An analog gateway consistently has the same number of voice channels as the number of interfaces. For instance, if there are 16 interfaces then it can handle 16 concurrent calls — not so for digital gateways. A digital gateway may have a particular number of digital trunk interfaces and each holds a specific number of voice channels inside.
Take T1 (which is used in the USA) for example. It has 24 channels or lines inside. Meaning if you order T1 trunk from the local telephony provider you’ll be getting 24 different lines with 24 numbers. Now if you’re expecting a heavy call load, it might be a better idea to get a DX4096, which handles up to 96 calls!
Another VoIP device is the router. This is the device which forwards the data packets along networks. Typically, a router is connected to at least two networks. This is either to two Local Area Network (LANS) or Wide Area Network (WAN) or a LAN and its ISP’s network. Routers can be found at the gateways, the place in which two or more networks connect.
Routers also use headers and forwarding tables in order to find out which is the best path for forwarding the packets. They use protocols like Internet Control Message Protocol (ICMP) in order to communicate with each other and configure the best route among the two hosts. However, the data are scarcely filtered through routers.