Choosing a Voice Gateway Solution
There are a number of different voice gateways available for CallManager and
VoIP implementations, which are divided into categories by type of gateway and
the protocol running for gateway communications.The gateway selection is based
on some of the following variables: analog or digital, capacity, connection type,
services, features, and country of installation.Table 3.2 lists the analog VoIP gateways
and the respective voice interface cards (VICs) supported.The analog gateways
provide connectivity to analog phone sets, central office, and PBX.The
Foreign Exchange Station (FXS) ports are used to provide dial tone for analog
phones, faxes, and speakerphones, while a Foreign Exchange Office (FXO) port
in a gateway is for connectivity to Central Office for analog access to the PSTN.
Ear-and-mouth (E&M) ports, on the other hand, are for PBX-to-PBX signaling
communication.You can determine what type of analog VoIP gateway you need
by answering one of the following questions:Are FXO ports required for PSTN
connectivity or is Direct Inward Dial (DID) a necessity? Another factor in
selecting an analog gateway may be capacity. For example, if you require a large
number of FXS ports for legacy analog connections, you would select a Cisco
3660 or a Catalyst 6000 with a 24-port FXS module rather than a smaller
capacity gateway such as a VG-200 or Cisco 2600.