Outgoing Communication

Description

In 3GPP terminology, 'Outgoing (communication)' refers to a communication that is initiated from the user side of an interface. This term is primarily used in the context of supplementary services, IMS (IP Multimedia Subsystem), and charging, where it is essential to distinguish between outgoing and incoming communications for correct routing, billing, and service logic. The definition is intentionally generic, covering voice calls, video sessions, messaging, and other real-time or non-real-time communications. The term appears in specifications such as 22.273 (Customized Alerting Tones), 24.407 (TISPAN), and 24.607 (IMS supplementary services), indicating its relevance across different service architectures.

The concept of outgoing communication is fundamental to how networks handle session establishment. When a user initiates a communication, the network must identify it as outgoing to apply the appropriate originating services, such as dialing plans, call barring, or charging. For example, in IMS, the originating session control function (S-CSCF) evaluates initial filter criteria (iFC) to determine which application servers should be invoked for an outgoing session. Similarly, in the circuit-switched domain, the mobile switching center (MSC) processes outgoing calls based on the subscriber's profile, which may include closed user group (CUG) restrictions or outgoing access permissions.

The term is also closely related to 'Outgoing access,' which is a specific arrangement allowing a member of a closed user group to place communications outside the group. While outgoing access is a feature, outgoing communication is the general direction of the session. In charging, outgoing communications are typically charged to the originating party, and the network generates call detail records (CDRs) that include indicators for outgoing direction. This distinction is crucial for roaming scenarios, where the home network must be able to differentiate between outgoing and incoming communications to apply the correct inter-operator tariffs.

From a protocol perspective, the direction of a communication is often signaled in session initiation messages. For instance, in SIP (Session Initiation Protocol), the initial INVITE request indicates an outgoing session attempt. In the 3GPP IMS architecture, the P-Asserted-Identity header and the From/To headers help identify the originating and terminating parties. The term 'outgoing' is also used in the context of SMS (Short Message Service), where an outgoing SMS is one sent by the subscriber, as opposed to an incoming SMS. In 5G, the concept remains relevant for network slicing and edge computing, where outgoing traffic from a UE may be steered to a local data network based on service requirements.

Overall, the definition of outgoing communication provides a clear directional reference that is essential for service logic, charging, and policy control. It ensures that network functions can consistently interpret the origin of a communication and apply the appropriate treatment, whether for routing, billing, or supplementary service invocation.

Purpose & Motivation

The term 'Outgoing (communication)' exists to provide a precise and unambiguous way to describe the direction of a communication from the user's perspective. In telecommunication networks, it is critical to distinguish between communications initiated by the user and those received by the user, as they are subject to different service logic, charging rules, and regulatory requirements. Without a clear definition, there could be confusion in specifications and implementations, leading to incorrect billing or service behavior. The 3GPP definition, introduced in Release 7, was motivated by the need to standardize terminology across the growing number of IP-based services, particularly in IMS and TISPAN environments.

Historically, as networks evolved from circuit-switched to packet-switched and then to all-IP, the distinction between outgoing and incoming communications became more complex. In circuit-switched networks, the direction was implicit in the call setup signaling. However, with IMS and the proliferation of supplementary services, a formal definition became necessary to ensure interoperability between different vendors and operators. The term was defined in specifications like 22.273 and 24.407 to support features such as Customized Alerting Tones (CAT) and IMS supplementary services, where the direction of the communication determines which service logic is triggered.

The definition also supports charging and policy control. For example, in online charging, the charging system must know whether a session is outgoing to apply the correct rating group and tariff. Similarly, in policy and charging control (PCC), the PCRF (Policy and Charging Rules Function) may apply different QoS rules for outgoing versus incoming sessions. By having a standardized definition, 3GPP ensures that all network elements interpret the direction consistently, reducing the risk of errors and enabling seamless roaming and interworking.