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I have Extreme 50/10, I get 50M downloads, with no packet loss, but uploads are terrible. I was on Blast with 4m up, and just spent 2 months getting upgraded to Extreme at 10m. (although I still only get 2-3m upload speeds). In any case, when I upload (aka Voice or Video) at rates higher then 256K, I get 10-20% packet loss. It is not my voice/video equip, since it all works perfectly from my office. It is not the new Motorola Surfboard 6120 (Motorola support and Comcast checked it). It is not my home wiring - Comcast checked it twice, and we connected the modem direct to the cable at the street, and got the same result. It is not in Comcast backbone - Comcast Tier 2 spent a month checking it. It is not in Atlanta service, since other co-workers in metro Atlanta have no issues. It pretty much leaves the "last mile" or I should say "last 600 feet of overhead telephone pole wires". Which appear to be impossible to get checked. In fact Comcast claims "they have no way to test or certify that uploads are at rates speed or quality". Yet they advertise EXtreme 10M uploads speeds!. (Ironically, I work for Cisco, managing video deployments TO Comcast for their own internal deployment).
The 1-800-comcast tier1 one can not escalate, and claims they can only send a truck, or add in Tier2. Tier2 says they can only do testing of modem and main network - not local service. The house visit guys barely understand internet, and will not climb poles. Everyone says "contact local Comcast office". The local office says they just do payments, and equipment - and all they can do for service is... roll a truck.
Comcast appears completely clueless on how to test, yet alone deliver, the internet service they advertise.
Anyone out there have ideas? Give up and switch to U-Verse? Unfortunately, Verizon FIOS is not available in Atlanta,
Also, I use
www.speedtest.net to test speeds, using multiple computers,
to test packet loss and jitter.
In addition, using H.323 and SIP video endpoints (which all measure packet loss and jitter). And I am really getting upload packet loss of 10-20% - the remote sites (and loopback) all show terrible video, and low quality audio. As for Download, I usually have 0% packet loss - even with 720p video at 2Mb. Upload is pretty consistent packet loss even at speeds of 256K (2% at 256K and 20% at 1M).
Status from Surfboard 6120
Bonding Channel Value Channel ID 4 1 2 3
Frequency 699000000 Hz 681000000 Hz 687000000 Hz 693000000 Hz
Signal to Noise Ratio 36 dB 36 dB 36 dB 36 dB
Downstream Modulation QAM256 QAM256 QAM256 QAM256
Power Level -5 dBmV -3 dBmV -4 dBmV -5 dBmV
Upstream Bonding Channel Value Channel ID 1
Frequency 34800000 Hz Ranging Service ID 1275
Symbol Rate 5.120 Msym/sec
Power Level 40 dBmV
Upstream Modulation  QPSK  64QAM
Ranging Status Success
Signal Stats (Codewords) Bonding Channel Value Channel ID 4 1 2 3
Total Unerrored Codewords 569978575 569978873 569979050 569979140
Total Correctable Codewords 50 0 0 0
Total Uncorrectable Codewords 676 530 520 553
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' (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. You could have a noise ingress issue in the upstream channel.
Comcast came by Friday (third visit) to "fix cable". He did change the connectors at the top of the pole, but no change. Like the previous guy, he assured me that maintenance would check the overhead lines within 24 hours, and I would get a call or note..... nothing (I guess they will get to it Monday :-). Just checked packet loss and it has changed - now instead of 10-20, it is 30%. Interesting that the Comcast guy said he had a docsis 3.0 modem in his truck, but it has no "internet" on the back side, and can only be accessed remotely for testing DB, SNR, power, Hz. You would think they would have a (known good) provisioned modem they could connect, and be able to prove that it is not (or is!) their problem. On the positive side, I got a $20 credit because the issue required a second visit.
Well - miracles can happen. This morning I am running 2Mb video, with 0% packet loss!!! So it appears that the local maintenance service (maybe this morning) did repair something. The ONLY way to get local lines (on the street) checked is to have a repair call, and to convince the the repair guy to escalate to maintenance. The thought on my service was that copper was ok, since SNR, dB, and Power showed excellent, AND HD TV service, and internet downloads were also good, so not a layer 1 issue. The next is the "repeater" (the big aluminum box) where local copper is connected to big copper or fiber (Comcast claims there is NO fiber to the curb or last mile anywhere in Atlanta). I am speculating that they did something in this repeater - fixed connections, or replaced a card - since this appears to be where upload traffic is split off.
I think it only took 3 comcast visits, a dozen calls, and 2 months - but it (knock on wood) all seems to work now!
WIW, that "box" is a line amp/extender or a node device. Glad things got worked out for you ! Thanks for reporting back.