A Preliminary Study of IMS service provision Method Based on SIP Application Server

Abstract: IP MultimediaSubsystem ( IMSThe user plane, control plane, and business plane are separated to facilitate the provision of services to users. This article will focus on analysis SIPApplication Server(SIP as) Issues related to the IMS service provision process, including the general process, billing functions at the business layer, and technical difficulties provided by the Service, analytics is based on a specific service (Message Service) provided by IMS.

Key words: IMS, sip, SIP as, billing, message

1. Introduction

　　3GPPThe IP Multimedia Subsystem (IMS) defined by Rel-5 realizes the separation of user plane, control plane and business plane, so that the service provision is independent of the lower layer.Network. On the business plane, as (Application Server) provides business logic to support various business attributes of users. Shows the service function architecture of IMS:

　　OperatorIt can provide IMS contracted users with services that access camel-based business environments, OSA and SIP. In this case, the SIP as is a SIP-based application server. Because the ISC interface between the S-CSCF and the business platform uses the SIP protocol, the SIP as can communicate directly with the S-CSCFSignalingConversion process. SIP as can provide a wide range of value-added multimedia services, such as presentations, messages, and conferences. This article will discuss the general process, technical difficulties, and billing of the IMS service carried out by SIP as, and take the message service as an example.

2. General process provided by services based on SIP

IMS aims to provide users with better and cheaper multimedia services and applications based on IP addresses. The Application Server (AS) plays the role of the business performer in the service provision process. The service provision process can be divided into the following four steps (Here we assume that the session initiation side is considered ):

1) download IMS business files

In the process of user registration, a business file containing business and user-related data is downloaded from the HSS to the Service in the user S-CSCF. The initial filtering criterion in the business file contains the trigger information for routing user requests to related. Here, the trigger information may be based on the request URI of the Request Message (for example,VoicemailVoice@ims.com) or the type of the request (such as the message request for immediate messages.

2) user request generation

When you need a service, you can use your own devices to generate related requests. For example, you want to create a voice call. He uses ue to generate an invite request (including the request URI, media description, and other information), which goes through the P-CSCF to reach S-cscf serving him.

Note: This article does not discuss the content related to the control layer such as the routing process.

3) select

After the user's request arrives at the S-CSCF, The S-CSCF retrieves the business file that matches the request's initiator. Based on the initial filtering criteria in the business file, the S-CSCF decides to route the request to the corresponding as or directly forward it.

4) as execution-related services

After receiving the request, as starts to execute related services. To provide services, as can work in the following four modes:

Terminate UA-In this mode, as acts as ue. For example, in a message service, assume that the receiver of a message sets a filter criterion. When the criteria are met, as may indicate that the receiver generates a final response when as is a sip ua. 2.

Redirect server-as notifies the initiator of a new location or session substitution service that may be satisfied. For example, when a certain trigger condition is met (for example, the receiver is temporarily inaccessible), The S-CSCF may route the request to a specific, this as redirects the request to an e-mail or voicemail. 2.

The SIP proxy-as processes the request and sends the request back to s-cscf. During Processing, as may add, modify, or delete the message header content in the SIP request. 3.
Third-party call control-as generates a new SIP request in a different SIP conversation and sends it to s-cscf. 5.

In addition, as may act as the initiator UA. For example, for the conference service, as of the conference server, a sip invite request may be sent to a predetermined meeting participant at an agreed time to create a meeting call. 5.

In addition to the process described above, users sometimes need to manage and configure business-related information when providing services. For example, in the conference business, you want to invite new users to the meeting. This can be achieved through the UT interface between the user (UE) and the. The functional architecture for managing user business-related information through the UT interface is shown in Figure 6:

3. Service-Level Billing

The system structure of IMS (divided by three planes) determines that the billing function of IMS should be described at the bearer layer, control layer, and service layer. The IMS system supports both online and offline billing capabilities. Online billing means that the online billing system interacts with the IMS entity in real time and controls and monitors the billing process related to service usage. Offline billing mainly refers to the collection of billing information after a session, and the billing system does not affect the services used in real time. All IMS network elements require offline billing, while as at the business layer requires online billing.

At the business level, it is required that the as can distinguish when online or offline billing is adopted. When online billing is adopted, the as sends the billing information to the OCs (online Charging System) through the rfinterface ), when offline billing is adopted, as sends the billing information to CCF (charging collection function) through the RO reference point ). Billing functions at the business layer (figure 7 ).

On both RF and Ro interfaces, as sends billing information to OCs or CCF using the Diameter protocol's ACR message, and receives response from OCs or CCF using the Diameter protocol's ACA message.

The billing method varies depending on the service applied and the policies specified by the carrier. For example, for conference businesses, you can charge based on the size of the Meeting (number of participants and other factors), the form of media used, and the time of the meeting.

4. Analysis of technical difficulties

At present, IMS has many technical difficulties, such as mobile networks and fixed networks at the control layer.Integration, End-to-endQoSAssurance System.

At the business layer, how to implement various services based on the SIP protocol, such as how the as performs the relevant notification mechanism may involve the formulation of new sip extensions, and information sharing between multiple business platforms, for example, how can a user's presentation information be shared between meetings and messaging business platforms? When a user triggers multiple services at the same time, authentication methods and user data security problems, for example, if a user triggers a business, whether it requires business authentication to access the business, or the operator's business management policy, etc.

5. Business example provided by IMS

This section takes the message service as an example to analyze the problems related to the provision of the IMS service by combining the content in sections 2 and 3 of this article.

Message Services are very familiar to users. Generally, the message service allows one entity to send messages to another entity. Currently, QQ chat systems andMobile CommunicationMultimedia Messaging Services in the field (MMS) All belong to the scope of the message service. The message service of IMS will give users more choices, and users can use multiple media methods, such as text, video, and sound, at their own discretion and at a low cost, at the same time, you can flexibly choose real-time business or non-real-time business to communicate information.

There are three forms of IMS Message Service:
-Instant Message
-Session-based messages
-Delayed messages

The following uses immediate messages as an example to describe them. Immediate messages must be transmitted almost in real time between the communication parties. The immediate message content is included in the message request.

As described in section 2, assume that the business file has been downloaded to the S-CSCF.

First, the User device (UE) needs to generate a message request, fill in the required content-text or multimedia clips (sound, images, etc.), and fill in the request URI as the recipient's address. The request is then forwarded in the IMS system in a similar way as the invite request until the message arrives at the destination ue. The UE must support the message method.

The message request then arrives at the S-CSCF, which routes the request to a SIP as it executes the business according to the trigger information in the business file, such as message based on the request type. This requires that sip as must support the message method.

Then, as executes certain business logic. For example, when the destination UE is temporarily unavailable, as may reserve a message request for the UE and submit the request when the UE is reachable. For group messaging (multiple receivers), as may act as an intermediate node, which has a sip URI called the Public Service Identifier (PSI) and maintains a user list. The request URI that initiates the UE is a public service identifier (PSI ). After the message arrives at the AS, it sends the message to the user in the list.

SIP as may work in a certain mode described in section 2, and may sometimes be a combination of several modes. For example, when a session is rejected, it works in the UA termination mode.

About billing-you can charge based on the number of sent messages, media format, message size, and so on. For example, when user a sends an immediate message to user B, the content of the message is a video with a size of 500 bytes. Assume that the billing is based on the message size, and the fee of 100 bytes is ￥0.05. When receiving an immediate message from a user, as will send a billing request to OCs and send the provided service notification to (that is, sending a 500 bytes message) OCS, OCS deducts ￥0.25 from the user account to perform its functions.

6. Conclusion

At the IMS business level, using SIP as, operators can easily provide services to users, while users can transmit multimedia information at a lower cost. SIP as plays the role of the business executor. Currently, billing-related functional architecture has been initially formed for the IMS service provision system, but some specific problems, such as some technical difficulties mentioned in this article, still need to be carefully studied.

As the future direction of mobile communication, IMS is attracting more and more attention. As one of the important members of the TD-SCDMA Industry Alliance, Putian Information Technology Research Institute is actively researching and developing IMS systems, and will finally provide complete IMS system solutions to operators.

References

[1] miikka unzip kselka, Georg Mayer, Hisham, kharbilirubin, Aki Niemi. The IMS: IP Multimedia concepts and services in the Mobile Domain, June, 2004
[2] 3GPP ts 23.228: "IP Multimedia Subsystem (IMS); Stage 2 ".
[3] 3GPP ts 32.260: "Charging management; IP Multimedia Subsystem (IMS) charging ".
[4] 3GPP ts 22.340: "IP Multimedia Subsystem (IMS) messaging; Stage 1 ".
[5] 3GPP ts 24.229: "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3 ". author: Han leisheng yunpeng Source: draft by China Communication Network