Hub 3 / Compal CH7465-LG (TG2492LG) and CGNV4 Latency Cause

[Datalink]

Good Day Ladies and Gentlemen,

Greetings from the other side of the pond, so to speak.  Over the last few weeks I've been perusing various user forums across North America and Europe for issues related to Intel Puma 6 modem latency.  Of those forums, your Hub 3 stands out as yet another Puma 6 based modem where users see continuous latency no matter what site is used or what online game is played. Considering all of the problems that are on the go, the following information should be of interest to all Hub 3, Compal CH7465-LG and Hitron CGNV4 modem users.  There is much more to post regarding this, so this is a start, to alert VM users as to the real cause of the latency and hopefully engage the VM engineering staff, via the forum staff, with Arris.  I am surprised to see that there has been no mention on this board of users from other ISPs who are suffering the exact same issues with their modems, so, this may come as a surprise to some, and possibly old news to others.

So, the short story ........

The Hub 3 / Compal CH7465-LG (TG2492LG) & Hiton CGNV4 modems are Intel Puma 6 / 6 Media Gateway (MG) based modems.  These modems exhibit high latency to the modem and high latency thru the modem.  The latency affects all IPV4 and IPV6 protocols, so it will be seen on every internet application and game.  The basic cause is the processing of the data packets thru a CPU software based process instead of thru the hardware processor / accelerator.  It appears that a higher priority task runs periodically, causing the packet processing to halt, and then resume.  This is observed as latency in applications and in ping tests to the modem and beyond.  For the last several weeks, Hitron, along with Intel and Rogers Communications in Canada have been addressing the latency issue within the Hitron CGNxxx series modems.  To date, only the IPV4 ICMP latency has been resolved.  Although this is only one protocol, it does show that a Puma 6MG modem is capable of using the hardware processor / accelerator with good results.  Currently Rogers is waiting for further firmware updates from Hitron which should include an expanded list of resolved protocol latency issues.  For Arris modems, "Netdog" an Arris engineer indicated last week that Arris was onboard to address the issue for the Arris SB6190 modem.  That should be considered as good news for any Arris modem (read Hub 3) user as Arris should be able to port those changes over to other Puma 6/6MG modems fairly quickly.  This is not a trivial exercise and will probably take several weeks to accomplish.  Note that there is no guarantee at this point that it is possible to shift all packet processing to the hardware processor / accelerator without suffering from any packet loss side effects.  Time will tell if all of the technical issues can be resolved with the current hardware included in the Puma 6/6MG chipset.  Last night, Netdog loaded beta firmware on selected test modems on the Comcast Communications network.  As this was only done last night, it's too soon to tell what this version resolves and if it was successful or not.  Netdog has contacts with staff at Comcast, Rogers, Charter and Cox Communications to fan out beta versions and modifications for testing.  I'd say its time to add Virgin Media and/or Liberty Global to that group as well.

Recent activity:

Approx three weeks ago a DSLReports user, xymox1 started a thread where he reported high latency to an Arris SB6190 and illustrated that with numerous MultiPing plots.  This is the same latency that I and other users with Rogers communications have been dealing with for months so it came as no surprise.  As well as reporting via that thread, xymox1 took it upon himself to email several staff members at Arris, Intel, Cablelabs and others.  The result of that campaign was Netdog's announcement, last week, that Arris was fully engaged at resolving the issue.  That has led to last nights release of beta firmware, although as I indicated its too early to determine what the beta firmware resolves, if anything.

The original thread that xymox1 started is here:

https://www.dslreports.com/forum/r31079834-ALL-SB6190-is-a-terrible-modem-Intel-Puma-6-MaxLinear-mis...

Yesterday, DSLReports issued a news story covering the thread:

https://www.dslreports.com/shownews/The-Arris-SB6190-Modem-Puma-6-Chipset-Have-Some-Major-Issues-138...

Today, Arris responded:

https://www.dslreports.com/shownews/Arris-Tells-us-Its-Working-With-Intel-on-SB6190-Puma6-Problems-1...

That response was also picked by Multichannel.com

http://www.multichannel.com/news/distribution/intel-arris-working-firmware-fix-sb6190-modem/409379

This is more news likely to appear in the next few days as additional tech and news staff pick up on this issue.

Hub 3 observations:

Like many others using a Puma 6/6MG modem, Hub 3 users are experiencing latency when they ping the modem, or ping a target outside of the home, game online or use low latency applications.  The common misconception is that this is Buffer Bloat. It's not. Its most likely a case of the packet processing stopping while the CPU processes a higher priority task.  The packet processing is done via the CPU no matter what mode the modem is operating in, modem mode or router mode and no matter what IPV4 or IPV6 protocol is used.  Normally, the latency is just that, latency.  The exception are UDP packets. In this case there is latency and packet loss.  The result of that is delayed and failed DNS lookups, and poor game performance for games that use UDP for player/server comms or player/player comms.

Can this be fixed?

So far, it appears that the answer is yes.  Rogers Communications issued beta firmware to a small group of test modems in October.  This version shifted the IPV4 ICMP processing from the CPU to the hardware processor / accelerator, resulting in greatly improved performance in ping latency.  At the present time we are waiting for the next version firmware which should shift other protocols over to the hardware processor / accelerator.  That can be seen in the following post:

http://communityforums.rogers.com/t5/forums/forumtopicpage/board-id/Getting_connected/message-id/369...

The details and results of last nights beta release to the Comcast group have yet to be seen.

At this point there is enough reading to keep most staff and users busy.  My intention is to post some of the history leading up to this point and instructions on how to detect the latency and packet loss.  This is not thru the use of a BQM.  I had hoped to post this all at once but events are moving much faster than I had thought they would.  For now this should suffice to get the ball rolling.

Below is a link to a post with a couple of HrPing plots from my 32 channel modem to the connected CMTS.  This shows the latency that is observed and reflects what others have posted in this forum using Pingplotter and HrPing.

https://www.dslreports.com/forum/r31106550-

HrPing is one of the freebie applications that can be used to monitor the latency to and thru the modem. 

Pingplots with Pingplotter which show the latency from my modem to the CMTS can be found in the first two to three rows of my online image library at Rogers Communications, located below.  They are essentially what the BQM would look like if you were able to zoom into the plot to the point where you could see the individual ping spikes.  Those ping spikes are common to Puma 6 and Puma 6MG modems.

http://communityforums.rogers.com/t5/media/gallerypage/user-id/829158

 [MOD EDIT: Subject heading changed to assist community]

[Sephiroth]

All this ping testing stuff only tells you that the firmware developers, presumably under guidance from Intel, have only dealt with improving the results of said tests. The "fix" has no bearing on real data handling. Many games were not affected by the Puma problem; many games were affected.

But there is no proper fix for this problem with the Puma chipset that has been placed into these el cheapo modems.

All records kept by users serve only to describe the phenomenon relating to pings/ICMP packets.

I hope that helps with understanding what's happened.

[deasmi]

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@Sephirothwrote:
All this ping testing stuff only tells you that the firmware developers, presumably under guidance from Intel, have only dealt with improving the results of said tests. The "fix" has no bearing on real data handling. Many games were not affected by the Puma problem; many games were affected.

But there is no proper fix for this problem with the Puma chipset that has been placed into these el cheapo modems.

All records kept by users serve only to describe the phenomenon relating to pings/ICMP packets.

I hope that helps with understanding what's happened.

---

I'm pretty aware of what's happened, it's been going on for long enough.

I also agree the ping tests aren't telling us anything, however it was my understanding that the dslreports puma6 test should tell us more; it is after all small tcp connections rather than icmp. But, conceivably they could have hacked a fix for that test as well.

You are assuming it hasn't been fixed, but I don't see any proof one way or the other, and I'd quite like to know.

I've yet to see, in these forums, a robust test that demonstrates empirically the issue so that we could run it on the new & old firmwares and verify that it's still there or not. 

If anyone has such a test I'm more than happy to run it on a patched SH3 to compare with an unmatched one.I'm trawling the dslrtports posts as they do seem to have some options.

If we don't get some more repeatable tests we'll never be able to tell if it's fixed or not and whilst I agree given it's a slow single threaded cpu plus from what has been published a full fix is unlikely, it's not in my view impossible.

After all I've had lots of slow cpu single threaded network equipment over the years that have managed just fine.

[Badvok]

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@deasmiwrote:

If we don't get some more repeatable tests we'll never be able to tell if it's fixed or not ...

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If you can't test if a problem exists does it?

When the patch is rolled out there will certainly be:

a) a few people with much better looking TBB BQM graphs that will stop complaining.

b) a few people for whom the dslreports test will provide much better results that will probably stop complaining.

c) a few people with other problems that are actually unrelated to the Puma 6 issue still complaining.

d) a handful of people who experienced real noticeable effects of the Puma 6 issue that may still see an issue.

Personally, if the patch stops some of the UDP drops then I'll be happy, the latency spikes which testing shows are present for me have no effect other than filling my BQM with yellow.

[Sephiroth]

It can’t be fixed by software.  A different DOCSIS chip is the only solution and VM know this in their stunning silence. They should be suing someone. 

[mitch84]

Has anyone on here got the new trial firmware and find online gaming better/fixed?

Seeing all these comments about it cant be fixed, but has any of you actually got the new firmware and tested it. I have it myself but Im yet to test online gaming as I only occasionally game online.

[Sephiroth]

The thing that can’t be fixed is the periodic housekeeping interrupt that stops DOCSIS handling in its tracks. Some apps are affected others not. 

By moving Ping handling onto the WiFi chip, it lessens the load on the Puma chip but only when you are doing ping stuff. It has no bearing on normal stuff.  Unless VM can be more explicit as to detail of what else may have been offloaded. 

[RidingTheFlow]

The valid point that if modern DSLReports puma test is truly using TCP it should pick spikes still if they are present.

Though when I've tested my spikes they happened roughly once a minute, and I don't think DSLReports test runs for that long - this may lead it to missing a spike.

[deasmi]

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@Sephirothwrote:

It can’t be fixed by software.  A different DOCSIS chip is the only solution and VM know this in their stunning silence. They should be suing someone. 

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I think that is conjecture, just because to date intel haven't issued a fix that has been proven to solve the problem does not mean they can't. As I said previously it's clearly possible to have single threaded CPUs happily work in routers without these kinds of of issues. I highly doubt this is a true hardware problem, much more likely to be low level firmware/microcode, and so potentially fixable.

iPerf is looking promising as a test platform, using large numbers of identical udp packets or short tcp connections and measuring jitter.

Edit: If anyone *without* the new firmware and is happy running iperf can drop me a DM I've setup an AWS server and would like to compare results.

[Sephiroth]

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@deasmiwrote:

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@Sephirothwrote:

It can’t be fixed by software.  A different DOCSIS chip is the only solution and VM know this in their stunning silence. They should be suing someone. 

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I think that is conjecture, just because to date intel haven't issued a fix that has been proven to solve the problem does not mean they can't. As I said previously it's clearly possible to have single threaded CPUs happily work in routers without these kinds of of issues. I highly doubt this is a true hardware problem, much more likely to be low level firmware/microcode, and so potentially fixable.

iPerf is looking promising as a test platform, using large numbers of identical udp packets or short tcp connections and measuring jitter.

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It’s not conjecture.  A DOCSIS modem is doing much more than a DSL modem because everything on your node hits it.  

[philjohn]

Edit: If anyone *without* the new firmware and is happy running iperf can drop me a DM I've setup an AWS server and would like to compare results.

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You shouldn't need to setup your own iperf server on AWS, there are publicly available ones, such as ping.online.net (and for if we ever get IPV6 ping6.online.net)