In the SMS PDU, the TP-Protocol-Identifier parameter consists of one octet, and the bits in the octet are used as follows.

The MS will interpret reserved or unsupported values as the value 00000000 but shall store them exactly as received.

The Service Center may reject messages with a TP-Protocol-Identifier containing a reserved value or one which is not supported.

Bit 7	Bit 6	Usage
0	0	Assigns bits 0..5 as defined below
0	1	Assigns bits 0..5 as defined below
1	0	Reserved
1	1	Assigns bits 0..5 for SMSC (Short Message Service Center) specific use

In case where bits 7 and 6 both are 0:

Bit 5	DeSMSC (Short Message Service Center)ription
0	no interworking, but SME-to-SME protocol
1	telematic interworking

In the case of telematic interworking, the following five bit patterns in bits 4..0 are used to indicate types of telematic devices:

Bits 4..0	DeSMSC (Short Message Service Center)ription
00000	implicit - device type is specific to this SMSC (Short Message Service Center), or can be concluded on the basis of the address
00001	telex (or teletex reduced to telex format)
00010	group 3 telefax
00011	group 4 telefax
00100	voice telephone (i.e. conversion to speech)
00101	ERMES (European Radio Messaging System)
00110	National Paging System (known to the SMSC (Short Message Service Center))
00111	Videotex (T.100/T.101)
01000	teletex, carrier unspecified
01001	teletex, in PSPDN
01010	teletex, in CSPDN
01011	teletex, in analog PSTN
01100	teletex, in digital ISDN
01101	UCI (Universal Computer Interface, ETSI DE/PS 3 01-3)
01110.. ..01111	(reserved, 2 combinations)
10000	a message handling facility (known to the SMSC (Short Message Service Center))
10001	any public X.400-based message handling system
10010	Internet Electronic Mail
10011.. ..10111	(reserved, 5 combinations)
11000.. ..11110	values specific to each SMSC (Short Message Service Center), usage based on mutual agreement between the SME and the SMSC (Short Message Service Center) (7 combinations available for each SMSC (Short Message Service Center))
11111	A GSM mobile station. The SMSC (Short Message Service Center) converts the SM from the received TP-DCS to any data coding SMSC (Short Message Service Center)heme supported by that MS (e.g. the default).

If bit 5 has value 1 in an SMS-SUBMIT PDU, it indicates that the SME is a telematic device of a type which is indicated in bits 4..0, and requests the SMSC (Short Message Service Center) to convert the SM into a form suited for that device type. If the destination network is ISDN, the SMSC (Short Message Service Center) must also select the proper service indicators for connecting to a device of that type.

If bit 5 has value 1 in an SMS-DELIVER PDU, it indicates that the SME is a telematic device of a type which is indicated in bits 4..0.

If bit 5 has value 0 in an SMS-DELIVER PDU, the value in bits 4..0 indicates the SM-AL protocol being used between the SME and the MS.

Note that for the straightforward case of simple MS-to-SMSC (Short Message Service Center) short message transfer the Protocol Identifier is set to the value 0.

In the case where bit 7 = 0, bit 6 = 1, bits 5..0 are used as defined below

Bits 5..0	DeSMSC (Short Message Service Center)ription
000000	Short Message Type 0
000001	Replace Short Message Type 1
000010	Replace Short Message Type 2
000011	Replace Short Message Type 3
000100	Replace Short Message Type 4
000101	Replace Short Message Type 5
000110	Replace Short Message Type 6
000111	Replace Short Message Type 7
001000..011110	Reserved
011111	Return Call Message
100000..111100	Reserved
111101	ME Data download
111110	ME De-personalization Short MEssage
111111	SIM Data download