Environment (residential): NETGEAR CM500 (self identifies as CM500100NAS, firmware is current=V1.01.12)
DOCSIS 3.0, rated for up to 680Mbps (Xfinity supports this modem up to 300Mbps)
All channels stable (16 down and 4 up are always Locked, SNR within 39.7 - 40.3 dB)
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How does an ISP control the max speed of your Internet service? Is it a setting within the modem or is max speed controlled within the ISP infrastructure? I.e. how do ISPs facilitate/cap service speeds when you are contracted for 100Mbps vs 200Mbps vs 300Mbps ... assuming installed premise equipment support these speeds?
I believe that Xfinity infrastructure or explicit provisioning is capping my service speed but I don't consider that Xfinity is being sufficiently helpful (or at least sufficiently knowledgeable to answer my troubleshooting questions) ...
1. On July 27, 2020 I contracted with Xfinity for 200Mbps but am only getting actual speeds of 90 - 95Mbps. This is measured direct-wired to the modem so no other in-network traffic is competing with bandwidth. I even moved the modem to the point of demark termination at the outside of my house (i.e. at the end of coax feed from the street) to prove to Xfinity that issue could not be related to in-building wiring issues. In this test I continued to measure the exact same speeds.
2. Prior to July 27 my active service plan reflected that I was contracted for 150Mbps however I was only seeing service in same general range of 90 - 95Mbps. At the beginning of my just expired contract period 2 years ago I was contracted for 100Mbps but was often seeing up to 120Mbps actual service.
3. Prior to July 27 I was using an ARRIS TM822 modem (also DOCSIS 3.0 & the modem I was seeing 120Mbps). For roughly the prior 6 – 10 months I have only been seeing speeds of 85 - 96 Mbps. After my July 27 contracting for 200Mbps my speed stayed exactly the same as before...a steady 90 - 95Mbps. I made no progress with Xfinity to improve speed and I had an idle Netgear CM500 so I swapped out the ARRIS modem for the Netgear but my throughput speed remained exactly the same. I engaged Netgear support in a person-to-person call. The agent reported that they saw no problems with the Netgear modem. She had me do a master rest of modem (hold reset button for 30 sec) and allow 4+ hours for modem to self-optimize. After this my throughput speed continues to remain exactly the same as before (90 - 95Mbps) even in the middle of the night (no neighbor traffic on shared medium).
I am now left with Netgear saying everything they can do checks out (nothing more they can do). Xfinity has essentially tried to wash their hands although I will call them back once I find an answer to the question as to how an ISP actually facilitates limiting throughput speed and after I poll local neighbors to see what speeds they are getting.
The highly predictable/stable observed speed of 90 - 95Mbps implies that explicit provisioning is capping my performance. Since Internet cable service is a shared neighbor medium it is possible that the system is self-protecting bandwidth to maintain stable service but number of neighbor's sharing the common medium can be adjusted as required.
> Are there specific, very pointed questions I can press Xfinity on to confirm service provisioning?
> Any other suggestions?
