* Re: [LARTC] voice based queuing
2002-07-02 3:09 [LARTC] voice based queuing ganesh kumar godavari
@ 2002-07-02 3:31 ` Gerry Creager N5JXS
0 siblings, 0 replies; 2+ messages in thread
From: Gerry Creager N5JXS @ 2002-07-02 3:31 UTC (permalink / raw)
To: lartc
ganesh kumar godavari wrote:
> hello group,
>
> i want to know if there is any way i can determine using iptables if
> the ip packet contains voice?
>
> i want to know this as i want to do some queuing for output packets and
> the voice packets are given high preference next ftp,telnet,ssh.....
>
>
> i want to know if this is possible using iptables and tc. if so how. if
> i can identify the packet to be voice then i can do the rest using tc.
I've followed (from afar, things are busy) your quest.
The issues are several.
1. The ports used, except for setup, are dynamic, as the Microsoft page
told you (although NetMeeting is hardly a good example of a compliant
H.323 app).
2. You can do stateful inspection of headers and have a good shot at
finding RTP and RTCP packets, and then mark those.
Where you probably need to go is toward marking all from the H.323
hosts. You will need to spend some time with TOS/DiffServ, and 802.1p.
Also, be aware that if you do not have priority queuing from endpoint to
endpoint (also known as E2E) you will not see an appreciable improvement
in handling.
We are engaged in a couple of efforts to identify Voice and Video Over
IP, and mark it for priority queuing on our campus. Cisco has a nice
simple strategy they're apparently trying to make a "standard" but it's
at odds with diffserv marking. If you go with the Cisco markings, and
you enable your queue disciplines based on the markings,
_throughout_the_entire_network_ then you may see some improvement.
Can you di this with LARTC, yes, I believe so. Sorry I cannot be more
certain, but while it's on my list to test, I'm still a bit busy... The
trick is getting the appropriate packets marked properly at the edge,
rather than trying to mark them at the core. And why, one might ask, is
this so? Well, we see a lot of congestion at the edge in wiring closet
aggregation switches. If these switches cannot handle priority queuing
AND they experience periods (even short ones) of congestion, then most
of the effort you're going to is for naught.
Gerry Creager
network Engineering
AATLT, Texas A&M University
College Station, Texas
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