What contractual obligations do I have with SIP trunks?

This depends on the SIP provider. Broadvox allows for month-to-month, 1-year, 2-year, and 3-year terms. Month-to-month contracts require that the customer pay monthly with an automatic credit card deduction.

How much bandwidth do I need for SIP trunks?

This depends on the type of codec (the mechanism used to compress the voice traffic over IP) and the number of simultaneous calls. Broadvox uses G.711 and G.729. G.711 is considered “higher quality” and usually consumes about 88 Kbps (with overhead). G.729 consumes about 38 Kbps. Most of our customers choose the G.729 codec because they get more use out of their bandwidth. We personally cannot hear the quality difference between the two codecs.

Does placing SIP calls over the Internet cause quality issues?

With SIP trunks, voice gets converted into IP packets. These IP packets then get sent to the SIP provider (and vice versa). Because voice is real-time sensitive, it requires that the voice packets arrive within a certain amount of time and in the right order (along with a number of other factors like jitter, packet loss, etc). If some of the voice packets get dropped or if they are sent too slow, audible quality issues can occur. So the quality of the connection between the customer’s phone system and the SIP provider directly affects the quality of the call.

Can I fax over SIP?

Yes, most SIP providers support G.711 or T.38 faxing protocols. We’ve been told that faxing over SIP trunks is about 95% reliable.