9 General PDU definitions and contents

3GPP48.016Base Station System (BSS) - Serving GPRS Support Node (SGSN) interfaceGeneral Packet Radio Service (GPRS)Network serviceRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

This sub-clause is not applicable to the Sub-Network Service protocol.

9.1 General structure of a PDU

This sub-clause defines the general structure of the PDUs on the Gb interface.

The general PDU structure is composed of:

a) a PDU type information element; and

b) other information elements, as required.

The PDU type IE occupies the first octet position in the PDU.

This general structure and the numbering convention used on the Gb interface are illustrated in figure 9.1.1. The bits are grouped into octets. The bits of an octet are shown horizontally and are numbered from 1 to 8. Multiple octets are shown vertically and are numbered from 1 to n.

The octets shall be transmitted by increasing order of octet number. Within each octet, the bits shall be transmitted by increasing order of bit number i.e. bit 1 of octet 1 shall be transmitted first, bit 8 of octet n shall be transmitted last.

	8	7	6	5	4	3	2	1
octet 1	PDU type
octets 2, 3, …n	other information elements

Figure 9.1.1: General PDU structure and numbering convention

Each PDU definition includes a table listing the information elements (IEs) known in the PDU and the order of their appearance in the PDU. Unless specified otherwise in the PDU descriptions, a particular information element shall not be present more than once in a given PDU. All information elements that may be repeated are explicitly indicated.

For each information element the table indicates:

a) The name of the information element (which may give an idea of the semantics of the element).

b) Possibly a reference to another GSM Technical Specification where the information element is described.

c) The presence requirement indication (M, C, or O) for the IE as defined in sub-clause "General protocol error handling".

d) The format (T, L, V) of the information element. See further description of the type (T), length (L) and V (value) fields in sub-clause "General structure of the information elements".

e) The length of the information element (or permissible range of lengths), in octets, in the PDU, where "?" means that the maximum length of the IE is only constrained by the lower layer protocol. This indication is non-normative. The indicated length includes all the T, L, V fields present in the IE.

f) Sub-clauses specifying, where appropriate, conditions for IEs with presence requirement C or O in the relevant PDU which together with other conditions specified in 3GPP TS 48.016 define when the information elements shall be included or not, what non-presence of such IEs means, and – for IEs with presence requirement C – the static conditions for presence and/or non-presence of the IEs, see sub-clause "General protocol error handling".

9.2 Network Service Control PDUs

The Network Service Control PDUs are also referred to as NS PDUs in the rest of the present document.

9.2.1 NS-ALIVE

This PDU is used to test an NS-VC.

PDU type: NS-ALIVE

Direction: BSS to SGSN, SGSN to BSS

Table 9.2.1.1: NS-ALIVE PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1

9.2.2 NS-ALIVE-ACK

This PDU acknowledges a received NS-ALIVE PDU and is sent on the NS-VC where the NS-ALIVE PDU was received.

PDU type: NS-ALIVE-ACK

Direction: SGSN to BSS, BSS to SGSN

Table 9.2.2.1: NS-ALIVE-ACK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1

9.2.3 NS-BLOCK

This PDU indicates that an NS-VC shall be blocked at the recipient entity.

PDU type: NS-BLOCK

Direction: BSS to SGSN, SGSN to BSS

Table 9.2.3.1: NS-BLOCK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
Cause	10.3.2	M	TLV	3
NS-VCI	10.3.5	M	TLV	4

9.2.4 NS-BLOCK-ACK

This PDU acknowledges that an NS-VC has been blocked for use.

PDU type: NS-BLOCK-ACK

Direction: SGSN to BSS, BSS to SGSN

Table 9.2.4.1: NS-BLOCK-ACK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NS-VCI	10.3.5	M	TLV	4

9.2.5 NS-RESET

This PDU indicates that the NS peer entity is trying to reset one NS-VC.

PDU type: NS-RESET

Direction: BSS to SGSN, SGSN to BSS

Table 9.2.5.1: NS-RESET PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
Cause	10.3.2	M	TLV	3
NS-VCI	10.3.5	M	TLV	4
NSEI	10.3.6	M	TLV	4

Typical cause values are: O&M intervention, Equipment failure.

9.2.6 NS-RESET-ACK

This PDU acknowledges the reset of the indicated NS-VC.

PDU type: NS-RESET-ACK

Direction: BSS to SGSN, SGSN to BSS

Table 9.2.6.1: NS-RESET-ACK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NS-VCI	10.3.5	M	TLV	4
NSEI	10.3.6	M	TLV	4

9.2.7 NS-STATUS

This PDU is used to report error conditions.

PDU type: NS-STATUS

Direction: SGSN to BSS, BSS to SGSN

Table 9.2.7.1: NS-STATUS PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
Cause	10.3.2	M	TLV	3
NS-VCI	10.3.5	C	TLV	4
NS PDU	10.3.3	C	TLV	3-?
BVCI	10.3.1	C	TLV	4
List of IP4 Elements	10.3.2c	C	TLV	10-?
List of IP6 Elements	10.3.2d	C	TLV	22-?

9.2.7.1 Static conditions for NS-VCI

The NS-VCI IE shall be included when the Cause IE is set to one of the following values:

a) "NS-VC blocked";

b) "NS-VC unknown";

and shall not be included otherwise.

9.2.7.2 Static conditions for NS PDU

The NS PDU IE shall be included if the NS-STATUS message is sent in response to a received NS PDU within which an error was detected i.e. when the Cause IE is set to one of the following values:

a) "Semantically incorrect PDU";

b) "PDU not compatible with the protocol state";

c) "Protocol error – unspecified";

d) "Invalid essential IE";

e) "Missing essential IE";

and shall not be included otherwise.

This is the whole PDU received with error. This PDU may be truncated if it exceeds the information carrying capacity of the NS.

9.2.7.3 Static conditions for BVCI

The BVCI IE shall be included when the Cause IE is set to one of the following values:

a) "BVCI unknown on that NSE";

and shall not be included otherwise.

9.2.7.4 Static conditions for List of IP4 Elements

The List of IP4 Elements IE shall be included when the Cause IE is set to one of the following values:

a) " IP test failed";

and the IP endpoints of the NS-VC that failed are IPv4 endpoints. The List of IP4 Elements IE shall be the only conditional IE sent in a NS-STATUS PDU.

The List of IP4 Elements IE shall not be included otherwise.

9.2.7.5 Static conditions for List of IP6 Elements

The List of IP6 Elements IE shall be included when the Cause IE is set to one of the following values:

a) " IP test failed";

and the IP endpoints of the NS-VC that failed are IPv6 endpoints. The List of IP6 Elements IE shall be the only conditional IE sent in a NS-STATUS PDU.

The List of IP6 Elements IE shall not be included otherwise.

9.2.8 NS-UNBLOCK

This PDU indicates that an NS-VC shall be unblocked at the recipient entity.

PDU type: NS-UNBLOCK

Direction: BSS to SGSN, SGSN to BSS

Table 9.2.8.1: NS-UNBLOCK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1

9.2.9 NS-UNBLOCK-ACK

This PDU acknowledges that an NS-VC has been unblocked.

PDU type: NS-UNBLOCK-ACK

Direction: SGSN to BSS, BSS to SGSN

Table 9.2.9.1: NS-UNBLOCK-ACK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1

9.2.10 NS-UNITDATA

This PDU transfers one NS SDU between the BSS and SGSN.

PDU type: NS-UNITDATA

Direction: BSS to SGSN, SGSN to BSS

Table 9.2.10.1: NS-UNITDATA PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NS SDU Control Bits	10.3.9	M	V	1
BVCI	10.3.1	M	V	2
NS SDU	10.3.4	M	V	1-?

The length of the NS SDU information element shall be derived by the Network Service Control entity from the length of the complete NS-UNITDATA PDU provided by the Sub-Network Service entity to the Network Service Control entity.

9.3 Sub-Network Service Control PDUs

The Sub-Network Service Control PDUs are also referred to as SNS PDUs in the rest of the present document. The Sub-Network Service Control PDUs are only used in an IP sub-network.

9.3.1 SNS-ACK

The SNS-ACK PDU is used to acknowledge the SNS-ADD PDU, the SNS-DELETE PDU, or the SNS-CHANGEWEIGHT PDU.

PDU type: SNS-ACK

Direction: BSS to SGSN, SGSN to BSS

Table 9.3.1.1: SNS-ACK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NSEI	10.3.6	M	TLV	4
Transaction ID	10.3.10	M	V	1
Cause	10.3.2	O	TLV	3
IP Address a)	10.3.2b	C	TV	6-18
List of IP4 Elements b)	10.3.2c	C	TLV	10-?
List of IP6 Elements b)	10.3.2d	C	TLV	22-?
a) the IP Address IE shall only be present if the "Cause" value is set to "Unknown IP address". b) one or more of these conditional IEs shall be present if the "Cause" value is set to "Unknown IP endpoint".

9.3.2 SNS-ADD

The SNS-ADD PDU is used to add additional IP Endpoints.

PDU type: SNS-ADD

Direction: BSS to SGSN, SGSN to BSS

Table 9.3.2.1: SNS-ADD PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NSEI	10.3.6	M	TLV	4
Transaction ID	10.3.10	M	V	1
List of IP4 Elements a)	10.3.2c	C	TLV	10-?
List of IP6 Elements a)	10.3.2d	C	TLV	22-?
a) one and only one of the conditional IEs shall be present.

9.3.3 SNS-CHANGEWEIGHT

The SNS-CHANGEWEIGHT PDU is used to change the signalling weight and/or data weight of an IP endpoint.

PDU type: SNS-CHANGEWEIGHT

Direction: BSS to SGSN, SGSN to BSS

Table 9.3.3.1: SNS-CHANGEWEIGHT PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NSEI	10.3.6	M	TLV	4
Transaction ID	10.3.10	M	V	1
List of IP4 Elements a)	10.3.2c	C	TLV	10-?
List of IP6 Elements a)	10.3.2d	C	TLV	22-?
a) one and only one of the conditional IEs shall be present.

9.3.4 SNS-CONFIG

The SNS-CONFIG PDU is used to configure a NSE to a peer NSE.

PDU type: SNS-CONFIG

Direction: BSS to SGSN, SGSN to BSS

Table 9.3.4.1: SNS-CONFIG PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
End Flag	10.3.2a	M	V	1
NSEI	10.3.6	M	TLV	4
List of IP4 Elements a)	10.3.2c	C	TLV	10-?
List of IP6 Elements a)	10.3.2d	C	TLV	22-?
a) one and only one of the conditional IEs shall be present.

9.3.5 SNS-CONFIG-ACK

The SNS-CONFIG-ACK PDU is used to acknowledge an SNS-CONFIG PDU. The SNS-CONFIG-ACK PDU shall be sent to the source IP Endpoint of the corresponding SNS-CONFIG PDU.

PDU type: SNS-CONFIG-ACK

Direction: BSS to SGSN, SGSN to BSS

Table 9.3.5.1: SNS-CONFIG-ACK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NSEI	10.3.6	M	TLV	4
Cause	10.3.2	O	TLV	3

9.3.6 SNS-DELETE

The SNS-DELETE PDU is used to delete previously configured IP Endpoints.

PDU type: SNS-DELETE

Direction: BSS to SGSN, SGSN to BSS

Table 9.3.6.1: SNS-DELETE PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NSEI	10.3.6	M	TLV	4
Transaction ID	10.3.10	M	V	1
IP Address a)	10.3.2b	C	TV	6-18
List of IP4 Elements a)	10.3.2c	C	TLV	10-?
List of IP6 Elements a)	10.3.2d	C	TLV	22-?
a) one and only one of the conditional IEs shall be present.

9.3.7 SNS-SIZE

The SNS-SIZE PDU is used to indicate to the peer NSE the maximum number of NS-VCs or a change in the NS-VC capacity. The SNS-SIZE PDU is used to signal the restart of a NSE to a peer NSE.

PDU type: SNS-SIZE

Direction: BSS to SGSN

Table 9.3.7.1: SNS-SIZE PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NSEI	10.3.6	M	TLV	4
Reset Flag		M	TV	2
Maximum Number of NS-VCs	10.3.2e	M	TV	3
Number of IP4 Endpoints a)	10.3.2f	C	TV	3
Number of IP6 Endpoints a)	10.3.2g	C	TV	3
a) At least one of these conditional IEs shall be present.

9.3.8 SNS-SIZE-ACK

The SNS-SIZE-ACK PDU is used to acknowledge an SNS-SIZE PDU. The SNS-SIZE-ACK PDU shall be sent to the source IP Endpoint of the corresponding SNS-SIZE PDU.

PDU type: SNS-SIZE-ACK

Direction: SGSN to BSS

Table 9.3.8.1: SNS-SIZE-ACK PDU contents

Information element	Reference	Presence	Format	Length
PDU type	10.3.7	M	V	1
NSEI	10.3.6	M	TLV	4
Cause	10.3.2	O	TLV	3