2.6Optimizing Your IP Network for VoIP

2.6.1 The Broadband Connection

For optimum quality of VoIP calls on your system, we recommend that you subscribe to a high-speed broadband connection from your Service Provider. ‘Lite’ broadband connections (typically 128 Kbps downstream and 64Kbps upstream) are not typically suitable for simultaneous voice and data traffic. The limiting factor for a broadband connection is typically the upstream bandwidth to the Internet Service Provider.

For example, if you have a typical 1Mbps ADSL connection from your service provider, this usually means that 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. For more information on VoIP calling, see chapter 1.

2.6.2 The Router/NAT/Firewall

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In a typical small office environment, there are several computers connected to an Ethernet switch which is sometimes integrated into a router. A router handles the connection between 2 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 typically identified as devices

TalkSwitch User Manual

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Talkswitch 48-CVA manual Optimizing Your IP Network for VoIP Broadband Connection, Router/NAT/Firewall