Fixing the Echo in Asterisk

One of the dirty little details of working with Asterisk is that, sometimes, there is echo. Larger organizations can avoid the problem because many medium density analog trunk cards have hardware-enabled echo cancellation.

But the smallest Asterisk deployments will not have this luxury, as the lowest density cards—like the Digium Wildcard 400p eWEEK Labs frequently tests with—do not support hardware echo cancellation. These customers must instead look to a software solution.

Stepping into the breach is OctWare, which in March started delivering high-end echo cancellation in software. A subsidiary of Octasic—a company with a long history with hardware echo cancellation technology—OctWare provides a software-only solution for small Asterisk deployments, with prices starting at the low cost of $10 per channel.

Resource Library:

Asterisk already includes a number of free, open-source echo cancellation algorithms that can be turned on when compiling the Zaptel module for analog trunk support.

However, we liked OctWares solution because we found it to be highly effective and configurable. For instance, we could modify and tailor settings like tail length and echo return loss for our particular installation.

Echo cancellation can be computationally expensive, but we found OctWares software to be efficient, placing minimal strain on our AsteriskNow servers CPU (a 2.4GHz, Pentium 4 system, in our case) resources, as long as we did not try to compensate for too long a tail.

We did find installation to be where OctWares software fell short. We had to download OctWare source code appropriate for our processor manufacturer and architecture, then compile and install the module and recompile Zaptel. But most Asterisk deployments are not created from source, but rather from the Trixbox distribution (and soon, we suspect, from AsteriskNow). And these distributions will not necessarily include the Linux kernel source and Zaptel source files needed to get OctWare up and running.

All you do is talk talk? Do it wirelessly. Click here to read more.

Even when we made sure to add those components individually to our AsteriskNow server, the install process failed because the install script did not write the module to the right place for an rPath based system. We had to throw in a few symlinks, once we figured out the problem.

However, relief is on the way: OctWare officials confirmed our findings and offered a workaround until the company creates a Conary package for rPath. We also learned that Fonality will be including free licenses for OctWares software echo cancellation with the forthcoming Trixbox appliance.

We surmise that support for OctWares software will also be more fully baked into Trixbox software-only downloads as well in the near future, although undoubtedly the licenses would not be included in this case.

Check out eWEEK.coms for the latest news, views and analysis on voice over IP and telephony.