[LAD] AoIP question

Reuben Martin reuben.m at gmail.com
Tue Oct 7 03:13:40 UTC 2014

On Monday, October 06, 2014 04:10:59 PM you wrote:
> On Mon, 6 Oct 2014, Reuben Martin wrote:
> > On Sunday, October 05, 2014 08:47:25 AM Len Ovens wrote:
> >> 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.
> > 
> > "Enterprise" switchs have hardware support for the PTP protocol. The
> > timing of PTP without hardware support in the switches is not 100%
> > deterministic.
> Meaning jitter may create over/under runs I am guessing. In AES67 switches
> with PTP are recommended but not "required".

For audio it's not really necessary. For super time sensitive industrial / 
military applications it's more applicable. Which is why you may notice that 
almost all switches supporting PTP are geared towards the high end industrial 
/ data processing / communications markets that are stupid expensive.

> >> I guess I am asking what parts of a switcher are important for audio?
> > 
> > IGMP Snooping built into the switch is very convenient. Otherwise the
> > multicast audio transport will flood your ports.
> IGMP is one of those things mentioned in the AES67 spec. that I have to
> read still. For some reason they have not bothered to spell out what IGMP
> stands for as they have with just about everything else.

IGMP is the protocol used to solicit membership to a multicast group. IGMP 
snooping is the switch probing layer3 in order to monitor which ports have 
connections subscribed to multicast groups, and uses that to determine which 
multicast traffic should be sent to which port. Without IGMP snooping, the 
multicast traffic is sent to all ports, which makes it no different than 
broadcast traffic. And with multicast flooding all ports, you actually eat up 
more bandwidth than if you sent duplicate unicast traffic to multiple locations. 

For low bandwidth control signaling this is generally not much of an issue. 
For high bandwidth transport signaling, this becomes an issue. Since multicast 
has to use UDP, it is critical to avoid un-needed traffic to avoid dropped 

I haven't been able to test various switches extensively, but I've used HP 
1900 series switches for large Dante transports with 5 Yamaha CL and QL 
consoles and 4 RIO-32 racks without any issues. And that is with half the 
ports mapped to a VLAN for the secondary connections. They seem to be a nice 
compromise between cost and functionality.

Also: The ip6 equivalent is MLD Snooping.


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