CODA-4582 - Open Issues for Investigation

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I Plan to Stick Around
Posts: 154

Re: CODA-4582 - Open Issues for Investigation

@Datalink wow, well done!

 

I'm very confused at your results though. You're highlighting 590mbit down but that seems to have 35-74% packet loss? Why settle at this number then?

 

Also why would 530mbit of UDP max out your high end i7 processor?  What sort of processing is it doing on this??

 

Also why would you need a 500Mb buffer size? That also seems crazy considering what's going on.

 

My 10 year old Core 2 Duo can handle gigabit TCP traffic without even causing any CPU load at all and buffers in the KB range...

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Re: CODA-4582 - Open Issues for Investigation

@Telek the iperf numbers are definitely strange.  I can repeatedly run up to 500 Mb/s UDP down without errors.  From 500 Mb/s up, the bandwidth and datagram numbers start to diverge between the received data and the server data, but, the loss result will indicate no losses.  And then you get to a tipping point and all of a sudden you see losses in the results.  I don't know why that happens, so, I have some reading to do and further testing to do.  My definition of success at this point with an iperf test is to end up with no errors and see a close association between the local data and the server data in terms of bandwidth and datagrams.  It doesn't make any sense to me at this point to see those last two data points diverge and yet see no loss declared by iperf.  So the numbers don't have to be exact, but, they should be pretty close unless someone with expertise in iperf tells me otherwise, as in "ah, its because of ........." as I nod my head in agreement.

 

What I was trying to highlight in that first section was the strange iperf behaviour where on one run I might see errors as you indicated, and yet, on the next run, it would turn out perfectly.  I didn't do anything different, same command, and yet the results are drastically different.  

 

If you look at the next section below that, running at 590 Mb/s, you can see that there are no errors. Thats the max Mb/s point that I saw today where I would see no lost datagrams.  If I went to 600 Mb/s down, I would end up with lost datagrams and you would see that in the results and in the % loss.  

 

In that section there are no errors, but, if you compare the bandwidth figures, bottom server data indicates 590 Mb/s, top receive data varies between 542 to 582 Mb/s.  The datagram numbers also have diverged at this point, but yet, iperf is still happy to say that there are no errors.  So, this is a little strange. 

 

"why would 530mbit of UDP max out your high end i7 processor?  What sort of processing is it doing on this??"  I wish I had that answer.  My immediate thought is that UDP doesn't follow the send and acknowledge routine.  Its a firehose with the iperf test, so, you either catch it or you don't.  Why is that any tougher than a much faster TCP/IP speedtest that I also run?  I don't have that answer at the moment.  One thing that I have to look at is the processor loading to see if the load stays on one processor or if it hops around.  But, as I indicated, I'm not sure that I can do anything about it with the windows version of iperf.

 

That buffer size is actually the socket buffer size.  What I found today is that if I didn't include that variable and increase the buffer size, I wouldn't have been able to run the UDP test at higher rates.  That leads to the question of whether or not an end user would have to increase that buffer size for games or any applications that use UDP, or, are they self adjusting?  

 

A Core 2 Duo, have one of those as well, what I'm typing on actually, and it runs rather well.  A little slower on a speedtest since Windows 10 but it still runs rather well.  My golden oldie Core 2 Quad Q6700 with its DDR2 runs 50 Mb/s up, 200 Mb/s down, UDP, without any errors.  Thats with the same settings as before, just throttled back on the download to get to an error free point.  That is also IPV4 only thru my Asus RT-AC68U.

 

If nothing else, today showed that there are more questions than answers.  The modem looks like it can run fast UDP up and down, the question is, is there an approximate 590 Mb/s cap on the modem, or is that just a pc problem?  That might take an overclocked CPU and 10 Gb/s nic card to determine that.

 

Maybe @RogersDave can explain some of the pitfalls of UDP.  

 

The one thing that was demonstrated was the UDP IPV4 performance versus the UDP IPV6 performance.  The IPV6 results are vastly superior to the IPV4 results, and the only explanation I can think of are either a NAT problem or some other issue that hasn't been identified as of yet.  Perhaps looking at this would benefit the Puma 6 modems as well. 



I Plan to Stick Around
Posts: 43

Re: CODA-4582 - Open Issues for Investigation

Hi @RogersDave 

 

Noticed that my net went down around 230-530am last night, and once it came back, all my signals went from being near 0 to closer to -7dBmV along with a changed IP and node. Do you know of any changes that happened in the Thornhill area?

Is -2.00 -> 7.8dBmV acceptable on the CODA? Upstreams are sitting at 29-32 (before was 32-37). Full signals here: https://pastebin.com/Lp6yimKJ

 

Thanks

I Plan to Stick Around
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Re: CODA-4582 - Open Issues for Investigation

>The one thing that was demonstrated was the UDP IPV4 performance versus the UDP IPV6 performance.  The IPV6 results are vastly superior to the IPV4 results, and the only explanation I can think of are either a NAT problem or some other issue that hasn't been identified as of yet.  Perhaps looking at this would benefit the Puma 6 modems as well. 

@Datalink Didn't you test in Bridge Mode using a 3rd party router capable of passing gbit from WAN to LAN? If the results were the same, that would suggest that it's not a NAT issue and perhaps something else. Not sure.. as I've said previously I'm a Systems guy who does networking as/where needed so i'm just guessing at this point. Weird as . . 
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I Plan to Stick Around
Posts: 10

Re: CODA-4582 - Open Issues for Investigation

>Is -2.00 -> 7.8dBmV acceptable on the CODA? Upstreams are sitting at 29-32 (before was 32-37).

For reference, what are the acceptable values for that anyways?
I Plan to Stick Around
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Re: CODA-4582 - Open Issues for Investigation

With firmware version .27 are there still restrictions to the characters that can be used for the WiFi SSID and login password (like no spaces etc.)?

 

Thanks.

I Plan to Stick Around
Posts: 43

Re: CODA-4582 - Open Issues for Investigation

I was told by an agent that -10 to +10 is acceptable on the downstream. Upstream should be 35-58 according to him as well. Not sure how true these values are, especially since the CODA handles it a bit differently than the Rocket modems.

I Plan to Stick Around
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Re: CODA-4582 - Open Issues for Investigation


@JohnyR wrote:

I was told by an agent that -10 to +10 is acceptable on the downstream. Upstream should be 35-58 according to him as well. Not sure how true these values are, especially since the CODA handles it a bit differently than the Rocket modems.


-12 to +12 is the max range that they will accept, although -10 to +10 is better -- 0 is "perfect".  36-40 is better for upstream, at least based on what we see most often on DOCSIS 3.0.

Network Architect
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Posts: 611

Re: CODA-4582 - Open Issues for Investigation


@JohnyR wrote:

I was told by an agent that -10 to +10 is acceptable on the downstream. Upstream should be 35-58 according to him as well. Not sure how true these values are, especially since the CODA handles it a bit differently than the Rocket modems.


@JohnyR, I can't be sure of easily of what happened during that 3 hour or downtime you experienced but I suspect it was a segmentation activation (when we break an area in half to increase capacity).

 

I checked your signal levels and everything is fine on the downlink but your uplink is out of spec. This also affects your neighbors so I'll have maintenance dispatched to make adjustments to the line amplifiers on the street.

 

For reference, 35 dBmV to 53 dBmV is the acceptable signal level for upstream for a DOCSIS 3.0 modem. The levels for a DOCSIS 3.1 modem are much lower because of a correction factor that is dependent on the channel bandwidth:

 

3.2 MHz channel: 32 dBmV to 50 dBmV

6.4 MHz channel: 29 dBmV to 47 dBmV

 

In your specific case, the channel at 23.7 MHz (6.4 MHz wide) is too low at 27.75 dBmV. The channel at 30.596 MHz (6.4 MHz wide) is right at the limit at 29.00 dBmV.

 

Dave

I Plan to Stick Around
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Re: CODA-4582 - Open Issues for Investigation

What would we do without you @RogersDave Heart