Q

ADSL bandwidth

We have two sites interconnected by a VPN. On this channel we are running VoIP in the following form - in one of the seats there is a IP Call Manager and in the other (remote site) there is a hard phone, an extension of the IP call manager.

At the moment, the remote side has installed an ADSL of 1Mb that is giving us 818Kbps. We need to know how to improve

our ADSL to 2Mb with the purpose of installing another hard phone (we have one) and improve the yield of the one we have. Any ideas?

With the ADSL connection you are going to have an upstream bandwidth and a downstream bandwidth. For example, you may have an ADSL connection that is specified for 384 kb/s upstream and 1Mb/s downstream. The bandwidth to be most concerned about is the ADSL upstream bandwidth because it is the bottleneck. If you're using G.729A for speech, you can estimate that about 30kb/s upstream and downstream is required per conversation. Adding a second hard phone would double this requirement to about 60 kb/s each direction. If you are using G.711 you can estimate about 90 kb/s upstream and downstream is required per conversation. It is a good idea to use G.729A speech compression to conserve bandwidth.
This was first published in April 2005

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