An SBC can exist as a single, independent hardware unit containing all of the resources necessary for call signalling and call control. Alternatively, the signalling and control functions can be divided between the communicating systems.
A Session Border Controller (SBC) can be used to connect your Lync environment to one or more SIP Trunk providers or to other Voice over IP (VoIP) systems. SBCs are very common in Service Provider networks, but they can be useful on-premise as well. The on-premise form of an SBC is also known as an Enterprise-SBC or E-SBC.
What functionality can an SBC provide?
There are several reasons that you might want to deploy an SBC. Such as the following:
- Application on the SBC
It is completely depends on how SIP trunks or connections with other VoIP. The risk is less with a MPLS (Multiprotocol Label Switching) or VPN (Virtual private network), While connecting to other networks some risk will be there such as Denial of Service (DoS) attacks , voice specific such as toll fraud or attempts to manipulate the media.
An SBC contains back-to-back user agent (b2bua) functionality. This provides the SBC the option to handle the media, as well as the signalling (SIP). This gives an SBC more control than an application layer firewall (ALG), which usually can handle SIP only. Another security based reason is topology hiding. From a security perspective an SBC is an addition to a firewall, not a replacement.
Not all VoIP solutions are created equal, and an SBC can be an excellent way of connecting those solutions. An SBC can handle TCP/UDP conversion, codec conversion, and connectivity to H.323 systems (so no need to upgrade the legacy system), to name a few.
Although SBC’s can also handle normalization, that is usually not necessary with Lync, because Lync is good at handling that itself. Lync also has quite a few settings available through Set-CsTrunkConfiguration, if you need additional adjustments in the SIP traffic.
Some interoperability issues can also be resolved of by manipulating SIP with Microsoft SIP Programming Language (MSPL).
Besides the interoperability functionality, there are some options that can simplify a migration. When migrating from another telephony solution, an AD lookup functionality can check to see if a user is enabled for Enterprise Voice and route accordingly to Lync or the legacy PBX. This could also include call forwarding and simultaneous ring provided by the gateway, which can be handled by Lync in most cases.
When using an SBC appliance, its Digital Signalling Processor (DSP) can help with encoding/decoding. An SBC can provide media bypass functionality, which shifts load from the Mediation role, thus requiring fewer Lync servers.
Applications on the SBC
Some vendors provide additional functionality on their SBC, such as call recording or Sip Phone Support (SPS). SPS is used to connect third-party IP phones or devices to Lync. This can result in limited functionality, but it can make sense for some migration or interoperability scenarios.
Types of SBC’s
Multiple vendors offer E-SBC solutions. This can be in the form of a physical or virtual appliance, a software product installed on a Windows server, or combined with a gateway product. When combined with a gateway product, an SBC can also provide PSTN failover functionality, for instance between SIP trunks and ISDN.
Some providers will deploy an on-premise SBC as part of their offering, in which case the providers can manage the SBC.
See Microsoft TechCenter: Infrastructure Qualified for Microsoft Lync (including SBC) for an overview of qualified SBC solutions.