arch.xml

The Kannel Open Source WAP and SMS gateway works as both an SMS gateway, for implementing keyword b

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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V3.1//EN" []>

<book>

<bookinfo>
	<title>Kannel Architecture and Design</title>
	<subtitle>$Revision: 1.20 $</subtitle>
	<author>
	<firstname>Lars</firstname>
	<surname>Wirzenius</surname>
	<affiliation>
		<jobtitle>Gateway architect</jobtitle>
		<orgname>Wapit Ltd</orgname>
		<address>
		<email>[e-mail]</email>
		</address>
	</affiliation>
	</author>
	
	<abstract>

		<para>This document examines the purpose of a gateway in
		the Wireless Application Protocol (WAP) architecture. WAP
		is a technology for implementing services on moible phones
		using hypertext similar to the World WideWeb (WWW). We
		examine a particular WAP gateway, called Kannel and will
		discuss its design and look how well it works.</para>
		
	</abstract>
	
</bookinfo>
  
<toc></toc>


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<chapter>
<title>Introduction</title>

	<para>It has been a long-time dream of science fiction authors
	and fans to have a computation device with you at all times.
	This dream device would allow you to do many of the same
	things a full-size device would, whenever and whereever you
	would need it. In addition, just by always being with you,
	it allows you to do things a static device won't. For example,
	in Arthur C. Clarke's novel <xref linkend="bib.imperialearth"
	endterm="bib.imperialearth.title"> everyone has a small device
	that works as a notebook, dictionary, encyclopedia, and recording
	device. This itself is nothing special: real-life computers have
	been doing such things for decades by now. However, by virtue of
	being small enough for its user to always carry it, it suddenly
	becomes much more powerful. You have instant access to all the
	information you need, when you need it. You always have all your
	notes with you, allowing you to get things done wherever you are,
	and not just in the office.</para>

	<para>A lone computer is nice, but quite boring compared to
	a networked one. Instant communication with anyone, anywhere,
	at anytime is another science fiction dream. The communication
	device worn by characters in the <xref linkend="bib.startrek"
	endterm="bib.startrek.title"> television series is an example:
	just by tapping the device once, you can talk to anyone.</para>

	<para>The real world has been catching up with science fiction.
	Mobile phones have allowed near-instant communication with anyone
	else for several years. They aren't as small as the Star Trek
	devices, nor as fast, but they are small enough to be carried
	at all times, and they're extremely popular.  </para>

	<para>Mobile computers are also reality. The first portable
	computer, the Osborne-1, was produced in 1981.	It was the size
	of a suitcase and weighed more than ten kilograms, so it wasn't
	particularly easy to carry, but its descendants have evolved into
	smaller and smaller versions each year. Current technology allows
	laptops that are small enough to be carried in a bag to most
	places. Even smaller devices, palmtops, really are small enough
	to be taken everywhere, in a pocket, just like modern mobile
	phones are.  Palmtops aren't as powerful as laptops, or desk
	computers, but powerful enough to do many useful things.</para>

	<para>We now have mobile phones, providing connectivity, and
	laptops and palmtops, providing processing power. Combining
	them is a natural next step, and actually one that has, to
	some extent, already been taken. Mobile phones can function as
	wireless modems to mobile computers, providing network access
	anywhere. This has some technical problems, however, due to the
	limited bandwidth and high error rates in mobile networks. It
	also requires carrying two devices, and connecting them in some
	way. Having a single device capable of both communication and
	data processing is likely irresistible to the mass market. Some
	such devices already exist, such as the Nokia Communicator and
	the Ericsson R380, but they have so far been priced out of reach
	for most consumers.</para>

	<para>With hundreds of millions of mobile phones in use all over
	the world, the market for services targeted at mobile users is
	already 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 a large number of people. More sophisticated services make
	things even more attractive to even more people.</para>

	<para>One technology for implementing mobile services is WAP,
	short for Wireless Application Protocol. It lets the phone act
	as a simple hypertext browser, but optimizes the markup language,
	scripting language, and the transmission protocols for wireless
	use. The optimized protocols are translated to normal Internet
	protocols by a <emphasis>WAP gateway</emphasis>.</para>

	<para>Designing and implementing a WAP gateway is a 
	straightforward excercise in well-established software
	engineering practices. However, when the system has to work
	efficiently and reliably for a huge number of concurrent
	users, some special problems arise.</para>

	<para>This Master's thesis discusses the problems and the design
	decisions of a particular WAP gateway, called Kannel.  We also
	provide benchmark results to justify the design. We do not only
	discuss technical issues, but touch some project management
	issues as well, since the Open Source nature of the gateway
	affects the way development has been and is being done.  </para>

	<para>Kannel is an Open Source project by the Wapit Ltd company
	launched in June, 1999. I was employed by Wapit to head the
	project.  It is not the first Open Source project with which I
	am involved, but it is the first one where I am getting paid for
	the work.  Kannel is an important and necessary part of Wapit's
	approach to implementing mobile services, but not one from which the
	company expects to make money directly. The reasons for making
	Kannel Open Source are discussed.</para>
	
	<para>This document was originally written to be a Master's thesis
	for Lars Wirzenius. The thesis has not (as of this writing) been
	finished, but a work-in-progress version has been converted to
	be the Kannel architecture document, since the old architecture
	document had not been updated for a year.  The thesis version
	and the architecture document version of the text will evolve
	in parallel.  </para>
	
</chapter>


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<chapter>
<title>Problems in implementing services for mobile phones</title>

	<highlights> <para>This chapter explains the problems in
	designing and implementing services for mobile phones. There
	are both technical problems (how to do it at all) and business
	problems (how to make money doing it, in the short and the long
	term). There are various approaches to solving these problems;
	we will briefly summarize the important ones.</para> </highlights>

<sect1>
<title>Technical problems</title>
  
	<para>In order to be usable to their users, mobile phones have
	to be small in size and light in weight. This puts rather severe
	limits on their design, which results on several problems:

		<itemizedlist>

		<listitem><para>The battery has a fairly low capacity,
		resulting in more limitations due to having to keep
		power consumption down for every part.
		</para></listitem>

		<listitem><para>Small screen and keyboard, resulting in
		very limited input and output possibilities and making
		user interfaces awkward.
		</para></listitem>

		<listitem><para>Slow processor and little memory,
		resulting in little computation being possible
		on the phone itself.
		</para></listitem>

		</itemizedlist>

	</para>

	<para>Some of these limitations apply only to phones and other
	mobile devices do better. For example, the screen size of
	a <glossterm>Palm</glossterm> or <glossterm>Psion</glossterm>
	device is large enough that simple text processing is doable. For
	every device meant to be mobile, however, the limitations will
	apply to some extent. It is not really possible to comfortably
	carry around a full size keyboard, mouse, and screen.</para>

	<para>The wireless mobile network also has severe limitations,
	compared to a wired local area network. The total amount of
	bandwidth that all mobile users in a geographical area can share
	is limited.  With cables it is always possible to expand the
	bandhwidth by installing more cables, but the total spectrum of
	radio waves available for mobile networking is limited, both by
	physics and by the way it has been allocated to various purposes
	by governments.</para>

	<para>Radio waves are also inherently error prone, since
	they are affected by many sources of disturbances: other	
	devices and the Sun cause intereferences by sending their
	own signals, and buildings, mountains and other parts of
	the landscape distort and in some cases prevent the radio
	signals from reaching their destination. Even if nothing
	else is a problem, the distance to the nearest base
	station for the mobile network may be too large.</para>

	<para>This results in a network with limited bandwidth and a
	high error rate. Normal networking protocols, such as TCP/IP,
	have been designed for an environment with low error rates, which
	makes them partly unsuitable for a mobile network. Additionally,
	the various protocols used in the Internet (and that's about
	the only interesting global network for mobile users as well)
	on top of TCP/IP are textual, meaning that the messages they send
	are plain text. This makes them easier to specify and understand,
	and much easier to implement them and debug the implementations,
	but when bandwidth is very limited, they do waste it.</para>
	
</sect1>

<sect1>
<title>Business problems</title>
  
	<para>The technical problems outlined in the previous section
	are fairly straightforward to solve in isolation. However, in
	order to be viable from a business point of view, the choice of
	technical solutions needs to be guided by business needs. The
	basic business requirement for a mobile network operator is that
	building a system for mobile services needs to be profitable:
	the cost of building the system must be less, in the long run,
	than the income generated from its users.  </para>

	<para>Mobile phone networks already support data connections,
	so the basic problem of getting data from and to the mobile
	devices is already solved. The current solutions are not optimal,
	but they are good enough for now.  The shortcomings of data
	connections in current networks will be solved by next generation
	mobile network technology, such as GPRS and UMTS. This, however,
	results in a new problem: the work done for implementing services
	in today's networks must not be wasted when newer networks are
	employed. Thus, today's solutions must be designed so that they
	will work tomorrow as well.  </para>

	<para>Telecommunications equipment needs to be interoperable:
	devices from different manufacturers must be able to talk to
	each other without problems. The interoperability requirement
	results in the need for a standard for the way mobile services
	are implemented. This standard may be a formal international
	standard, or an industry de facto standard, as long as it is
	open and adhered.</para>

	<para>The standard should also be as broadly applicable worldwide
	as possible. This makes it easier to reach a critical mass of
	users: when there are enough users, it becomes easier to mass
	produce devices and that keeps the cost of the devices low, thus
	allowing even more users to buy one. Also, a mobile device is more
	attractive, if it allows interaction with many other users.</para>

	<para>Reaching critical mass is impossible, if the devices or
	services are hard to use. Thus, whatever solution is chosen,
	it must allow user interfaces that are easy to learn and use.
	</para>

	<para>Business requires that service users can be billed.
	For real mass market use, billing needs to be efficient and
	simple, both for the service provider and the user. Billing can
	be arranged in various ways: pre-paid, paid with phone bill,
	or via credit card, for example.</para>

	<para>In summary, the way mobile services are implemented must
	fill the following requirements:

		<itemizedlist>

		<listitem><para>Leverages on existing mobile phone
		networks.</para></listitem>

		<listitem><para>Must be adaptable to future mobile
		networks.</para></listitem>

		<listitem><para>Standardized, for interoperability and
		mass market.</para></listitem>

		<listitem><para>Allows easy user
		interfaces.</para></listitem>

		<listitem><para>Allows billing.</para></listitem>

		</itemizedlist>

	We will next look at how current solutions work.
	</para>