10 General information elements coding

08.163GPPBase Station System (BSS) - Serving GPRS Support Node (SGSN) interfaceGeneral Packet Radio Service (GPRS)Network serviceRelease 1999TS

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

10.1 General structure of the information elements

The general information element structure is composed of (see figure 7/3GPP TS 08.16):

a) an Information Element Identifier (also referred to as the T field),

b) a length indicator (also referred to as the L field),

c) the information element value (also referred to as the V field).

Information elements have the TLV or the V format, as specified in the relevant protocol specification. The format of any given information element may depend on the context e.g. on the message type.

8

7

6

5

4

3

2

1

octet 1

Information Element Identifier (IEI)

octets 2, 2a

length indicator

octet 3

information element value

octet … n

Figure 8/3GPP TS 08.16: Information element structure, TLV format

8

7

6

5

4

3

2

1

octet 1

information element value

octet … n

Figure 9/3GPP TS 08.16: Information element structure, V format

When a field extends over more than one octet, the order of bit values progressively decreases as the octet number increases. The least significant bit of the field is represented by the lowest numbered bit of the highest numbered octet of the field.

10.1.1 Information Element Identifier

The first octet of an information element having the TLV format contains the IEI of the information element. If this octet does not correspond to an IEI known in the PDU, the receiver shall assume that the next octet is the first octet of the length indicator field and shall interpret it as described in the "Length indicator" clause.

This rule allows the receiver to skip unknown information elements and to analyse any following information elements.

10.1.2 Length indicator

The length indicator shall be included in all information elements having the TLV format.

Information elements may be variable in length. The length indicator is one or two octet long, the second octet may be absent. This field consists of the field extension bit, 0/1 ext, and the length of the value field which follows, expressed in octets. The field extension bit enables extension of the length indicator to two octets.

Bit 8 of the first octet is reserved for the field extension bit. If the field extension bit is set to 0 (zero), then the second octet of the length indicator is present. If the field extension bit is set to 1 (one), then the first octet is the final octet of the length indicator.

The length of the value field of the IE occupies the rest of the bits in the length indicator.

8

7

6

5

4

3

2

1

octet 2

0/1 ext

length

octet 2a

length

Figure 10/3GPP TS 08.16: Length indicator structure

The BSS or SGSN shall not consider the presence of octet 2a in a received IE as an error when the IE is short enough for the length to be coded in octet 2 only.

10.2 Information element description

The descriptions of the information elements are organized in alphabetical order of the IE name. Each IE is described in one subclause.

A figure of the subclause defines the structure of the IE indicating:

– the position of the IEI, when present;

– the fields the IE value part is composed of;

– the position of the length indicator, when present;

– possibly octet numbers of the octets that compose the IE.

Finally, the subclause may contain figures defining the structure and value range of the fields that compose the IE value part.

Where the description of information elements in this Technical Specification contains bits defined to be "spare bits", these bits shall set to zero by the sending side, and their value shall be ignored by the receiving side.

The term "default" may be used, implying that the value defined shall be used in the absence of any assignment, or that this value allows negotiation of alternative values in between the two peer entities.

10.3 Network Service Control information element description

The IEI values defined for the Network Service Control protocol are indicated in table 1/3GPP TS 08.16:

Table 12/3GPP TS 08.16: IEI coding

IEI coding

Information element name

8

7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

Cause

0

0

0

0

0

0

0

1

NS-VCI

0

0

0

0

0

0

1

0

NS PDU

0

0

0

0

0

0

1

1

BVCI

0

0

0

0

0

1

0

0

NSEI

other values

reserved for future use

10.3.1 BVCI

This IE is used for multiplexing BVCs on NS-VCs.

8

7

6

5

4

3

2

1

octet 1

IEI

octets 2, 2a

length indicator

octet 3

most significant octet of BVCI

octet 4

least significant octet of BVCI

Figure 13/3GPP TS 08.16: BVCI information element

10.3.2 Cause

This IE may be used to indicate to the peer NS entity the reason which triggered a procedure, or the reason of an abnormal condition.

8

7

6

5

4

3

2

1

octet 1

IEI

octets 2, 2a

length indicator

octet 3

cause value

Figure 12/3GPP TS 08.16: Cause information element

The cause values are indicated in Table 2/3GPP TS 08.16:

Table 13/3GPP TS 08.16: Cause values

Cause value coding

Cause name

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7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

Transit network failure

0

0

0

0

0

0

0

1

O&M intervention

0

0

0

0

0

0

1

0

Equipment failure

0

0

0

0

0

0

1

1

NS-VC blocked

0

0

0

0

0

1

0

0

NS-VC unknown

0

0

0

0

0

1

0

1

BVCI unknown on that NSE

0

0

0

0

1

0

0

0

Semantically incorrect PDU

0

0

0

0

1

0

1

0

PDU not compatible with the protocol state

0

0

0

0

1

0

1

1

Protocol error – unspecified

0

0

0

0

1

1

0

0

Invalid essential IE

0

0

0

0

1

1

0

1

Missing essential IE

other values

reserved for future use

10.3.3 NS PDU

This IE is included in the NS-STATUS PDU sent in answer to an erroneous NS PDU. This IE contains the erroneous PDU received. The erroneous PDU may be truncated in order to fit in the maximum size of the NS-STATUS PDU.

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7

6

5

4

3

2

1

octet 1

IEI

octets 2, 2a

length indicator

octet 3

NS PDU

octet n

Figure 13/3GPP TS 08.16: NS PDU information element

10.3.4 NS SDU

This IE contains one and only one NS SDU transmitted across the Gb interface. This IE has the V format.

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7

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5

4

3

2

1

octet 1

NS SDU

octet n

Figure 14/3GPP TS 08.16: NS SDU information element

In this "NS SDU" information element, bit i of octet j is equal to bit i of octet j of the NS SDU, as defined in the NS user protocol specification.

10.3.5 NS-VCI

This IE unambiguously identifies one NS-VC amongst all the NS-VCs used between one SGSN and the connected BSSs.

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7

6

5

4

3

2

1

octet 1

IEI

octets 2, 2a

length indicator

octet 3

most significant octet of NS-VCI

octet 4

least significant octet of NS-VCI

Figure 15/3GPP TS 08.16: NS-VCI information element

10.3.6 NSEI

This IE unambiguously identifies one NSE

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7

6

5

4

3

2

1

octet 1

IEI

octets 2, 2a

length indicator

octet 3

most significant octet of NSEI

octet 4

least significant octet of NSEI

Figure 16/3GPP TS 08.16: NSEI information element

10.3.7 PDU type

The PDU type has the V format.

Table 14/3GPP TS 08.16: PDU type coding

PDU type coding

PDU name

8

7

6

5

4

3

2

1

0

0

0

0

0

0

0

0

NS-UNITDATA

0

0

0

0

0

0

1

0

NS-RESET

0

0

0

0

0

0

1

1

NS-RESET-ACK

0

0

0

0

0

1

0

0

NS-BLOCK

0

0

0

0

0

1

0

1

NS-BLOCK-ACK

0

0

0

0

0

1

1

0

NS-UNBLOCK

0

0

0

0

0

1

1

1

NS-UNBLOCK-ACK

0

0

0

0

1

0

0

0

NS-STATUS

0

0

0

0

1

0

1

0

NS-ALIVE

0

0

0

0

1

0

1

1

NS-ALIVE-ACK

other values

reserved for future use

10.3.8 Spare octet

This IE is included in a PDU e.g. when it is needed to align another IE on a 32 bit boundary. This IE has the V format. All bits are spare.

8

7

6

5

4

3

2

1

octet 1

spare

Figure 17/3GPP TS 08.16: NS-VCI information element