name: B2BUA
full_form: Bach-to-Back User Agent
context: according to the Proxy rules specified in IETF RFC 3261 [404]. The main task of a proxy is to route the request to an entity that is nearer to the terminating UAS. 4. Application Server performing 3rd party call control: - The Application Server performing 3rd party call control acts as a B2BUA. IETF RFC 7092 [412] defines the B2BUA taxonomy and different roles more in detail. IETF RFC 7092 [412] differentiates for B2BUA between SIP and Media layer. For Application Server the SIP layer is relevant. When the Application Server triggers MRFC then the media layer may need additional consideration. - Within TS 23.218 [208] are two roles described for Application Server applying the B2BUA role: 1. The routeing B2BUA Application Server which terminates a SIP request as UAS and generates as UAC a new SIP request for a different SIP dialog, which is based on the received SIP request. In this mode the Application Server behaves as a B2BUA for the multiple SIP dialogs as specified in IETF RFC
description: A Back-to-Back User Agent (B2BUA) is a network function that acts as an intermediary between two or more user agents, routing requests and responses between them. In the context of Application Servers performing 3rd party call control, B2BUA plays a crucial role in managing SIP dialogs and routing requests to the appropriate entities.
explanation: The provided text describes B2BUA as an intermediary network element that manages communication between user agents, particularly within the context of SIP-based call control. This functionality aligns with the definition of a Network Function.
section_title: 4.2Consideration of different Application Server (AS) types and roles
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