are

• 6 and 6
• 8 and 10
• 9 and 12
• 4 and 4

Question 40

Which of the following problems is undecidable?

• Deciding if a given context-free grammar is ambiguous.
• Deciding if a given string is generated by a given context-free grammar.
• Deciding if the language generated by a given context-free grammar is empty.
• Deciding if the language generated by a given context-free grammar is finite.