Computer Networks | Set 5

Following questions have been asked in GATE CS 2005 exam.

1) Packets of the same session may be routed through different paths in:
(a) TCP, but not UDP
(b) TCP and UDP
(c) UDP, but not TCP
(d) Neither TCP nor UDP

Answer (b)
Packet is the Network layer Protocol Data Unit (PDU). TCP and UDP are Transport layer protocols. Packets of same session may be routed through different routes. Most networks don’t use static routing, but use some form of adaptive routing where the paths used to route two packets for same session may be different due to congestion on some link, or some other reason.

2) The address resolution protocol (ARP) is used for:
(a) Finding the IP address from the DNS
(b) Finding the IP address of the default gateway
(c) Finding the IP address that corresponds to a MAC address
(d) Finding the MAC address that corresponds to an IP address

Answer (d)
Address Resolution Protocol (ARP) is a request and reply protocol used to find MAC address from IP address.

3) The maximum window size for data transmission using the selective reject protocol with n-bit frame sequence numbers is:
(a) 2^n
(b) 2^(n-1)
(c) 2^n – 1
(d) 2^(n-2)

Answer (b)
In Selective Reject (or Selective Repeat), maximum size of window must be half of the maximum sequence number.

4) In a network of LANs connected by bridges, packets are sent from one LAN to another through intermediate bridges. Since more than one path may exist between two LANs, packets may have to be routed through multiple bridges. Why is the spanning tree algorithm used for bridge-routing?
(a) For shortest path routing between LANs
(b) For avoiding loops in the routing paths
(c) For fault tolerance
(d) For minimizing collisions

Answer (b)
The main idea for using Spanning Trees is to avoid loops. See Spanning Tree Protocol for more details.

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