In today's world there are many different types of messaging services available both in the wired and wireless worlds. Some messaging services are supported in both environments; others are only to be found in one. The expectations of the services differ in that some are designed to be used in what is perceived as 'real' time, whereas others are designed as a 'mailbox' service where the message is stored ready for collection or delivery at a later stage. The 3GPP Technical Report TR 22.940 identifies the issues and needs surrounding messaging solutions related to the 3GPP IP Multimedia Subsystem (IMS) taking into consideration use cases that illustrate the needs of both service providers and users. This Technical Specification takes the Technical Report into account when defining the requirements for the support of IMS Messaging. IMS Messaging services incorporates one or more of the following messaging types Immediate messaging and Session based messaging. With Immediate messaging the sender expects immediate message delivery in what is perceived as real time. With Session based messaging a communications association is established between two or more users before communication can take place. In the simplest form Session based messaging maybe a direct communication between two users. This specification defines the requirements for both the Immediate message type and the Session based message type. The specification provides the ability to develop interoperable messaging services that use Immediate and/or Session based message types.

The present document specifies the stage one description of the IMS Messaging services. Stage one is an overall service description and defines service requirements, primarily from the subscriber's and service providers' points of view, and does not deal with the details of the human interface itself. The present TS includes information applicable to network operators, service providers and terminal, switch and database manufacturers. The present TS contains the requirements for IMS Messaging services, which are sufficient to provide a complete service. The messaging types identified in this document are: immediate messaging and session based messaging. It is highly desirable that technical solutions for IMS Messaging services should be sufficiently flexible to allow for possible enhancements. Additional functionalities not documented in this 3GPP TS may implement requirements which are considered outside the scope of this 3GPP TS. Such additional functionality shall not compromise conformance to the core requirements of the service.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

As 3GPP has developed the concept of IMS it is thought useful to consider how a SIP based IP network can be utilised to provide messaging capabilities. One of the chief characteristics of SIP is its ability to rapidly and efficiently create real-time sessions between groups of users. It therefore appears that SIP based messaging would be a potential candidate to provide the equivalent of "Chat Room" and "Instant Messaging" (IM) type services found on the Internet today. Typical characteristics instant messaging are instant delivery of the messages to the targeted recipient(s) and interaction with presence information where users are able to see who is on-line as well as their status. A chat room is a "place" where multiple persons can join, follow and contribute to the ongoing discussion and leave the "room" at any time. Chat rooms are more permanent in nature when compared to IM exchanges and may be created by users or service providers. Additionally, chat rooms can be further divided to the private and public chat rooms. Normally, users who are participating in chat room will receive all the messages that are sent by the other participants. Similarly, the users are also able to send private messages to the chat room or even privately to some participant. Unfortunately, the most popular internet based instant messaging services are usually based upon closed and proprietary protocols which has made it impossible for different service providers to allow interoperable messaging between their respective users. Additionally, internet based services do not take into consideration the wireless environment and the needs of operators to provide services that are commercially viable by for example, providing support for charging. This technical specification will further elaborate the essential messaging characteristic of these services and state how they may be enhanced, e.g. operators may be able to create and then advertise chat rooms containing specific content where users who join the room may be charged an 'entrance' fee,

Messaging can be divided to two different main classes based on the expectation of the sender. The sender either expects the message to be delivered immediately or he does not care so much whether the message is delivered immediately or later. The immediate case can be further divided to two different sub-classes based on the actions required form the user before he can engage in a communication. The user can both send and receive messages without any prior actions or he may be required to join to a messaging session before the message exchange can take place. The messaging types considered in this specification are

• Immediate messaging:
  Typically, sender is aware of the availability of the recipient(s) (possibly through the use of the Presence service) before sending this type of message as, if the recipient is not available, the message may be discarded or deferred. An immediate message may be deferred by the recipient's network based on the message filtering settings defined by the recipient or by the recipient's IMS service provider.
• Session based messaging:
  The sender and recipient expect near real time message delivery. Typically, recipients of the session based messaging that are not joined to a group or are not available will not receive the messages. Typically, a sender may send a message to all participants in the messaging session without addressing them individually.

It shall be possible to use a single address to identify the recipient. The single address shall be either a SIP URL, a network address identifier (NAI as defined in RFC 2486) or a MSISDN. IMS Messaging shall be based on existing IMS address resolution and routing mechanisms.

The user shall be able to use IMS Messaging and access messages in a secure manner. It shall be possible for the contents of messages to be read only by the intended recipient(s). A recipient shall be informed of the reliability of the identity of the sender in case the sender has authorised his identity to be transmitted. The integrity of messages during transit shall be assured to extent of the network capabilities. IMS Messaging shall be intrinsically resistant to attempts of malicious or fraudulent use. The "Security Threats and Requirements" specified in TS 21.133 shall not be compromised.

Charging for IMS Messaging shall be based on existing IMS charging mechanisms as appropriate. IMS Messaging shall be able to support various charging models, including:

1. sender only pays;
2. both sender and recipient pay their respective charges for message delivery; and
3. recipient pays.

IMS Messaging shall be able to support different charging approaches:

1. volume based charging;
2. QoS based charging;
3. service based charging;
4. number of messages sent and/or received; and
5. offline charging or/and online charging.

IMS Messaging shall be able to support various charging mechanisms. The following charging characteristics may be considered:

1. message content type and length;
   Message content type should be declared using a standardised declaration [the note may need to be moved to a different section e.g. message filtering].
2. roaming conditions;
3. prepaid subscriptions;
4. time when the message is sent;
5. time when the message is delivered;
   [FFS, "delivered" could indicate message stored, message read, message received by the terminal and so on…]
6. message origin and destination;
7. access network employed; and
8. the charging information shall describe the amount of data sent and received to and from the external data network [Note: this is introduced to take into account the network(s) transited by message].