Next Generation Wireless Applications: Creating Mobile Applications in a Web 2.0 and Mobile 2.0 World, 2nd Edition

7.4 THE CHALLENGES OF USING HTTP OVER A WIRELESS LINK

Having discovered how HTTP enables chunks of information to be retrieved from an origin server, we might well ask what impact a wireless link has on the process. Firstly, let's look at what the characteristics of an RF connection might be with respect to establishing HTTP-like communications over the link. During a communications session between a mobile device and its communications companion (e.g. server), the data to be passed is sporadic; sometimes there is something to be sent, sometimes there isn't. But when there is data to be sent, such as a picture file, then the two ends have to synchronise to ensure that the communication is successful.

Figure 7.7 Browser checks its cache to see if content is already loaded.

Figure 7.8 Links can be shared using a packet approach.

It is generally the case that, even in relatively reliable wired transmissions, it is not possible to transmit data without experiencing some errors in the transmission, which manifest themselves as small parts of corrupted data. Also, there are times when the link is not available at all and these times vary in length from very transitory to lengthy outages. These two effects combined are a problem, but one that can be ameliorated by sending data in chunks ...