Embedded network appliances usher in a new level of compatibility through the use of standards-based protocols and data formats. At the center is XML, the Extended Markup Language. It's the basis for protocols, such as the Simple Object Access Protocol (SOAP), that in turn are used with the Universal Plug and Play (UPNP) device discovery protocol. It's also the basis for XHTML, the heir apparent to HTML.
Current Internet appliances typically have a Web server that presents a configuration and status interface using HTML pages. A Web browser is used to view the pages and configure the device. This works well when a user is configuring or using the device. But the same interface is very difficult to use when another device is trying to perform this configuration because parser HTML is a rather tedious task at best. XML documents have a much simpler and consistent structure compared to HTML.
XML documents, with the exception of XHTML, try to keep presentation information separate from content. HTML normally mixes both in one document. XHTML includes some formatting in the document.
The SOAP protocol uses XML documents. SOAP is used to communicate between devices. It isn't as efficient as the Simple Network Management Protocol (SNMP), but it's more extensible. SOAP also is used as the basis for a variety of control and data-exchange protocols for which SNMP is unsuitable.
More information on XML, XHTML, SOAP, and related standards can be found at www.w3c.org.
HTML—Hypertext Markup Language
Advantages
- Works with almost any browser
- Well-documented
- Extensive HTML tool support
Disadvantages
- Combines content and formatting
- Browser-dependent presentation
- Difficult to parse
XML—Extended Markup Language
Advantages
- User-definable tags and attributes
- Supports arbitrary data structures
- Separates data from formatting
- Sophisticated style-sheet support
Disadvantages
- Requires XML parser
- Performance limited by hardware
SOAP—Simple Object Access Protocol
Advantages
- Simple transaction protocol
- Based on XML and HTTP
- Extensible
Disadvantages
- Requires XML support
- Limited embedded implementations at this time
