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Today’s telecommunications networks are a delicate blend of clients and servers that together attempt almost endless possibilities when it comes to services and applications. For every fashionable client amplified, there seems to be a score more above the course ― from mobile handsets, PDAs, finals, telephones, movie calls,[link widoczny dla zalogowanych], IP set-top-boxes, and so on.
There are essentially two types of servers that connect between clients on large networks: Proxy servers and Back-to-Back User Agent (B2BUA) servers. The more prevalent Proxy servers feature predictable action ― simply connecting between clients. Effectively, B2BUA servers are much stronger and intelligent entities that execute actions which Proxy servers cannot. Moreover,[link widoczny dla zalogowanych], B2BUA servers provide a malleable solution for a wide range of applications and services and are appropriate the primary engine for speed up SIP servers in NGN and IMS networks.
The difference between Proxy servers and B2BUA servers is sometimes not entirely understood. In this article, we will explore what makes B2BUA servers such an praying alternative to standard Proxy servers. Better understanding of B2BUA servers can assist managers know the value, and the tradeoffs, of choosing a B2BUA server, as well as the structures needed to develop a wide range of SIP applications and SIP services using it.
Figure 1 - Architectural distinction between Proxy servers and B2BUA servers
B2BUA Server Defined
B2BUA servers are used to provide amount joined functions for point-to-point calls and manage multi-point calls. The power behind a B2BUA server is derived mostly from the fact that it has a quite generic definition, which gives it virtually unlimited power. However, this same specific is the root of the argument circling it.
IETF criterion (RFC 3261) defines a back-to-back user proxy as “a logical entity that receives a request and processes it as a consumer surrogate server (UAS). In mandate to decide how the request ought be answered, it deeds as a user agency client (UAC) and generates requests. Unlike a Proxy server,[link widoczny dla zalogowanych], it maintains a talk state and have to partake in always requests sent on the dialogues it has created.”
B2BUA servers have capabilities that far exceed those of other types of SIP servers, and reply the need for formative sophisticated value added SIP applications that cannot be implemented as Proxy applications.
Some of these capabilities, which are distinctive to B2BUA servers, are profiled below:
3rd Party Call Control (3PCC) Features
3rd Party Call Control (3PCC) namely the competence of an entity (normally a controller) to set up and administer communication among 2 or extra parties. 3PCC namely often used because worker services and conferencing.
3PCC actions are important capabilities, exclusive to B2BUA servers since “passive” non call-stateful factors, such for Proxy servers, cannot initiate these types of activities. Some samples of 3PCC services are online billing, QoS, resource prioritization, call convey, click-to-dial, mid-call proclamation and more.
3PCC movements tin be initiated automatically along B2BUA server petitions, like loosening a cry following honor breath in an online-billing system. Or they tin be initiated by remote managerial control (OSS), e.g. invite parties to a multi-point conferencing session.
Figure 2 - Schematic outline of B2BUA server offering 3PCC functionality
Inter-working Function (IWF) for Interoperability
SIP was devised as a extremely flexible and extendible protocol. The very strength of this flexibility is too an inherent disability, since the extensive order of client types in the mall still need to connect.
B2BUA Inter-working Functions (IWF) defines a broad range of mighty SIP servers that connect SIP customers that “speak” in another protocol dialects, or assist assorted capabilities. This Inter-working function is ve