Part IV Building Services with the IMS ´ıa- M ar t´ın The 3G IP Multimedia Subsystem (IMS): Merging the Internet and the Cellular Worlds Third Edition Gonzalo Camarillo and Miguel A. Garc © 2008 John Wiley & Sons, Ltd. ISBN: 978- 0- 470- 51662- 1 Now that we have introduced all of the technologies used in the IMS (see Parts II and III), we are ready to describe how we can use those technologies to achieve the main goal of IMS: providing services. In previous sections we looked at how the IMS provide s some services ( e .g., multimedia sessions). Other services do not need extra standardization and can be provided with all of the tools we have d escribed (e.g., a voicemail service). In addition, there are services that require extra standardization. It is these services that Part IV focuses on. We have chosen some of the most significant services that will be initially provided by the IMS: presence, instant messaging, and Push-to-talk. Still, the reader should keep in mind that this is not, by any means, an exhaustive list of IMS services. Many other new and innovative services will be developed in the future using the IMS infrastructure. For instance, 3GPP and the IETF are currently working on standards for conferencing. However, we have decided not to include them in this part because they are still at an early stage of development. 369 . Part IV Building Services with the IMS ´ıa- M ar t´ın The 3G IP Multimedia Subsystem (IMS) : Merging the Internet and the Cellular Worlds Third Edition Gonzalo. any means, an exhaustive list of IMS services. Many other new and innovative services will be developed in the future using the IMS infrastructure. For instance, 3GPP and the IETF are currently. ISBN: 97 8- 0- 47 0- 5166 2- 1 Now that we have introduced all of the technologies used in the IMS (see Parts II and III), we are ready to describe how we can use those technologies to achieve the main