11-08-2011 10:15 AM - edited 11-08-2011 10:49 AM
I live in the Minneapolis, MN market and I have attempted to use 2 brand new Moto SB6121's. Both are reciving the 'No ranging response received, T3 timeout' errors you described, I receive this error every few minutes. Each time one of the timeouts occurs I drop 2-3 pings. This results in a net loss of 3%-4% of my packets over the course of 1000 pings. I have run this test multiple times and with multiple computers going both inbound to just the modem IP and outbound to a multiple remote host's from two different computers on my network with a wired connection. The issue IS the modem but comcast can't isolate why. I am also running 188.8.131.52 moto firmware.
If I swap the modem for the Arris Gateway the tech gave me when he was onsite everything works flawlessy. My plan is to go to the local comcast service center and swap my rented Arris gateway for a rental modem. Whatever rental modem I receive I will likely try and purchase online if it works instead of the SB6121.
FYI. I have swapped ethernet cables, used two different computers and I tried both NICs in each computer. I have also disconnected my router and direct connected to the modem. No matter what, I still receive the 'no ranging response received, t3 timeout', resulting in dropped ICMP packets. Lastly, Comcast TAC indicated when they ping my modem with not ethernet attached they still see the dropped packets. The comcast tech that came onsite verified mutlitple times he receives zero packet loss when direct connecting to the cable with his testing unit.
I called Motorola about the issue and we verified SNR and power levels. Motorola said I couldn't ask for a more perfect signal. 4 downstream with 36-37-37-37 SNR and 0dBmV power across the board. My single upstream connection power level was 43dBmV. There was almost no flucuation in power or SNR levels when refresshing over the course of a few minutes. The only thing that changed was the SNR value of downsteam channel 2, the SNR went from 37 -> 36 once.
I have no other explanation for this besides that there is some capatability issue between the comcast node I am attached to and the SB6121 with firmware 184.108.40.206.
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11-08-2011 10:21 AM - edited 11-08-2011 10:22 AM
There are two additional signal stats which can't be read at the modem level. They can only be read from their end by them polling the CMTS (Cable Modem Termination System) at the local headend facility.
They are the 'Upstream Receive Power Level' and the 'Upstream uSNR' (upstream Signal To Noise Ratio). Both of these are as equally important in diagnosing connectivity issues as are the modem's stats.
You can call in and ask what these figures are. The Upstream Receive Power Level should fall within the range of -10dB to +10dB with 0dB being in the middle and perfect.
The Upstream SNR should be least 30dB, and the higher it is the better. Perhaps there is an intermittent noise ingress issue in the upstream channel.
11-08-2011 10:44 AM - edited 11-08-2011 11:09 AM
Unfortunately I didn't ask for those stats when I was on the phone with Comcast support. The fact that both SB6121's are exhibiting identical behavior in the T3 timeouts and dropped packets leads me to believe it is not a modem hardware issue.
I also don't believe this to be a 'line' issue since the Arris Gateway doesn't have any issues. Line issues being interference that may affect the uSNR and receive power. I believe this is key as it rules out not only the line outside my residence but it also rules out the splitter I am using at the ingress that splits to the cable TV connection and the other to my modem.
I could reprovision the SB6121 tonight and grab those stats if anything thinks getting them would really be beneficial knowing everything I just mentioned.
11-08-2011 07:59 PM
I have heard nothing but great things about the SB6121 so I don't know if I would call this evidence to not get it. I believe my case is unique.
In fact, I went to a comcast service center tonight and picked up a Cisco DPC-3000 and I just got it provisioned. I am experiencing the exact same packet loss behavior with this modem as well. The only thing that has worked for me is the Arris Gateway device, which I hate because it is a Gateway and I want to do my own routing.
I have a second tech visit scheduled for tomorrow or Thursday, we'll see what happens.
11-09-2011 06:22 PM
Well guys the second tech came onsite and replaced my Cisco DPC3000 device with another Arris Gateway. Once again the Arris Gateway is working flawlessy from a packet loss perspective. The tech said this was the only device they stock at the warehouse and he was unable to get me just a modem. I was told by both the onsite tech and the Comcast call center all I can do is try my luck at the local Comcast Service center and see if they have the particular modem I want in stock.
What I want to try next is the Arris WBM760A modem as Arris devices are all that have worked at my residence so far. Unforunately no one at Comcast was able to help me get this device, including the Duty Manager at the call center.
Note everyone, you will get far better results from Comcast support and all support vendors in general if you are patient and calm with them. Everyone I spoke with was very helpful and did everything they had in their power to do.
I am likely going to try my luck at the service center for a few weeks on lunch break and I may even call the tech that came onsite and ask him to keep his eye out for the modem.
Can anyone thing of anything else I can do?
11-10-2011 12:21 AM
The frustration ends.... while over at broadband forums I found out we can set the gateway mode to bridged. I called Comcast and was able to get it switched over within a 60 second phone call. Ideally I wouldn't be renting a modem and using this god foresaken device, but it does give me fanstictic speeds and it doesn't drop packets, so I am happy.
Thanks for the help everybody.
06-23-2012 12:58 AM
Since I found this posting trying to solve my problem, it seemed to be a good place to post what I found out when I was getting a Packet lost about every 8 pings, determined by running the following from a windows command prompt: "ping -t 220.127.116.11". I did item number 2 below first which seemed to improve performance but when I would download a large file the download would keep pausing and I'd get Packets lost in the ping results, item number 1 seemed to help with that.
I tried the 2 individually while downloading large files on multiple computers and had issues, it seems most of the issues I had went away when I had both of these 2 options set, though I did just set this up today.
My Devices are SB6121 Modem, Linksys EA3500 Dual-Band Router, Intel Wireless AGN Adapter. I use Comcast Performance Internet only, 12 mbps
Here's what I did and is working for me, your hardware might be different so this might not work for you. MAKE A NOTE OF WHAT YOU CHANGED IN CASE YOU NEED TO CHANGE IT BACK:
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