April 2000
NI222 : NETWORKS AND THE INTERNET

QUESTION 2

Total Marks: 15 Marks

• Question 1
• Question 3
• Question 4
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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(a)What are the two mail protocols standards currently in use?How do you overcome the compatibility problems between them.[3 marks ]
SMTP (1) MOTIS (1) Use mail gateways to translate between these different protocols (1)

(b)Explain a typical FTP session with a suitable diagram f FTP architecture.[4 marks ]
The user ftp command opens a TCP control channel between the server protocol on the target machine and the user rotocol on the local machine (1).The actual data is sent over a separate TCP data channel between the target and local file system (1).
Suitable FTP architecture diagram (2).

(c)Discuss the potential security problems you may come across within SMTP and MIME. [4 marks ]
SMTP:There is no reliable way for the local machine to verify the return address (1), Hence you can never be sure of who sent you mail based on SMTP (1). MIME:Ability to transfer executable rograms (1) and to mail postscript files that themselves can contain dangerous actions may cause damage to the system (1).

(d)Direct Multicast support at the transport level can greatly enhance applications such as Web television.Explain how is this currently implemented n the Internet and why this approach is not effcient.Also suggest the most effcient way of providing such a service.[4 marks ]
Currently,the multicast is implemented as a series of point-to-point transfers (1).This is ineffcient,as the message is sent once per viewer (1).
The most effcient way of roviding such services is broadcasting (1).This is very effcient,as the message is sent only once (1).