The company I work for recently purchased a WAN load balancer for our office as we converted to VoIP phones from our old POTS system and we need them to work ALL the time. We are an Ecessa partner and like to eat our own dog food so to speak so this was a natural fit for us.
Ecessa has been in the WAN virtualization business since 2000 and the company (previously known as Astrocom) has been around since 1968. The device we decided to implement is called a ClariLink 175. There are a number of things that this little gem is capable of doing. For our primary purposes, it is able to perform transparent failover of SIP calls without losing the session. This means that if I start a VoIP call that goes out our Comcast link and that link goes down, the ClariLink fails that call over to our Century Link connection without dropping the call. Slick huh?
This is all well and good, however there are a number of intricacies to how this works under the hood and they all differ based on your VoIP provider. Ours (ANPI/Voyant) is a hosted solution provider meaning that the PBX is in “the cloud” and our IP phones connect to it over the internet to make calls. Because of this, they enforce SIP authentication to make sure someone can’t fire up a desktop and pretend to be me and call a bunch of 1-900 numbers!
The ClariLink has numerous configuration options including the ability to proxy SIP traffic. This is how it can perform seamless failover of calls even though our external IP address changes when traffic starts coming from a different provider. The ClariLink sends a SIP reinvite to the provider with the new source IP address mid-call when it detects that one of the internet connections goes down. Because the device is proxying the traffic, it is able to modify the SIP packets and change some bits of information to make sure the provider maintains the call even though the source IP address is different. I don’t know of any desktop phones today that are capable of doing that- cool stuff.
We’re actually in the process of implementing this feature with our phone system and haven’t quite got it working just yet. I plan on posting a second article once things are up and running to talk in more detail about how it works. In the meantime, I’m having a lot of fun setting up QoS rules to keep someone from chewing up all our bandwidth by uploading pictures to their google drive ;).