Apr 1999 NI222: Networks and the Internet (Question 4)

(a)	Briefly describe three standards used for data sharing on the Internet.	[3]
	ASCII (American Standard Code for Information Technology) EBCDIC (Extended Binary Code Decimal Information Code) MIME (Multipurpose Internet Mail Extension)
(b)	Network applications are distinguished from traditional applications by four main issues. Explain what these are.	[8]
	(i) Data Representation The data formats are in multimedia objects in network applications, they are not just simple text in characters as before. Images, audio, video data are very commonly found in the network applications. (ii) Security In the network environment, data transmission can be easily disclosed to authorised users if they are not protected. Encryption is the most common security measure currently. (iii) Compression Data transmission over the network has to be efficient. This also applies to the storage space available. All these are costs to the use of network applications. Hence, data must be compressed and this also partially overlaps into the function of encryption. (iv) Interaction This is concerning the way of communication between computers. There are client-server connection such as the one used by the Web browser and the Web server. Another type of interaction is the peer-to-peer communication such as two computers transferring data within a bank.
(c)	Electronic mail (email) functionally is usually divided between a Mail User Agent and a Mail Transport Agent. Explain the role of each of these.	[3]
	The Mail User Agent provides the functions to the sender and recipient mail formatting and mail creation. The Mail Transport Agent is involved in the transfer of email message with the assistance of MHS (Mail Handling System) for the message to pass on from its sender to it recipient.
(d)	Email using the Simple Mail Transfer Protocol (SMTP) is an example of a network application. Explain how each of the issues you identified in part (b) applies, or does not apply, to SMTP.	[6]
	(i) Data Representation SMTP with the help of MIME to encode the multimedia objects has no problem with this issue. (ii) Security SMTP has the header that contains the sender's and recipient's addresses undecoded for proper transfer, this pose a danger to be attacked by malicious users. (ii) Compression SMTP is simple and not providing any compression to the message. This is an issue for large text transfer. However, normally there is a size limitation per message set in to the email application to limit the sending of huge message especially those that contain attachment files. (iv) Interaction This is not applicable to SMTP which is only an application at the highest level of the 4-layer ARPANET. TCP transport connections are used to move messages. Transfer is essentially one-way, but an option exists in the protocol to reverse the roles of sender and receiver.