What is causing TCP errors?

Hi all,

This post is in relation to a past post I made titled "Unsolvable ADSL
problem".

Further analysis of the problem has shown that the reason I have slow
downloads is because I am experiencing lots of TCP/IP errors. I've
checked using an Ethernet packet sniffer (Ethereal) and there are
basically continuous Out-Of-Order segments, lost segments,
retransmissions, duplicate ACK's, etc.

I am absolutely certain this is not caused by any of my hardware. My
Ethernet card has been changed (and has never shown any errors), all
cables have been changed, the modem and splitter have also been
changed. I am also certain these errors are not caused by my ISP
because I have now tried 5, and 3 of them work perfectly well for
friends.

The next logical explanation is line errors, but the modems own
diagnostics show 0 errors.

What else could cause these errors?

A reminder of the problem:

Using a 384kbps ADSL service (which is actually sync'd at 448kbps, so
I can get full 384kbps bandwidth) I have download speeds of between
26-32kbps, and an average ping to my ISP gateway of 80ms.

I can always download at 26K/sec but when I run VOIP applications
(that use ONLY about 4K/sec) the ping to my ISP's gateway continuously
increases until the connection times out.

To me this means that the amount of available bandwidth is NOT the
problem!

My telco keeps telling me there are no problems with their equipment
and if I am having problems it must be because of contention ratios
and is perfectly normal. I know this isn't the case otherwise I would
have persistently low speed independant of the protocol used. Also I
have seen many other ADSL installations and they all reach maximum
speed (48K/sec) and have a ping of about 15-30ms to the ISP gateway.

Does anybody have any ideas what I can do? The telco now refuses to
help me at all because they claim they have tried and checked
everything. I really need to find a solution to this problem, even if
i am the one that has to suggest it.

P.S - I have tried Interleaved mode, didn't make any difference.

TIA for any help,
dave

(E-Mail Removed) (dave) wrote in message news:<(E-Mail Removed). com>...
> Hi all,
>
> This post is in relation to a past post I made titled "Unsolvable ADSL
> problem".
>
> Further analysis of the problem has shown that the reason I have slow
> downloads is because I am experiencing lots of TCP/IP errors. I've
> checked using an Ethernet packet sniffer (Ethereal) and there are
> basically continuous Out-Of-Order segments, lost segments,
> retransmissions, duplicate ACK's, etc.
>
> I am absolutely certain this is not caused by any of my hardware. My
> Ethernet card has been changed (and has never shown any errors), all
> cables have been changed, the modem and splitter have also been
> changed. I am also certain these errors are not caused by my ISP
> because I have now tried 5, and 3 of them work perfectly well for
> friends.
>
> The next logical explanation is line errors, but the modems own
> diagnostics show 0 errors.
>
> What else could cause these errors?
>
> A reminder of the problem:
>
> Using a 384kbps ADSL service (which is actually sync'd at 448kbps, so
> I can get full 384kbps bandwidth) I have download speeds of between
> 26-32kbps, and an average ping to my ISP gateway of 80ms.
>
> I can always download at 26K/sec but when I run VOIP applications
> (that use ONLY about 4K/sec) the ping to my ISP's gateway continuously
> increases until the connection times out.
>
> To me this means that the amount of available bandwidth is NOT the
> problem!
>
> My telco keeps telling me there are no problems with their equipment
> and if I am having problems it must be because of contention ratios
> and is perfectly normal. I know this isn't the case otherwise I would
> have persistently low speed independant of the protocol used. Also I
> have seen many other ADSL installations and they all reach maximum
> speed (48K/sec) and have a ping of about 15-30ms to the ISP gateway.
>
> Does anybody have any ideas what I can do? The telco now refuses to
> help me at all because they claim they have tried and checked
> everything. I really need to find a solution to this problem, even if
> i am the one that has to suggest it.
>
> P.S - I have tried Interleaved mode, didn't make any difference.
>
> TIA for any help,
> dave

What is your MTU ? what is the packet size of the VOIP packets? and
what voip hardware is at your end and the gateways.

From what you say it sounds like the backbone connection to the
gateway. what you need to find out what the avalible bandwidth to them
is.



Ian

dave schrieb:
>
> Hi all,
>
> This post is in relation to a past post I made titled "Unsolvable ADSL
> problem".
>
> Further analysis of the problem has shown that the reason I have slow
> downloads is because I am experiencing lots of TCP/IP errors. I've
> checked using an Ethernet packet sniffer (Ethereal) and there are
> basically continuous Out-Of-Order segments, lost segments,
> retransmissions, duplicate ACK's, etc.
>
> I am absolutely certain this is not caused by any of my hardware. My
> Ethernet card has been changed (and has never shown any errors), all
> cables have been changed, the modem and splitter have also been
> changed. I am also certain these errors are not caused by my ISP
> because I have now tried 5, and 3 of them work perfectly well for
> friends.
>
> The next logical explanation is line errors, but the modems own
> diagnostics show 0 errors.
>
> What else could cause these errors?
>
One possible cause of errors could be a mismatch in half/full duplex on
the connection to your modem.
The usual setup is auto sensing, but there could be reasons why this
doesn't work correctly.
If you go into the control panel and select the advanced tab on your
ethernet adaptor, you find a bunch of settings, including speed and
half/full duplex. If it's set to auto, try overriding to half or full.
If it's set to half or full, set it back to auto and try that.
Hope this helps. I've seen this problem happen at commercial sites, and
it causes exactly the problems you describe.

Tom

> A reminder of the problem:
>
> Using a 384kbps ADSL service (which is actually sync'd at 448kbps, so
> I can get full 384kbps bandwidth) I have download speeds of between
> 26-32kbps, and an average ping to my ISP gateway of 80ms.
>
> I can always download at 26K/sec but when I run VOIP applications
> (that use ONLY about 4K/sec) the ping to my ISP's gateway continuously
> increases until the connection times out.
>
> To me this means that the amount of available bandwidth is NOT the
> problem!
>
> My telco keeps telling me there are no problems with their equipment
> and if I am having problems it must be because of contention ratios
> and is perfectly normal. I know this isn't the case otherwise I would
> have persistently low speed independant of the protocol used. Also I
> have seen many other ADSL installations and they all reach maximum
> speed (48K/sec) and have a ping of about 15-30ms to the ISP gateway.
>
> Does anybody have any ideas what I can do? The telco now refuses to
> help me at all because they claim they have tried and checked
> everything. I really need to find a solution to this problem, even if
> i am the one that has to suggest it.
>
> P.S - I have tried Interleaved mode, didn't make any difference.
>
> TIA for any help,
> dave

My MTU is 1500 but I have tried other settings (1492 all the way down
to 576) without any success.

I don't think its the backbone connection to the gateway because over
ISDN via the same ISP as my ADSL there is no problem.

Cheers,
-dave

> What is your MTU ? what is the packet size of the VOIP packets? and
> what voip hardware is at your end and the gateways.
>
> From what you say it sounds like the backbone connection to the
> gateway. what you need to find out what the avalible bandwidth to them
> is.
>
>
>
> Ian

> One possible cause of errors could be a mismatch in half/full duplex on
> the connection to your modem.
> The usual setup is auto sensing, but there could be reasons why this
> doesn't work correctly.

This was one of the very first things I checked... not the problem
unfortunately.

I should probably rephrase my original question to say "What can I
suggest my telco checks in THEIR configuration that might be causing
the problem?"

Personally from what they have told me it seems they have a faulty
DSLAM card, but apparently they don't have the capacity to add another
one for a few more months...

Cheers,
-dave

dave schrieb:
>
> > One possible cause of errors could be a mismatch in half/full duplex on
> > the connection to your modem.
> > The usual setup is auto sensing, but there could be reasons why this
> > doesn't work correctly.
>
> This was one of the very first things I checked... not the problem
> unfortunately.
>
> I should probably rephrase my original question to say "What can I
> suggest my telco checks in THEIR configuration that might be causing
> the problem?"
>
Maybe they should check their circuits for half/full dupplex mismatches
;-)

> Personally from what they have told me it seems they have a faulty
> DSLAM card, but apparently they don't have the capacity to add another
> one for a few more months...
>
> Cheers,
> -dave

"dave" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> > One possible cause of errors could be a mismatch in half/full duplex on
> > the connection to your modem.
> > The usual setup is auto sensing, but there could be reasons why this
> > doesn't work correctly.
>
> This was one of the very first things I checked... not the problem
> unfortunately.
>
> I should probably rephrase my original question to say "What can I
> suggest my telco checks in THEIR configuration that might be causing
> the problem?"
>
> Personally from what they have told me it seems they have a faulty
> DSLAM card, but apparently they don't have the capacity to add another
> one for a few more months...
>
> Cheers,
> -dave
The DSLAM wouldn't know about anything layer 3 or above, it only deals in
ATM cells. Only something that deals with IP packets and above could cause
your problem, especially if you say you are getting out of order packets.
The packets are there, just out of order. Sounds like the packets are
taking different routes. RUn pingplotter and see if you can see the route
changes. Or send a continuous ping to some site with a HUGE size to see
what happens. TCP is supposed to deal with out of order IP packets, but
there is delay in doing so...
J--
www.pccitizen.com Safe Computing, Home wired and wireless networking tips.
....You spend your whole life figuring out what you should have done with it,
let alone what it was all about. And then your children get to do it all
over again..

> The DSLAM wouldn't know about anything layer 3 or above, it only deals in
> ATM cells. Only something that deals with IP packets and above could cause
> your problem, especially if you say you are getting out of order packets.
> The packets are there, just out of order. Sounds like the packets are
> taking different routes.

I doubt the packets are taking different routes, because it happens
with any ISP I try and a friend who uses the same ISP as I usually do
has no problems at all.

About the DSLAM - if it is losing/corrupting/whatever ATM packets that
is bound to affect the IP contained within. As my modem shows no
errors my best guess at the moment is that my outgoing packets are
being lost and that is causing retransmissions etc and explains why my
modem error count is not increasing.

I'm just guessing really though, I don't know anything about DSLAM's.
Perhaps somebody here can enlighten me?

Cheers,
-dave

"dave" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> > The DSLAM wouldn't know about anything layer 3 or above, it only deals
in
> > ATM cells. Only something that deals with IP packets and above could
cause
> > your problem, especially if you say you are getting out of order
packets.
> > The packets are there, just out of order. Sounds like the packets are
> > taking different routes.
>
> I doubt the packets are taking different routes, because it happens
> with any ISP I try and a friend who uses the same ISP as I usually do
> has no problems at all.
>
> About the DSLAM - if it is losing/corrupting/whatever ATM packets that
> is bound to affect the IP contained within. As my modem shows no
> errors my best guess at the moment is that my outgoing packets are
> being lost and that is causing retransmissions etc and explains why my
> modem error count is not increasing.
>
> I'm just guessing really though, I don't know anything about DSLAM's.
> Perhaps somebody here can enlighten me?
>
> Cheers,
> -dave
Rereading your post,
"out of order segments" would certainly indicate a layer 3 or above problem.
In retrospect, I am not sure how you could infer this.
Corrupted segments (and therefore dropped) could well be dropped ATM cells.
Would have to be within the DSLAM card, if there are no ADSL errors present.
DSLAM card might be your best guess as to what is wrong....
J--
Check my web site for tips on insuring safe computing in wired and wireless
homenetworking environments!
www.pccitizen.com
You spend your whole life figuring out what you should have done with it,
let alone what it was all about. And then your children get to do it all
over again.