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How do VoIP-TDM gateways differ from SBCs?

How do VoIP-TDM gateways compare with session border controllers? How do they differ? Expert Michael Brandenburg explains how the two perform similar, but separate, functions.

Media gateways, as the name suggests, provide a bridge between legacy TDM-based and IP-based platforms and services....

Also known as TDM gateways, these hardware appliances are deployed in a number of places within the enterprise. The most common use is to connect VoIP access or SIP trunking services to a legacy TDM-based PBX.

Conversely, businesses that are deploying IP-based unified communications platforms but are not ready to adopt SIP trunking might leverage a VoIP-TDM gateway to connect the new platform to existing trunking circuits. Gateways are also often deployed to interface modern platforms to analog phones, paging services and fax machines.

Session border controllers (SBCs), on the other hand, deal strictly in IP. Like media gateways, they are typically deployed "in the middle" -- between UC platforms and SIP trunking services -- but their role is slightly different.

SBCs provide translation, security and remote access options to the UC platform. Unlike media gateways that require TDM-based hardware interfaces, the all-IP focused SBC can be deployed as standalone hardware or as part of a virtualized server environment.

While VoIP-TDM gateways and SBCs serve different roles, many vendors have integrated their individual capabilities within a single hardware appliance. A number of media gateway products also include some SBC functionality. A number of SBC products on the market include legacy TDM-based interfaces to offer media gateway functions.

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