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Caching
Applications specify the caching attributes of an object or a number of objects. The default is to optimistically replicate objects on the mobile device. Explicit synchronization can be used to make the cache consistent with the wired network if the wireless link is up. (Watson, 1995)
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Prefetching
As a document is loaded and displayed on a mobile device, the links in a hiarchial fashion are used to prefetch the relevant documents and cached. In a hyperobject application the system will use its knowledge of the relevancy and the position of various objects in order to anticipate and prefetch other objects. Prefetching can only be done if the system resources allow it. For example, as a user is viewing the first page of a document, the relevant objects for that document are being prefetched into the cache, given the wireless link is up and functioning. Prefetching hides the latency of the link, and it will also filter the burstiness by spreading the traffic over a longer time.
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Data reduction
Data reduction can be dynamically decided by the user for various high bandwidth applications such as video transmissions. A video stream delivers certain number of frames per constant unit of time. As the number of frames are reduced, it adversely affects the quality of the video, but the bandwidth needed is also reduced; hence, the user can dynamically find a balance between what the available resources and the desired video quality. The same principal can be applied to the sound, and also any real-time stream of data over the wireless link.
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Mobile WWW Browsers
Web infrastructure as it exists today can not easily accommodate mobile clients, because of the fact that almost all information resides statically in HTML documents. The dynamic information that the Web supports is returned to the client without incorporating any user context, or is incorporated explicitly using forms-based interfaces that require user input on the client. Extensions to the Web have been created to include:
ТЗ A network server that maintains mobile computing contexts within a client-specific domain.
ТЗ An asynchronous callback mechanism to notify Web clients when a user's dynamic computing environment changes.
ТЗ A syntax for referencing dynamic information in URLs and documents. (Voelker)
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Active documents
Active documents are HTML documents that allow the Web client to automatically react to changes in mobile computing environment. If the information in an active document that the client is displaying becomes invalid, then the client can be notified of that change so that more relevant information can be displayed. Variables such as location can be updated as the mobile user roams from one cell area to the next. Active documents are written just like any other HTML file with only a minor addition. A subscribe command is embedded in an HTML comment line. By having the subscribe command embedded in a comment line, backward compatibility can be preserved, thus allowing regular Web browsers to view the documents. (Voelker)
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Dynamic URLs
Ordinarily URLs are links to set static documents on the Web. Dynamic URLs will reference a user to a different document based upon other variables, such as the location variable. Dynamic URLs exist in active documents in order to receive the variables from the client. When a user selects a dynamic URL in a document, the client browser is responsible for resolving all references to dynamic variables within the URL. When all variable references have been resolved, the result is a standard URL that the client then sends to the server. (Voelker)
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Data over Cellular links
The analog cellular telephone system uses FM (Frequency Modulation) radio waves to transmit voice grade signals. To accommodate mobility, this cellular system switches radio connection from one cell to another as the mobile user moves from one cell to another (roaming). Every cell within the network has a transmission tower that links mobile callers to a Mobile Telephone Switching Office (MTSO). The MTSO, which is owned and operated by the cellular carrier in each area provides a connection to the public switched telephone network. The public telephone networks acts also as gateways to the Internet.
Most modems that operate over wireline telephone services will also interface and interoperate with cellular phones; however, modem software optimized to work with cellular phones minimizes battery usage. There are problems with modem communica...
