Cellular GSM Technology - How do I send long SMS (more than 500 characters) using AT commands

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How do I send long SMS (more than 500 characters) using AT commands

modemseeker

2008-01-09, 10:33 pm

Can someone please tell me how do I send using a UMTS modem and extra
long SMS message in text mode.

Thanks
jami

John Henderson

2008-01-09, 10:33 pm

modemseeker wrote:

> Can someone please tell me how do I send using a UMTS modem
> and extra long SMS message in text mode.

Well, you could try tricking the modem by setting the UDHI (user
data header indicator) bit on within the PDU-type octet of the
4 individual messages which 500 characters would require. Then
you'd need to encode the UDH (user data header) fields
yourself, and then re-encode those into 7-bit characters which
the modem will accept as if they were text.

You'd use the

AT+CSMP=<fo>

command to set the UDHI bit (<fo> = "first octet" = PDU-type)
prior to submitting the message. Numbering the 8 bits in <fo>
from zero on the right to 7 on the left, UDHI is bit 6.

But encoding the UDH as pseudo-text might prove to be as hard as
using PDU-mode in the first place.

Other than that, if your modem won't break it down into parts
for you, then you'd need to abandon text-mode, use PDU-mode,
and encode the PDUs yourself.

A total of 3 parts seems to be a common limit for enoding (not
sure about reassembling) a multi-part message. Given the
payload reduction necessary for the information required in the
UDH, that's 459 (3 x 153) characters from the default 7-bit
alphabet.

You could send up to 255 parts (39,015 characters) in PDU-mode.

John

John Henderson

2008-01-28, 10:33 pm

kaiserb@gmail.com wrote:

> I found how to code SMS text in PDU mode, but i didn't find
> yet UDH format. Can you give us more information?

The primary source is 3GPP 23.040. These can be downloaded from
www.etsi.org for free after registering. Section 9.2.3.24 is a
good starting point.

For long messages, you'll need to use SMS concatenation (section
9.2.3.24.1).

Apologies for the late response - I went to Adelaide to watch
the Tour Down Under :)

John

Andreas Wenzel

2008-01-29, 3:33 pm

John Henderson schrieb:
> kaiserb@gmail.com wrote:
>
>
> The primary source is 3GPP 23.040. These can be downloaded from
> www.etsi.org for free after registering. Section 9.2.3.24 is a
> good starting point. [...]

Or get it from it's home at 3gpp.org without any registering:

http://www.3gpp.org/ftp/Specs/archi...Fseries/23.040/

Andreas

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