[c-nsp] Shaping vs. queuing

[Mikael Abrahamsson]

On Fri, 8 Aug 2008, David Curran wrote:

> Any thoughts or links would be appreciated.

1. File transfers based on TCP generally work better with shaping, 
especially if they are few and have high bw per TCP session.

2. Interactive protocols (cli terminal sessions over ssh for instance) 
generally work better with policing as it doesn't really matter if a 
packet is lost compared to a constant long delay due to queuing (in case 
file transfers are filling up the queues). This is at least true if the 
session is between hosts that are fairly close to each other.

3. Gamers want low latency and games usually handle packet loss fairly 
well.

4. IP telephony can generally handle a few percent packet loss without any 
major trouble (echo cancellation might be hurt in case of packet loss 
though).

5. IPTV transfer over UDP generally do not have error correction and are 
very sensitive to packet loss.

6. You do not want to queue ACKs if you can avoid it, as this slows down 
TCP based communications going the other way.

So it's all down to what you want to prioritize. With the current traffic 
mix on the internet I don't really see any reason to ever queue a packet 
more than 30-40ms, then you might as well drop it (using WRED for 
instance).

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se