CODEWITHSUNDEEP
gsmat-commandmodem
ezpzlmnsqz1337
ezpzlmnsqz1337

Reputation: 424

How to make a CSD call from modem

I recently bought a modem that supports CSD (Circuit Switched Data) calls. I put SIM card in it and I am able to make calls via AT commands. But these are always VOICE calls. I have another modem and I need to connect to it via CSD.

I know it is possible because our colleagues are using it this way to access some network.

They are using windows dial-up connection, but I guess that is just something that in the background calls the AT commands.

Nevertheless the dial-up is still giving me "Error 678: Remote computer did not respond". I have tried many settings, but still the same error. I even tried different computer and still got the same error.

So I found out that when I call CSD, then on the receiving side (if AT+CRC=1) it should display +CRING: REL ASYNC. So I setup another modem and called it and it showed +CRING: VOICE.

So how do I convince my modem to call in the REL ASYNC mode? I already tried:

AT+IPR=115200 or AT+IPR=9600
AT+FCLASS=0 (this is default though)
AT+CSNS=4
AT+CBST=7,0,0 or AT+CBST=71,0,1
AT^SXRAT=0 (this changes the network to GSM)

But still when I do ATDNUMBERIWANTTOCALL; the receiving side shows +CRING: VOICE.

Also my mobile provider ensured me, that the CSD technology is still supported in my country and that I do not need any kind of special SIM card.

Upvotes: 0

Views: 3948

Answers (3)

ezpzlmnsqz1337
ezpzlmnsqz1337

Reputation: 424

In the end the number could be called normally like it is written in the question, but it only worked in Germany, not abroad...

Upvotes: 0

Mychaela Falconia
Mychaela Falconia

Reputation: 21

You need to remove the semicolon after the phone number in the ATD command: that semicolon is what tells the modem to make a voice call rather than CSD.

Upvotes: 2

Nautilus137
Nautilus137

Reputation: 1

Check with your teleoperator does your sim card have separate data number.

Sometimes postpaid (and/or M2M) cards have three different numbers 1. voice 2. fax 3. data

Upvotes: 0

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