How can I get rid of continuous CM Errors - Uncorrectable Codewords ?

[LuizAlexandre]

I'm a brand new Comcast/Xfinity user and I got my internet (300Mbps) installed 10 days ago. Since the beginning I've noticed some intermitent and random packet loss (1% - 2%). I changed the modem 3 times and all 4 modems showed the same CM Errors with Uncorrectable Codewords in all columns.

I connected the modem to the grey box, outside of my house, and I noticed the errors are also happening when I plug it over there, so it doesn't seem to be related to my internal cabling.

I've opened a dozen of tickets with Comcast and a techinician came to my house, but he didn't have the tools nor the knowledge to do anything. He simply left, leving all my wires and cables exposed to the weather, and with the modem connected to the grey box.

I think it is an easy thing over the "last mile" but it seems nobody from Comcast is really trying to help me get it fixed.

Is there anybody from Comcast here that could help me with this issue?

[LuizAlexandre]

Here you are the data from my XB6 modem:

Downstream
Index	9	6	7	8	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32	33	34	35	36	37
Lock Status	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked
Frequency	543 MHz	525 MHz	531 MHz	537 MHz	555 MHz	561 MHz	567 MHz	573 MHz	579 MHz	585 MHz	591 MHz	597 MHz	603 MHz	609 MHz	615 MHz	621 MHz	627 MHz	633 MHz	639 MHz	645 MHz	651 MHz	657 MHz	663 MHz	669 MHz	675 MHz	681 MHz	687 MHz	762 MHz	693 MHz	699 MHz	705 MHz	711 MHz	659600000
SNR	40.4 dB	40.0 dB	39.7 dB	40.7 dB	39.6 dB	40.1 dB	40.3 dB	38.1 dB	41.2 dB	40.8 dB	40.6 dB	40.7 dB	41.0 dB	40.4 dB	40.7 dB	40.6 dB	40.0 dB	40.5 dB	40.3 dB	38.4 dB	40.6 dB	39.8 dB	39.3 dB	39.3 dB	40.5 dB	39.6 dB	39.9 dB	39.1 dB	40.4 dB	39.5 dB	38.9 dB	38.5 dB	NA
Power Level	-1.2 dBmV	-2.2 dBmV	-2.0 dBmV	0.2 dBmV	-2.9 dBmV	-2.8 dBmV	-2.5 dBmV	-1.0 dBmV	0.4 dBmV	0.1 dBmV	-2.1 dBmV	-1.7 dBmV	0.9 dBmV	0.2 dBmV	0.4 dBmV	0.4 dBmV	-2.0 dBmV	-2.0 dBmV	-1.8 dBmV	-1.8 dBmV	-1.8 dBmV	-3.4 dBmV	-4.1 dBmV	-2.6 dBmV	-1.7 dBmV	-2.0 dBmV	-2.8 dBmV	-5.2 dBmV	-3.2 dBmV	-4.6 dBmV	-5.3 dBmV	-4.5 dBmV	NA
Modulation	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	OFDM	256 QAM	256 QAM	256 QAM	256 QAM	OFDM
Upstream
Index	1	2	3	4
Lock Status	Locked	Locked	Locked	Locked
Frequency	35 MHz	29 MHz	23 MHz	16 MHz
Symbol Rate	5120	5120	5120	5120
Power Level	43.3 dBmV	43.5 dBmV	43.8 dBmV	42.5 dBmV
Modulation	QAM	QAM	QAM	QAM
Channel Type	ATDMA	ATDMA	ATDMA	ATDMA
CM Error Codewords
Index	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32
Unerrored Codewords	129741384	129677779	129683737	129688132	129690008	129693662	129698301	129703047	129709181	129713324	129718688	129722873	129725898	129730171	129734808	129738059	129741000	129744988	129745882	129749890	129752246	129754279	129754522	129757195	129758848	129752495	129749240	8564857	129742276	129741795	129741245	129741384
Correctable Codewords	41023	9617	9066	9668	10891	11734	11823	12148	11845	12471	12662	13235	14057	14441	14776	14986	16891	17598	18918	19678	20857	22613	25496	26216	27899	28801	31647	1071287	33712	36697	39313	41023
Uncorrectable Codewords	32337	5493	6312	6447	7501	7778	8188	8278	8358	8656	9234	9098	9566	10217	10441	11009	11824	12640	13851	14824	15697	17110	19098	20230	21858	22928	25251	0	26109	28413	31349	32337

[EG]

What do the modem's signal stats look like ? Try getting them here http://192.168.100.1 or here http://10.0.0.1

Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.

What is the exact make and model number of the modem ?

Is this a WiFi connection ?

[LuizAlexandre]

---

@EG wrote:

What do the modem's signal stats look like ? Try getting them here http://192.168.100.1 or here http://10.0.0.1

Please post the *Downstream Power Level*, the *Upstream Power Level*, and the *SNR* (Signal to Noise Ratio) numbers.

What is the exact make and model number of the modem ?

Is this a WiFi connection ?

---

Hi @EG , I included the power levels and SNR info in my first reply. Here you are the details of my modem:

HW Version:2.2

Vendor:Technicolor

BOOT Version:S1TC-3.49.18.14

Core Version:1.0

Model:CGM4140COM

Product Type:XB6

Flash Part:8192 MB

Download Version:Prod_18.1_d31 & Prod_18.1

I'm getting those errors in both cases, even if I disable wifi and only work using the ethernet cable.

Thanks,

Luiz

[EG]

Sorry, my bad. The stats are o/k. See if you can get the RF error log entries and post them too please.

[LuizAlexandre]

I can only see System, Event or Firewall logs. This is the System Logs since the last reboot:

System Logs
All logs for Today
GUI: User:admin login	11/19/2019 14:33	Notice
GUI: User:admin logout	11/19/2019 14:28	Notice
[IGD][10025]: Delete Port mapping (null):36395	11/19/2019 14:16	Notice
IGD[10025]: igd.info IGD_pii_del_portmapping_entry: remote-host (null), ext_port 36395, protocol UDP	11/19/2019 14:16	Notice
[IGD][10025]: Add Port mapping :36395 to 10.0.0.163:36395	11/19/2019 14:15	Notice
IGD[10025]: igd.info IGD_pii_add_portmapping_entry: desc WhatsApp (1574190899) (), ext_port 36395, int_port 36395	11/19/2019 14:15	Notice
GUI: User:admin login	11/19/2019 14:11	Notice
GUI: User:admin logout	11/19/2019 13:56	Notice
[IGD][10025]: Add Port mapping :49525 to 10.0.0.236:49525	11/19/2019 13:45	Notice
IGD[10025]: igd.info IGD_pii_add_portmapping_entry: desc Teredo 10.0.0.236:49525->49525 UDP, ext_port 49525, int_port 49525	11/19/2019 13:45	Notice
GUI: User:admin login	11/19/2019 13:39	Notice
GUI: User:admin logout	11/19/2019 13:36	Notice
GUI: User:admin login	11/19/2019 12:53	Notice

[EG]

The router component logs are not helpful, sorry. Yep, we've seen many posts here recently indicating that they have now blocked the end user from accessing the error logs in the Comcast supplied gateway devices. A BIG mistake in my opinion......

[EG]

---

@LuizAlexandre wrote:

I'm getting those errors in both cases, even if I disable wifi and only work using the ethernet cable.

---

O/k but are you getting packet loss via hardline ethernet ?

[LuizAlexandre]

Since that's intermitent and I changed the modem 3 times already,  I'll work hardwired tomorrow to validate that's still happening.

I'll post an update tomorrow.

[LuizAlexandre]

I've tested internet connectivity this morning and I did not miss any "ping" packets while connected via wireless or wired, but my CM errors are still piling up:

CM Error Codewords
Index	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32
Unerrored Codewords	4020924988	4023106335	4023030075	4022990056	4022826309	4022799098	4022785301	4022794968	4022790033	4022773107	4022727686	4022681407	4022655799	4022610742	4022553746	4022499611	4022390197	4022306239	4022216140	4022122979	4022022301	4021905841	4021783980	4021728565	4021613416	4021538057	4021402659	601993134	4021302061	4021151652	4021004116	4020924988
Correctable Codewords	1397702	553294	580428	593651	657425	667036	676404	671482	672856	679465	702511	723220	730743	749328	771900	787584	834981	868115	898634	934160	973910	1026920	1079709	1086947	1139066	1153714	1208323	36773924	1247911	1317106	1376695	1397702
Uncorrectable Codewords	2304959	850453	904351	936423	1039345	1061897	1072269	1072666	1088807	1102634	1131541	1161924	1183051	1216226	1255418	1296960	1366097	1421331	1486117	1547833	1614216	1681894	1756046	1808898	1875936	1934385	2015871	57	2066356	2153594	2247925	2304959

[LuizAlexandre]

Hi @EG , is there anything I can/should do to eliminate the CM Errors?

[EG]

Well there will always be a certain amount of errors accumulating, it's how rapidly that there are (or are not) building up that matters. And depending on the total amount of uptime of the modem from the last re-boot / reset operation, If you compare the ratio of uncorrectable codewords to the un-errored codewords, there really may not be all that many considering. The bottom line is if you are actually having any noticeable connection / speed / performance problems.

[LuizAlexandre]

Got it .... I'll keep an eye on it and get back here if I see anything impacting my connectivity or performance.

Thanks !!!

Luiz

[EG]

Re-boot / power cycle the modem to start from scratch in order to be able to judge how fast that they are accumulating.

[LuizAlexandre]

Hi EG,

The issue is a lot worse over the past months and I'm now being disconnected from the internet several times a day. The connection is restablished in a matter of a minute, or sometimes around 30 seconds.

I restart my modem every once in a while, but it doesn't help. I really think there is some noise coming from outside since I already connected the modem to the grey box, outside of my house, and I noticed the errors are also happening when I plug it over there, so it doesn't seem to be related to my internal cabling.

Is it possible to open the logs of my modem to identify if it is losing the sync to the Xfinity equipments?

Thanks,

Luiz

[LuizAlexandre]

These are the current numbers of my modem and they grow really fast:

Downstream	Channel Bonding Value
Index	29	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45
Lock Status	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked
Frequency	621 MHz	525 MHz	531 MHz	537 MHz	543 MHz	555 MHz	561 MHz	567 MHz	573 MHz	579 MHz	585 MHz	591 MHz	597 MHz	603 MHz	609 MHz	615 MHz	627 MHz	633 MHz	639 MHz	645 MHz	651 MHz	657 MHz	663 MHz	669 MHz	675 MHz	681 MHz	687 MHz	693 MHz	699 MHz	705 MHz	711 MHz	762 MHz	659600000
SNR	41.1 dB	40.4 dB	40.3 dB	40.8 dB	40.9 dB	39.6 dB	40.3 dB	40.4 dB	41.0 dB	40.6 dB	41.3 dB	40.1 dB	40.5 dB	40.6 dB	40.9 dB	40.7 dB	40.3 dB	40.0 dB	40.2 dB	40.1 dB	40.2 dB	39.5 dB	39.5 dB	40.1 dB	39.4 dB	40.4 dB	39.7 dB	39.5 dB	39.4 dB	39.1 dB	39.3 dB	38.5 dB	NA
Power Level	-3.6 dBmV	-5.3 dBmV	-4.7 dBmV	-2.8 dBmV	-3.4 dBmV	-4.9 dBmV	-4.9 dBmV	-4.5 dBmV	-3.2 dBmV	-3.0 dBmV	-2.2 dBmV	-4.4 dBmV	-4.6 dBmV	-4.0 dBmV	-3.3 dBmV	-3.3 dBmV	-5.2 dBmV	-5.2 dBmV	-4.8 dBmV	-4.9 dBmV	-4.6 dBmV	-6.2 dBmV	-6.9 dBmV	-5.2 dBmV	-4.3 dBmV	-4.6 dBmV	-5.2 dBmV	-5.5 dBmV	-6.7 dBmV	-7.3 dBmV	-7.0 dBmV	-7.6 dBmV	NA
Modulation	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	OFDM	OFDM

Upstream	Channel Bonding Value
Index	1	2	3	4	5
Lock Status	Locked	Locked	Locked	Locked	Locked
Frequency	35 MHz	29 MHz	23 MHz	16 MHz	39 MHz
Symbol Rate	5120	5120	5120	5120	1280
Power Level	43.3 dBmV	43.5 dBmV	43.8 dBmV	42.5 dBmV	44.0 dBmV
Modulation	QAM	QAM	QAM	QAM	QAM
Channel Type	ATDMA	ATDMA	ATDMA	ATDMA	ATDMA

CM Error Codewords
Index	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32
Unerrored Codewords	260147780	608227786	607522424	608393007	606958161	606090728	606000572	605764928	605830284	603925662	602571657	599687139	596625175	594765827	592754474	589707915	582817198	578765005	575833726	572711272	570760509	564640766	560314259	558159164	553519010	551447054	546264275	541408640	535083170	528868274	525594229	260147780
Correctable Codewords	3311262301	25646852	25814973	25266786	25825756	26319100	26342109	26356857	26274268	26934422	27355153	28562487	29723707	30305792	30911090	31989662	34863269	36289132	37245592	38470316	39055643	41644056	43522445	43643718	45533513	45879610	47899351	49710757	52473698	54898234	55801870	3311262301
Uncorrectable Codewords	145170	42898991	43456354	43129988	44026878	44408060	44478274	44724787	44911154	46162468	47113882	48800451	50654336	51982099	53398941	55363623	59809951	62438642	64422700	66324457	67679251	71241379	73695911	75722521	78452388	80202720	83381819	86443163	90004488	93772384	96161219	145170

[LuizAlexandre]

Interesting ... today I got the results of the modem while I had an outage. It seems the upload channels are the ones losing the sync:

Downstream	Channel Bonding Value
Index	29	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	30	31	45
Lock Status	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked	Locked
Frequency	621 MHz	447 MHz	453 MHz	459 MHz	465 MHz	471 MHz	477 MHz	483 MHz	489 MHz	495 MHz	501 MHz	507 MHz	513 MHz	519 MHz	525 MHz	531 MHz	537 MHz	543 MHz	555 MHz	561 MHz	567 MHz	573 MHz	579 MHz	585 MHz	591 MHz	597 MHz	603 MHz	609 MHz	615 MHz	627 MHz	633 MHz	762 MHz	659600000
SNR	39.5 dB	39.4 dB	38.9 dB	39.0 dB	39.9 dB	39.9 dB	38.4 dB	38.6 dB	38.4 dB	38.6 dB	35.9 dB	34.1 dB	38.2 dB	36.5 dB	39.2 dB	38.9 dB	40.2 dB	39.0 dB	39.6 dB	39.4 dB	39.3 dB	37.4 dB	38.7 dB	39.6 dB	39.4 dB	39.4 dB	39.7 dB	39.8 dB	39.3 dB	39.1 dB	38.9 dB	37.5 dB	NA
Power Level	-5.8 dBmV	-6.7 dBmV	-7.2 dBmV	-7.0 dBmV	-5.9 dBmV	-5.2 dBmV	-6.7 dBmV	-8.4 dBmV	-7.8 dBmV	-7.5 dBmV	-6.8 dBmV	-7.0 dBmV	-7.0 dBmV	-7.4 dBmV	-6.9 dBmV	-6.5 dBmV	-4.7 dBmV	-5.4 dBmV	-7.6 dBmV	-7.5 dBmV	-7.2 dBmV	-5.7 dBmV	-5.4 dBmV	-4.5 dBmV	-6.7 dBmV	-6.8 dBmV	-6.2 dBmV	-5.5 dBmV	-5.5 dBmV	-7.3 dBmV	-7.2 dBmV	-10.1 dBmV	NA
Modulation	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	256 QAM	OFDM	OFDM

Upstream	Channel Bonding Value
Index	1	2	3	4	5
Lock Status	Not Locked	Locked	Not Locked	Locked	Not Locked
Frequency	35 MHz	29 MHz	23 MHz	16 MHz	39 MHz
Symbol Rate	5120	5120	5120	5120	1280
Power Level	44.5 dBmV	43.5 dBmV	43.8 dBmV	42.3 dBmV	39.3 dBmV
Modulation	QAM	QAM	QAM	QAM	QAM
Channel Type	ATDMA	ATDMA	ATDMA	ATDMA	ATDMA

CM Error Codewords
Index	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31	32
Unerrored Codewords	52078866	233856138	233789808	233641051	233449452	233599205	233893586	233976706	233948926	233888447	233843283	233772597	233688156	233604826	233573037	233586179	233603461	233583207	233582915	233574902	233574722	233573891	233557214	233532804	233497471	233452270	233444190	233413089	233366984	233257915	233182872	52078866
Correctable Codewords	45954107	143094	170756	233491	313507	252114	136453	106329	119088	145642	164886	196522	232959	269280	281168	277639	270561	281065	283663	290657	289978	292066	298902	310384	331744	349746	353655	365626	386471	429757	461875	45954107
Uncorrectable Codewords	7	195546	238433	329372	446265	361917	188441	140408	160833	199453	230965	274437	327555	378916	403653	398817	393038	407828	410346	416213	421665	425095	441986	459976	479486	510842	520273	544725	573496	640846	684937	7

[EG]

The downstream power is even weaker now than when you first posted here last November, and it may be intermittently fluctuating even lower to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, and latency problems.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

[LuizAlexandre]

Hi EG,

I have this same issue even if I connect my modem to the Comcast box that's outside of my house.

Is there a way to ask Comcast to review their outside cabling knowing it is bad when it gets into my house ?

Thanks,

Luiz

[EG]

A premises facing tech can check the cabling / hardware (including the drop line) up to the tap on the pole / pedestal. From the tap and farther up the line is the responsibility of their line / maintenance dept. techs.

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home.