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

Datalink
Up to speed

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]

4,478 REPLIES 4,478


@Xymox wrote:

 

The reason Intel and Arris and Virgin did not catch it is there are *NO* standards in place for DOCSIS modems for performance. They meet spec even if they dont pass UDP at all. There simply are no testing procedures at all for performance. SOOO no one was testing AT ALL. As utterly insane as that sounds its 100% true. Ive talked to a lot of people, even some who make modem chips, no one was testing for performance because there is not standard for performance testing and no requirement for it.

 


Intel and Arris are one thing, but ISP's like Virgin actually have a bit of a get out here when it comes to the Puma 6. Back when the SH3 was being tested, by far the most common network configuration here was 8 downstream channels, with upgrades to 10 or 12 starting in the month or two following the initial tests. On 8 channels the Puma 6/SH3 actually compares fairly favorably. Latency is a little bit worse (which was picked up on in late 2015), but not as significantly so and thus very easily 'ignored' as not a big issues for the ISP seeing those results. Now once the bonded group grows the issue gets much much worse which is what we started to see at >16 channels, however this was a few months down the line and I suspect the roll out was already committed by that time.

I'm not sure what network configurations other cable ISPs around the world would have been running at that time (Q3 2015), but any tests on a ~8 DS group wouldn't have looked all that bad in initial testing.

Just to add to this, when the Puma 6 chipset was first announced, back around 2012, 24 and 32 channel DOCSIS CMTS servers probably hadn't been built or manufactured.  So, the chipset was built with future expansion in mind, but, I doubt that there was any method of testing the higher channel configurations. Fast forward a few years where 24 to 32 channels downstream are common, and now the choice of software processing in the CPU instead of thru the hardware processor/accelerator onboard the chipset starts to look like a bad design choice in terms of what the firmware does with the available hardware resources, and when. 

Yep we are now starting to correlate that the Puma 6 is way worse the more channels. AND we have a good report that the number of upstream channels is a big factor in addition to downstream. I would also guess the constallation size might even matter, so QAM 256 vs say QAM 64..

What we need is a CMTS on a bench with a modem where we can try out all modulations and configs. IE Cablelabs should have done this.

This is kinda a fun chart..  The Puma 6 is producing jitter and latency that makes it a way worse performer then a 2009 modem.

2100VS6190TCP.gif

wotusaw
Superfast

Amazingly, amazing!

You would think that they might like to know how their machine was performing before throwing it out to the hungry masses, wouldn't you.

Thanks for all the info, Xymox1. Very enlightening.Smiley Surprised


@wotusaw wrote:

Amazingly, amazing!

You would think that they might like to know how their machine was performing before throwing it out to the hungry masses, wouldn't you.

Thanks for all the info, Xymox1. Very enlightening.Smiley Surprised


Well they would have known how it was performing on the most common configuration at the time the unit was developed, these things don't just produce themselves overnight and despite the hub3 being "new" to VM, the unbadged unit isn't exactly new tech http://www.arris.com/globalassets/resources/data-sheets/tg2492s3.pdf the copyright on this document is 2015, so assuming it was probably being developed for atleast 6 months prior to that if not longer, you're looking at testing done in about 2014, in which time a LOT can change


@shanematthews wrote:

@wotusaw wrote:

Amazingly, amazing!

You would think that they might like to know how their machine was performing before throwing it out to the hungry masses, wouldn't you.

Thanks for all the info, Xymox1. Very enlightening.Smiley Surprised


Well they would have known how it was performing on the most common configuration at the time the unit was developed, these things don't just produce themselves overnight and despite the hub3 being "new" to VM, the unbadged unit isn't exactly new tech http://www.arris.com/globalassets/resources/data-sheets/tg2492s3.pdf the copyright on this document is 2015, so assuming it was probably being developed for atleast 6 months prior to that if not longer, you're looking at testing done in about 2014, in which time a LOT can change


That's great and all but the latency issues were brought up in the SH3 beta trials so VM were very much aware there was an issue before deploying it to the masses....


@boltedenergy wrote:

@shanematthews wrote:

@wotusaw wrote:

Amazingly, amazing!

You would think that they might like to know how their machine was performing before throwing it out to the hungry masses, wouldn't you.

Thanks for all the info, Xymox1. Very enlightening.Smiley Surprised


Well they would have known how it was performing on the most common configuration at the time the unit was developed, these things don't just produce themselves overnight and despite the hub3 being "new" to VM, the unbadged unit isn't exactly new tech http://www.arris.com/globalassets/resources/data-sheets/tg2492s3.pdf the copyright on this document is 2015, so assuming it was probably being developed for atleast 6 months prior to that if not longer, you're looking at testing done in about 2014, in which time a LOT can change


That's great and all but the latency issues were brought up in the SH3 beta trials so VM were very much aware there was an issue before deploying it to the masses....


Thing is, they say "beta trials" at this point they are already set on ordering and deploying the unit and are likely already training staff to install and troubleshoot them along with stocking up the required warehouses, the issue also doesn't affect most standard traffic and unless the closed pre-beta testing involved a lot of hardcore gamers and streamers the unit wasn't stress tested before the beta trial, at which point they probably could have backed out of the deal, once its wearing VM colours its almost guaranteed to arrive, so yes they would have been aware of a few instances of issues but they were clearly not widespread enough to actually need drastic action taken and likely would have fallen within the margin of error for testing purposes, they would also have assumed most issues could be patched with a firmware update, they now know better but hindsight is a wonderful thing

One of the core guys on our DSLReports thread has a very clear description of whats going wrong. In case anyone was wondering..

Mackey:

The observed behavior of this modem is clearly unintentional, just like the IPv6 TCP option mangling bug in the SB6183

The hardware packet processor just cannot handle the DOCSIS required filtering, so packets are processed by the software. For protocols/connections it knows about, once a connection is established it hands just that connection off to the hardware packet processor. The observed behavior shows that once the hardware accelerator takes over there are no more losses or huge spikes, though there does seem to be a bit more baseline jitter (which affects every protocol) then Broadcom based units. In order to correctly identify a flow the modem needs to understand the underlying protocol, so unknown or unhandled protocols cannot be hardware accelerated.

Peter_JS
On our wavelength

Hi Xymox,

Thanks for this, this explanation is useful. Such a design makes the device quite flexible; however the level of performance impact (circa 5 to 6ms) is really poor. It also suggests that for certain flows or protocols it may always perform fairly badly. It does not obviously explain why the latency issue appears to scale with number of channels being bonded; unless there is a resource trade off within the device between physical layer aggregation, (or channel equalisation, say) and packet inspection/flow processing; ie there's not enough resource like internal RAM or cache(?) to do it all at once.

BR

Peter

 

Peter_JS
On our wavelength

Hi guys,

Short follow up. Package arrived in the post yesterday from VirginMedia! Its my Superhub2ac!??

No.... its not....its another Superhub 3. <sigh>

1.5 hours later on the phone and I have the following result:

1) A SuperHub 2ac was ordered, but was fulfilled by a Superhub3, according to the person I spoke to, its likely Virgin has run out.

2) I have managed a downgrade to my original Superhub...which is a SH1 (boo, I thought it was a SH2)

Spot the difference below.

 

 

Switch from SH3 to SH1Switch from SH3 to SH1

Note the difference not just in peak, but also in minimum and average.

Here's a graph of a local ping to the SH1, via my Asus router. Please refer to my original graphs of SH3 on page 53 of this thread for comparison.

Local ping of SH1Local ping of SH1

 

BR

Peter