9.2.2 PDU Type repertoire at SM‑TL
23.0403GPPRelease 17Technical realization of the Short Message Service (SMS)TS
The SM‑TL comprises the following six PDUs:
SMS‑DELIVER, conveying a short message from the SC to the MS;
SMS‑DELIVER‑REPORT, conveying;
a) a failure cause (if necessary);
b) information as part of a positive or negative acknowledgement to an SMS-DELIVER or SMS-STATUS-REPORT;
SMS‑SUBMIT, conveying a short message from the MS to the SC;
SMS‑SUBMIT‑REPORT, conveying;
a) a failure cause (if necessary);
b) information as part of a positive or negative acknowledgement to an SMS-SUBMIT or SMS-COMMAND;
SMS‑STATUS‑REPORT, conveying a status report from the SC to the MS;
SMS‑COMMAND, conveying a command from the MS to the SC.
9.2.2.1 SMS‑DELIVER type
Basic elements of the SMS‑DELIVER type:
|
Abbr. |
Reference |
P1) |
R2) |
Description |
|
TP‑MTI |
TP‑Message‑Type‑Indicator |
M |
2b |
Parameter describing the message type. |
|
TP‑MMS |
TP‑More‑Messages‑to‑Send |
M |
b |
Parameter indicating whether or not there are more messages to send |
|
TP-LP |
TP-Loop-Prevention |
O |
b |
Parameter indicating that SMS applications should inhibit forwarding or automatic message generation that could cause infinite looping. |
|
TP‑RP |
TP‑Reply‑Path |
M |
b |
Parameter indicating that Reply Path exists. |
|
TP‑UDHI |
TP‑User‑Data‑Header‑Indicator |
O |
b |
Parameter indicating that the TP‑UD field contains a Header |
|
TP‑SRI |
TP‑Status‑Report‑Indication |
O |
b |
Parameter indicating if the SME has requested a status report. |
|
TP‑OA |
TP‑Originating‑Address |
M |
2‑12o |
Address of the originating SME. |
|
TP‑PID |
TP‑Protocol‑Identifier |
M |
o |
Parameter identifying the above layer protocol, if any. |
|
TP‑DCS |
TP‑Data‑Coding‑Scheme |
M |
o |
Parameter identifying the coding scheme within the TP‑User‑Data. |
|
TP‑SCTS |
TP‑Service‑Centre‑Time‑Stamp |
M |
7o |
Parameter identifying time when the SC received the message. |
|
TP‑UDL |
TP‑User‑Data‑Length |
M |
I |
Parameter indicating the length of the TP‑User‑Data field to follow. |
|
TP‑UD |
TP‑User‑Data |
O |
3) |
1) Provision; Mandatory (M) or Optional (O).
2) Representation; Integer (I), bit (b), 2 bits (2b), Octet (o), 7 octets (7o), 2‑12 octets (2‑12o).
3) Dependent on the TP‑DCS.
Layout of SMS‑DELIVER:
|
Bit no. |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|||||
|
1 |
TP-MTI, TP-MMS, TP-LP, TP-SRI, TP-UDHI, TP-RP |
||||||||||||
|
Number of |
octets |
1 |
|||||||||||
|
2 |
|||||||||||||
|
2 to |
12 |
TP-OA |
|||||||||||
|
1 |
TP-PID |
||||||||||||
|
1 |
TP-DCS |
||||||||||||
|
TP-SCTS |
|||||||||||||
|
1 |
TP-UDL |
||||||||||||
|
1 |
|||||||||||||
|
TP-UD |
|||||||||||||
NOTE: Any unused bits shall be set to zero by the sending entity and shall be ignored by the receiving entity.
9.2.2.1a SMS‑DELIVER‑REPORT type
An SMS‑DELIVER‑REPORT TPDU is carried as a RP‑User‑Data element within an RP‑ERROR PDU and is part of the negative acknowledgement to an SMS‑DELIVER or SMS‑STATUS‑REPORT.
An SMS‑DELIVER‑REPORT TPDU is also carried as a RP‑User‑Data element within an RP‑ACK PDU and is part of a positive acknowledgement to a SMS‑DELIVER or SMS‑STATUS REPORT.
(i) SMS‑DELIVER‑REPORT for RP‑ERROR
Basic elements of the SMS‑DELIVER‑REPORT type:
|
Abbr. |
Reference |
P1) |
P2) |
Description |
|
TP‑MTI |
TP‑Message‑Type‑Indicator |
M |
2b |
Parameter describing the message type |
|
TP-UDHI |
TP-User-Data-Header-Indication |
O |
b |
Parameter indicating that the TP-UD field contains a Header |
|
TP‑FCS |
TP‑Failure‑Cause |
M |
I |
Parameter indicating the reason for SMS‑DELIVER failure |
|
TP‑PI |
TP‑Parameter‑Indicator |
M |
o |
Parameter indicating the presence of any of the optional parameters which follow |
|
TP‑PID |
TP‑Protocol‑Identifier |
O |
o |
see clause 9.2.3.9 |
|
TP‑DCS |
TP‑Data‑Coding‑Scheme |
O |
o |
see clause 9.2.3.10 |
|
TP‑UDL |
TP‑User‑Data‑Length |
O |
o |
see clause 9.2.3.16 |
|
TP‑UD |
TP‑User‑Data |
O |
3) 4) |
see clause 9.2.3.24 |
1) Provision: Mandatory (M) or Optional (O).
2) Representation: Integer (I), bit (b), 2bits (2b), octet (o).
3) Dependent upon the TP‑DCS.
4) The TP‑User‑Data field in the SMS‑DELIVER‑REPORT is only available for use by the MT.
Layout of SMS‑DELIVER‑REPORT:
Bit Number
|
Number of Octets |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
||
|
1 |
TP‑MTI, TP-UDHI |
|||||||||
|
1 |
TP-FCS |
|||||||||
|
1 |
TP‑PI |
|||||||||
|
0,1 |
TP‑PID |
|||||||||
|
0,1 |
TP‑DCS |
|||||||||
|
0,1 |
TP‑UDL |
|||||||||
|
0 to 158 |
TP‑UD |
Bits 7 and 5 ‑ 2 in octet 1 are presently unused and the sender shall set them to zero. If any of these bits is non‑zero, the receiver shall not examine the other field and shall treat the TP‑Failure‑Cause as "Unspecified error cause".
(ii) SMS‑DELIVER‑REPORT for RP‑ACK
Basic elements of the SMS‑DELIVER‑REPORT type:
|
Abbr |
Reference |
P1) |
P2) |
Description |
|---|---|---|---|---|
|
TP‑MTI |
TP‑Message Type Indicator |
M |
2b |
Parameter describing the message type |
|
TP-UDHI |
TP-User-Data-Header-Indication |
O |
b |
Parameter indicating that the TP-UD field contains a Header |
|
TP‑PI |
TP‑Parameter‑Indicator |
M |
o |
Parameter indicating the presence of any of the optional parameters which follow |
|
TP‑PID |
TP‑Protocol‑Identifier |
O |
o |
see clause 9.2.3.9 |
|
TP‑DCS |
TP‑Data‑Coding‑Scheme |
O |
o |
see clause 9.2.3.10 |
|
TP‑UDL |
TP‑User‑Data‑Length |
O |
o |
see clause 9.2.3.16 |
|
TP‑UD |
TP‑User‑Data |
O |
3) 4) |
see clause 9.2.3.24 |
1) Provision: Mandatory (M) or Optional (O).
2) Representation: Integer (I), Bit (b), 2 bits (2b), octet (o).
3) Dependent upon the TP‑DCS.
4) The TP‑User‑Data field in the SMS‑DELIVER‑REPORT is only available for use by the MT.
Layout of SMS‑DELIVER‑REPORT:
Bit Number
|
Number of Octets |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
||
|
1 |
TP‑MTI, TP-UDHI |
|||||||||
|
1 |
TP‑PI |
|||||||||
|
0,1 |
TP‑PID |
|||||||||
|
0,1 |
TP‑DCS |
|||||||||
|
0,1 |
TP‑UDL |
|||||||||
|
0 to 159 |
TP‑UD |
Bits 7 and 5 ‑ 2 in octet 1 are presently unused in the SMS‑DELIVER‑REPORT and the sender shall set them to zero. If any of these bits is non‑zero, the receiver shall ignore them.
9.2.2.2 SMS‑SUBMIT type
Basic elements of the SMS‑SUBMIT type:
|
Abbr. |
Reference |
P1) |
P2) |
Description |
|---|---|---|---|---|
|
TP‑MTI |
TP‑Message‑Type‑Indicator |
M |
2b |
Parameter describing the message type. |
|
TP‑RD |
TP‑Reject‑Duplicates |
M |
b |
Parameter indicating whether or not the SC shall accept an SMS‑SUBMIT for an SM still held in the SC which has the same TP‑MR and the same TP‑DA as a previously submitted SM from the same OA |
|
TP‑VPF |
TP‑Validity‑Period‑Format |
M |
2b |
Parameter indicating whether or not the TP‑VP field is present. |
|
TP‑RP |
TP‑Reply‑Path |
M |
b |
Parameter indicating the request for Reply Path. |
|
TP‑UDHI |
TP‑User‑Data‑Header‑Indicator |
O |
b |
Parameter indicating that the TP‑UD field contains a Header. |
|
TP‑SRR |
TP‑Status‑Report‑Request |
O |
b |
Parameter indicating if the MS is requesting a status report. |
|
TP‑MR |
TP‑Message‑Reference |
M |
I |
Parameter identifying the SMS‑SUBMIT. |
|
TP‑DA |
TP‑Destination‑Address |
M |
2‑12o |
Address of the destination SME. |
|
TP‑PID |
TP‑Protocol‑Identifier |
M |
o |
Parameter identifying the above layer protocol, if any. |
|
TP‑DCS |
TP‑Data‑Coding‑Scheme |
M |
o |
Parameter identifying the coding scheme within the TP‑User‑Data. |
|
TP‑VP |
TP‑Validity‑Period |
O |
o/7o |
Parameter identifying the time from where the message is no longer valid. |
|
TP‑UDL |
TP‑User‑Data‑Length |
M |
I |
Parameter indicating the length of the TP‑User‑Data field to follow. |
|
TP‑UD |
TP‑User‑Data |
O |
3) |
1) Provision; Mandatory (M) or Optional (O).
2) Representation; Integer (I), bit (b), 2 bits (2b), Octet (o), 7 octets (7o), 2‑12 octets (2‑12o).
3) Dependent on the TP‑DCS.
Layout of SMS‑SUBMIT:
|
Bit no |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|||||
|
1 |
TP-MTI, TP-RD, TP-VPF TP-SRR, TP-UDHI, TP-RP |
||||||||||||
|
1 |
TP-MR |
||||||||||||
|
Number of |
1 |
||||||||||||
|
octets |
2 |
||||||||||||
|
2 to |
12 |
TP-DA |
|||||||||||
|
1 |
TP-PID |
||||||||||||
|
1 |
TP-DCS |
||||||||||||
|
1 |
|||||||||||||
|
0, 1 |
or 7 |
TP-VP |
|||||||||||
|
1 |
TP-UDL |
||||||||||||
|
1 |
|||||||||||||
|
0 to |
140 |
TP-UD |
|||||||||||
NOTE: Any unused bits shall be set to zero by the sending entity and shall be ignored by the receiving entity.
9.2.2.2a SMS‑SUBMIT‑REPORT type
An SMS‑SUBMIT‑REPORT TPDU is carried as a RP‑User‑Data element within an RP‑ERROR PDU and is part of the negative acknowledgement to an SMS‑SUBMIT or SMS‑COMMAND.
An SMS‑SUBMIT‑REPORT TPDU is also carried as a RP‑User‑Data element with an RP‑ACK PDU and is part of a positive acknowledgement to a SMS‑SUBMIT or SMS‑COMMAND.
(i) SMS‑SUBMIT‑REPORT for RP‑ERROR
Basic elements of the SMS‑SUBMIT‑REPORT type:
|
Abbr. |
Reference |
P1) |
P2) |
Description |
|---|---|---|---|---|
|
TP‑MTI |
TP‑Message‑Type‑Indicator |
M |
2b |
Parameter describing the message type |
|
TP-UDHI |
TP-User-Data-Header-Indication |
O |
b |
Parameter indicating that the TP-UD field contains a Header |
|
TP‑FCS |
TP‑Failure‑Cause |
M |
I |
Parameter indicating the reason for SMS‑SUBMIT failure |
|
TP‑PI |
TP‑Parameter‑Indicator |
M |
o |
Parameter indicating the presence of any of the optional parameters which follow |
|
TP‑SCTS |
TP‑Service‑Centre‑Time‑Stamp |
M |
7o 5) |
Parameter identifying the time when the SC received the SMS‑SUBMIT See clause 9.2.3.11 |
|
TP‑PID |
TP‑Protocol‑Identifier |
O |
o |
See clause 9.2.3.9 |
|
TP‑DCS |
TP‑Data‑Coding‑Scheme |
O |
o |
see clause 9.2.3.10 |
|
TP‑UDL |
TP‑User‑Data‑Length |
O |
o |
see clause 9.2.3.16 |
|
TP‑UD |
TP‑User‑Data |
O |
3) 4) |
see clause 9.2.3.24 |
1) Provision: Mandatory (M) or Optional (O).
2) Representation: Integer (I), bit (b), 2bits (2b), octet (o).
3) Dependent upon the TP‑DCS.
4) The TP‑User‑Data field in the SMS‑SUBMIT‑REPORT is only available for use by the SC.
5) This same time value shall also be carried in the SMS‑STATUS‑REPORT relating to a particular SM. See clause 9.2.2.3. This shall allow the submitting SME to associate a particular SMS‑SUBMIT with a subsequent SMS‑STATUS‑REPORT by correlating the TP‑SCTS values.
Layout of SMS‑SUBMIT‑REPORT:
Bit Number
|
Number of Octets |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
||
|
1 |
TP‑MTI, TP-UDHI |
|||||||||
|
1 |
TP-FCS |
|||||||||
|
1 |
TP‑PI |
|||||||||
|
7 |
TP‑SCTS |
|||||||||
|
0,1 |
TP‑PID |
|||||||||
|
0,1 |
TP‑DCS |
|||||||||
|
0,1 |
TP‑UDL |
|||||||||
|
0 to 151 |
TP‑UD |
Bits 7 and 5 ‑ 2 in octet 1 are presently unused and the sender shall set them to zero. If any of these bits is non‑zero, the receiver shall not examine the other field and shall treat the TP‑Failure‑Cause as "Unspecified error cause".
(ii) SMS‑SUBMIT‑REPORT for RP‑ACK
Basic elements of the SMS‑SUBMIT_REPORT type:
|
Abbr |
Reference |
P1) |
P2) |
Description |
|
TP‑MTI |
TP‑Message Type‑Indicator |
M |
2b |
Parameter describing the message type |
|
TP-UDHI |
TP-User-Data-Header-Indication |
O |
b |
Parameter indicating that the TP-UD field contains a Header |
|
TP‑PI |
TP‑Parameter‑Indicator |
M |
o |
Parameter indicating the presence of any of the optional parameters which follow |
|
TP‑SCTS |
TP‑Service‑Centre‑Time‑Stamp |
M |
7o 5) |
Parameter identifying the time when the SC received the SMS‑SUBMIT See clause 9.2.3.11 |
|
TP‑PID |
TP‑Protocol‑Identifier |
O |
o |
See clause 9.2.3.9 |
|
TP‑DCS |
TP‑Data‑Coding‑Scheme |
O |
o |
see clause 9.2.3.10 |
|
TP‑UDL |
TP‑User‑Data‑Length |
O |
o |
see clause 9.2.3.16 |
|
TP‑UD |
TP‑User‑Data |
O |
3) 4) |
see clause 9.2.3.24 |
1) Provision: Mandatory (M) or Optional (O).
2) Representation: Integer (I), Bit (B), 2bits (2b), octet (o).
3) Dependent upon the TP‑DCS.
4) The TP‑User‑Data field in the SMS‑SUBMIT‑REPORT is only available for use by the SC.
5) This same time value shall also be carried in the SMS‑STATUS‑REPORT relating to a particular SM. See clause 9.2.2.3. This shall allow the submitting SME to associate a particular SMS‑SUBMIT with a subsequent SMS‑STATUS‑REPORT by correlating the TP‑SCTS values.
Layout of SMS‑SUBMIT REPORT
Bit Number
|
Number of Octets |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
||
|
1 |
TP‑MTI, TP-UDHI |
|||||||||
|
1 |
TP‑PI |
|||||||||
|
7 |
TP‑SCTS |
|||||||||
|
0,1 |
TP‑PID |
|||||||||
|
0,1 |
TP‑DCS |
|||||||||
|
0,1 |
TP‑UDL |
|||||||||
|
0 to 152 |
TP‑UD |
Bits 7 and 5 ‑ 2 in octet 1 are presently unused in the SMS‑SUBMIT‑REPORT and the sender shall set them to zero. If any of these bits is non‑zero, the receiver shall ignore them.
9.2.2.3 SMS‑STATUS‑REPORT type
Basic elements of the SMS‑STATUS‑REPORT type:
|
Abbr. |
Reference |
P1) |
R2) |
Description |
|---|---|---|---|---|
|
TP‑MTI |
TP‑Message‑Type‑Indicator |
M |
2b |
Parameter describing the message type |
|
TP-UDHI |
TP-User-Data-Header-Indication |
O |
b |
Parameter indicating that the TP-UD field contains a Header |
|
TP‑MMS |
TP‑More‑Messages‑to‑Send |
M |
b |
Parameter indicating whether or not there are more messages to send |
|
TP-LP |
TP-Loop-Prevention |
O |
b |
Parameter indicating that SMS applications should inhibit forwarding or automatic message generation that could cause infinite looping. |
|
TP‑SRQ |
TP‑Status‑Report‑Qualifier |
M |
b |
Parameter indicating whether the previously submitted TPDU was an SMS-SUBMIT or an SMS‑COMMAND |
|
TP‑MR |
TP‑Message‑Reference 3) |
M |
I |
Parameter identifying the previously submitted SMS‑SUBMIT or SMS‑COMMAND |
|
TP‑RA |
TP‑Recipient‑Address |
M |
2‑12o |
Address of the recipient of the previously submitted mobile originated short message |
|
TP‑SCTS |
TP‑Service‑Centre‑Time‑Stamp |
M |
7o |
Parameter identifying time when the SC received the previously sent SMS‑SUBMIT |
|
TP‑DT |
TP‑Discharge‑Time |
M |
7o |
Parameter identifying the time associated with a particular TP‑ST outcome |
|
TP‑ST |
TP‑Status |
M |
o |
Parameter identifying the status of the previously sent mobile originated short message |
|
TP-PI |
TP-Parameter-Indicator |
O |
o |
Parameter indicating the presence of any of the optional parameters which follow |
|
TP-PID |
TP-Protocol-Identifier |
O |
o |
see clause 9.2.3.9. TP-PID of original SMS-SUBMIT |
|
TP-DCS |
TP-Data-Coding-Scheme |
O |
o |
see clause 9.2.3.10 |
|
TP-UDL |
TP-User-Data-Length |
O |
o |
see clause 9.2.3.16 |
|
TP-UD |
TP-User-Data |
O |
5) |
see clause 9.2.3.24 |
1) Provision: Mandatory (M) or Optional (O).
2) Representation: Integer (I), bit (b), 2 bits (2b), Octet (o), 7 octets (7o), 2‑12 octets (2‑12o).
3) Where the SMS‑STATUS‑REPORT is the result of an SMS‑COMMAND and the TP‑Command‑Type was an Enquiry, the TP‑MR returned in the SMS‑STATUS‑REPORT shall be the TP‑MN which was sent in the SMS‑COMMAND (i.e. the TP‑MR of the previously submitted SM to which the Enquiry refers).
4) Mandatory if any of the optional parameters following TP-PI is present, otherwise optional.
5) TP-UD contains information related to a SMS-DELIVER; can contain information transported in the TP-UD of SMS-DELIVER-REPORT, and information inserted by the SMSC. The length of the TP-UD field is limited and might not be long enough to fit information both from the original receiving terminal (as included into the SMS-DELIVER-REPORT) and information added by the SMSC. In these cases the former information has higher priority, and the latter shall be truncated.
Layout of SMS‑STATUS‑REPORT:
|
Bit no. |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|||||||||||||
|
Number of |
octets |
1 |
TP-MTI, TP-MMS, TP-LP, TP-SRQ, TP-UDHI |
||||||||||||||||||
|
1 |
TP-MR |
||||||||||||||||||||
|
1 |
|||||||||||||||||||||
|
2 |
TP-RA |
||||||||||||||||||||
|
2 to |
12 |
||||||||||||||||||||
|
7 |
TP-SCTS |
||||||||||||||||||||
|
7 |
TP-DT |
||||||||||||||||||||
|
1 |
TP-ST |
||||||||||||||||||||
|
1 |
TP-PI |
||||||||||||||||||||
|
1 |
TP-PID |
||||||||||||||||||||
|
1 |
TP-DCS |
||||||||||||||||||||
|
1 |
. |
. |
. |
. |
. |
. |
TP-UDL |
||||||||||||||
|
1 |
|||||||||||||||||||||
|
0 to |
143 |
. |
. |
. |
. |
. |
. |
. |
. |
TP-UD |
|||||||||||
NOTE: Any unused bits shall be set to zero by the sending entity and shall be ignored by the receiving entity.
The maximum guaranteed length of TP-UD is 131 octets. In order to achieve the maximum stated above (143 octets), the TP-RA field must have a length of 2 octets and TP-PID and TP-DCS must not be present.
9.2.2.4 SMS‑COMMAND type
Basic elements of the SMS‑COMMAND type:
|
Abbr. |
Reference |
P1) |
R2) |
Description |
|---|---|---|---|---|
|
TP‑MTI |
TP‑Message‑Type‑Indicator |
M |
2b |
Parameter describing the type |
|
TP-UDHI |
TP-User-Data-Header-Indication |
O |
b |
Parameter indicating that the TP-CD field contains a Header |
|
TP‑SRR |
TP‑Status‑Report‑ Request |
O |
b |
Parameter indicating if the SMS Command is requesting a status report. |
|
TP‑MR |
TP‑Message Reference |
M |
I |
Parameter identifying the SMS‑COMMAND |
|
TP‑PID |
TP‑Protocol‑ Identifier |
M |
o |
Parameter identifying the above layer protocol, if any |
|
TP‑CT |
TP‑Command‑Type |
M |
o |
Parameter specifying which operation is to be performed on a SM |
|
TP‑MN |
TP‑Message‑Number |
M3) |
o |
Parameter indicating which SM in the SC to operate on |
|
TP‑DA |
TP‑Destination‑Address |
M4) |
2‑12o |
Parameter indicating the Destination Address to which the TP‑Command refers |
|
TP‑CDL |
TP‑Command‑Data‑Length |
M |
o |
Parameter indicating the length of the TP‑CD field in octets |
|
TP‑CD |
TP‑Command‑Data |
O |
o |
Parameter containing user data |
1) Provision: Mandatory (M) or Optional (O).
2) Representation: Integer (I), bit (b), 2bits (2b), octet (o).
3) For TP‑Command‑Types which are not for a specific SM this field shall be ignored when received. Its value is of no concern but the field must be present to maintain the structure.
4) For certain TP‑Command‑Types which operate on a specific SM (e.g. Enquire, Delete etc.) the full TP‑DA must be specified. For TP‑Command‑Types which do not operate on a specific SM, the address length must be set to zero indicating that the Address‑Value fields are not present. The Type‑of‑Address field must be present (see 9.1.2.5) and shall be set to zero and ignored.
Layout of SMS-COMMAND:
|
Bit no. |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|||
|
Number |
1 |
TP-MTI, TP-SRR, TP-UDHI |
|||||||||
|
of octets |
1 |
TP-MR |
|||||||||
|
1 |
TP-PID |
||||||||||
|
1 |
TP-CT |
||||||||||
|
1 |
TP-MN |
||||||||||
|
2 to 12 |
TP-DA |
||||||||||
………….…………………….
|
1 |
TP-CDL |
………….…………………….
|
0 to 156 |
TP-CD |
NOTE: The maximum guaranteed length of TP-CD is 146 octets. In order to achieve the maximum stated above (156 octets), the TP-DA field must have a length of 2 octets.