[LAD] AoIP question

Len Ovens len at ovenwerks.net
Sun Oct 5 15:47:25 UTC 2014

I have been doing some reading on audio over IP (or networking of any 
kind) and one of the things that comes up from time to time is collisions. 
Anything I read about ethernet talks about collisions and how to deal with 
them. When I was thinking of a point to point layer two setup, my first 
thought was there should be no collisions. Having read all the AES67 and 
other layer 3 protocols there does not seem to be mention of collisions 
really. My thought is that on a modern wired network there should be no 
collisions at all. The closest thing would be a delay at a switch while it 
transmitted another packet that in a hub would have been a collision.

So my thought is that AoIP at low latencies depends on a local net with no 
collision possible. Am I making sense? or am I missing something?

The various documents do talk about three kinds of switches, home, 
enterprise and AVB. It is quite clear what makes an AVB switch, but what 
does an "enterprise" switch have over any other switch aside from 
speed? I am sure I am being small minded in my thoughts here. For example, 
I am expecting very little non-audio bandwidth and I am guessing that the 
average home switch does not prioritize any style of packet over another.

I guess I am asking what parts of a switcher are important for audio? I am 
guessing that HW encription (offloading the SSL from the server to the 
switch) is not something that helps audio. Even with proprietary 
protocols, it would not make sense to use encription. There seems to be a 
real plug and play emphasis where the audio enabled LAN is firewalled from 
the rest of the world. The streams are multicast so any box that 
recognizes the packets can use those channels and offer it's own audio 
channels. Any box can send control messages to reroute audio... there must 
be some kind of authentication for that.... (light bulb) this is why AES67 
does not include controls and perhaps discovery either. I can just see 
someone walking into a concert with a notepad and deciding they want 
their own mix... I am guessing the promoter would not want people walking 
away with their own "direct from the mixer" audio track of the event 
either. Not quite plug and play then. The wireless router wants to limit 
what traffic it deals with.

So AES67 allows the control to be offloaded to a web interface with access 
control (switch SSL offloading would not help here anyway). Discovery ends 
up being manual at first glance. I am thinking it will not be long before 
the control and setup will automate loging into the web IF and setting 
things up. A system wide user/password and an interface that defaults to 
streaming it's own inputs as multicast is already discoverable.

Len Ovens

More information about the Linux-audio-dev mailing list