the net result is this: high packet loss means forget about real time services such as voip or video conferencing. they are asynchronous services that don't retransmit and are also not very tolerant of packet loss (over about 10%). long ping times means that synchronous services such as email are very slow, coupled with packet loss you might as well be on a dial up.
our solution in a commercial environment was to keep upgrading until we found a service level that works (more or less). we moved from adsl to fibre. found an isp at each end that we could talk to and who could give assistance with routing issues. eg if they have multiple gateways we experimented until we found the most efficient gateway.
we also know of larger comapnies who pay substantial fees to achieve end to end qos.
all of this means there's not a lot you can do at your end with limited choices except to accept that there is no bandwidth at some times of the day and go have a beer instead :)
regards
rick
Chris Bennett wrote:
Quick answer is: you can't. You need to know the bandwidth so that you can control the queue.
You bring up some interesting theoretical ideas about monitoring the overall congestion level and forcing back-offs when you sense that you're reaching the current level, though. That would sort of involve dynamically adjusting the shaping rules. As far as I know there is nothing in existance that does this, but its an interesting idea to think about. If you were going to try something like this I think you'd need some sort of reliable indicator of what the current congestion is like... perhaps some steady ping to use as your "canary in the coal mine". Then set up several shaping scripts that assume different levels of bandwidth, and depending on the current "canary ping", either upgrade or downgrade your assumed bandwidth by calling the appropriate script. So I guess if you wanted to try this, maybe you could set up three scripts, one set to 80% of your bandwidth, one set to 50%, and one set to 20%. Then set up a cron job that checks the "ping" for your high priority traffic, and calls the appropriate script to adjust. I doubt it'll work, but it could be an interesting experiment.
----- Original Message ----- From: "Justin Schoeman" <justin@xxxxxxxxxxxxxxx>
To: <lartc@xxxxxxxxxxxxxxx>
Sent: Thursday, November 25, 2004 3:17 AM
Subject: Shaping traffic on heavily oversubscribed links?
Hi all,
I am having some fun with traffic shaping, and have run into an interesting situation. Here is South Africa, most internet links are heavily oversubscribed, which means that in most cases the local link is _not_ the bottleneck, and shaping on the local link does not help that much...
Does anybody have some tips on shaping such links? How can you get interractive traffic if you don't know how much bandwidth to reserve for it? How can you give fair access to a link if you don't know what the link capacity is?
Are there perhaps some tools to monitor retransmissions to try and determine congestion levels, and from that adjust shaped bandwidth?
Am I perhaps missing something simple in this scenario?
Thanks! -justin _______________________________________________ LARTC mailing list / LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/
_______________________________________________ LARTC mailing list / LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/
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