Many companies are integrating Voice over IP (VoIP) into their networks. Figure 7-1 shows some components of a VoIP system, which can include the following:
Figure 7-1. Some Components of a VoIP System
IP phones—. Provide voice and applications to the user.
Voice gateways—. Translates between PSTN and IP calls and provides backup to the Cisco CallManager (IP PBX, or Call Agent).
Gatekeepers—. An optional component that can do call admission control, allocate bandwidth for calls, and resolve phone numbers into IP addresses.
Cisco CallManager—. Serves as an IP PBX. Registers phones, controls calls.
Video conferencing ...