Quote:
Originally Posted by Ignitionnet
Two issues at play here.
1) DOCSIS upstream is TDMA which is more prone to latency caused by utilisation - there are 2 contention points at play, contending to send your request for a grant and then waiting for the grant time to actually transmit the data.
2) DOCSIS allows large traffic bursts to request more bandwidth as part of a data burst so favours continuous large amounts of upstream traffic over small bursts such as a response to a TBB ping.
Downstream uses a scheduler at the CMTS. The pipe has to max out, with interest, in order to increase latency substantially.
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Which makes sense but what about the relationship between download speed and latency.
At peak times my download drops to 50% (50Mb/s from 100Ms/s) but the peak latency on the graph does not increase significantly (outside of the test window).
If my download packets cannot be scheduled at the required rate to achieve 100Mb/s and are buffered in the CMTS then surely ICMP packet would be delayed too?
Also, the TBB speed test during peak hours shows a big drop in the x1 speed even before the x6 rate gets reduced. This x1 rate always starts high (close to 100Mb/s) and drops back to 20M/s or so.
To my mind this suggest some packet priority scheme on the downstream based on how close together packets are received by the CMTS for a particular CPE.
So if you're gaming with infrequent bursts these get scheduled immediately but if you are downloading the packets get delayed.
This is my speed test at ~11am
Ian