Sony Ericsson Construction of SMS PDU's Installation and operating instructions

Application Note
Construction of SMS PDU’s

First edition (June 2003)
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© Sony Ericsson Mobile Communications., 2003

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Contents
1INTRODUCTION....................................................................................................................4
2ABOUT SMS.......................................................................................................................... 5
3WHAT IS A PDU?..................................................................................................................5
3.1 TRANSMISSION ORDER ...................................................................................................... 6
3.2 REPRESENTATIONS ........................................................................................................... 7
4SMS-SUBMIT ........................................................................................................................ 8
4.1 THE SERVICE CENTER ADDRESS (SCA)............................................................................. 8
4.2 THE NEXT OCTET (TP-MTI AND FRIENDS) ......................................................................... 11
4.2.1 Message Type indicator (TP-MTI) ......................................................................... 11
4.2.2 Reject Duplicates (TP-RD) .................................................................................... 12
4.2.3 Validity Period Format (TP-VPF) ........................................................................... 12
4.2.4 Status Report Request (TP-SRR) ......................................................................... 12
4.2.5 User Data header Indicator (TP-UDHI) ................................................................. 13
4.2.6 Reply Path (TP-RP)............................................................................................... 13
4.2.7 Back to our example – what does it mean? .......................................................... 13
4.3 MESSAGE REFERENCE FIELD (TP-MR)............................................................................. 14
4.4 DESTINATION ADDRESS (TP-DA)....................................................................................... 14
4.5 PROTOCOL IDENTIFIER (TP-PID) ..................................................................................... 15
4.6 DATA CODING SCHEME (TP-DCS).................................................................................... 16
4.7 VALIDITY PERIOD (TP-VP) ............................................................................................... 19
4.8 USER DATA LENGTH (TP-UDL) ........................................................................................ 20
4.9 USER DATA (TP-UD) ...................................................................................................... 20
5SMS-DELIVER.....................................................................................................................25
5.1 SERVICE CENTRE ADDRESS ............................................................................................. 25
5.2 TP-MTI AND MORE FRIENDS ............................................................................................ 25
5.2.1 Message Type indicator (TP-MTI) ......................................................................... 26
5.2.2 More Messages to Send (TP-MMS) ...................................................................... 26
5.2.3 Status Report Indication (TP-SRI) ......................................................................... 26
5.2.4 User Data header Indicator (TP-UDHI) ................................................................. 26
5.2.5 Reply Path (TP-RP)............................................................................................... 27
5.2.6 Back to our example .............................................................................................. 27
5.3 THE ORIGINATING ADDRESS (TP-OA)............................................................................. 27
5.4 PROTOCOL IDENTIFIER (TP-PID) ..................................................................................... 28
5.5 DATA CODING SCHEME (TP-DCS).................................................................................... 28
5.6 THE SERVICE CENTRE TIME STAMP (TP-SCTS) ................................................................ 28
5.7 USER DATA LENGTH (TP-UDL) ....................................................................................... 29
5.8 USER DATA (TP-UD) ................................................................................................... 29

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1 Introduction
This document is to help an integrator in getting started with sending SMS
messages in the PDU format. Enough information is given here for anyone
to begin constructing the most basic PDU’s and send them, using AT
commands, from one GSM module/mobile to another.

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2 About SMS
SMS, as you already probably know stands for Short Message Service.
SMS provides a means of sending messages of limited size from and to
GSM mobile stations. SMS makes use of something called a Service
Centre, which acts as a store and forward centre for the SMS messages.
Two different types of SMS services can be defined:
Mobile Originated (MO) – Mobile originated SMS will be transported from
a mobile station to the Service Centre. These may be destined for other
mobiles or may even be destined for other services which the GSM
network and Service Centre supports.
Mobile Terminated (MT) – Mobile terminated SMS will be transported from
a Service Centre to a mobile Station.
3 What is a PDU?
PDU is short for Protocol Data Unit (or it could even be Packet Data Unit,
the different meanings are in use). These data units represent how the
digital information is coded and structured when it sent over the air
interface.
When we use a mobile phone, we usually enter a text message by the
keypad of the phone, give it a phone number to be sent to, press the
“YES” button and, usually, receive a “MESSAGE SENT” notification from
the phone. With a GSM module this process has to be performed with AT
commands from a terminal of some kind, since there is no keyboard. In
some cases the module does not support text mode SMS, and the
message must be coded as a PDU.
Using the PDU mode gives the user much more power over the
information to be sent and how it is sent. For instance one may not wish to
send a text message, but may wish to send raw Data. PDU format will
allow you to do this.
There are different kinds of PDU involved in SMS messaging, from SMS-
REPORT, SMS-COMMAND etc. etc. but we will consider only two
different types here, probably the most important as well.
Related to Mobile originated SMS is the PDU of type SMS-SUBMIT. This
is a PDU that is sent from one Mobile terminal to the Service centre.
SMS-
SERVICE
CENTER
Mobile Station Mobile Station
MO SMS MT SMS
(
SMS-SUBMIT PDU
)
(
SMS-DELIVER PDU
)

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Related to Mobile terminated SMS, an SMS that is received by a Mobile
from the Service centre is SMS-DELIVER PDU.
What does a PDU look like?
Well, just to complicate things a PDU is a Service Centre Address (SCA),
followed by a Transport Protocol Data Unit.
PDU = SCA + TPDU
An SMS-SUBMIT PDU looks something like this:
07916407058099F911000A8170607896200000A71554747A0E4ACF416
110945805B5CBF379F85C06
The SCA is shown in bold. The rest is the TPDU.
The PDU format is a hexadecimal encoded binary format, which means
that 2 hexadecimal digits represent a byte of data. When one refers to
Data being transmitted, a byte is usually called an octet (bytes are stored,
and octets are transmitted). The TPDU consists of a header containing
control information, and a “payload” containing the User Data. We will
examine the different parts in detail later.
Some Modules and mobiles do not support the PDU format but only the
TPDU format. In that case it’s just a simple matter to remove the SCA and
work with TPDU only.
You may ask the question: If a SMS must be sent via a Service Centre
doesn’t the SMS have to include the SCA?
The answer here is that the SCA is stored on the SIM card and is taken
from there. It can be changed via the use of AT commands. The good
thing about the PDU format is that by changing the SCA in the PDU the
SMS can be sent via any Service centre of your choice (as long as your
network operator allows it).
If one wishes to use the default SCA (from the SIM card) in the PDU, the
SCA part of the PDU can be replaced with 00. The PDU would look like
this:
0011000A8170607896200000A71554747A0E4ACF416110945805B5CBF
379F85C06
Before we take a look at the meaning of all this hexadecimal and what it
means, we need to consider a few other things first.
3.1 Transmission order
Octets in a PDU are transmitted according to their order. Octets at the
beginning of the PDU are transmitted first. This is the same for the
individual bits of the octets. Thus the low order bits are transmitted first.
Here is an example of octet transmission.
Say for example we wanted to send the following octets from one mobile
to another (if it were possible):
03FFFFE0

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We could write a table a table using the binary representation:
BINARY REPRESENTATION
OCTET
7 6 5 4 3 2 1 0
03 0 0 0 0 0 0 1 1
FF 1 1 1 1 1 1 1 1
FF 1 1 1 1 1 1 1 1
E0 1 1 1 0 0 0 0 0
The transmission order would be as follows (the first bit sent being the
rightmost):
11100000111111111111111100000011→
3.2 Representations
There are a few different meanings given to the hexadecimal
representations. The information in a PDU takes the form of pure
hexadecimal integers, decimal digits, and alphanumeric information
(although still represented as hexadecimal).
For instance some fields in the PDU are squeezed into one octet, and will
be seen as a hexadecimal number. One octet is two hexadecimal digits.
Sometimes the information can clearly seen to be decimal digits. For a
decimal digit only a half octet (4-bits) is required.
Alphanumeric representation is based on the default alphabet defined
later on and in GSM 03.38. This mainly applies to the User Data.
All this should come naturally as we follow the examples in the text.

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4 SMS-Submit
Recall that an SMS-SUBIT type PDU is what we want to send to another
mobile. It is what we “submit” to the service centre to be delivered to the
chosen destination.
To understand the various field of a TPDU of type SMS-SUBMIT it is best
to begin with an example and then break the TPDU down into its various
fields. Also we will consider the whole PDU (PDU = SCA + TPDU) when
discussing SMS-SUBMIT and SMS-DELIVER type TPDU’s.
We can begin with the example from the earlier sections:
07916407058099F911000A8170607896200000A71554747A0E4ACF416
110945805B5CBF379F85C06
We can start by breaking it down into the various fields:
4.1 The Service Center Address (SCA)
07916407058099F911000A8170607896200000A71554747A0E4ACF416
110945805B5CBF379F85C06
This is the Service Centre Address (SCA). It has its own special address
field. We can break it down as follows:
BINARY REPRESENTATION
OCTET
7 6 5 4 3 2 1 0
FIELD MEANING
07 0 0 0 0 0 1 1 1
ADDRESS LENGTH: This
octet declares the number
of octets to follow.
91 1 0 0 1 0 0 0 1
This is the Type of Address
field. There are two different
fields in this octet. Bits 0-3
are the Numbering plan
Identification. Bits 4-6 are
the Type of Number. Bit 7 is
a fill bit. See below for more
details.
64 0 1 1 0 0 1 0 0 The digits 4 and 6
07 0 0 0 0 0 1 1 1 The digits 7 and 0
05 0 0 0 0 0 1 0 1 The digits 5 and 0
80 1 0 0 0 0 0 0 0 The digits 0 and 8

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99 1 0 0 1 1 0 0 1 The digits 9 and 9
F9 1 1 1 1 1 0 0 1
The digit 9. Since there are
an odd number of digits in
this SCA then the bits 4-7 in
this octet are fill bits.
We can look in more detail at the Type of Address Octet:
7 6 5 4 3 2 1 0
1 Type-of-number Numbering-plan-identification
The values for the two fields, Type of number and numbering plan
identification can be chosen according to the table below:
BIT
NUMBER BIT VALUE EXPLANATION
7 1 ALWAYS Fill bit
Type of number:
0 0 0 Unknown
0 0 1 International number
0 1 0 National number
0 1 1 Network specific number
1 0 0 Subscriber number
1 0 1 Alphanumeric, (coded according to
GSM TS 03.38 7-bit default alphabet)
1 1 0 Abbreviated number
6,5,4
1 1 1 Reserved for extension
Numbering-plan-identification:
0 0 0 0 Unknown
0 0 0 1 ISDN/telephone numbering plan
0 0 1 1 Data numbering plan (X.121)
0 1 0 0 Telex numbering plan
3,2,1,0
1 0 0 0 National numbering plan

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1 0 0 1 Private numbering plan
1 0 1 0 ERMES numbering plan
1 1 1 1 Reserved for extension
All other values are reserved.
Now going back to our example we have enough information to
understand the SCA address:
07916407058099F9
First we know that after the first octet, there are 7 octets to follow in the
SCA address field.
Secondly looking closely at our example we see that the octet for the type
of address is 91. According to the table above, this means that we have
an International number and that it uses the ISDN/telephone numbering
plan.
And thirdly, looking at the rest of the SCA, we see that indeed we have an
international number:
46 705008999 (46 being the dialing code for Sweden)
Looking closely at the SCA number and remembering the transmission
order of the octet bits, we see that quite simply each pair of digits in the
number are reversed. This means that it is quite simple to convert from a
telephone number to the PDU format:
1) Write down the number (international or national format it
doesn’t matter).
46705008999
2) If the number has an odd number of digits then add an F at the
end. This means that the number will need fill bits (represented
by the hexadecimal F) in the last octet.
46705008999F
3) Pair the numbers.
46 70 50 08 99 9F
4) Reverse the digits
64 07 05 08 99 F9 Easy!!