Pervasive Client Device Support

Users increasingly want to access Internet information from portable devices such as cell phones or PDAs (personal digital assistants). Known as pervasive client devices, they represent the latest major trend in Internet access. We mention them here because they present special performance issues for web sites supporting their access. Not surprisingly, cell phones and PDAs do not provide the same graphical and functional support as traditional web browsers. Pages viewed on pervasive devices often contain less content and few (if any graphics). Also, many of these devices simply do not support HTML or cookies.

Many web sites provide special areas in the site for pervasive users. The applications in these areas generate content for the devices, and they may use different page flows or logic to eliminate the need for cookies. Other web sites often use special pervasive gateways to provide cookie support, as well as other functions. These gateways manage the cookies for each user , and provide protocol conversion between the pervasive device and the web site. Also, the gateways manage any SSL traffic between the web site and the pervasive device. (Many pervasive devices do not support SSL encryption/decryption.)

Figure 5.3 shows such a gateway in action. In this case, the gateway provides HTTP/WAP protocol conversion. The pervasive requests enter the web site using the WAP protocol; the gateway converts them to HTTP. This allows the web site to process the request using its existing HTTP servers. Likewise, the gateway converts the outbound request from HTTP to WAP for display at the device.

Figure 5.3. Web site configuration supporting access by pervasive devices

Caching Potential

Because many pervasive devices support only text formats, caching graphics and other static content provides little benefit to the web site. However, caching frequently accessed pages (like a common homepage) may provide some benefits to very busy sites.

Special Considerations

Pervasive device support requires work at the web site to deliver palatable information to these special devices. Also, providing such support frequently changes web site traffic patterns.

Traffic Patterns

Adding pervasive support to your web site often dramatically increases your daily user visits . Most pervasive device visitors interact with the site very briefly (but perhaps frequently) throughout the day. If you use existing web applications to handle pervasive visitors, proper user management becomes a critical concern. Existing applications may create an HTTP session for each visitor. As the number of visitors surges, the application may run out of memory.

Also, pervasive devices tend to be slow. If your site currently receives most of its traffic from LAN-connected users, adding support for pervasive devices often changes your network landscape. Consider the potential impact of longer connection times in your network planning.

Conversion Overhead

Some web sites support pervasive devices through translation servers. Rather than change their web applications to support an ever-changing variety of pervasive devices, they simply convert the web application's output to fit the device. These servers automatically remove or convert graphics elements, trim the pages to the right size , and generally make the page ready for viewing at the device. Translation servers must process every page returned, adding significant overhead to the web site and impacting response times. Caching provides some relief for common pages, but custom pages still require the translation step.

Performance Testing Sites That Support Pervasive Devices

Pervasive performance testing begins by ignoring the pervasive devices themselves . The initial testing generates the HTTP normally sent from the pervasive gateway device, and drives the appropriate load against the web site.

Simulating lots of brief users visits is the goal of pervasive performance testing. Some of the think time strategies for reducing virtual user licenses discussed in Chapter 6 apply to these test situations.

Testing the full web site, including the gateway, from a device's perspective often proves difficult. The small test simulators provided by many pervasive vendors do not drive enough load to test a large system. However, some commercial test driver products have recently added support for scripting and testing with pervasive protocols.

Nonetheless, testing as a pervasive device drives load against the gateway and any auxiliary systems it uses. For example, some gateways use a database to assist with cookie tracking. Driving load through the gateway exercises the performance of both the gateway and its database. This testing gives us a complete end-to-end understanding of the web site's performance, including the components interacting directly with the pervasive devices.