DC-SBC is Data Connection's portable software-based session border controller solution designed specifically for manufacturers of next-generation network equipment. DC-SBC and its underlying signaling protocols (DC-SIP, DC-Megaco/H.248) have been substantially enhanced to handle border control and signaling functions required in IMS networks. These new features and functions include
- Proxy Call Session Control Function (P-CSCF)
- Interconnect Border Control Function (IBCF)
- (Interconnect) Border Gateway Function (I-BGF/BGF)
Each function may be distributed independently to separate hardware modules and/or geographical locations enabling the solutions to be deployed in a wide variety of network and service architectures.
SBCs in IMS networks
The IMS architecture consists of interconnected core networks belonging to different carriers, with endpoints connected through attached access networks, and gateways to non-IMS networks. Border gateways control access into and out of each core network, monitoring and regulating the data flows on each interface. This architecture is shown in the diagram below.
Unlike architectures defined by other standards bodies, for example the Multi-service Switching Forum (MSF), the IMS architecture does not include a device labeled "SBC". However, the functions SBCs provide play a vital role in IMS networks. The following describes how SBC function (and DC-SBC) fits onto the IMS functional architecture at the UNI and NNI.
DC-SBC at UNI
At the IMS UNI, session border control functionality is encompassed by the following components and subsystems.
- The P-CSCF, which handles border control for the SIP signaling interface.
- The SPDF and A-RACF, which handle call admission control and media path reservation.
- The BGF, which handles policing and monitoring of media-plane traffic.
This is illustrated in the following diagram.
The I-CSCF could also be part of an SBC in some situations.
A UNI session border controller device in an IMS network may provide all these functions, or a subset of them. In particular,
many SBCs will only have responsibility for managing core network resources, and so will omit A-RACF functionality. Our white paper
Session Border Control in IMS discusses the options in more detail.
DC-SBC at NNI
At the IMS NNI, session border control functionality is encompassed by the following components and subsystems.
- The IBCF, which handles border control for the SIP signaling interface, topology hiding and interworking with non-IMS networks.
- The SPDF, which handles call admission control and media path reservation.
- The I-BGF, which handles policing and monitoring of media plane traffic.
This is illustrated in the following diagram.
As at the UNI, the I-CSCF could also be part of an SBC in some situations. An NNI session border control device may encapsulate some or all of these functions.
DC-SBC Modularity and Scale
Most current SBC products are implemented as a single stand-alone device that is placed in front of existing equipment in the path of all the signaling and media traffic on an interface. This one box includes the media (BGF) and signaling processing (BCF/P-CSCF) as well as the media resource control (PDF/RACS).
Although in some small-scale applications it makes sense to include all these functions in a single device, this solution does not scale well to the requirements of service providers. For these applications, the media, signaling and CAC processing will often be split into separate devices, with the signaling processing clustered into regional server farms, the CAC processing centralized (and possibly supplied wholesale by a third party supplier) and the media processing distributed closer to the user. This provides economies of scale on the signaling processing and increases network manageability, whilst maintaining direct media routing to minimize network transit delays.
The IMS functions of DC-SBC may be distributed independently to separate hardware modules and/or geographical locations, enabling the solutions to be deployed in a wide variety of network and service architectures. The following diagram illustrates the possibilities.
For more information about DC-SBC or IMS, contact us at or see
- the technical data sheet on DC-SBC
- the technical data sheet on IMS Enabled Solutions
- our whitepaper on Session Border Controller: Enabling the VoIP Revolution
- our whitepaper on Session Border Control in IMS Networks
- our webpages on What is a Session Border Controller? and DC-SBC Architecture.
For more information about Data Connection's Session Border Control for IMS product and expertise contact dcsbc@dataconnection.com.