August 1999
NI222 : NETWORKS AND THE INTERNET

QUESTION 1 (Compulsory)

Total Marks: 20 Marks

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(a) Explain each of the following terms:

(i) Message Handling System

(ii) Mail Gateway

(iii) Remote Procedure Call

(iv) Process Server

  

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(i) Message Handling System
One of the components within the standard Email Architecture. Takes care of message transfer through a network of Mail Transfer Agents (MTA).

 
(ii) Mail Gateway
Translates between different Email protocols. Provides compatibility between different Mail Transfer Agents (MTA).

 
(iii) Remote Procedure Call
One of the approaches used to design the network applications. Similar to procedure call in a programming language, but the call is made to a procedure that may not reside on the same machine as the caller.

 
(iv) Process Server
Determines the TCP port address for network applications without a defined transport address. Finds the unused address and activates the application with this address.

 
(b) Explain the differences between each of the following pairs of terms:

(i) State diagram and Event diagram

(ii) Deadlock and Livelock

(iii) Name Resolution and Address Resolution

  

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(i) State diagram and Event diagram

State diagram: Bubbles represent the current state of a communicating entity. Arrows represent the change of state based on the incoming or outgoing message at that entity.

Event diagram: Bold lines represent the states of two hosts. The arrows between the bold lines represents the message transfer.

 
(ii) Deadlock and Livelock

Deadlock: Occurs when underlying network can lose or duplicate messages. The sending host would be stuck forever in the PEND-O state, and the system is unable to proceed.

Livelock:
Occurs when both host A and B sends CR message at about same time and enters WACK state. The protocol does not get stuck, but still does not make any progress.

 
(iii) Name Resolution and Address Resolution

Name Resolution: Service provided by the Domain Name System (DNS). Process of translating the domain names in to IP addresses.

Address Resolution: Service provided by the Address Resolution Protocol (ARP). Process of translating the IP address into physical address, e.g Ethernet address.