Subscriber B

Description

Subscriber B is a conceptual term used in 3GPP specifications (22.091, 23.093) to denote the remote party in a call originated by or involving Subscriber A. It is not a network element or a physical entity but a role assigned to a subscriber for the purpose of describing call flows, supplementary service interactions, and network procedures. The definition explicitly states that, by convention, the connection has been established on this call, meaning that for the scenarios described in the specifications, the call is considered to be in an active or connected state between Subscriber A and Subscriber B.

In the context of supplementary services such as Call Forwarding, Call Waiting, or Multiparty, Subscriber B may be the original called party or the party to whom the call is forwarded. The specifications use Subscriber B to represent the terminating side of a call, allowing clear and unambiguous description of service behavior. For example, in a call forwarding scenario, Subscriber A calls Subscriber B, but the call is forwarded to Subscriber C. Here, Subscriber B is the originally dialed party, while Subscriber C is the forwarded-to party.

The term is part of a naming convention that includes Subscriber A (the calling party), Subscriber B (the called party), and Subscriber C (the forwarded-to party). This convention simplifies the description of complex call scenarios and ensures consistency across different specifications. The network elements associated with Subscriber B (e.g., MSC B, VLR B, HLR B) are similarly named to indicate the network components serving that subscriber.

Subscriber B does not have a specific technical implementation; it is a modeling artifact. However, understanding its role is essential for interpreting call flow diagrams and service descriptions in 3GPP specifications. It helps engineers and students to follow the logic of supplementary services and to design and test network features that involve multiple parties.

The term has been stable since its introduction in Release 4 and remains unchanged through Release 19, reflecting its foundational role in service description. Its simplicity and clarity make it a useful tool for standardizing the documentation of telecommunications services.

Purpose & Motivation

The term Subscriber B exists to provide a clear and consistent way to refer to the remote party in a call scenario within 3GPP specifications. Without such a convention, describing supplementary services that involve multiple parties would be cumbersome and prone to ambiguity. By defining Subscriber B as the other party in Subscriber A's call, the specifications can describe call flows, service interactions, and network procedures in a standardized manner.

The motivation for this term comes from the need to model complex call scenarios, such as call forwarding, call waiting, and multiparty calls, where multiple subscribers are involved. Using generic labels like Subscriber A, B, and C allows the specifications to focus on the logic of the service rather than on specific subscriber identities. This abstraction is particularly useful when describing interactions between different network elements and when defining service behavior that must be consistent across various implementations.

Historically, as supplementary services became more sophisticated, the need for a common vocabulary to describe multi-party scenarios grew. The introduction of Subscriber B in Release 4 coincided with the maturation of GSM supplementary services and the beginning of 3G service definitions. Since then, it has been carried forward unchanged, demonstrating its enduring utility. It solves the problem of referencing the called party in a way that is independent of the specific service or network configuration, thereby facilitating clear and concise specification writing.