| Kannel: an Open Source WAP and SMS gateway |
(Last updated: Oct. 18, 2000)
Kannel is a WAP gateway.
WAP, short for Wireless Application Protocol, is a collection of languages and tools and an infrastructure for implementing services for mobile phones. Traditionally such services have worked via normal phone calls or short textual messages (e.g., SMS messages in GSM networks). Neither are very efficient to use, nor very user friendly. WAP makes it possible to implement services similar to the World Wide Web.
Unlike marketers claim, WAP does not bring the existing content of the Internet directly to the phone. There are too many technical and other problems for this to ever work properly. The main problem is that Internet content is mainly in the form of HTML pages, and they are written in such a way as to require fast connections, fast processors, large memories, big screens, audio output, and may require fairly efficient input mechanisms. That's OK, since they hopefully work better for traditional computers and networks that way. However, portable phones have very slow processors, very little memory, abysmal and intermittent bandwidth, and extremely awkward input mechanisms. Most existing HTML pages simply will not work on them, nor will they ever do that.
WAP defines a completely new markup language, the Wireless Markup Language (WML), which is simpler and much more strictly defined than HTML. It also defines a scripting language, WMLScript, which all browsers are required to support. To make things even simpler for the phones, it even defines its own bitmap format (Wireless Bitmap, or WBMP).
HTTP is also too inefficient for wireless use. By using a semantically equivalent, but binary and compressed format it is possible to reduce the protocol overhead to a few bytes per request, instead of up to hundreds of bytes. Thus, WAP defines a new protocol stack to be used. However, to make things simpler also for the people actually implementing the services, WAP introduces a gateway between the phones and the servers providing content to the phones.
The WAP gateway talks to the phone using the WAP protocol stack, and translates the requests it receives to normal HTTP. Thus, the content providers can use any HTTP servers, and can utilize existing know-how about HTTP service implementation and administration.
In addition to protocol translations, the gateway also compresses the WML pages into a more compact form, to save bandwidth on the air and to further reduce the phone's processing requirements. It also compiles WMLScript programs into a bytecode format.
Kannel is not just a WAP gateway. It also works as an SMS gateway. Although WAP is the hot and technically superior technology, SMS phones exist in huge numbers and SMS services are thus quite useful. Therefore, Kannel functions simultaneously as both a WAP and an SMS gateway.
The above text is reproduced from the home page of www.kannel.org.
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