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]

[yabba]

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@WildWayzwrote:
Would love to be on this trial, purely because I test firmwares / routers for a day job...

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So do the guys at the various cable companies, virgin media included, that signed off on procuring the the puma 6 chipset and the buffoons at arris et al that made the routers.

They're the last people I'd pick.

[wotusaw]

@cje85

Were you on the original trial firmware (9.1.116BA3)? VM told trialists to do a factory reset if they wanted to return to the standard firmware, but perhaps now it downloads the latest trial version instead. I might give it a go tomorrow when no one's using the internet. 

Yes, I was on the trial software. So think you are right.....https://www.youtube.com/watch?v=4An1BrG2u_4

[philjohn]

To be fair, testing in a lab is very different from it being in the real world, and they probably didn't bother to test latency spikes, only throughput.

Fortunately, Docsis 3.1 should improve things somewhat.

[Sephiroth]

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@philjohnwrote:

To be fair, testing in a lab is very different from it being in the real world, and they probably didn't bother to test latency spikes, only throughput.

Fortunately, Docsis 3.1 should improve things somewhat.

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Given that VM's engineers (the real ones) knew exactly what the PUMA 6 problem entailed (and which I set out a few posts back), they also knew that work towards a "fix" would have to be some sort of kludge that provided a better BQM and released some load on the Puma 6.  The lab tests would have been focused on that - the BQM.

[Guybrush85]

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@Sephirothwrote:

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@philjohnwrote:

To be fair, testing in a lab is very different from it being in the real world, and they probably didn't bother to test latency spikes, only throughput.

Fortunately, Docsis 3.1 should improve things somewhat.

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Given that VM's engineers (the real ones) knew exactly what the PUMA 6 problem entailed (and which I set out a few posts back), they also knew that work towards a "fix" would have to be some sort of kludge that provided a better BQM and released some load on the Puma 6.  The lab tests would have been focused on that - the BQM.

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Actually this passed cablelabs testing, which is just a tad higher up the chain as indeed it seems testing of latency doesn't seem to be a thing. There is also an argument to question the amount of channels bonded, the amount of CMTS load (ARP) for these tests, as there seems to be correlation between that an the issue. I think Xymox spent a fair bit of time trying to question if the testing methods are true to todays world. Ironically, it was cablelabs themselves bringing in AQM into 3.1 as they realise latency is a big deal 

At hub 3 trial, it wasn't until the 16+ DS channels came in that BQM started to look ugly, but despite this they sent it out. I don't think anyone knew the scale of the issue at that point, but it was certainly a warning!

[dossdes]

Update from a call I have just had with the broadband expert from virgin media ( I managed to get through to him after pushing for a 2ac for the last 3 months and having been promised one on 2 separate occasions and receiving SH3’s instead).

The firmware is being trialled for 3 weeks with selected users. Following that trial the firmware will be pushed out (which he reckons is slated for a three week period but reckons in his experience it will take more like 4). So in c 6-7 weeks all the hub 3’s will have the new firmware on them.

[richto]

Just to further feedback on the trial firmware - the latency is directly dependent on the load on the SH3. Which implies that it cant cope with even moderate traffic / connection loads without latency impact. See the graph below - the first part of which is downloading BitTorrent at circa 2MB/s and the second part is much lower background / email traffic:

 However it's certainly an improvement on the previous firmware.

[philjohn]

That's normal - any connection will see increased latency if you are hammering it with a torrent - lots of open connections and data flowing.

If you have your own router behind with proper QOS it won't be affected to the same extent.

My BT Infinity connection has increased latency during large downloads.

[Andrew-G]

"the latency is directly dependent on the load on the SH3"

So, as we all knew, the puny, gutless innards of the Hub 3 still aren't up to the job and never will be, and that's because they'd spent half the budget on the fancy designer casing, and the bulk of the remainder on the cardboard box the Hub 3 is delivered in.

Which doesn't bode well for the DOCSIS 3.1 Hub 4, does it?  Not only are DOCSIS 3.1 modems much more expensive than 3.0, but the processing required for speeds five times faster is going to be immense.  I wonder which corners they'll cut on that?

[richto]

"That's normal - any connection will see increased latency if you are hammering it with a torrent - lots of open connections and data flowing."

No it isn't. I see NO increase in latency on a non virgin connection / router with similar downloads. This is at only a circa 10% loading of the download bandwidth. The router cant keep up with even moderate traffic levels without latency spikes. That is not normal for such a device and you would not expect latency to climb until you saturate the link.

 "If you have your own router behind with proper QOS it won't be affected to the same extent."

I do, and it still is. This is running in modem mode.