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]

[shanematthews]

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@rio_w wrote:
How do you change the channel? I don't think you can do that from the Hub 3 web interface? Would it affect TV also?

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You can't, the modem channel config isn't user editable

[Datalink]

That would require a configuration change by the network engineering staff.  They could change the configuration of any one class or type of device without changing the configuration for any other class of device.  

[PhilHornby]

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@cje85 wrote:

The latency is bad on 24 channels, it doesn't have to be 32. 

I'm on a Cisco CMTS which sometimes only provides 8 downstream channels after a reboot, instead of 24.

When connected to 24 channels the latency spikes are noticeable, but on 8 channels it's almost as good as a Superhub 2.

I rebooted yetserday evening and went from 24 down to 8, and it made a clear difference with no random spikes

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 So...just musing...

If a "filter" were to be introduced into the link between Hub 3 and VM network, which lowered the amplitude of a large range of channels - to the point where the Hub 3 could no longer sync. with them, would that cure the problem?...

Such a "filter" might be something as simple as a Forward-Path Equaliser... or might need to be something more "active"...

[MUD_Wizard]

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@cje85 wrote:

The latency is bad on 24 channels, it doesn't have to be 32. 

No-one said it has to be 32.

"Also, the Puma 6 problem is worse the more channels you have. In the USA 32 channels are now more common, which is why they complain of jitter/latency spikes up to 200ms. Whereas here 16 to 24 channels are more common. When the hubs were supplied for use with 8 channels they worked fine with much less issue (excluding the early firmware bugs)."

[Exoticcshot]

When we getting a better router virgin media? So many problems with this hub3 and I think is time to go back to netgear just a modem will do so we can buy a good router from shops

[MUD_Wizard]

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@PhilHornby wrote:

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 So...just musing...

 If a "filter" were to be introduced into the link between Hub 3 and VM network, which lowered the amplitude of a large range of channels - to the point where the Hub 3 could no longer sync. with them, would that cure the problem?...

So you want to put your hub into partial service mode, where it can only lock-on to a subset of the Receive Channel Set. Even if it were possible the Hub is going to know it's only getting a subset as the channel list is given in the Mac Domain Descriptor broadcast on each channel. That problem is then going to be broadcast back to the CMTS. Expect some SYNC timeouts and some other side affects. The CMTS may automatically try to reboot your hub for example.

Such a "filter" might be something as simple as a Forward-Path Equaliser... or might need to be something more "active"...

A Forward Path Equaliser changes the slope of the channels power levels, but you still receive all the channels. 

[Datalink]

Yup, and that would probably result in data errors due to the low signal levels.  That's simply a result of the upper channel signal levels decreasing with frequency.  The only really good approach to this is for the CMTS to shut down those channels in the modem, but as I indicated earlier, that's a configuration change that has to occur. 

[PhilHornby]

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@Datalink wrote:

Yup, and that would probably result in data errors due to the low signal levels.

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I was looking to lower the levels of certain channels, to a point where the Hub 3 effectively didn't see them at all. Of course, I have no idea how much attenuation that requires in practice. I guess it would probably need to be much more 'notchy' than an FPE. See: http://www.electronics-tutorials.ws/category/filter

The question is, as @MUD_Wizard pointed out,  what would the Hub 3 make of it...

[BlackDwarf]

Last Sunday and today (while I was working from home I might add), my line was hit with 50%+ packetloss and pretty much entire loss of service. Router reboot didn't help, no line changes, no faults on the line or head end. In banging my head against a wall with first-line support, I was cold transferred to a Virgin Media Business tech rep (because I wondered if I could somehow be provisioned a business Hitron router), which actually ended up with me speaking to a nice sales rep and putting an order in for the 350/20 business service, which works out £20 cheaper than I'm paying for my **bleep** 300Mb Homeworks service and TV nobody watches.

Clarified strongly before ordering some issues I'd read on (e.g the Hitron can't do modem mode with a static - Apparently it can't with a single static, but is fine with a block (went with 5 free static IP's, why not), and throttling out of non-business hours, apparently there's none and business lines are less contended).

[MUD_Wizard]

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@BlackDwarf wrote:
Last Sunday and today (while I was working from home I might add), my line was hit with 50%+ packetloss and pretty much entire loss of service. Router reboot didn't help, no line changes, no faults on the line or head end.

If you have 50% packet loss on the VM end then you have a noise fault.

In banging my head against a wall with first-line support, I was cold transferred to a Virgin Media Business tech rep (because I wondered if I could somehow be provisioned a business Hitron router), which actually ended up with me speaking to a nice sales rep and putting an order in for the 350/20 business service, which works out £20 cheaper than I'm paying for my **bleep**ty 300Mb Homeworks service and TV nobody watches.

That's nice.

Clarified strongly before ordering some issues I'd read on (e.g the Hitron can't do modem mode with a static - Apparently it can't with a single static, but is fine with a block (went with 5 free static IP's, why not),

I wasn't aware they'd finished the firmware with the modem mode feature?

Modem mode with multiple static IP's works but not with a single static IP? That's odd. I'll have to get my Hitron out of moth-balls and try it as I have multiple static IP's.

The Hitron in router mode uses a dynamic IP address on the modem part the same way residential hubs do. The static IP's are implemented via a GRE tunnel between the Hitron and VM business, so terminate at the VMB server end, not at the Hitron. So if you switch it into modem mode how does it do the multiple IP's?

If you have issues with the static IP's, should I say when you have issues, ask business tech support to change to dynamic IP and the issues should disappear.. if they were related to the Hitron setup and not a repeat of your noise fault above, which can still happen because you're on the same coax cable, cabinets and node.

Difference between business and residential:

http://community.virginmedia.com/t5/Tech-Chatter/Business-vs-Residential-Broadband/m-p/3422163#M3165...

About the troubles business users have had getting static IP's to work reliably:

http://community.virginmedia.com/t5/Networking-and-WiFi/Business-Hitron-Router/m-p/3393501#M140026

and throttling out of non-business hours, apparently there's none and business lines are less contended).

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That's true, you're on a different line card and port at the CMTS from residential but you're still using the same frequencies as residential so can still get congestion on those frequencies (downstreams/upstreams) before it gets to the line card.