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sunmast
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Friday, March 29th, 2024 5:50 AM

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Upload Speed being throttled from 200Mbps to 40Mbps

I have a 1.2Gbps plan. A few months ago I received an email asking me to upgrade my modem to increase the upload speed from 40Mbps to 200Mbps. So I bought a new modem (Hitron CODA56), and the uploaded speed is indeed increased.

But since a while ago (maybe a few weeks back) the upload speed is throttled to 40Mbps again. It's obviously due to throttling because in every speed test the upload can reach about 200Mbps in the first few seconds, and then it will drop to about 40Mbps only.

The test is performed on my x86 router which is directly connected to the modem. I've tried restarting the modem, renewing IP addresses. Nothing helped.

To Xfinity support: please help/explain.

Thanks.

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2 months ago

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sunmast

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13 Messages

7 months ago

DOCSIS WAN

This menu displays both upstream and downstream signal parameters

Downstream Overview
Port ID Frequency (Hz) Modulation Signal strength (dBmV) Signal noise ratio (dB) Octets Correcteds Uncorrectables Channel ID
1 435000000 256QAM -2.700 40.946 3 * 2e32 + 1184038408 16 25 4
2 483000000 256QAM -1.100 40.366 3 * 2e32 + 1183033720 1 0 12
3 531000000 256QAM -0.200 40.946 3 * 2e32 + 1183042867 0 0 20
4 579000000 256QAM -0.400 40.946 3 * 2e32 + 1183043034 0 0 28
5 417000000 256QAM -2.900 40.366 3 * 2e32 + 1183047664 0 0 1
6 423000000 256QAM -2.800 40.946 3 * 2e32 + 1183052366 3 0 2
7 429000000 256QAM -2.600 40.366 3 * 2e32 + 1183038747 0 0 3
8 441000000 256QAM -2.400 40.946 3 * 2e32 + 1183015851 22 0 5
9 447000000 256QAM -2.300 40.366 3 * 2e32 + 1183025422 23 0 6
10 453000000 256QAM -2.200 40.946 3 * 2e32 + 1183057366 9 0 7
11 459000000 256QAM -1.700 40.946 3 * 2e32 + 1183061781 0 0 8
12 465000000 256QAM -1.600 40.946 3 * 2e32 + 1183075828 0 0 9
13 471000000 256QAM -1.500 40.946 3 * 2e32 + 1183080453 0 0 10
14 477000000 256QAM -1.000 40.946 3 * 2e32 + 1183085107 8 0 11
15 489000000 256QAM -0.900 40.946 3 * 2e32 + 1183071662 10 0 13
16 495000000 256QAM -0.700 40.946 3 * 2e32 + 1183089964 8 0 14
17 501000000 256QAM -0.800 40.366 3 * 2e32 + 1183021965 3 0 15
18 507000000 256QAM -0.700 40.946 3 * 2e32 + 1183094768 3 0 16
19 513000000 256QAM -0.600 40.366 3 * 2e32 + 1183076658 0 0 17
20 519000000 256QAM -0.500 40.946 3 * 2e32 + 1183031396 0 0 18
21 525000000 256QAM -0.400 40.366 3 * 2e32 + 1183099714 0 0 19
22 537000000 256QAM -0.200 40.366 3 * 2e32 + 1183104362 0 0 21
23 543000000 256QAM -0.300 40.946 3 * 2e32 + 1183109022 0 0 22
24 549000000 256QAM -0.200 40.366 3 * 2e32 + 1183113693 0 0 23
25 555000000 256QAM -0.400 40.946 3 * 2e32 + 1183118381 0 0 24
26 561000000 256QAM -0.400 40.366 3 * 2e32 + 1183132102 0 0 25
27 567000000 256QAM -0.300 40.946 3 * 2e32 + 1183136764 0 0 26
28 573000000 256QAM -0.300 40.946 3 * 2e32 + 1183123272 0 0 27
29 585000000 256QAM -0.100 40.946 3 * 2e32 + 1183141553 0 0 29
30 591000000 256QAM 0.100 40.366 3 * 2e32 + 1183146222 0 0 30
31 597000000 256QAM 0.000 40.946 3 * 2e32 + 1183128153 0 0 31
32 603000000 256QAM 0.500 40.366 3 * 2e32 + 1183151003 11 0 32
Reset FEC Counters
OFDM Downstream Overview
Receiver FFT type Subcarr 0 Frequency(Hz) PLC locked NCP locked MDC1 locked PLC power(dBmv) SNR(dB) Octets Correcteds Uncorrectables
0 NA NA NO NO NO NA NA NA NA NA
1 4K 803600000 YES YES YES 7.199997 44 81695839955 1510370529 54
Upstream Overview
Port ID Frequency (Hz) BandWidth (Hz) Modulation Type DOCSIS Mode Signal Strength (dBmV) Channel ID
1 35600000 6400000 64QAM ATDMA 42.500 4
2 16400000 6400000 64QAM ATDMA 42.500 1
3 29200000 6400000 64QAM ATDMA 42.500 3
4 22800000 6400000 64QAM ATDMA 42.500 2
OFDMA Upstream Overview
Channel Index State Subcarr 0 Frequency(Hz) lin Digital Att Digital Att BW (sc's*fft) Report Power Report Power1_6 FFT Size
0 OPERATE 36200000 0.2002 4.4094 44.4000 62.9326 48.5000 4K
1 DISABLED 0 0.0000 0.0000 0.0000 0.0000 0.0000 2K

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XfinityJosephA

Official Employee

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1.4K Messages

Hello. @sunmast at Xfinity we believe in an open internet connection, and we will never throttle speeds. Many variables can influence your internet performance and the activity you see with the speed test dial is 100% typical. Are you able to completely bypass your router and test again with an Ethernet connection directly to your modem? 

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick

7 months ago

0

sunmast

Visitor

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13 Messages

The test is performed on the router itself which is seeing the interface with the internet IP address, so no nating/routing is involved.

7 months ago

0

XfinityKassie

Official Employee

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1.3K Messages

 

sunmast Thank you for these details! I'd like to take a look on my side, and see if there is anything that could be causing the issue. To begin, can you please send a Direct Message with your name and service address? 
 
Click "Sign In" if necessary
Click the "Direct Messaging" icon at the top of the page (looks like a text bubble)
Click the "New message" (pencil and paper) icon
Type "Xfinity Support" in the "To:" line and select "Xfinity Support" from the drop-down list which appears. The "Xfinity Support" graphic replaces the "To:" line
Type your message in the text area near the bottom of the window
Press Enter to send it

 

I am an Official Xfinity Employee.
Official Employees are from multiple teams within Xfinity: CARE, Product, Leadership.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Please, mark a reply as the Accepted Answer.tick

7 months ago

0

sunmast

Visitor

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13 Messages

Direct messages sent.

7 months ago

0

sunmast

Visitor

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13 Messages

It turns out the speed wasn't throttled by Comcast because the UDP test can always reach the rated speed at 200Mb/s. The TCP test was struggling on retransmissions and so the speed varies wildly.

The problem is solved by removing a 6db forward path attenuator in the line (it's designed to knock down the downstream signal strength only, but it does impact upstream signal strength too).

In my case, 42.5dbmv is too high for upstream. Now its only 36.5 and it works perfectly.

Thanks Xfinity supports.

7 months ago

0

EG

Expert

 • 

106.9K Messages

7 months ago

@sunmast 

FWIW, are you sure that was a forward path only attenuator ? An FPA shouldn't also knock down the upstream power by as much as it knocks down the downstream power (6 dB in both directions). The insertion loss should be negligible in the return path. What is the make and model number of it ?

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sunmast

Visitor

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13 Messages

7 months ago

It was bought in last year:

PPC FPA6-54 in-Line Forward Path Attenuator 6dB 75 Ohms for DOCSIS Cable TV Box & Modem for Fast Internet - New Version

https://www.amazon.com/gp/product/B08KTRC3XZ

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EG

Expert

 • 

106.9K Messages

7 months ago

Ok well, that's the correct device. It shouldn't cause any noticeable loss in the upstream power level. Perhaps it's defective ?

1

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sunmast

Visitor

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13 Messages

@EG​ Yeah it might be the case

7 months ago

0

sunmast

Visitor

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13 Messages

7 months ago

Closing this thread.

The problem is solved by removing a 6db attenuator in the line.

In my case, 42.5dbmv is too high for upstream. With 36.5dbmv it works perfectly.

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XfinityJustinC

Official Employee

 • 

893 Messages

7 months ago

 

sunmast we definitely appreciate you taking the time to follow up and provide the fix. I'm sure this will be helpful information for Xfintiy Forums members who may be experiencing similar issues. We're available here for employe support 7 days a week between 6 am - 12am. Have a wonderful rest of your weekend. 

 

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user_n3otpj

4 Messages

2 months ago

I just signed up to Xfinity and I am having the exact same problem. The upload was perfect at around 300Mbps (celebrations began!) and then I start uploading large files it drops right away to 40Mbps :(

Please help!

(edited)

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