We all know that g711 (alaw / ulaw) is meant to sound the best. It’s uncompressed and equivalent quality to ISDN, which most businesses are used to with their traditional PABX System.

However, it comes at a price, 64kbps + overheads means around 111kbps when you factor in everything else over an ADSL PPPoA / PPPoE connection.

Now that’s a LOT when you think about it, considering on a standard ADSL2+ line you’re going to max out at around 5-7 SIP lines, especially if it’s a shared connection. This is where a compressed codec such as (My personal favorite) iLBC, or g729, can be incredibly cost effective, as you can load up around 15-20 on the same sort of bandwidth. When you’re a small business, that means with the right kind of QoS, you can share your ADSL Broadband connection and still have 5-10 concurrent phone calls, all happily living together.

So do away with expensive BRI interfaces and monthly charges, and go SIP!

We’re going to look at a few things very briefly:

1) MOS – What is it and why do I care?

2) Which codec is right for me?

3) g729 – Installation

4) iLBC – Installation

5) Trunk and Extension setup

6) Testing the codecs

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SIP combined with Elastix is nothing short of amazing.

Cost savings, flexibility, functionality, and I’ll say it again: Cost savings!

When deploying Elastix to use SIP over ADSL (for example), many find their existing Broadband connection does not quite provide satisfactory call quality, usually due to sharing the connection with other traffic.

We will follow this post up later with another on Diagnosing connectivity / quality issues.

NOTE: This is not the only way to do QoS, but after having struggled with the likes of pfsense, the budget / useless junk that many routers build in, and a host of other software / hardware solutions, I found Tomato did it the easiest, the best, and the most reliably! It’s a breeze to setup, and you’ll be kicking yourself for not having set something like this up earlier. (more…)