Example: If you have a 1Mbps ADSL connection from your service provider, it usually means you have an upstream bandwidth of approximately 380 Kbps. Just because the service provider says that you have 380 Kbps upstream bandwidth does not mean that the full 380 Kbps is available at all times. In fact, a conservative approach is to estimate about half of the upstream bandwidth as being available. In this case, you could safely support 2 simultaneous G.711 calls or 4 simultaneous G.726 calls or 10 simultaneous G.729 calls. These estimates do not factor in other data traffic on the network at the same time. With additional traffic on the Internet or private IP network, the number of simultaneous calls supported by the link is reduced.
5.2.2 The Router/NAT/Firewall
In a typical small office environment, there are several computers connected to an Ethernet switch, sometimes integrated into a router. A router handles the connection between two or more IP networks. Routers spend all their time looking at the destination IP addresses of the packets passing through and routing them accordingly. In a network that shares both data and voice, it is critical that the voice traffic has priority over the data packets. Some routers support Quality of Service (QoS) functionality for such purposes. These routers are identified as devices that support QoS, VoIP or prioritization. An inexpensive router for the small office market is the Linksys BEFSR81. It can be configured to provide prioritization of the voice traffic on the broadband connection to ensure that voice traffic gets through. It also supports DHCP, UPnP and VPN Pass Through.
TalkSwitch uses UPnP (Universal Plug and Play) to automatically configure port forwarding VoIP ports, and receive updates whenever the WAN IP address changes so that it can properly update SIP messages.
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