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Problems uploading data over ADSL

Problems uploading data over ADSL

Problems uploading data over ADSL


I've been having trouble uploading data to the Internet from home over my Qwest ADSL connection.  When trying to upload pictures to Picasa or Shutterfly, or various files via E-Mail, I receive timeout errors.  Only after numerous upload attempts am I ever able to upload my data.  Using Wireshark, I see a tremendous amount of "TCP Dup ACK", "TCP ACKed lost segment", and "TCP retransmission" messages.

I've uploaded my Wireshark logs to:


According to Wireshark's website:


TCP Dup ACK - Occurs when the same ACK number is seen AND it is lower than the last byte of data sent by the sender. If the receiver detects a gap in the sequence numbers, it will generate a duplicate ACK for each subsequent packet it receives on that connection, until the missing packet is successfully received (retransmitted). Clear indication of dropped/missing packets.

TCP Acked lost segment - These are ack's that ethereal can't match with a sent segment. Are ACK that Ethereal detects, but cant see the segment sent.

TCP Retransmission - Occurs when all the data in the packet has been seen in one or more previous packet.

According to Iljitsch van Beijnum (Author of BGP, published by O'Reilly):


Upon receiving a duplicate ACK, the sending TCP assumes the unacknowledged data has been lost because of congestion...

Looking at these error messages and their meaning, it looks like I have an OSI layer 3, or higher, problem.  I heard that Qwest does packet shaping.  Perhaps they've miss configured something?  When sending data from work, school, or my neighbor's Internet connection (Comcast), I don't have any problems whatsoever.  I do occasionally see one or more of the error messages listed above, but only one or two, not 50+!

I contacted Qwest's tech support regarding this issue about a month ago.  As tier 1 support, they had me reboot everything, power cycle everything, and then asked that I replace my modem.  I purchased an  Actiontec GT701D from BestBuy for trouble-shooting.  With this new router, I'm experiencing the exact same upload problem.  When none of this fixed my problem, they said that they wouldn't provide me with any more support until I replaced my modem (again) because my modem (Cisco 678) was unsupported (even though it's listed on Qwest's modem support page).

Because my modem is in bridge mode and not participating in any OSI layer 3 or above activities, it's not possible for my modem to be causing these issues.  If I were having an OSI layer 1 or 2 problem, I'd get "Destination Unreachable" errors.

I'm using a Cisco 678 DSL router in bridge mode for my ADSL connection.  Looking at the line quality, I have a good connection.


bos#show interface wan0
wan0   ADSL Physical Port
       Line Trained
Actual Configuration:
  Overhead Framing:           3
  Trellis Coding:             Disabled
  Standard Compliance:        T1.413
  Downstream Data Rate:       7200 Kbps
  Upstream Data Rate:         896 Kbps
  Interleave S Downstream:    1
  Interleave D Downstream:    64
  Interleave R Downstream:    16
  Interleave S Upstream:      8
  Interleave D Upstream:      4
  Interleave R Upstream:      16
  Modem Microcode:            G96
  DSP version:                0
  Operating State:            Showtime/Data Mode
  Echo Cancellation:          Disabled
  Overhead Framing:           3
  Coding Gain:                Auto
  TX Power Attenuation:       0dB
  Trellis Coding:             Enabled
  Bit Swapping:               Disabled
  Standard Compliance:        T1.413
  Remote Standard Compliance: T1.413
  Tx Start Bin:               0x6
  Tx End Bin:                 0x1f
  Data Interface:             Utopia L1
  Local SNR Margin:           16.5dB
  Local Coding Gain:          5.0dB
  Local Transmit Power:       12.3dB
  Local Attenuation:          17.0dB
  Remote Attenuation:         5.5dB

My download capability is working just fine.  On any given day, I'm pulling down Linux ISOs, patches, games, etc.  As another test, I checked out two Internet speed test websites:


Last Result:
Download Speed: 5.793 Mbps (0.7 MB/sec transfer rate)
Upload Speed: 0.718 Mbps (0.1 MB/sec transfer rate)
The closest server located in Denver, CO performed this test with a latency of 38 milliseconds.
Test Date: Sunday, December 05, 2010 9:53:54 AM

http://www.speedtest.net showed almost the same results.

So, it looks like my "speed" is what I expect.  I am getting some "TCP ACTed lost segment" errors during the upload portion of those tests.  I don't think that a lot of data is being pushed up or down during the test, so I'm not having significant enough upload problems for the upload tests to fail or register slow.

I don't believe that calling the support phone number is going to yield any results (based on my last e-mail and voice exchange).  Is there any way to reach Qwest's backline support directly?  Does anyone have any ideas on how to fix this issue?



RE: Problems uploading data over ADSL

Is the cisco handling the mtu?
try to set the mtu to 1492 (if pppoe) or 1500 (if pppoa)

if not, adjust it on the pc

M. Knorr


RE: Problems uploading data over ADSL

Hello Lemon13,

The Cisco 678 is only operating at OSI layer 2 so I don't see how it could be an MTU issue on that device specifically.  My routing device is a Pix 501 firewall (PPPoE on the outside).

My Pix shows an MTU size of 1480.  I didn't hard code this so it must have been negotiated.  I also plugged my Windows 7 laptop directly into my Cisco 678, configured my laptop for PPPoE, and hard coded my Ethernet interface to an MTU of 1300.  I'm still having the same upload problem and error messages in Wireshark.

Is there something else I should try?



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