tailieunhanh - Chapter 22 - The Instant Messaging Service in the IMS

Chapter 21 described the basic components of the instant messaging service. We learnt that there are two modes of operation: pager mode and session-based mode. In this chapter we analyze how these two modes are applied to the IMS. We explore the basic call flows and present examples of services that can be enriched with instant message capabilities. | Chapter 22 The Instant Messaging Service in the IMS Chapter 21 described the basic components of the instant messaging service. We learnt that there are two modes of operation pager mode and session-based mode. In this chapter we analyze how these two modes are applied to the IMS. We explore the basic call flows and present examples of services that can be enriched with instant message capabilities. Pager-mode Instant Messaging in the IMS The pager-mode instant messaging service was introduced with the first phase of IMS that came as part of Release 5 of the 3GPP specifications. 3GPP TS 43 already contained requirements for Application Servers ASes and S-CSCFs to be able to send textual information to an IMS terminal. 3GPP TS 37 introduces support for the MESSAGE method extension. The specification mandates IMS terminals to implement the MESSAGE method specified in RFC 3428 115 and to allow implementation to be an optional feature in S-CSCFs and ASes . if required by the service . Obviously pager-mode instant messages are subject to the constraints . message size etc. that we described in Section . The main purpose of a pager-mode instant message is to allow the S-CSCF or ASes to send short instant messages to the IMS terminal. Since the MESSAGE method is already implemented in IMS terminals users are able to send pager-mode instant messages to other IMS users. The flow is simple as depicted in Figure . An example of a service provided with the SIP MESSAGE method is shown in Figure . An AS is the controller of a voicemail system. The AS is interested to know when the user successfully logs on to the IMS so that the AS can inform the user that there are pending voicemails to be retrieved. The service is implemented as follows the user registers with the IMS as usual 1 - 20 in Figure . When the registration is complete the S-CSCF evaluates the initial filter criteria. One of the initial filter criteria indicates that the .