Voice over IP (VoIP) Gateways
Voice over IP (VoIP) Gateways
Gateways not only provide basic telephony and fax services, but can also enable lots of value-added services, e.g., call-centers, integrated messaging, least-cost routing, … .
Such gateways provide three basic functions:
- Interface between the PSTN network and the Internet
Terminate incoming synchronous voice calls, compress the voice, encapsulate it into packets, and send it as IP packets. Incoming IP voice packets are unpacked, decompressed, buffered, and then sent out as synchronous voice to the PSTN connection.
- Global directory mapping
Translate between the names and IP addresses of the Internet world and the E.164 telephone numbering scheme of the PSTN network.
- Authentication and billing
Voice representation
Commonly: ITU G.723.1 algorithm for voice encoding/decoding or G.729 (CS-ACELP voice compression).
Transcript
[slide38] So we'll get started again. Not surprisingly, one of the important things in Voice over IP systems are Voice over IP gateways. And these gateways not only provide for voice services, but also fax services and lots of value-added services. They can be used to support things like call centers, integrated messaging systems, lease cost routing, etc. But they need to support three basic functions. And the first of these, of course, is they need to actually give you an interface between the public switched telephony network and the Voice over IP system via the Internet. But they also need this global directory mapping to map from E.164 numbers, which are traditional telephony numbers, into somehow the address that's going to be used for the other party that you want to communicate [with] on the Voice over IP system. And they need to do authentication and billing. Now the way that we can represent the voice can be done in lots of different methods. For ITU's G723.1 algorithm for voice encoding and decoding, or G729, or G.711, etc. There are bunches of different methods of encoding the voice. But that's really only associated with that interfacing. We'll see that there are other protocols we need to look at for these other two functions.