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?

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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.

If I’m going to use an Internet connection to deliver SIP trunks, what’s the best type?

Well obviously the best connection is a direct link to the SIP provider. This isn’t always (more often than not) a very economical solution for the small office. Low cost / high bandwidth Internet connections (DSL and cable) are very popular for our customers with 15 or less trunks. Keep in mind, these Internet connections are low cost for a reason. You are sharing the access to that Internet connection with your neighbors. This introduces a number of factors outside your control that can affect quality – the number of neighbors, their Internet usage, the quality of the cable or copper, etc.

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.

What security features are offered with SIP trunks?

This depends on the SIP provider. Broadvox can implement SIP trunks over a dedicated or VPN-enabled connection. Actually, it’s much harder for somebody to intercept a VOIP call than a traditional PRI or analog call.

How does the SIP provider determine if a call is local (and doesn’t meter at long distance rates)?

Again, this depends on the SIP provider. We’ll stick with the Broadvox answer. Like 911, it all depends on what number is out-pulsed to Broadvox. The following Broadvox products support local calling:

Can I mix long distance and local SIP trunks?

Yes. We often mix long distance SIP trunks with local SIP trunks. By least-cost routing long distance calls over the long distance trunks, you save the maximum amount of money.

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.

Do I need a SIP-enabled Phone System?

No. We have many customers that use an Integrated Access Device (IAD) that converts the SIP trunks back to traditional analog or PRI connections.
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