VoIP Voice and Fax Signal Processing

2.4 VoIP SYSTEMS WORKING PRINCIPLES

In this section, some high-level architectures and working principles are presented. VoIP supporting systems specific to the current context have to perform two different tasks—namely signal processing and network processing. While representing the architecture, two processors-based approach is also used in this book. A digital signal processor (DSP) is used for voice and fax processing, and a network processor is referred to as a host processor for networking functions. It is also common practice to use a single processor for the whole functionality. Processor architectures for VoIP and networking functions are presented in Chapter 19. The VoIP systems considered in this chapter are as follows:

1. VoIP adapter and extensions
2. RG or IAD
3. IP phones
4. WiFi phones
5. Personal computer (PC)-based VoIP softphones
6. VoIP-to-PSTN gateway
7. IP–PBX adapters to interface with existing PBX systems
8. Hosting VoIP through PSTN lines
9. Subscribed VoIP services

2.4.1 VoIP Adapter

VoIP adapters are used when IP service is available through another LAN interface in residential applications. The other names used for VoIP adapter are terminal adapter, CPE, and gateway. In this section, a VoIP adapter is presented as an end-user system with an accompaning example. Functional block-level representation, signal flow, and module level software blocks of the adapter are given in this section. A residential gateway can completely make use of the VoIP operation presented under the VoIP ...