B party

Description

In 3GPP terminology, the B party refers to the user who receives a call, unless the call is forwarded. This is a fundamental concept in telephony and is used in specifications such as 22.053 (Tandem Free Operation) and 23.903 (Redial). The B party is the destination of a call initiated by the A party (the calling party). The term is used to distinguish between the two ends of a communication session for various service features, including call forwarding, call waiting, and multiparty calls.

The definition includes the caveat 'unless the call is forwarded', which means that if the call is forwarded to another user, the B party becomes the forwarded-to user. This is important for services like call forwarding, where the original called party may not be the one who ultimately receives the call. The B party is then the final recipient of the call after any forwarding has been applied.

In the context of 3GPP specifications, the B party is often used in service descriptions and procedures. For example, in Tandem Free Operation (TFO), the B party's codec capabilities may influence the negotiation of codecs between the two ends. In redial services, the B party is the number that is redialed. The term is also used in charging and billing, where the B party may be charged for the call depending on the service agreement.

The B party concept is essential for understanding call flows and service logic. It allows network elements to identify the terminating user and apply appropriate services, such as call forwarding, call barring, or voicemail. It also helps in routing the call to the correct destination, whether that is the original B party or a forwarded number.

Overall, the B party is a simple but crucial term that defines the receiving end of a call in 3GPP networks. It is used across many releases and specifications to describe service behavior and network procedures.

Purpose & Motivation

The term B party exists to provide a clear and unambiguous way to refer to the called party in a call, distinguishing it from the calling party (A party). In telephony, it is essential to differentiate between the two ends of a call for service logic, charging, and routing. The B party is the user who receives the call, and this definition is fundamental to many supplementary services.

The caveat 'unless the call is forwarded' addresses the common scenario where a call is redirected to another user. Without this clarification, there could be confusion about whether the B party is the original called number or the final recipient. By specifying that the B party is the user receiving the call (unless forwarded), the definition ensures that service logic correctly identifies the terminating user for features like call forwarding, voicemail, and call waiting.

This term was introduced in Rel-5 and has been carried forward unchanged, reflecting its stability and fundamental nature. It is used in specifications related to Tandem Free Operation and Redial, where the B party's characteristics may affect the service. For example, in TFO, the codec capabilities of the B party's terminal are considered during negotiation.

Overall, the B party concept solves the problem of identifying the recipient of a call in a way that accommodates call forwarding and other redirection services. It is a building block for more complex service descriptions and ensures consistent behavior across different network implementations.