Mobile World

Mobile World

A number of new communications devices have sprung up over the last decade, including the cell phone and the PDA, that are making people increasingly independent within their work and leisure environments. Now that networks are converging on an IP infrastructure, it is becoming possible to make sense of these different forms of communication. Because SIP client software is lightweight, it can be embedded in all these different devices bringing them under a single umbrella so that services can cross all platforms. Using SIP as the signalling protocol means that sessions can be established between different devices that then negotiate the appropriate media capability. The devices become means of accessing those services associated with a user instead of being closed, proprietary systems.

A simple example of this is single number reachability. Because of SIP's inherent presence capability, at any one time the network knows where a user is, by what means he/she is accessible and whether he/she is available to take a call. The network will divert any incoming calls to the correct device automatically.

The same services will apply to mobile devices as to fixed telephones and PCs. For example, IN-type services such as find-me/follow-me, call hold, call forward etc., can be used on mobile phones in a SIP-based architecture.

The only limitations to services will be related to bandwidth and screen size: bandwidth problems should be eliminated with the advent of 3G networks*; handsets will display information in an appropriate format.

*Note - SIP has been selected as the signalling protocol for 3G networks. Every call made in a 3G network will be established using SIP. See the SIP and 3G Technology section opposite for more information on this.

User Profiling

Profile information can be associated with a user with varying degrees of sophistication. A user can set up a profile on a central database that will handle calls based on a number of criteria such as time of day, caller identity and location. So, calls between 9am and 6pm could first be directed to your SIP phone, between 6pm and 8pm to your cell phone, and after 8pm to voice mail; or, while I am in this afternoon's meeting I would like all calls to go to voice mail unless they are from my boss in which case I will take them on my cell phone.

The user profile will reside on a database that all devices can access. Any changes to your profile can be updated via SIP phone, PC, PDA or mobile device.

Unified Messaging

All user devices can have information associated with them, such as messaging information or user profiles. Since a single user is usually associated with a number of devices, it makes sense to tie the user information to the user rather than to the device. Hence the requirement for unified messaging.

SIP, as the signalling protocol for IP networks, enables many different services to be offered from an IP platform. SIP's flexibility and support for MIME types means that it can broker different streams to and from a media server e.g. it can carry text in, audio out.

SIP's similarity to SMTP and its use of the Domain Name System simplifies the integration of voice and email. Servers along the call path can easily create and forward email messages enabling various combined services.

IM and Presence

A SIP-enabled mobile device will be able to support all the IM and presence services associated with SIP. The buddy list concept is easily applied to the world of mobile and instant messaging is a natural successor to the text message phenomenon. See the IM and Presence section for more information.

Location-based services

The services previously mentioned have been cross-platform services that will operate in a mobile environment. There are also services that can be triggered in association with the location of a mobile user. Examples of these include: local services such as pizza delivery, ordering a taxi; automatic notification of real-time content such as flight information; regular updates of delivery tracking or stock-watch. SIP allows real-time transmission of any media to any end device so the service possibilities are vast.

SIP and 3G technology

The 3GPP (Third Generation Partnership Project) is producing globally applicable Technical Specifications and Technical Reports for a third generation mobile system. The group is using IP technology end-to-end to deliver multimedia content to mobile handsets so IETF protocols are a must. The call control and signalling function will be fulfilled by SIP.

Users will be identified by SIP URLs and/or E.164 numbers, the numbering system of the telephone system. The bearer system (GPRS or mobile IP) will manage micro-mobility. This is the movement of the mobile user from one base station to another. Macro-mobility, the movement of the mobile user from one domain to another, will be handled by SIP. SIP will route signalling so that services are available from the originating or terminating network.

3GPP has identified the Call State Control Function (CSCF) in the network. This is the equivalent of a SIP server. There will be three different kinds of CSCF:

  • Proxy CSCF - this is the first point of contact in a visited network and will find the user's home network and provide some translation, security and authorization functions.
  • Serving CSCF - controls sessions, acts as registrar and triggers and executes services. The serving CSCF will access the user's profile. It can be located in the home network.
  • Interrogating CSCF - the first point of contact in the home network. It assigns the serving CSCF, contacts the HSS and forwards SIP request.