ECN for RTP

[Faisal Yawar Ali]

Hi,

I need to know if we have any successful cases where IP phones were able to receive CE (congestion experience) and reduce their data rate?

Mainly VoIP use UDP which is a challenge to insert ECN bits to get notified.

Any thoughts on this?

Thanks.

Faisal

[Philip D'Ath]

Never heard of it - and don't see how it could work.  If you have negotiated to use a particular codec that uses a particular bitrate I don't see how could suddenly reduce it.  It's not like copying a file where you can simply reduce the data rate.

[Faisal Yawar Ali]

Yes to avoid degrade in VoIP quality, we can change the codecs, but wouldn't be better if endpoints would be aware about the congestion and limit their datarates?

Its like reducing the water flow of the running tap which wont make the bucket overflow later on.

I read about WRED with ECN and want to know its use cases, has anyone deployed in their networks?

Were ECN capable hosts able to reduce their TX rate?

Currently UDP isn't supported, but ECN is extended to IP level. (https://tools.ietf.org/html/rfc3168)

[Mohammed al Baqari]

ECN isn't supported in IP Phones. Cisco Routers and New Catalyst switches (3750-X, 3650, 3850) can set ECN part of WRED implementation.

This feature needs queuing engines which aren't in IP Phones. QoS processes or ASICs can do it.

[Faisal Yawar Ali]

Yes, but has anyone ever tested with end hosts with ECN capability that were able to reduce line rate once they receive CE  (congestion experience)?

[Mohammed al Baqari]

Used it on routers but not end hosts.