Communication Diversion Session Identifier Uniform Resource Identifier

Description

The CDIV Session Identifier URI is a specific type of Uniform Resource Identifier (URI) used in the context of Communication Diversion (CDIV) services within the IP Multimedia Subsystem (IMS). It is defined in 3GPP specifications 24.173 (IMS Multimedia Telephony Communication Service and Supplementary Services), 24.404 (PSTN/ISDN simulation services), 24.504 (Communication Diversion (CDIV) using IP Multimedia (IM) Core Network (CN) subsystem), and 24.604 (Communication Diversion (CDIV) using IP Multimedia (IM) Core Network (CN) subsystem; Protocol specification). This URI is created and inserted by a diverting Application Server (AS) when a communication is diverted, and it is used to ensure that the diverted session is routed through the same AS.

In IMS, communication diversion allows a user to redirect incoming sessions to another destination, such as voicemail or another number. When a diversion occurs, the diverting AS (which could be the originating AS or the terminating AS) inserts a CDIV Session Identifier URI into the session signaling. This URI serves as a unique identifier for the diverted session, allowing the AS to recognize that the session has been diverted and to apply appropriate service logic. The URI is typically a SIP URI or a Tel URI, and it is included in the Request-URI or a header field of the SIP INVITE request.

The primary purpose of the CDIV Session Identifier URI is to ensure that the diverted session is routed through the same AS that performed the diversion. This is important because the AS may need to apply further services or charging rules to the diverted session. By including the URI, the AS can identify the session when it returns, even if the original session was redirected to a different endpoint. This mechanism also prevents loops and ensures that the diversion is handled consistently.

The CDIV Session Identifier URI is generated by the diverting AS based on the diversion parameters. It may include information such as the diverting user's identity, the diversion reason, and a unique session identifier. The URI is then inserted into the outgoing SIP request. When the request reaches the target AS or the terminating user, the URI can be used to correlate the diverted session with the original diversion request. This is particularly useful in scenarios where multiple diversions occur, such as call forwarding chains.

Key components involved in the CDIV Session Identifier URI include the diverting AS, which creates and inserts the URI; the SIP protocol, which carries the URI; and the receiving AS or User Equipment (UE), which may use the URI for routing or service logic. The URI is typically stored in the SIP message headers, such as the History-Info header, which records the diversion history. The 3GPP specifications define the exact format and usage of the URI to ensure interoperability between different vendors.

The CDIV Session Identifier URI is an essential element for implementing communication diversion services in IMS. It enables the network to track diverted sessions and apply the correct service treatment. Without it, the AS would not be able to identify the diverted session, leading to potential service failures or incorrect charging. As IMS networks evolve, the CDIV Session Identifier URI continues to be a fundamental part of the supplementary services framework.

Purpose & Motivation

The CDIV Session Identifier URI was introduced to solve the problem of routing and identifying diverted sessions in IMS networks. Before its introduction, communication diversion services lacked a standardized way to mark a session as diverted, which could lead to routing errors, service inconsistencies, and charging inaccuracies. The URI provides a unique identifier that allows the diverting AS to recognize the session when it returns, ensuring that the correct service logic is applied.

The motivation behind the CDIV Session Identifier URI was to enable seamless communication diversion across different network domains and vendors. In a multi-vendor environment, it is crucial to have a standardized identifier that all entities can understand. The URI serves this purpose by providing a common format that can be used by any AS or SIP entity. It also helps in preventing diversion loops, where a session could be diverted indefinitely, by allowing the AS to detect and break such loops.

Furthermore, the CDIV Session Identifier URI supports advanced diversion scenarios, such as sequential diversion, where a session is diverted multiple times. By carrying the URI through each diversion, the network can maintain a history of the diversion and apply the appropriate policies. This is particularly important for regulatory requirements, such as lawful interception, where the diversion history must be recorded. The URI also facilitates charging, as it allows the charging system to correlate the diverted session with the original session and apply the correct tariffs.