PDU 编码格式
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SMS (Short Message Service) is specified by the ETSI (standards GSM 03.40 and 03.38). It can contain up to 160 characters, where each character is written according to the7-bits GSM default alphabet.[ 7 bits default table ]

SMS also contains some meta-data, e.g.

  1. Info about the senders ( Service center number, sender number)
  2. Protocol information (Protocol identifier, Data coding scheme)
  3. Timestamp


There are 2 ways to receive and send SMS messages , PDU (protocol discription unit) and Text mode. In this document we focus on PDU mode.

PDU format can be used on any encoding.
As an example:
07911326040000F0040B911346610089F600002080629 17314080CC8F71D14969741F977FD07

The above PDU string contains the message "How are you?" and was read from a jindi gsm modem.The string is built from hexadecimal-octets and semi decimal-octets.As mentioned, SMS contains metadata about itself.
We explain it using the example above:
Octet(s) Description format In this example
07 Length of the SMSC information

hex-octet

7 octets

91 Type of address of SMSC hex-octet internation format
13 26 04 00 00 F0 SMSC number decimal semi-octets 31624000000
04 First octet of this SMS-DELIVER message. hex-octet TP-MMS
0B Length of the sender address hex-octet 11 (decimal)
91 Type of address of the sender number hex-octet ...
13 46 61 00 89 F6 Sender number decimal semi-octets 31641600986
00 Protocol identifier hex-octets ...
00 Data encoding scheme hex-octets ...
20 80 62 91 73 14 08 Time stamp decimal semi-octets 06-08-02 29:17:31
0C Length of User data (SMS message) hex-octets 12 (decimal)
C8 F7 1D 14 96 97 41 F9 77 FD 07 User data 8-bit octets respresenting 7-bit data How are you?
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