IMSG Session Border Control Solution Overview
The IMSG provides the session border controller (SBC) role in the European Telecommunications Standards Institute (ETSI) Telecommunications and Internet Converged Services and Protocols for Advanced Networks (TISPAN) architecture as shown in Figure 1. The SBC functionality encompasses the AF, SPDF, and BGF components.
Figure 1: IMSG in the ETSI-TISPAN Architecture
IMSG Terms and Abbreviations
Table 1 defines the terms and abbreviations used in this topic.
Table 1: Terms and Abbreviations
Term | Description |
|---|---|
B2BUA | Back-to-back user agent. A B2BUA is a SIP user agent to both ends of a SIP call. That is, it both establishes and terminates a call. In the TISPAN model, the B2BUA provides the application functions (AF). In the IMSG, the BSG acts as a B2BUA. |
BGF | Border gateway function. Resides in the transport layer and polices and enforces traffic flows based on instructions from the SPDF. |
BSG | Border signaling gateway. The BSG controls VoIP media resources on the router and is responsible for all SIP processing. The border signaling gateway provides a full B2BUA implementation and an embedded SPDF. |
Dialog | A peer-to-peer SIP relationship between two user agents that persists for some time. |
Gq’ | Interface between the AF (in the IMSG, this is the B2BUA) and the SPDF that is used to exchange session-based policy setup information between the SPDF and the AF. |
Ia | A profile of the interface between an SPDF and the BGF. |
SIP | Session Initiation Protocol. |
SPDF | Service policy decision function. The BSG contains an embedded SPDF that controls the instructions that the BSG sends to the BGF. |
