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Fast upload speed, super slow download speed

New Poster

Fast upload speed, super slow download speed

We cancelled television service and the boost package that came with it, thinking that we'd save money.  Now we have the performance tier our bill went up just enough so that we are paying the exact same amount that we were before.  Funny how that works out.  


The thing is, since the downgrade on internet tiers, the download speed we see in our house has plummeted through the floor.  The upload speed is consistently 5.5-6 Mbps, but I rarely see higher than 2Mbps download on, the speed is more likely to be around 0.6-0.8Mbps.


If I restart the modem, I can test at 18-20Mbps download speed for several minutes until we start a streaming app, or online game, or begin browsing the web.  Shortly after commencing any of these activities, the download speed suffers.  After cancelling all streaming/download apps, the measured download speed will not get over the 2Mbps barrier.


I get very similar results whether testing through the router, or modem->PC directly.


Hopefully somebody in the know can help me out here?  Thanks in advance!


Router is: Netgear N600 Wireless Duall Band WND83400


Cable Modem Report:


Modem Serial Number


Cable Modem MAC Address


Hardware Version


Software Version


Receive Power Level

 -4.1 dBmV

Transmit Power Level

 53.3 dBmV

Cable Modem Status



Shaper Detection Module:

DiffProbe release. January 2012. Build 1008.
Shaper Detection Module.

Connected to server

Estimating capacity:
Upstream: 5537 Kbps.
Downstream: 26482 Kbps.

The measurement will take upto 2.5 minutes. Please wait.

Checking for traffic shapers:

Upstream: No shaper detected.
Median received rate: 5469 Kbps.

Downstream: Measurement aborted due to high packet loss rate.

For more information, visit:


Results from

WEB100 Kernel Variables:

Client: localhost/

CurMSS: 1460

X_Rcvbuf: 87380

X_Sndbuf: 22512

AckPktsIn: 314

AckPktsOut: 0

BytesRetrans: 86140

CongAvoid: 139

CongestionOverCount: 0

CongestionSignals: 30

CountRTT: 167

CurCwnd: 5840

CurRTO: 234

CurRwinRcvd: 65700

CurRwinSent: 5888

CurSsthresh: 2920

DSACKDups: 0

DataBytesIn: 0

DataBytesOut: 973704

DataPktsIn: 0

DataPktsOut: 660

DupAcksIn: 98

ECNEnabled: 0

FastRetran: 18

MaxCwnd: 8760

MaxMSS: 1460

MaxRTO: 444

MaxRTT: 226

MaxRwinRcvd: 65700

MaxRwinSent: 5888

MaxSsthresh: 4380

MinMSS: 1460

MinRTO: 217

MinRTT: 15

MinRwinRcvd: 54216

MinRwinSent: 5840

NagleEnabled: 1

OtherReductions: 3

PktsIn: 314

PktsOut: 660

PktsRetrans: 59

RcvWinScale: 7

SACKEnabled: 3

SACKsRcvd: 70

SendStall: 0

SlowStart: 45

SampleRTT: 17

SmoothedRTT: 31

SndWinScale: 2

SndLimTimeRwin: 0

SndLimTimeCwnd: 10031809

SndLimTimeSender: 43355

SndLimTransRwin: 0

SndLimTransCwnd: 38

SndLimTransSender: 38

SndLimBytesRwin: 0

SndLimBytesCwnd: 760720

SndLimBytesSender: 212984

SubsequentTimeouts: 0

SumRTT: 6402

Timeouts: 12

TimestampsEnabled: 0

WinScaleRcvd: 2

WinScaleSent: 7

DupAcksOut: 0

StartTimeUsec: 761465

Duration: 10077032

c2sData: 4

c2sAck: 4

s2cData: 8

s2cAck: 3

half_duplex: 0

link: 100

congestion: 1

bad_cable: 0

mismatch: 0

spd: 0.77

bw: 1.36

loss: 0.045454545

avgrtt: 38.34

waitsec: 2.81

timesec: 10.00

order: 0.3121

rwintime: 0.0000

sendtime: 0.0043

cwndtime: 0.9957

rwin: 0.5013

swin: 0.1718

cwin: 0.0668

rttsec: 0.038335

Sndbuf: 22512

aspd: 0.00000

CWND-Limited: 251.12

minCWNDpeak: 1460

maxCWNDpeak: 8760

CWNDpeaks: 20


The theoretical network limit is 1.36 Mbps

The NDT server has a 10.0 KByte buffer which limits the throughput to 4.48 Mbps

Your PC/Workstation has a 64.0 KByte buffer which limits the throughput to 13.07 Mbps

The network based flow control limits the throughput to 1.74 Mbps

Client Data reports link is 'T3',

Client Acks report link is 'T3'

Server Data reports link is 'OC-48',

Server Acks report link is 'Ethernet'


No duplex mismatch condition was detected.
The test did not detect a cable fault.
Network congestion may be limiting the connection.
No network address translation appliance was detected.



Another common result reported by other tests:

The slowest link in the end-to-end path is a 45 Mbps T3/DS3 subnet

Other network traffic is congesting the link





Re: Fast upload speed, super slow download speed

Your upstream level is too high (should be less than 50dBmV) -- this is part of your problem. Usually this is caused by too many splitters or bad/substandard wiring. It's possible it is a Comcast issue, but most likely the problem exists between the tap (pole) and your modem. Also, your modem was End Of Life about a year and a half ago, it needs to be replaced.

I am not a Comcast Employee.
I am a Customer Expert volunteering my time to help other customers here in the Forums.
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New Poster

Re: Fast upload speed, super slow download speed

Thanks, I'd suspected as much.  I'm probably behind 2 splitters (cable line goes through a building I don't have access to).  I'll definitely get a new modem in here.

New Poster

Re: Fast upload speed, super slow download speed

I spent months with fast speeds and then my downloads speeds fell off a cliff (0.24 MB/s download with regular 5.5 MB/s upload).  I later figured out that the splitter I had to divide the cable coming off the wall was the problem. Once I removed that-- my download speeds were back. Now to just figure out the tv.... Smiley Happy