Unsolicited Response (+STCR) from SIM Toolkit not visible

Question

I'm testing a SIM Toolkit application using AT Commands. I have a USB modem that supports SIM Toolkit Class 2 features and is based on the Open AT Firmware. I am able to successfully interact with the SIM Toolkit by using the +STSF, +STGI, and +STGR commands. I also receive +STIN replies as per the message flow shown here. What I do not receive is the Unsolicited Response (+STCR) from the SIM when an SMS message or USSD message is sent out. I am using the following Terminal Profile during initialization:

AT+STSF=2,"5FFFFFFF7F",3,1

Based on the Terminal Profile, the Call Control bit is set to 1 or enabled. You will also notice that the Autoresponse is set to 1. Therefore, I receive an +STGI response when a message is sent. Here is the lead up to when the SIM sends an SMS message:

AT+STGR=6,1,1
OK

+STIN: 9

+STGI: ""

OK

You can see that +STIN: 9 means an SMS message is sent out. I believe based on my initialization, I should also see an +STCR and there should be some text in the +STGI. If anyone is familiar with the SIM Toolkit and accessing it through the AT Command set, then I would appreciate some insight as to why I do not receive a response when an SMS message is sent out. Thanks.

Reference: 1: Wavecom AT Commands Interface Guide for X51a - WM_ASW_OAT_UGD_00016

Answer 1

I think the USB modem is busy for doing other task.

If you send response with 0x91xx instead of 0x9000 again and again while you don't receive Instruction byte ie 0x12 ie FETCH command.

where XX means no of STK byte .