While VoIP relies upon H.323 for call control and management functions across a voice-enabled network, a number of hardware and software components must be in place in order to enable VoIP on a Cisco network. The bullet points below outline some of the specific hardware and software typically found on a Cisco VoIP network.
The four main components of a VoIP network include:
- Network infrastructure. A network that supports VoIP requires a number of different architectural elements in order to function correctly. Outside of the media (typically Ethernet and WAN links) used on the network, a combination of Layer 2 and 3 switches, as well as voice-enabled routers are used to transport IP packets that contain voice data. IP telephones are typically plugged into a Layer 2 or Layer 3 switch on the Ethernet network, with the switch providing inline power to the phone (a technique known as power over Ethernet). When a user of an IP telephone needs to communicate with a user on the PSTN, a voice-enabled router acts as a gateway between the devices, interconnecting the IP and PSTN networks. When an IP phone user needs to connect to another IP phone user, a voice-enabled router is not required.
- Call processing software. On a Cisco VoIP network, Cisco CallManager software handles call control functions including route selection, last-number redial, billing, quality monitoring, and more. CallManager carries out many of the same functions as a PBX would on a traditional voice network.
- Applications. In the same way that users on a traditional voice network require additional features like voice mail, so do users of IP telephones. A variety of different applications can be added to a VoIP network including voice mail, automatic call distribution software, and so forth.
- Terminal devices. Users ultimately interface with a VoIP network via terminal devices like IP phones. While IP phones may be the most popular choice for business users, other possibilities such as headsets that connect to a PC can also be used.