《The 3G IP Multimedia Subsystem(IMS)》

 

Chapter 1. IMS Vision: Where Do We Want to Go?

1.3 Why do we need the IMS?

The packet-switched domain provides IP access to the Internet. While 2G terminals can act as a modem to transmit IP packets over a circuit, 3G terminals use native packet-switched technology to perform data communications.

So, again the same question: why do we need the IMS, if all the power of the Internet is already available for 3G users through the packet-switched domain? The answer is threefold: QoS (Quality of Service),charging, and integration of different services.