pppd hangs: problem found and solved (almost)

Hello.

On April 5th, there was a thread on this group titled "pppd and ttyS0 -
AGRRH!". (I do not know how to quote the past thread link here). In
this thread the problem discussed was that on a server that is setup as
dialin, pppd would start and hang for no apperent reason.

Exactly same thing happened to me. Struggled a lot before I found this
thread. Fedora core 3, with and without yum update. Reinstalled FC3.
With different kernels. No Go.

To cut a long story short, here is what I saw in
/var/log/mgetty.log.ttyS0:
WARNING: starting login while DCD is low!

So I thought this is something to do with the modem. I changed modem to
Multitech ZDX on the server. And Voila! it worked on the first attempt
and every attempt thereafter. The earlier modem was SupraExpress
external.

Seems pppd starts and waits for modem to push up dcd or some such and
some modems don't seem to do that by default. Can you please tell me
what AT command to put in /etc/mgetty+sendfax/mgetty.config to make
this happen? Multitech modems are more expensive than Supra.

Thanks in advance.
Regards.
J Dubal.

dubal <(E-Mail Removed)> wrote:

> To cut a long story short, here is what I saw in
> /var/log/mgetty.log.ttyS0:
> WARNING: starting login while DCD is low!

> So I thought this is something to do with the modem. I changed modem to
> Multitech ZDX on the server. And Voila! it worked on the first attempt
> and every attempt thereafter. The earlier modem was SupraExpress
> external.

> Seems pppd starts and waits for modem to push up dcd or some such and
> some modems don't seem to do that by default. Can you please tell me
> what AT command to put in /etc/mgetty+sendfax/mgetty.config to make
> this happen? Multitech modems are more expensive than Supra.

Perhaps something similar to the lines

port ttyS0
init-chat "" AT&F OK

answer-chat "" ATA CONNECT \c
answer-chat-timeout 25

would work. What timeout is up to you, the default is 80 seconds.

--
Clifford Kite Email: "echo xvgr_yvahk-(E-Mail Removed)|rot13"
PPP-Q&A links, downloads: http://ckite.no-ip.net/
/* The generation of random numbers is too important to be left
to chance. */

Hi there


Clifford Kite wrote:

> Perhaps something similar to the lines
>
> port ttyS0
> init-chat "" AT&F OK
>
> answer-chat "" ATA CONNECT \c
> answer-chat-timeout 25
>
> would work. What timeout is up to you, the default is 80 seconds.

It's a better idea to config the modem with sensible defaults, write
those to non volatile memory and use ATZ instead of AT&F (some factory
defaults don't make any sense) as your init string.
The correct AT commands should be in your modem documentation. It's
probably something like;

- Fixed baud rate (no auto baud)
- Hardware bidirectional RTS-CTS flow control (no x-on/x-off)
- 8 Bits, no parity, 1 stopbit
- The modem should produce the TRUE DCD status (&C1)
- The modem should NOT ignore the DTR status (&D2 or &D3)
- Reset on DTR toggle (&D3, this is sometimes a S register) [1]

Write those with something like AT&W.

mgetty and fax software send their own additional AT commands.

If it's an external modem, get a RS232 tester with leds to indicate the
status of the lines.

[1] I hardwired my modems to do a hadware reset on DTR toggle.
This way the pc will revive a crashed modem.


Regards,
Rob
--
+----------------------------------------------------------------------+
| Intensieve Menshouderij |
| http://www.intensievemenshouderij.nl/ |
+----------------------------------------------------------------------+

Rob van der Putten <(E-Mail Removed)> wrote:
>Hi there
>
>Clifford Kite wrote:
>
>> Perhaps something similar to the lines
>>
>> port ttyS0
>> init-chat "" AT&F OK
>>
>> answer-chat "" ATA CONNECT \c
>> answer-chat-timeout 25
>>
>> would work. What timeout is up to you, the default is 80 seconds.
>
>It's a better idea to config the modem with sensible defaults, write
>those to non volatile memory and use ATZ instead of AT&F (some factory

I distinctly *disagree* with that.

>defaults don't make any sense) as your init string.
>The correct AT commands should be in your modem documentation. It's
>probably something like;

The init script *depends* on beginning from a known point. The
NVRAM in a modem is *not* a guaranteed to always be the same
point to start with. But the factory settings are.

It is just as easy to reset factory defaults and then initialize
whatever state is desired, as it is to reset to nvram's saved
state and initialize whatever state is desired. The difference
is that factory defaults, for any given modem, will always be
the same.

>- Fixed baud rate (no auto baud)
>- Hardware bidirectional RTS-CTS flow control (no x-on/x-off)
>- 8 Bits, no parity, 1 stopbit
>- The modem should produce the TRUE DCD status (&C1)
>- The modem should NOT ignore the DTR status (&D2 or &D3)
>- Reset on DTR toggle (&D3, this is sometimes a S register) [1]
>
>Write those with something like AT&W.

I would say skip writing it to nvram, and just simply put the
commands necessary into your init strings.

>mgetty and fax software send their own additional AT commands.
>
>If it's an external modem, get a RS232 tester with leds to indicate the
>status of the lines.
>
>[1] I hardwired my modems to do a hadware reset on DTR toggle.
>This way the pc will revive a crashed modem.

This is a very good idea!

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)

Hi there


"Floyd L. Davidson" wrote:

> I distinctly *disagree* with that.

> The init script *depends* on beginning from a known point. The
> NVRAM in a modem is *not* a guaranteed to always be the same
> point to start with.

Under which circumstances do they change?

> But the factory settings are.
>
> It is just as easy to reset factory defaults and then initialize
> whatever state is desired, as it is to reset to nvram's saved
> state and initialize whatever state is desired. The difference
> is that factory defaults, for any given modem, will always be
> the same.

The disadvantage is that you have to put very long strings in the config
files of every piece of software that communicates with modems.
Further more, you have to change all those settings whenever you change
your modem.
It's also incompatible with leased lines (does anyone still use those?).

> I would say skip writing it to nvram, and just simply put the
> commands necessary into your init strings.

> This is a very good idea!

It has been online for years;
http://www.sput.nl/hardware/modem-reset.html


Regards,
Rob
--
+----------------------------------------------------------------------+
| Intensieve Menshouderij |
| http://www.intensievemenshouderij.nl/ |
+----------------------------------------------------------------------+

Rob van der Putten <(E-Mail Removed)> wrote:
>Hi there
>
>"Floyd L. Davidson" wrote:
>
>> I distinctly *disagree* with that.
>
>> The init script *depends* on beginning from a known point. The
>> NVRAM in a modem is *not* a guaranteed to always be the same
>> point to start with.
>
>Under which circumstances do they change?

Anytime any program writes AT&W to the modem! Which is to say,
whenever you shoot yourself in the foot.

>> But the factory settings are.
>>
>> It is just as easy to reset factory defaults and then initialize
>> whatever state is desired, as it is to reset to nvram's saved
>> state and initialize whatever state is desired. The difference
>> is that factory defaults, for any given modem, will always be
>> the same.
>
>The disadvantage is that you have to put very long strings in the config
>files of every piece of software that communicates with modems.

Yes. And the need to change any one of them does not cause a
need to change all of them.

>Further more, you have to change all those settings whenever you change
>your modem.

You have to do that *anyway*.

>It's also incompatible with leased lines (does anyone still use those?).

Yes, and no it is *not* necessarily imcompatible.

However, in cases where it is, there is also only one
application using the modem, hence nvram is has a very different
significance.

>> I would say skip writing it to nvram, and just simply put the
>> commands necessary into your init strings.
>
>> This is a very good idea!
>
>It has been online for years;
>http://www.sput.nl/hardware/modem-reset.html

Trust me, it has been known for a lot longer than that.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)

Hi there


"Floyd L. Davidson" wrote:

> Anytime any program writes AT&W to the modem! Which is to say,
> whenever you shoot yourself in the foot.

Apart from shooting yourself in the foot.

> Yes. And the need to change any one of them does not cause a
> need to change all of them.

> You have to do that *anyway*.

Once vs for every program.
Unless they all use a common config file.

> Yes, and no it is *not* necessarily imcompatible.

Remember, there is no dial tone or ring signal.
To avoid being hyjacked it's a good idea to disable the esc command
(useally '+++'.
It's best to disable AT commands alltogether.

> However, in cases where it is, there is also only one
> application using the modem, hence nvram is has a very different
> significance.

> Trust me, it has been known for a lot longer than that.

So are proper POR cirquits.
I've never seen them in anything else then TVs.

Most cirquits generate a reset on a fast rise of the supply voltage.
The proper way of doing things is to check wether the supply voltage is
high enough and generate a reset on a power low to power OK transition,
regardsless of the speed at which the supply voltage rises.


Regards,
Rob
--
+----------------------------------------------------------------------+
| Intensieve Menshouderij |
| http://www.intensievemenshouderij.nl/ |
+----------------------------------------------------------------------+

Rob van der Putten <(E-Mail Removed)> wrote:
>Hi there
>
>"Floyd L. Davidson" wrote:
>
>> Anytime any program writes AT&W to the modem! Which is to say,
>> whenever you shoot yourself in the foot.
>
>Apart from shooting yourself in the foot.

That is a common problem though, which should not be either
ignored or assumed will not happen. With multiple applications
that each require a specific configuration in nvram, *someone*
has to *remember* all of them. Two years later, if someone
(else perhaps) decides to change the way just one of them works,
and sees what appears to be a basic change that should be
written to nvram... a foot gets shot off. And of course if
this is a business, where system administrators may change, that
is very likely and is *really* annoying.

>> Yes. And the need to change any one of them does not cause a
>> need to change all of them.
>
>> You have to do that *anyway*.
>
>Once vs for every program.
>Unless they all use a common config file.

No, once for *every* program. You just aren't going to find a
"common denominator" nvram configuration which is as common as
would be hoped for. Different modems, different programs,
etc. etc....

>> Yes, and no it is *not* necessarily imcompatible.
>
>Remember, there is no dial tone or ring signal.
>To avoid being hyjacked it's a good idea to disable the esc command
>(useally '+++'.
>It's best to disable AT commands alltogether.

That may be true, in /some/ situations... and not in others.

Your perception of Private Line usage may be limited to some
degree. I worked for an IXC for 34 years, my perception of
Private Line usage is that anything I think is "the" way, is
going to be done differenctly by the next guy that buys a PL.
:-)

Keep in mind that some uses for a Private Line modem might have
a modem connected to a computer, just like a dialup modem, and
it might be used by multiple applications with different
configuration needs, just as would a dialup modem. The only
difference is that there probably (though even this is not
necessarily true either) will never be a need for ring detection
or dial commands.

>> However, in cases where it is, there is also only one
>> application using the modem, hence nvram is has a very different
>> significance.
>
>> Trust me, it has been known for a lot longer than that.
>
>So are proper POR cirquits.
>I've never seen them in anything else then TVs.

What are "proper POR cirquits"?

>Most cirquits generate a reset on a fast rise of the supply voltage.
>The proper way of doing things is to check wether the supply voltage is
>high enough and generate a reset on a power low to power OK transition,
>regardsless of the speed at which the supply voltage rises.

What is the significance of that in relationship to using or not
using nvram configuration in a modem????

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) (E-Mail Removed)

Rob van der Putten <(E-Mail Removed)> writes:

>Hi there


>Clifford Kite wrote:

>> Perhaps something similar to the lines
>>
>> port ttyS0
>> init-chat "" AT&F OK
>>
>> answer-chat "" ATA CONNECT \c
>> answer-chat-timeout 25
>>
>> would work. What timeout is up to you, the default is 80 seconds.

>It's a better idea to config the modem with sensible defaults, write
>those to non volatile memory and use ATZ instead of AT&F (some factory

No, experience says it is not. Many programs will reprogram your modem for
you apparently. It is far better to use the factor defaults and then to set
the extra config you need.

>defaults don't make any sense) as your init string.

That may be, but they form a stable platform from which to set up
reasonable ones. ATZ does not.

>The correct AT commands should be in your modem documentation. It's
>probably something like;

>- Fixed baud rate (no auto baud)
>- Hardware bidirectional RTS-CTS flow control (no x-on/x-off)
>- 8 Bits, no parity, 1 stopbit
>- The modem should produce the TRUE DCD status (&C1)
>- The modem should NOT ignore the DTR status (&D2 or &D3)
>- Reset on DTR toggle (&D3, this is sometimes a S register) [1]

Nothing wrong with these ( except the hardware rewiring), but again, AT&F
forms a stable platform on which to impliment them.


>Write those with something like AT&W.

>mgetty and fax software send their own additional AT commands.

>If it's an external modem, get a RS232 tester with leds to indicate the
>status of the lines.

>[1] I hardwired my modems to do a hadware reset on DTR toggle.
>This way the pc will revive a crashed modem.


>Regards,
>Rob
>--
>+----------------------------------------------------------------------+
>| Intensieve Menshouderij |
>| http://www.intensievemenshouderij.nl/ |
>+----------------------------------------------------------------------+

Rob van der Putten <(E-Mail Removed)> writes:

>Hi there


>"Floyd L. Davidson" wrote:

>> Anytime any program writes AT&W to the modem! Which is to say,
>> whenever you shoot yourself in the foot.

>Apart from shooting yourself in the foot.

The legions of software writers out there who think they know how you
should run your machine, and write &W for you.