Re: Queue & Priority

[Sean Murphy <murphys@teltec.dcu.ie>]

> I will try to build a small "network" in ns. As input I will have both
> voice and data and I want to see the delay characteristics. I will use
> a router to rout the voice and data.
>
> I would like to know if it is possible in ns to have 2 or more queue
> buffers on one link. And I wonder if it is possible to assign priority
> so the voice don't have to wait to long.
> 
> Do I have to build these functions by my own or there are some options
> in ns.

A few options spring to mind -

1. there's a priority queue implementation with ns that simply puts
priority packets at the head of the queue - the intention is that network
control traffic be priority traffic, but you could easily modify is so
that, say, RTP packets are prioritised. One caveat here, I think that if a
priority packet arrives it is inserted at the head of the queue, so the
situation could arise that two priority packet arrive close together and
the one that arrives second actually gets served first.

2. you could use cbq, which enables you to have different traffic
priorities and definitely separate queues. I don't know very much about
this, but it's described in an IEEE/ACM TON paper (v3n4 according to
cbq.cc)

3. I've implemented some diffserv functionality that you can easily add to
ns - it doesn't give strict priority to the EF traffic, through. Check out

http://www.teltec.dcu.ie/~murphys/diffserv/diffserv.html

if you're interested.

Hth,
Sean.

-----
Sean Murphy,			Email: sean.murphy@teltec.dcu.ie
Teltec Ireland,			Phone: +353-1-7045080
DCU, Dublin 9,			Fax:   +353-1-7045092
Ireland.