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Downstream OFDM Power Level (New Gigabit Install)

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Downstream OFDM Power Level (New Gigabit Install)

I am a new comcast customer and don’t know what to really expect with DOCSIS 3.1 and power levels. I’m running an SB8200 with Gigabit tire speed. I have been getting some packet loss and speed fluctuations under load. Tested with ethernet from the modem, router and computer. I have read that downstream OFDM channels are used for gigabit. Is 12.0 dBmV on my downstream OFDM channel (159) normal? If feels high? I called Comcast and they basically told me to call Arris for support or lease a modem (XB6) to troubleshoot further as they didn’t see any issues. The call center tech also said that he couldn’t see anything on the signal specs for the SB8200. The only thing he could do is reprovison the modem which didn’t fix things.
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Accepted Solutions
Authorized Vendor

Re: Downstream OFDM Power Level (New Gigabit Install)

Your looking better right now then you did before..  Are you seeing the same on your side?

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Network Engineer, IP Engineer, Docsis..; the views expressed on this post are mine and do not necessarily reflect the views of my employer..

Gamer.. Living the dream one catastrophe at a time Smiley Happy ..

All Replies
Regular Contributor

Re: Downstream OFDM Power Level (New Gigabit Install)

Personally I wouldn't worry about it too much.  Your power levels look consistent on the non-OFDM channels and that's where the bulk of your data will be passing.  I've got the MB8600 and it's been rock solid for the most part other than needing a reboot on 1/1 for some reason IP traffic dropped.  I haven't seen much issue with pings dropping either and got IPv6 enabled on the router the other day and traceroute's are mostly in v6 now and the hops are performing quite well for response times.  

 

If you're having issues though a direct Ethernet connection rules out any interference from the router.  I found an issue with my previous router even branded as AC / gig ports for the LAN it bottlenecked things to 250M but a direct connect yielded 950 x 45 on speedtests.  With some other equipment I was having issues with ping spikes from 10-20ms to 800+ ms and finally figured out it was the WIFI on the modem when I hooked up the router and put it in bridge mode it went away.  So, sometimes it just takes a few tries to get things optimised.

Authorized Vendor

Re: Downstream OFDM Power Level (New Gigabit Install)


mrumppe wrote:

Personally I wouldn't worry about it too much.  Your power levels look consistent on the non-OFDM channels and that's where the bulk of your data will be passing.


Just an FYI this is not true and it really depends on the gear..  But basicly the bulk of the traffic will run on the OFDM channel in most cases..

-------------------------------------
Network Engineer, IP Engineer, Docsis..; the views expressed on this post are mine and do not necessarily reflect the views of my employer..

Gamer.. Living the dream one catastrophe at a time Smiley Happy ..
Authorized Vendor

Re: Downstream OFDM Power Level (New Gigabit Install)


McPolygon wrote:
I am a new comcast customer and don’t know what to really expect with DOCSIS 3.1 and power levels. I’m running an SB8200 with Gigabit tire speed.

I am going send you a PM I will need the CM-MAC to take a look at the modem and the CMTS side of things..

-------------------------------------
Network Engineer, IP Engineer, Docsis..; the views expressed on this post are mine and do not necessarily reflect the views of my employer..

Gamer.. Living the dream one catastrophe at a time Smiley Happy ..
Authorized Vendor

Re: Downstream OFDM Power Level (New Gigabit Install)

Your looking better right now then you did before..  Are you seeing the same on your side?

-------------------------------------
Network Engineer, IP Engineer, Docsis..; the views expressed on this post are mine and do not necessarily reflect the views of my employer..

Gamer.. Living the dream one catastrophe at a time Smiley Happy ..
Regular Visitor

Re: Downstream OFDM Power Level (New Gigabit Install)

Solution was to get an XB6 gateway. I get the full 940mbps with that modem/router. I’ll hold onto the SB8200 until whatever is going on with it is resolved via firmware. Not sure why but the speed would range from 500-780mbs on the Arris modem but full speeds with the XB6...