Why is it not possible to reach some mobile numbers?

Question

Telephony

Hello.
Faced a problem. There is a voice VOIP-gateway Eltex TAU-24.
I made basic settings, registered numbers, outgoing / incoming communication is available. But there is a catch, for some reason it is not possible to call some mobile numbers.
That is, it calls some mobile numbers, and immediately resets some. How the gateway chooses which to call and which not, I don’t understand. It would be nice to have one OpSoSa, but it turns out MTS and Beeline and Megafon.
Rebooting the device does not help. Already tried everything, nothing works.
The provider also makes a helpless gesture. Tell me where to dig and what could be the problem?

Answer 1

Wireshark generally said that there are no SIP connections :) but the valiant Syslog reported a lot of interesting things. Answer from TP Eltex:
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Clearly judging according to the log, the following happens:
- we send an INVITE with the tag Supported: 100rel, in this case, the interacting gateway, at its discretion, can transmit provisional responses either reliably or not;
- the interworking gateway (% SIP_SERVER%) chooses to transmit preliminary responses reliably, because the Require tag is present in message 183: 100rel - having
received this message, tau confirms it accordingly with a PRACK message
- which is then scolded by the SIP provider with the message 481 Call Leg / Transaction Does Not Exis -
and then we (tau) beat off the call.
Solutions:
1) (NOT RECOMMENDED) Change the "100rel" option in the SIP profile settings to off. Then we will not pass the Supported: 100rel tag to INVITE and this chain will not be repeated. But then when an incoming call comes in with a Supported: 100rel or Require: 100rel tag,
tau will swear with a 420
message. ? after all, he himself says that they say I support confirmation, therefore tau transmits PRACK.
If the SIP server does not support provisional response acknowledgment (RFC 3262), then it MUST NOT send Require: 100rel in message 183.
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Made on the first variant, everything earned. The provider did not manage to find out anything.

Answer 2

Actually, it's enough just to look at your logs and the log provider. instead of throwing up your hands

Answer 3

Do you use your own softswitch or a provider?

Answer 4

Do you take telephony from a normal operator or did you find a goip'schik on the forum? Is there any pattern (code / region / time of day)?