GSM 03.40

GSM 03.40 or 3GPP TS 23.040^[1] is a mobile telephony standard describing the format of the Transfer Protocol Data Units (TPDU) of the Short Message Transfer Protocol (SM-TP) used in the GSM networks to carry Short Messages. This format is used throughout the whole transfer of the message in the GSM mobile network. In contrast, application servers use different protocols, like Short Message Peer-to-Peer or Universal Computer Protocol, to exchange messages between them and the Short message service centre.

GSM 03.40 is the original name of the standard. Since 1999 it is being developed by the 3GPP under the name 3GPP TS 23.040. However, the original name is often used to refer even to the 3GPP document.

Usage

The GSM 03.40 TPDUs are used to carry messages between the Mobile Station (MS) and Mobile Switching Centre (MSC) using the Short Message Relay Protocol (SM-RP),^[2] while between MSC a Short Message Service Centre (SMSC) the TPDUs are carried as a parameter of a Mobile Application Part (MAP)^[3] package.^[4]

In emerging networks which use IP Multimedia Subsystem (IMS) are Short Messages carried in MESSAGE command of Session Initiation Protocol (SIP). Even in these IP-based networks an option exists which (due to compatibility reasons) defines transfer of Short Messages in the GSM 03.40 format embedded in 3GPP 24.011 as Content-Type: application/vnd.3gpp.sms.^[5][6]

TPDU Types

GSM 03.40 defines 6 types of messages, which are distinguished by the message direction and the 2 least significant bits in the first octet of SM-TP message (the TP-MTI field):

TPDU Types

TP-MTI	direction	message type
0 0	MS → SC	SMS-DELIVER-REPORT
0 0	SC → MS	SMS-DELIVER
0 1	MS → SC	SMS-SUBMIT
0 1	SC → MS	SMS-SUBMIT-REPORT
1 0	MS → SC	SMS-COMMAND
1 0	SC → MS	SMS-STATUS-REPORT
1 1	any	Reserved

SMS-SUBMIT is used to submit a short message from a mobile phone to a short message service centre (SMSC).

SMS-SUBMIT-REPORT is an acknowledgement to the SMS-SUBMIT; in case of success it means that the message was stored (buffered) in the SMSC, in case of failure the message was rejected by the SMSC.

SMS-COMMAND may be used to query for a message buffered in the SMSC, to modify its parameters or to delete it.

SMS-DELIVER is used to deliver a message from SMSC to a mobile phone. The acknowledgement returned by the mobile phone may optionally contain a SMS-DELIVER-REPORT. When home routing applies, SMS-DELIVER is used to submit messages from an SMSC to another one.

SMS-STATUS-REPORT may be sent by the SMSC to inform the originating mobile phone about the final outcome of the message delivery or to reply to a SMS-COMMAND.

TPDU Fields

The fields of SM-TP messages, including their order and size, are summarized in the following table, where M means a mandatory field, O an optional field, E is used for fields which are mandatory in negative responses (RP-ERR) and not present in positive responses (RP-ACK), x is a field present elsewhere:

SM-TL TPDU fields

SMS-COMMAND							size	Field name
SMS-STATUS-REPORT
SMS-SUBMIT-REPORT
SMS-SUBMIT
SMS-DELIVER-REPORT
SMS-DELIVER
field
TP-MTI	M	M	M	M	M	M	2 bits	Message Type Indicator
TP-MMS	M				M		1 bit	More Messages to Send
TP-RD			M					Reject Duplicates
TP-LP	O				O		1 bit/ 2 bits	Loop Prevention
TP-VPF			M					Validity Period Format
TP-SRI	O						1 bit	Status Report Indication
TP-SRR			O			O		Status Report Request
TP-SRQ					M			Status Report Qualifier
TP-UDHI	O	O	O	O	O	O	1 bit	User Data Header Indicator
TP-RP	M		M				1 bit	Reply Path
TP-FCS		E		E			1 octet	Failure Cause
TP-MR			M		M	M	1 octet	Message Reference
TP-DA			M			x	2-12 octets	Destination Address
TP-OA	M						2-12 octets	Originating Address
TP-RA					M		2-12 octets	Recipient Address
TP-SCTS	x			x	M		7 octets	Service Centre Time Stamp
TP-DT					M		7 octets	Discharge Time
TP-ST					M		1 octet	Status
TP-PI		M		M	O		1 octet	Parameter Indicator
TP-SCTS	x			M	x		7 octets	Service Centre Time Stamp
TP-PID	M	O	M	O	O	M	1 octet	Protocol Identifier
TP-DCS	M	O	M	O	O		1 octet	Data Coding Scheme
TP-SCTS	M			x	x		7 octets	Service Centre Time Stamp
TP-VP			O				0, 1 or 7 octets	Validity Period
TP-UDL	M	O	M	O	O		1 octet	User Data Length
TP-UD	O	O	O	O	O		given by TP-UDL	User Data
TP-CT						M	1 octet	Command Type
TP-MN						M	1 octet	Message Number
TP-DA			x			M	2-12 octets	Destination Address
TP-CDL						M	1 octet	Command Data Length
TP-CD						O	given by TP-CDL	Command Data

The first octet of the TPDU contains various flags including the TP-MTI field described above:

Bit fields in the first octet of SM-TL TPDU

bit(s)	Meaning
1-0	TP-Message-Type-Indicator (TP-MTI)
2	TP-More-Messages-to-Send (TP-MMS) in SMS-DELIVER (0 = more messages)
2	TP-Reject-Duplicates (TP-RD) in SMS-SUBMIT
3	TP-Loop-Prevention (TP-LP) in SMS-DELIVER and SMS-STATUS-REPORT
4-3	TP-Validity-Period-Format (TP-VPF) in SMS-SUBMIT (00 = not present)
5	TP-Status-Report-Indication (TP-SRI) in SMS-DELIVER
5	TP-Status-Report-Request (TP-SRR) in SMS-SUBMIT and SMS-COMMAND
5	TP-Status-Report-Qualifier (TP-SRQ) in SMS-STATUS-REPORT
6	TP-User-Data-Header-Indicator (TP-UDHI)
7	TP-Reply-Path (TP-RP) in SMS-DELIVER and SMS-SUBMIT

When TP-UDHI has value 1, the TP-UD field starts with User Data Header.

Both SM-RP and MAP used to transmit GSM 03.40 TPDU carry enough information to return acknowledgement—the information whether a request was successful or not. However, a GSM 03.40 TPDU may be included in the acknowledgement to carry even more information. The GSM 03.40 has undergone the following development:

• Up to GSM 03.40 5.2.0 SMS-DELIVER-REPORT and SMS-SUBMIT-REPORT was sent only in the case of an error. Since 5.3.0 they are sent in case of success as well.
• Up to GSM 03.40 6.0.0 SMS-DELIVER-REPORT and SMS-SUBMIT-REPORT sent in case of an error contained only TP-MTI and TP-FCS fields and the last field in SMS-STATUS-REPORT was TP-ST. Since version 6.1.0 these TPDUs has format shown in the table above.

Although these changes are ancient (version 6.1.0 occurred in July 1998), old formats of MAP are frequently seen even in today's networks.

Message Content

The content of the message (its text when the message is not a binary one) is carried in the TP-UD field. Its size may be up to 160 x 7 = 140 x 8 = 1120 bits. Longer messages can be split to multiple parts and sent as a Concatenated SMS. The length of message content is given in the TP-UDL field. When the message encoding is GSM 7 bit default alphabet (depends on TP-DCS field), the TP-UDL gives length of TP-UD in 7-bit units; otherwise TP-UDL gives length of the TP-UD in octets.

When TP-UDHI is 1, the TP-UD starts with User Data Header (UDH); in this case the first octet of the TP-UD is User Data Header Length (UDHL) octet, containing the length of the UDH in octets without UDHL itself. UDH eats room from the TP-UD field. When the message encoding is GSM 7 bit default alphabet and a UDH is present, fill bits are inserted to align start of the first character of the text after UDH with septet boundary. This behaviour was designed for older mobile phones which don't understand UDH; such mobile phones might display the UDH as a jumble of strange characters; if the first character after UDH was Carriage Return (CR), the mobile phone would rewrite the mess with the rest of the message.

Addresses

A GSM 03.40 message contains at most one address: destination address (TP-DA) in SMS-SUBMIT and SMS-COMMAND, originator address (TP-OA) in SMS-DELIVER and recipient address (TP-RA) in SMS-STATUS-REPORT. Other addresses are carried by lower layers.

The format of addresses in the GSM 03.40 is described in the following table:

octet	Meaning
0	address length in nibbles or semi-octets
1	EXT, TON, NPI
2-11	address digits

Type of number (TON):

Bit 6 5 4	Meaning
0 0 0	Unknown 1)
0 0 1	International number 2)
0 1 0	National number 3)
0 1 1	Network specific number 4)
1 0 0	Subscriber number 5)
1 0 1	Alphanumeric, (coded according to 3GPP TS 23.038 [9] GSM 7 bit default alphabet)
1 1 0	Abbreviated number
1 1 1	Reserved for extension

The `+' sign at the start of a telephone number indicates that an `International number' follows which has TON=1 (0 0 1). Such number must have country code just after the `+'. Numbers beginning with a trunk or international prefix has TON=0.

Numbering plan identification (NPI):

Bits 3 2 1 0	Meaning
0 0 0 0	Unknown
0 0 0 1	ISDN/telephone numbering plan (E.164/E.163)
0 0 1 1	Data numbering plan (X.121)
0 1 0 0	Telex numbering plan
0 1 0 1	Service Centre Specific plan 1)
0 1 1 0	Service Centre Specific plan 1)
1 0 0 0	National numbering plan
1 0 0 1	Private numbering plan
1 0 1 0	ERMES numbering plan (ETSI DE/PS 3 01 3)
1 1 1 1	Reserved for extension

Telephone numbers should have NPI=1. Application servers may use alphanumeric addresses which have TON=5, NPI=0 combination.

Address Examples

U.S. number +1 555 123 4567 would be encoded as 0B 91 51 55 21 43 65 F7 (the F in upper four bits of the last octet is a filler which is used when the number length is odd).

Alphanumeric address is at first put to the GSM 7 bit default alphabet, then encoded the same way as any message text in TP-UD field (that means it is 7-bit packed) and then the address is supplied with the "number" length and TON and NPI.

For example, a fictional alphanumeric address Design@Home is converted to the GSM 7 bit default alphabet which yields 11 bytes 44 65 73 69 67 6E 00 48 6F 6D 65 (hex), the 7-bit packing transforms it to 77 bits stored in 10 octets as C4 F2 3C 7D 76 03 90 EF 76 19; 77 bits is 20 nibbles (14 hex) which is the value of the first octet of the address. The second octet contains TON (5) and NPI (0), which yields D0 hex. The complete address in the GSM format is 14 D0 C4 F2 3C 7D 76 03 90 EF 76 19.

Time Format

A date and time used in TP-SCTS, TP-DT and in Absolute format of TP-VP is stored in 7 octets:

Format of Date and Time Fields in SM-TL TPDU

octet	Content
0	Last two digits of the year
1	Month
2	Day
3	Hour
4	Minute
5	Second
6	Time zone

In all octets the values are stored in binary coded decimal format with switched digits (number 35 is stored as 53 hex).

Time zone is given in quarters of an hour. If the time zone offset is negative (in Western hemisphere) the bit 3 of the last octet is set to 1.

23:01:56 Mar 25th 2013 PST (GMT-7) would be encoded as 31 30 52 32 10 65 8A.

Validity Period

Validity Period format is defined by the Validity Period Format field:

Validity Period Formats

TP-VPF	TP-VP format	TP-VP length
0 0	TP-VP not present	0
0 1	Enhanced format	7
1 0	Relative format	1
1 1	Absolute format	7

Relative format

Relative Validity Period Values

TP-VPF value	Validity period	Possible validity periods
0-143	(TP-VP + 1) x 5 minutes	5, 10, 15 minutes ... 11:55, 12:00 hours
144-167	(12 + (TP-VP - 143) / 2 ) hours	12:30, 13:00, ... 23:30, 24:00 hours
168-196	(TP-VP - 166) days	2, 3, 4, ... 30 days
197-255	(TP-VP - 192) weeks	5, 6, 7, ... 63 weeks

Absolute format

The absolute format is identical to the other time formats in GSM 03.40.

Enhanced format

Enhanced format of TP-VP field is seldom used. It has always 7 octets, although some of them are not used. The first octet is TP-VP Functionality Indicator. Its 3 least significant bits have the following meaning:

Bits 2 to 0 of TP-VP Functionality Indicator meaning

2 1 0	Meaning
0 0 0	No validity period specified
0 0 1	The following octet is a relative validity period as described in the Relative Validity Period Values table
0 1 0	The following octet contains a relative validity period in seconds in the range 0 to 255
0 1 1	The following 3 octets contain a relative validity period in hours, minutes and seconds as the 3rd to 5th octet of time format
1 X X	Reserved

The value of 1 in the bit 6 of the first octet means that the message is Single-shot. The value of 1 in the bit 7 of the first octet indicates that TP-VP functionality indicator extends to another octet. However, no such extensions are defined.

Protocol Identifier

Protocol identifier either refers to the higher layer protocol being used, indicates interworking with a certain type of telematic device (like fax, telex, pager, teletex, e-mail), specifies replace type of the message or allows download of configuration parameters to the SIM card. Plain MO-MT messages have PID=0.

Data Coding Scheme

A special 7 bit encoding called GSM 7 bit default alphabet was designed for Short Message System in GSM. The alphabet contains the most-often used symbols from most Western-European languages (and some Greek uppercase letters). Some ASCII characters and the Euro sign did not fit into the GSM 7 bit default alphabet and must be encoded using two septets. These characters form GSM 7 bit default alphabet extension table. Support of the GSM 7-bit alphabet is mandatory for GSM handsets and network elements.^[7]

Languages which use Latin script, but use characters which are not present in the GSM 7 bit default alphabet, often replace missing characters with diacritic marks with corresponding characters without diacritics, which causes not entirely satisfactory user experience, but is often accepted. For best look the 16-bit UTF-16 (in GSM called UCS-2) encoding may be used at price of reducing length of a (non segmented) message from 160 to 70 characters.

The messages in Chinese, Korean or Japanese languages must be encoded using the UTF-16 character encoding. The same was also true for other languages using non-Latin scripts like Russian, Arabic, Hebrew and various Indian languages. In 3GPP TS 23.038 8.0.0 published in 2008 a new feature, an extended National language shift table was introduced, which in the version 11.0.0 published in 2012 covers Turkish, Spanish, Portuguese, Bengali, Gujarati, Hindi, Kannada, Malayalam, Oriya, Punjabi, Tamil, Telugu and Urdu languages. The mechanism replaces GSM 7 bit default alphabet code table and/or extended table with a national table(s) according to special information elements in User Data Header. The non-segmented message using national language shift table(s) may carry up to 155 (or 153) 7-bit characters.

The Data Coding Scheme (TP-DCS) field contains primarily information about message encoding. GSM recognizes only 2 encodings for text messages and 1 encoding for binary messages:

• GSM 7 bit default alphabet (which includes using of National language shift tables as well)
• UCS-2
• 8 bit data

The TP-DCS octet has a complex syntax to allow carrying of other information; the most notable are message classes:

Message Classes

Value	Message Class
0 0	0 - Flash messages
0 1	1 - ME-specific
1 0	2 - SIM / USIM specific
1 1	3 - TE-specific

Flash messages are received by a mobile phone even though it has full memory. They are not stored in the phone, they just displayed on the phone display.

Another feature available through TP-DCS is Automatic Deletion: after reading the message is deleted from the phone.

Message Waiting Indication group of DCS values can set or reset flags of indicating presence of unread voicemail, fax, e-mail or other messages.

A special DCS values also allows message compression, but it perhaps is not used by any operator.

The values of TP-DCS are defined in GSM recommendation 03.38. Messages sent via this encoding can be encoded in the default GSM 7-bit alphabet, the 8-bit data alphabet, and the 16-bit UCS-2 alphabet.^[7]

Parameter Indicator

The TP-PI field indicate presence of further fields in the SUBMIT-REPORT, DELIVER-REPORT or SMS-STATUS-REPORT TPDU.

TP-PI bits

bit	Meaning
0	TP-PID
1	TP-DCS
2	TP-UDL and TP-UD
8	another TP-PI octet (extension bit)

As currently there are still 4 free bits in TP-PI, it can be expected that the extension bit will be zero even in the future, which helps to distinguish TP-PI field from TP-FCS field when information whether TPDU is part of positive or negative response is not available: if the most significant bit of the second octet of TPDU is 1, the second octet is TP-FCS (in a negative response), otherwise it is TP-PI (in a positive response).

See also

• Short Message Service
• GSM 03.38
• User Data Header
• Concatenated SMS
• Short message service technical realisation (GSM)
• Enhanced Messaging Service
• Multimedia Messaging Service
• Short Message Peer-to-Peer
• Universal Computer Protocol

References

External links