Kannel: Overview

With hundreds of millions of mobile phones in use all over the world at the moment, the market for services targeted at mobile users is mindbogglingly immense. Even simple services find plenty of users, as long as they're useful or fun. Being able to get news, send e-mail or just be entertained wherever you are is extremely attractive to lots of people.

Kannel is an open source WAP gateway. It attempts to provide this essential part of the WAP infrastructure freely to everyone so that the market potential for WAP services, both from wireless operators and specialized service providers, will be realized as efficiently as possible.

Kannel also works as an SMS gateway for GSM networks. Almost all GSM phones can send and receive SMS messages, so this is a way to serve many more clients than just those using a new WAP phone.

Open Source is a way to formalize the principle of openness by placing the source code of a product under a Open Source compliant software license. The BSD-style license was chosen over other Open Source licenses by the merit of placing the least amount of limitations on what a third party is able to do with the source code. In practice this means that Kannel is going to be a fully-featured WAP implementation and compatible with a maximum amount of bearers with special emphasis on SMSC compatibility.

Kannel is a compact and very powerful open source WAP and SMS gateway, used widely across the globe both for serving trillions of short messages (SMS), WAP Push service indications and mobile internet connectivity.

Kannel is a WAP and SMS gateway.

SMS, short message services, are widely used all over the world in huge amounts. The main use for Kannel is to link HTTP based services to various SMS centers using obscure protocols.

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, little screens and extremely awkward input mechanisms. Most existing HTML pages simply will not work on them.

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.