December 1999
NI222 : NETWORKS AND THE INTERNET

QUESTION 1 (Compulsory)

Total Marks: 30 Marks

• Question 2
• Question 3
• Question 4
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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Explain each of the following terms:

(i)Remote Procedure Call [2 marks ]

Remote Procedure Call [2 marks ] One of the approaches used to design the network applications (1).
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 (1).

(ii)Network Algorithm and Implementation [2 marks ]

Network Algorithm and Implementation [2 marks ] Network algorithms capture the how aspect of networks and include techniques to handle connections,route messages, flow control, error detection and correction (1).
Network implementation is program code derived from an algorithm and can have many different implementations, offering different levels of performance and reliability (1).

(iii)Bridge and Router[2 marks ]

Bridge and Router [2 marks ] Bridge is a device used to interconnect networks using similar protocols (1).
Router is a device used to interconnect networks using dissimilar protocols (1).

Explain the role of the IETF in the Internet.

Helps establish standards and creates technologies and services through various working groups of IETF (1).
Publishes all its technologies widely in Internet Drafts (1)and in Requests For Comments (RFCs)(1).

Explain briefly three different types of addressing used in the various layers of the Internet.

Any three from the following: Application layer:host/domain names (from DNS)(1).Transport layer:Transport address or TCP Port address (1).Network layer:IP address or logical address (1). Interface layer:Ethernet address or physical address (1).

Briefly describe the three components of the Standard Email Architecture

User Agent (UAs):to support sender and recipient functions to create and present messages (1).
Message Transfer Agent (MTAs):are typically system daemons that run in thebackground and move the message from the source to destination through the Email system (1).
Message Handling System (MHS):takes care of message transfer through a network of MTAs (1).

Write down the protocol stack and TCP port addresses for Email,Web and FTP on the Internet.

Email application:SMTP/TCP/IP/ETHERNET,port 25 (1)
Web application:HTTP/TCP/IP/ETHERNET,port 80 (1)
FTP application:FTP/TCP/IP/ETHERNET,port 20 (1)

The following are examples of TCP service primitives.Identify which are request and which are confirm primitives,and explain the function of each.

•ACTIVE -OPEN -DATA
•STATUS
•FULL -PASSIVE -OPEN V
•DELIVER

Request primitives:Active-Open-Data:used to initiate a connection and transmit data (1).
Full-Passive-Open:to tell TCP to listen for connection requests from a specified remote site (1).
Confirm primitives:Status:to obtain the connection status at a given point of time (1).
Deliver:indicates the application that data has arrived over the network (1).

Explain the difference between the State and Event diagram that is used to represent the TCP connection establishment and termination.

State diagram:Bubbles represent the current state of a communicating entity (1).
Arrows represent the change of state based on the incoming or outgoing message at
that entity (1).
Event diagram:bold lines represent the states of two hosts (1).
The arrows between the bold lines bold lines represent the message transfer (1).

Explain static and dynamic routing as used in the network layer. Include in your answer one advantage of each.

Static routing: All routes between all possible nodes in a network are computed beforethe network is up and running (1).
Advantage: very efficient,no overhead of making decisions at routers (1).
Dynamic routing: Routes are recomputed and configured during the operation of the network (1).
Advantage:can redirect the packets by reacting to changing network traffic patterns (1).