hinking about developing multiplayer interactive games, multimedia messengers, content-sharing applications, audio/video conferencing applications, or maybe the next cool Web 2.0 application on a smartphone? You might want to consider developing for Nokia's S60 smartphones and take advantage of the platform's extensible features and SIP support.
The S60 platform is now in its third edition, bringing SIP support in both IETF and 3GPP modes. IETF SIP support was available on some S60 second edition devices.
Session Initiation Protocol (SIP) is essentially a text-based request response protocol similar to HTTP used for creating, modifying, and terminating peer-to-peer (P2P) sessions. It is specified in RFC 3261 and has been extended by 3GPP to support the requirements of cellular networks. In a cellular environment2G, 2.5G, 3G, 3.5Git is used to communicate with the operators’ IMS (IP Multimedia Subsystem) networks and in a Wi-fi environment it could be used to connect to SIP-based application servers on the Internet. The basic SIP server-side elements allow different kinds of SIP-enabled devices to establish direct connections with each other, bringing about convergence and opening new opportunities for S60 developers.
|Figure 1. Overview: The Simplied IMS/SIP Network.|
P2P connections cannot be established in most cellular networks without IMS and usually require the development of proprietary session handling protocols and servers. With support for SIP on S60 and IMS in operator networks, it is now possible to have applications communicate in a P2P fashion-- even when roaming from one operator network to another. SIP helps reduce the time-to-market of multi-user applications and greatly improves the user experience for such applications.
Figure 1 shows a simplified IMS/SIP network that S60 smartphones use in order to establish a SIP session in a GSM or Wi-fi environment. A registered SIP application is "reachable" by other SIP applications on the network. Its first contact point into the SIP/IMS network is the SIP proxy server or equivalent through which all SIP requests pass. The Registrar server provides the service to store the mapping between the SIP username and the IP address of the device with which it registers. The SIP Proxy and Registrar servers are configured on an S60 device in an SIP profile.
The kinds of services an IMS network could provide are varied: presence, group management, push-to-talk-over cellular (PoC), gaming servicesbut these specific services depend on applications servers' integration to the IMS network. However, it is possible for third parties to develop their own services by using standard SIP Servlet APIs or third-party SIP application server environments like Ubiquity.