[Outages-discussion] RoadRunner/Bright House cablemodem problems

[Frank Bulk]

Yes, there was/is an interop issue with how some CMTS and D3 modems dealt
with losing one or more bonded channels.  One of the ways to deal with a
missing service flow was just to reset the CM.  I've seen this feature
described as "cable modem reboot due to partial service" and "cable modem
reboot due to bonding recovery".

 

The DOCSIS MULPI spec, as written, has a very weak recovery mechanism for
downstream flows that get out of sync. It says that both 2 minutes *and*
1,000 out of order packets have to be passed for a service flow to be
recovered. Cisco CMTS, ARRIS CMTS, and many (most) operators that have
encountered out-of-range (OOR) agree that the MULPI specification is
insufficient in terms of out-of-order downstream flow recovery.  See section
9.2.4 bullet point four of
http://www.broadbandreports.com/r0/download/2055956~e8c5b3cd040e9b60a2e56421
526f80b9/365-095-20591_x2.pdf for details.

 

CM-STATUS messages are supposed to communicate the status of flows, but
earlier versions of one vendor's eMTA firmware did not support CM-STATUS
well. However, this vendor (not Moto) says they haven't had CM-STATUS
interop issues with ARRIS C4 CMTSs and Cisco 10K CMTSs in a couple of years.


 

Frank

 

From: Ryan McIntosh [mailto:rmcintosh at nitemare.net] 
Sent: Monday, September 16, 2013 3:43 PM
To: Frank Bulk
Cc: Jay Ashworth; outages-discussion
Subject: Re: [Outages-discussion] RoadRunner/Bright House cablemodem
problems

 

Sorry frank for the double post, I'm hating gmail today as I hit "reply" and
not "reply to all".

 

Generally speaking that sounds like a signal issue. The newer docsis 3
modems tend to issue a reboot or temporary port down while it resyncs the
channels (depending how many up/down its using). When a channel drops off or
is intermediate you'll get this temporary state of non-working port where it
reboots or blocks the port. So all in all, sounds like a signal problem,
even though you might have perfect signal.

Ryan

 

On Mon, Sep 16, 2013 at 4:35 PM, Frank Bulk <frnkblk at iname.com
<mailto:frnkblk at iname.com> > wrote:

Is this a Motorola gateway or cable modem?  Non-gateway cable modems
typically have just one Ethernet port.  How do you know it reboots versus
doing a T4 reset because of communication issues?

Frank


-----Original Message-----
From: Outages-discussion [mailto:outages-discussion-bounces at outages.org
<mailto:outages-discussion-bounces at outages.org> ] On
Behalf Of Jay Ashworth
Sent: Monday, September 16, 2013 3:11 PM
To: outages-discussion
Subject: [Outages-discussion] RoadRunner/Bright House cablemodem problems

On a new install for a client, we're seeing that the cable modem drops
out on us, and in a very interesting way.

Every so randomly often, it apparently does an uncommanded reboot (this
according to a guy who was logged into the CMTS looking at it one time it
did so), and when it does, 2 connected devices see the ethernet drop for 3-5

seconds, come back up for 15, then drop again for 3-5, and then go back
to normal.  I see this behavior logged exactly to the second on both the
attached Fortigate router and my Linux laptop; we've replaced the cable
modem and the ethernet cables coming out of it.

Oddly, it only seems to happen when there's traffic on the link; I haven't
seen a drop get logged when the link is idle (overnight/weekends).

The cablemodem is a DOCSIS3, Motorola Surfboard Extreme (that's not exact,
but I can provide a model number if anyone thinks it's critical).
Everything
in the cage is on a brand new 2000VA UPS.

Anyone ever seen a cablemodem misbehave in this particularly peculiar way
before?

Cheers,
-- jra
--
Jay R. Ashworth                  Baylink
jra at baylink.com <mailto:jra at baylink.com> 
Designer                     The Things I Think                       RFC
2100
Ashworth & Associates     http://baylink.pitas.com         2000 Land Rover
DII
St Petersburg FL USA               #natog                      +1 727 647
1274
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