Objectives

The objective of this project will be to produce a high reliability instant messaging(IM) system for use on the Internet. The system must also address the problems of mobile communication (i.e. from any Internet workstation with a suitable client installed) and security.

It is possible to identify three distinct types of user of such a system.

• User 1 is on a local area network with Internet access. They use the system to chat to friends and/or colleagues on the same LAN as well as communicating with people all over the Internet. Since the link from their LAN to the rest of the world might be slow and/or prone to failure, they still wish to be able to chat to local users even when the Internet link is down. (e.g. a University student with a network connection in their room).

• User 2 is a dialup user. They use the system to communicate with people all over the Internet but mainly they use it to chat to local and long distance friends. While this means their contacts are likely to be in a similar geographical area to them, this is not the same as them being on the same physical network as all the contacts will not be using the same ISP.

• User 3 uses the system for business communication. They may be on a LAN or dialup connection but either way they need a system that is as reliable as their Internet connection.

Mobility is useful to user types one and two since they might want to check their messages or chat to their friends while on holiday, or from someone else's computer. If user three is required to travel as part of their job then mobility is less of an issue as they are likely to have a form of mobile office set up for their other data, allowing them to also transport their IM data.

The security of the system is likely to be of greater importance to user three since business information is often highly confidential, but even so security may be of use to users of types one and two.

Table 2.1: Priority of properties to each user type (3=high, 1=low)

	Reliability	Security	Mobility	Local access pattern1
User 1	2	1	3	3
User 2	2	1	3	1
User 3	3	3	1	3

¹ i.e. high proportion of contacts on same network

The importance of these properties is summarised in table 2.1, where 3 represents very important and 1 not important.