I have problem with USSD-String structure, which has no explicit
description in specifications.
GSM 09.02 says:
<<USSD-String ::= OCTET STRING (SIZE (1..maxUSSD-StringLength))
-- The structure of the contents of the USSD-String is dependent
-- on the USSD-DataCodingScheme as described in TS GSM 03.38.>>
GSM 03.38 has DataCodingScheme, but has no information about
GSM 03.38 says:
<<See GSM 04.90 for specific coding values applicable to Unstructured
SS Data for MS originated USSD messages and MS terminated USSD
USSD messages using the default alphabet are coded with the 7-bit
alphabet given in subclause 6.2.1. The message can then consist of up
to 182 user characters.>>
GSM 04.90 has no information about USSD-String structure too.
I have several different messages from MS (all with
USSD-dataCodingScheme = 00110000), and I suppose that the USSD-String
has following structure:
00001010 USSD-String length without this octet
00000100 This and three next octets have the same value in all
received messages (I have no idea about purpose this octets!)
00000101 Number of octets for Data String
10101010 Data String (In this example *100#) (coded with the 7-bit alphabet)
What purpose have four octets after USSD-String length field?
What structure has USSD-String and where it can be described?