These messages are the direct result of return path noise causing frequent profile change requests from the CMTS. I’m confident that the root cause we are seeing with DOCSIS 3.1 modems when using OFDMA on noisy upstreams is likely related to DBC messages. I have seen this on DOCSIS 2.0 modems when we started load balancing and for dynamic quality of service (DQoS), and DOCSIS 3.0 modems for channel bonding changes, load balancing and DQoS. This change is done dynamically.ĭynamic changes to modems have historically caused them to crash. If so, the CMTS will use a dynamic bonding change (DBC) messages to move each modem a higher order modulation profile. Once the modem is online, the CMTS will check if the upstream supports a higher order modulation for each modem. This should be configured to be a low order modulation like 16-QAM so that it is resilient to any noise and ensures the modem will come online. When a DOCSIS 3.1 modem first comes online and communicates with the CMTS using an upstream OFDMA channel, the CMTS will first set the modem’s OFDMA upstream data profile (OUDP) to IUC 13.
This is what often triggered DOCSIS 2.0 and 3.0 crashes, so it’s very likely this is what is causing DOCSIS 3.1 crashes. These mechanisms are usually associated with dynamic changes in the modem. To understand why a cable modem crashes, we must understand what mechanisms are at play that can cause the potential crash or BSoD. But why is this noise causing the modems to crash? Unfortunately, but to be expected, crashed cable modems are back again for DOCSIS 3.1 when they are locked to an OFDMA channel with lots of noise.
#OFDM DOCSIS 3.1 WINDOWS#
We rarely see the dreaded blue screen of death in Windows anymore and it is infrequent in cable modems as long as their firmware is kept up to date. Along the way vendors fixed the bugs, just like Microsoft has fixed their bugs. With new technology there will always be bugs to work out of the system. It happened when DOCSIS 2.0 modems got off the ground, then again when DOCSIS 3.0 modems rolled out. Being the resident helpdesk for my friends, family and neighbors I can say this with some degree of confidence that all these emotions are felt by subscribers.Ĭrashed modems are not new to the industry. To some subscribers this will cause just a bit of an annoyance, however, to other subscribers this will cause fear, panic and irritation. The CSR usually will instruct the subscriber to reboot the modem. This means the CMTS will report the modem as “online,” but if you ask the subscriber, they will respond with “my service is down and after this call I’m going on Facebook to trash talk you since clearly you cannot even tell that my service is down.” Now there are tools you can use to help avoid this situation which I will cover below.Ĭrashed modems can be hard to detect and they may result in a call to a CSR from the subscriber.
This creates a unique problem as most monitoring systems query the CMTS directly for the modem online status. Typically, we find that the cable modem stops passing traffic, however, the DOCSIS chipset is still online and shows “online” from the perspective of the CMTS.
A crashed modem happens when its internal operating system crashes. It indicates a system crash, in which the operating system has reached a condition where it can no longer operate safely.” įor years I and other fellow DOCSIS troubleshooting experts have referred to crashing modems as BSoD’d modems because just like Microsoft Windows it requires a reboot to fix. What is BSoD and how does it relate to modems?Īccording to Wikapedia, BSoD, is “A stop error or exception error, commonly called the blue screen of death (BSoD) or blue screen, is an error screen displayed on Windows computers following a fatal system error.
#OFDM DOCSIS 3.1 HOW TO#
What gives? I will cover what and why in this article and recommendations on how to avoid BSoD on OFDMA in the upstream. It’s the equivalent of the Microsoft Windows blue screen of death (BSoD) and it’s back with a vengeance for cable operators running DOCSIS 3.1 OFDMA with a noisy upstream.
The cable modem is on but there is no data flowing through it. Yes, we’ve seen this before: OFDMA + DBC = BSoD
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