What I was meaning (and I didn't state very clearly) was whether the
link is at full ADSL speed and packets thrown away at exchange that
exceed traffic rate or whether the link is running at speed purchased.
On Fri, 18 Mar 2005 16:28:10 +1300, Simon Byrnand
At 14:27 18/03/2005, Ian McDonald wrote:
Allegedly (it has been published in IDG but don't want to guarantee it is correct) to get to a lower speed then ADSL capable on UBS Telecom just throws the packets away semi-randomly. This obviously has huge effect on TCP sessions and UDP streams as you are going to get far less than what you have paid for as they will retransmit the packet loss etc
There seems to be a bit of confusion by some people as to how traffic rate limiting and shaping works - to put it simply it is impossible to NOT drop packets, if you're trying to rate limit traffic, that is the whole basis of how rate limiting works.
If packets are coming in too fast, you can only buffer them so much before you're forced to simply throw some away. TCP automatically recognises this loss and throttles the speed back until the loss no longer occurs, so the packet loss is only momentary usually just after a download starts, and a normal part of how things work.
No way does it imply that you're going to have (for example) 30% packet loss on a continuous basis, so the "paying for retransmitions" argument is bogus.
UDP on the other hand has no rate limiting mechanism, unless its handled at an application layer, but if you try to send faster than your link speed or the smallest bottleneck in a path with UDP you'll run into problems no matter what.
Having a queue (buffer) too large only buys your more latency, and can actually be detrimental to overall performance, unless you start seperating different streams or types of traffic into different queues. (QoS stuff)
Regards, Simon
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