What Type of Circuits Are Suitable for SIP Trunking?

This is our 3rd of 12 blogs on the subject of SIP Trunks. Subscribe in the box to the right to receive an email notification for each one in the series.

Click here to read the previous blog in this series.

Here we tackle the question of the type of circuits that are suitable for SIP Trunking. Although speed is certainly a consideration and will be given full attention here, there are many other elements that go into determining the suitability of a given Internet connection for SIP Trunking.


Old analog and PRI service was reliable, but also very expensive and has tinny voice quality.With VoIP, reliability and voice quality are variable, with a large factor being the type and quality of your Internet service. If you place an extremely high value on voice quality, VoIP service can be engineered to be superior to analog phone calls. That’s right, VoIP can provide a clearer voice than the old service.  This is possible due to a technology called “Wideband” or “HD Audio”. On the other hand, if your business has a very low volume of calls and you are on a budget, an inexpensive data circuit with a bit lower quality may be acceptable.

Synchronous Vs. Asynchronous

Sheesh, you didn’t know that there would be so much to know about a simple Internet connection, did you?

Synchronous circuits maintain the same speed in both directions, uploads as well as downloads. Synchronous circuits are typically “business quality” meaning that they have greater reliability, closer monitoring and guaranteed service level agreements (SLA’s). Synchronous is best.

Asynchronous circuits have a higher downstream speed (from the Internet to your office), and a considerably lower upload speed. A typical asynchronous circuit has five times more download capacity than upload capacity. If the circuit is used primarily for browsing web sites and downloading information, this speed difference isn’t really relevant. However, if the circuit is used for cloud applications, substantial file uploading and voice, the slower upload speed becomes a substantial factor.

Cable and DSL are the two most popular asynchronous circuits. The bottom line is asynchronous circuits have much higher bandwidth and are much less expensive. However, they are less reliable than synchronous circuits. 

A quality SIP Trunk provider should work with you to provide multiple options and help you weigh the pros and cons of each type of circuit. Professional advice is highly recommended in this area as it can make or break your SIP trunking conversion.

In my next blog in this series, we discuss Single Solution vs. Over the Top (OTT) Providers. Be sure to come back for that important info!

We offer business-class communication solutions with responsive local support

To learn more, call us today at (510) 785-2480