Generic NACK

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Mudit Agrawal
New member
Username: Mudit_test

Post Number: 3
Registered: 12-2020
Posted on Monday, January 18, 2021 - 08:53 am:   

Hi Team,

I'm receiving Generic NACK in the SMPP debug logs. What is the error code we have received for this Generic NACK. PFB the screenshot. Please let us know how to decode the error codes.
Des - NowSMS Support
Board Administrator
Username: Desosms

Post Number: 6216
Registered: 08-2008
Posted on Monday, January 18, 2021 - 01:14 pm:   

Hi,

This is an error being returned by the SMSC.

It is not normal for an SMSC to return such an error. The SMPP specification says this error should only be used as follows:


quote:

This is a generic negative acknowledgement to an SMPP PDU submitted with an invalid message header. A generic_nack response is returned in the following cases:
• Invalid command_length
If the receiving SMPP entity, on decoding an SMPP PDU, detects an invalid command_length (either too short or too long), it should assume that the data is corrupt. In such cases a generic_nack PDU must be returned to the message originator.
• Unknown command_id
If an unknown or invalid command_id is received, a generic_nack PDU must also be returned to the originator.




From the context of the log, it would appear that NowSMS sent a submit_sm packet to the SMSC. Normal behaviour for the SMSC would be for the SMSC to send a submit_sm_resp packet in response ... whether the response is success or an error ... the submit_sm_resp packetvformat is what the SMSC is expected to use.

If the SMSC is sending a generic_nack packet, it is saying that it does not understand the request.

This generic NACK includes an error command_status value of 0x233B. That error code is outside of the range of error codes defined in the SMPP specification.

I would suggest inquiring with the SMSC vendor to understand what this error condition means in their implementation.

Regards,

Des
NowSMS Support
Des - NowSMS Support
Board Administrator
Username: Desosms

Post Number: 6217
Registered: 08-2008
Posted on Monday, January 18, 2021 - 01:29 pm:   

Follow-up ... I did have one additional thought after posting that reply.

Is there any consistency as to when this error occurs? Is it random, or does it seem to be related to specific message content and/or multipart messages only?

One of the conditions that is defined as a reason for an SMSC to return this error is an "invalid command_length". While I am confident that this "command_length" is correct, if you are seeing this error only with multipart messages, there is some ambiguity in the SMPP specification with regard to message formatting and a different length parameter, sm_length. Because different SMSCs have different expectations for how long messages are encoded, there is an advanced setting in NowSMS for "Use 7-bit Packed Encoding for long text messages". Try changing this setting to see if either turning this setting on or off fixes the problem, as your SMSC may have a different preference for how long messages are encoded.

Regards,

Des
NowSMS Support

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