3 Win 10 PCs/All Download Speeds Dropped from 1 Gigabit to 200 Mbps!

[paulmoverman]

Hi, first time posting, really would appreciate help. Comcast 1Gig service worked from December 2017 until about 2 mos ago. 3 pcs all running Win 10 Pro affected. Problems exists in Firexfox, IE, Edge and Chrome! Output of Arris SB8200 modem tests indicate 1.1Gb/sec on Comcast test rig running Safarai. 2 desktops are running Gigabyte boards with two different LAN cards. 3rd pc is a Toshiba laptop with a different LAN card. All ethernet connections are CAT6 cabling.All 3 pcs running Win 10 direct connect to modem test (Ookla) at 200 - 300 Mb/s. All 3 pcs booting to Linux test at about 980 Mb/sec behind router and switch!

Definitely appears to be a Windows issue and so far Microsoft has not come up with a solution. ALL tweaks suggested on Internet have been tried. Msft also did a new install of the October Windows Update in case that had somehow created a problem. I am pasting the results of the SC TCP/IP Analyzer and some system info below. Any help will be greatly appreciated!

SG TCP/IP Analyzer

IP Address: 75.67.252.127 (c-75-67-252-127.hsd1.nh.comcast.net)
Client OS: Windows 10
Browser: Firefox 66.0
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:66.0) Gecko/20100101 Firefox/66.0
Please Read the Analyzer FAQ if the above is not your IP address.
TCP options string = 020405b401010402
MTU = 1500
MTU is fully optimized for broadband.
MSS = 1460
Maximum useful data in each packet = 1460, which equals MSS.
Default TCP Receive Window (RWIN) = 64240
RWIN Scaling (RFC1323) = 0 bits
Unscaled TCP Receive Window = 64240

In Windows 10, unless "TCP/IP Auto-Tuning" is disabled, only the Current TCP Window is displayed. Use the latest TCP Optimizer for tweaking.
RWIN is a multiple of MSS
Other RWIN values that might work well with your current MTU/MSS:
64240 (up to 2 Mbit lines, depending on latency. MSS * 44) <-- current value
128480 (1-5 Mbit lines, depending on latency. MSS * 44 * 2)
256960 (2-15 Mbit lines, depending on latency. MSS * 44 * 2^2)
513920 (10-30 Mbit lines, depending on latency. MSS * 44 * 2^3)
1027840 (30-100 Mbit lines depending on latency. MSS * 44 * 2^4)
bandwidth * delay product (Note this is not a speed test):

Your current TCP Window limits you to: 2570 kbps (321 KBytes/s) @ 200ms latency
Your current TCP Window limits you to: 1028 kbps (128 KBytes/s) @ 500ms latency
MTU Discovery (RFC1191) = ON
Time to live left = 115 hops
TTL value is ok.
Timestamps (RFC1323) = OFF
Selective Acknowledgements (RFC2018) = ON
IP type of service field (RFC1349) = 00000000 (0)

*********************************************

OS Name Microsoft Windows 10 Pro
Version 10.0.17763 Build 17763
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name DESKTOP-6SADFNR
System Manufacturer Gigabyte Technology Co., Ltd.
System Model Z97X-UD3H
System Type x64-based PC
System SKU To be filled by O.E.M.
Processor Intel(R) Pentium(R) CPU G3258 @ 3.20GHz, 3201 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date American Megatrends Inc. F7, 6/17/2014
SMBIOS Version 2.7
Embedded Controller Version 255.255
BIOS Mode Legacy
BaseBoard Manufacturer Gigabyte Technology Co., Ltd.
BaseBoard Product Z97X-UD3H-CF
BaseBoard Version x.x
Platform Role Desktop
Secure Boot State Unsupported
PCR7 Configuration Binding Not Possible
Windows Directory C:\WINDOWS
System Directory C:\WINDOWS\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "10.0.17763.194"
User Name DESKTOP-6SADFNR\Paul
Time Zone Eastern Daylight Time
Installed Physical Memory (RAM) 8.00 GB
Total Physical Memory 7.86 GB
Available Physical Memory 5.15 GB
Total Virtual Memory 9.74 GB
Available Virtual Memory 7.20 GB
Page File Space 1.88 GB
Page File C:\pagefile.sys
Kernel DMA Protection Off
Virtualization-based security Not enabled
Device Encryption Support Reasons for failed automatic device encryption: TPM is not usable, PCR7 binding is not supported, Hardware Security Test Interface failed and device is not InstantGo, Un-allowed DMA capable bus/device(s) detected, Disabled by policy, TPM is not usable
Hyper-V - VM Monitor Mode Extensions Yes
Hyper-V - Second Level Address Translation Extensions Yes
Hyper-V - Virtualization Enabled in Firmware Yes
Hyper-V - Data Execution Protection Yes

Thank you very much inn advance for any insight and suggestions!

[Philip]

You seem to suggest that it may be related to Microsoft updates. It is also possible that something on the line changed, and Windows is not as capable of dealing with the issue as well as Linux (different congestion avoidance algorithms, etc.)? Are your Cable modem signal levels good, no packet loss, normal latency?

The CPU seems a bit on the slower side for a 1Gbps transfer in the above post, how is the CPU utilization during transfers?
It may be a good idea to try a different approach to speed testing, like a direct download from a multi-source (torrent of a Linux distro, for example). That would eliminate the browser/HTML5/Java, etc. from the equation.
When you do a direct file transfer between your PCs, are you able to achieve the 1GBps? It could be a NIC driver issue in general in Windows.

[paulmoverman]

You seem to suggest that it may be related to Microsoft updates. It is also possible that something on the line changed, and Windows is not as capable of dealing with the issue as well as Linux (different congestion avoidance algorithms, etc.)? Are your Cable modem signal levels good, no packet loss, normal latency?

The CPU seems a bit on the slower side for a 1Gbps transfer in the above post, how is the CPU utilization during transfers?
It may be a good idea to try a different approach to speed testing, like a direct download from a multi-source (torrent of a Linux distro, for example). That would eliminate the browser/HTML5/Java, etc. from the equation.
When you do a direct file transfer between your PCs, are you able to achieve the 1GBps? It could be a NIC driver issue in general in Windows.

Here are the modem levels (all of which Comcast says are good):

Downstream Bonded Channels
Channel ID Lock Status Modulation Frequency Power SNR/MER Corrected Uncorrectables
25 Locked QAM256 651000000 Hz -3.0 dBmV 40.3 dB 1 0
1 Locked QAM256 507000000 Hz -2.0 dBmV 40.8 dB 0 0
2 Locked QAM256 513000000 Hz -1.6 dBmV 40.8 dB 0 0
3 Locked QAM256 519000000 Hz -1.7 dBmV 40.8 dB 0 0
4 Locked QAM256 525000000 Hz -2.7 dBmV 40.3 dB 0 0
5 Locked QAM256 531000000 Hz -2.1 dBmV 40.6 dB 0 0
6 Locked QAM256 537000000 Hz -1.4 dBmV 41.1 dB 0 0
7 Locked QAM256 543000000 Hz -1.6 dBmV 41.0 dB 0 0
8 Locked QAM256 549000000 Hz -2.1 dBmV 40.6 dB 0 0
9 Locked QAM256 555000000 Hz -1.9 dBmV 40.7 dB 0 0
10 Locked QAM256 561000000 Hz -1.7 dBmV 40.8 dB 0 0
11 Locked QAM256 567000000 Hz -2.0 dBmV 40.7 dB 0 0
12 Locked QAM256 573000000 Hz -2.3 dBmV 40.6 dB 0 0
13 Locked QAM256 579000000 Hz -2.1 dBmV 40.8 dB 0 0
14 Locked QAM256 585000000 Hz -1.7 dBmV 40.8 dB 0 0
15 Locked QAM256 591000000 Hz -1.8 dBmV 40.9 dB 0 0
16 Locked QAM256 597000000 Hz -1.9 dBmV 40.9 dB 0 0
17 Locked QAM256 603000000 Hz -2.2 dBmV 40.8 dB 0 0
18 Locked QAM256 609000000 Hz -2.1 dBmV 40.7 dB 0 0
19 Locked QAM256 615000000 Hz -2.0 dBmV 40.0 dB 0 0
20 Locked QAM256 621000000 Hz -2.1 dBmV 40.6 dB 0 0
21 Locked QAM256 627000000 Hz -2.6 dBmV 40.5 dB 0 0
22 Locked QAM256 633000000 Hz -2.4 dBmV 40.6 dB 0 0
23 Locked QAM256 639000000 Hz -2.7 dBmV 40.3 dB 0 0
24 Locked QAM256 645000000 Hz -2.8 dBmV 40.2 dB 0 0
26 Locked QAM256 657000000 Hz -3.0 dBmV 40.2 dB 0 0
27 Locked QAM256 663000000 Hz -2.7 dBmV 40.5 dB 0 0
28 Locked QAM256 669000000 Hz -2.5 dBmV 40.4 dB 0 0
29 Locked QAM256 675000000 Hz -3.0 dBmV 39.5 dB 0 0
30 Locked QAM256 681000000 Hz -2.9 dBmV 40.2 dB 0 0
31 Locked QAM256 687000000 Hz -3.2 dBmV 40.0 dB 0 0
32 Locked QAM256 693000000 Hz -3.0 dBmV 40.2 dB 0 0
159 Locked Other 702000000 Hz -2.6 dBmV 38.0 dB 4387 0

How do these levels look in your opinion/

[Philip]

Yeah, power/SNR looks good to me. Here is a bit of info on how to read them:
https://www.speedguide.net/faq/what-cab ... ed-good-78