[Asterisk-Users] OT: VoIP over bonded link

[Rich Adamson]

> I have to provision several dozen * users to a seperate building on our
> campus in the same subnet. Ordinarily, I'd just run a gigabit cat6 cable to
> another switch if it doesn't violate the 100 metre rule, but this building
> is several hundred metres away from my backbone. My only option for cabling
> to the remote building is copper. My plan is to provision them with a Linux
> bridge with 4 NIC's: 1 gigabit to the backbone, and three bonded together as
> a single interface (90 mbit aggregate), then plugged into this dealie:
> 
> http://www.blackbox.com/Catalog/Detail.aspx?cid=425,1423,1424&mid=4946
> 
> At the remote building, the reverse: another Linux box with 4 NIC's that
> de-aggregates the link to a gigabit connection on a switch, and then to the
> wall plates. I'm pretty sure this will work for data no problem, but I'm a
> little concerned about latency on a timing-sensitive applicaiton like VoIP. 
> 
> Anyone have experience with VoIP over bonded link? Is there a gotcha? Is
> this a stupid idea? On my whiteboard it looks fine! 

Some thoughts that you might want to consider...

The vdsl box runs at speeds "up to 15 meg". That translates into the longer
the copper loop, the slower the speed. You'll probably want to accurately
measure the copper loop length and translate that into some 'expected' speed.
Probably won't be 15 meg, and whatever the documentation suggests, it
will likely be a fair amount slower then that.

Does the vdsl truly operate in a full duplex mode with equal bandwidth
in either direction?

We've worked with many corporations and institutions in over 40 states
doing network performance assessments, and seldom (if ever) do bonded
interfaces actually work the way that you might think they work. I've not
spent any time with the linux bonding that you're considering, but you
might want to better understand exactly how that works. E.g., some bonding
actually functions at 'per packet' level, which implies the maximum speed
of any single packet is the speed of one vdsl circuit. 

If one of the bonded circuits has errors, what impact does it have on the
other three error-free circuits. (Its not uncommon for one interface to
have very significant impact on all other interfaces.)

If all of the above can be answered with positive thoughts, you'll still
want to consider some form of QoS on those links to ensure the voip
packets are not held in a queue.