10 General information elements coding
3GPP48.016Base Station System (BSS) - Serving GPRS Support Node (SGSN) interfaceGeneral Packet Radio Service (GPRS)Network serviceRelease 17TS
This sub-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 10.1.1):
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, the TV 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) |
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|
octets 2, 2a |
length indicator |
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|
octet 3 |
information element value |
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|
… |
||||||||
|
octet … n |
||||||||
Figure 10.1.1: Information element structure, TLV format
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
information element value |
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|
… |
||||||||
|
octet … n |
||||||||
Figure 10.1.2: 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" sub-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.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
||
|
octet 2 |
0/1 ext |
length |
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|
octet 2a |
length |
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Figure 10.1.2.1: 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 sub-clause.
A figure of the sub-clause 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 sub-clause 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 the present document 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 Information elements
The IEI values are indicated in table 10.3.1:
Table 10.3.1: IEI coding
|
IEI coding |
Information element name |
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|
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 |
|
0 |
0 |
0 |
0 |
0 |
1 |
0 |
1 |
List of IP4 Elements |
|
0 |
0 |
0 |
0 |
0 |
1 |
1 |
0 |
List of IP6 Elements |
|
0 |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
Maximum Number of NS-VCs |
|
0 |
0 |
0 |
0 |
1 |
0 |
0 |
0 |
Number of IP4 Endpoints |
|
0 |
0 |
0 |
0 |
1 |
0 |
0 |
1 |
Number of IP6 Endpoints |
|
0 |
0 |
0 |
0 |
1 |
0 |
1 |
0 |
Reset Flag |
|
0 |
0 |
0 |
0 |
1 |
0 |
1 |
1 |
IP Address |
|
other values |
reserved for future use |
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10.3.1 BVCI
This IE is used for multiplexing BVCs on NS-VCs.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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octet 1 |
IEI |
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|
octets 2, 2a |
length indicator |
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|
octet 3 |
most significant octet of BVCI |
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octet 4 |
least significant octet of BVCI |
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Figure 10.3.1.1: 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.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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|
octet 1 |
IEI |
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octets 2, 2a |
length indicator |
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|
octet 3 |
cause value |
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Figure 10.3.2.1: Cause information element
The cause values are indicated in table 10.3.2.1:
Table 10.3.2.1: Cause values
|
Cause value coding |
Cause name |
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8 |
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 |
|
0 |
0 |
0 |
0 |
1 |
1 |
1 |
0 |
Invalid number of IP4 Endpoints |
|
0 |
0 |
0 |
0 |
1 |
1 |
1 |
1 |
Invalid number of IP6 Endpoints |
|
0 |
0 |
0 |
1 |
0 |
0 |
0 |
0 |
Invalid number of NS-VCs |
|
0 |
0 |
0 |
1 |
0 |
0 |
0 |
1 |
Invalid weights |
|
0 |
0 |
0 |
1 |
0 |
0 |
1 |
0 |
Unknown IP endpoint |
|
0 |
0 |
0 |
1 |
0 |
0 |
1 |
1 |
Unknown IP address |
|
0 |
0 |
0 |
1 |
0 |
1 |
0 |
0 |
IP test failed |
|
other values |
reserved for future use |
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10.3.2a End Flag
This IE is used to indicate last SNS-CONFIG PDU to be sent to the peer NS entity. All unused bits are spare.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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octet 1 |
spare |
E-bit |
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Figure 10.3.2a.1: End Flag information element
The "E-bit" is coded as shown below:
0 Additional PDUs will be sent.
1 Last PDU sent.
10.3.2b IP Address
This IE identifies an IP address.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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Octet 1 |
IEI |
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Octet 2 |
Address Type |
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Octets 3 -n |
Address value |
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Figure 10.3.2b.1: IP Address information element
Where "n" is 6 if the Address Type is IPv4 and "n" is 18 if the Address Type is IPv6.
The "Address Type" is coded as shown in table 10.3.2b.1.
Table 10.3.2b.1: "Address Type" coding
|
coding |
Address Type |
|
0 |
Reserved |
|
1 |
IPv4 |
|
2 |
IPv6 |
|
Reserved |
All values not explicitly shown are reserved for future use. |
10.3.2c List of IP4 Elements
This IE identifies a list of IPv4 elements.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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octet 1 |
IEI |
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octet 2, 2a |
Length Indicator |
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octets 3-10 |
IP4 Element 1 |
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|
octets … – (2+8n) |
IP4 Element n |
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Figure 10.3.2c.1: List of IP4 Elements information element
The length depends on the number of IP4 Elements: n. The coding of an IP4 Element is:
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet (x+1)-(x+4) |
IPv4 Address |
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|
octet (x+5)-(x+6) |
UDP Port Value |
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|
octet (x+7) |
Signalling Weight |
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|
octet (x+8) |
Data Weight |
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where x = 8i – 6 (1 i n).
10.3.2d List of IP6 Elements
This IE identifies a list of IPv6 elements.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
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octet 1 |
IEI |
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|
octet 2, 2a |
Length Indicator |
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|
octets 3- 22 |
IP6 Element 1 |
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|
octets … – (2+20n) |
IP6 Element n |
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Figure 10.3.2d.1: List of IP6 Elements information element
The length depends on the number of IP6 Elements: n . The coding of an IP6 Element is:
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet (x+1)-(x+16) |
IPv6 Address |
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|
octet (x+17)-(x+18) |
UDP Port Value |
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|
octet (x+19) |
Signalling Weight |
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|
octet (x+20) |
Data Weight |
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where x = 20i – 18 (1 i n).
10.3.2e Maximum Number of NS-VCs
This IE identifies the maximum number of NS-VCs.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
IEI |
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|
octet 2 octet 3 |
most significant octet of Maximum Number of NS-VCs least significant octet of Maximum Number of NS-VCs |
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Figure 10.3.2e.1: Maximum Number of NS-VCs information element
10.3.2f Number of IP4 Endpoints
This IE identifies the number of IPv4 endpoints.
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8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
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octet 1 |
IEI |
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|
octet 2 octet 3 |
most significant octet of Number of IP4 Endpoints least significant octet of Number of IP4 Endpoints |
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Figure 10.3.2f.1: Number of IP4 Endpoints information element
10.3.2g Number of IP6 Endpoints
This IE identifies the number of IPv6 endpoints.
|
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
IEI |
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|
octet 2 octet 3 |
most significant octet of Number of IP6 Endpoints least significant octet of Number of IP6 Endpoints |
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Figure 10.3.2g.1: Number of IP6 Endpoints information element
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.
|
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
IEI |
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|
octets 2, 2a |
length indicator |
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|
octet 3 |
NS PDU |
|||||||
|
… |
||||||||
|
octet n |
||||||||
Figure 10.3.3.1: NS PDU information element
10.3.4 NS SDU
This IE contains one and only one NS SDU transmitted across the Gb interface.
|
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
NS SDU |
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|
… |
||||||||
|
octet n |
||||||||
Figure 10.3.4.1: 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.
|
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
IEI |
|||||||
|
octets 2, 2a |
length indicator |
|||||||
|
octet 3 |
most significant octet of NS-VCI |
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|
octet 4 |
least significant octet of NS-VCI |
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Figure 10.3.5.1: NS-VCI information element
10.3.6 NSEI
This IE unambiguously identifies one NSE.
|
8 |
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 10.3.6.1: NSEI information element
10.3.7 PDU type
Table 10.3.7.1: PDU type coding
|
PDU type coding |
PDU name |
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|
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 |
|
0 |
0 |
0 |
0 |
1 |
1 |
0 |
0 |
SNS-ACK |
|
0 |
0 |
0 |
0 |
1 |
1 |
0 |
1 |
SNS-ADD |
|
0 |
0 |
0 |
0 |
1 |
1 |
1 |
0 |
SNS-CHANGEWEIGHT |
|
0 |
0 |
0 |
0 |
1 |
1 |
1 |
1 |
SNS-CONFIG |
|
0 |
0 |
0 |
1 |
0 |
0 |
0 |
0 |
SNS-CONFIG-ACK |
|
0 |
0 |
0 |
1 |
0 |
0 |
0 |
1 |
SNS-DELETE |
|
0 |
0 |
0 |
1 |
0 |
0 |
1 |
0 |
SNS-SIZE |
|
0 |
0 |
0 |
1 |
0 |
0 |
1 |
1 |
SNS-SIZE-ACK |
|
other values |
reserved for future use |
|||||||
10.3.7a Reset Flag
This IE is used to indicate if the peer NS entity shall reset all configuration information. All unused bits are spare.
|
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
IEI |
|||||||
|
octet 2 |
Spare |
Reset-bit |
||||||
Figure 10.3.7a.1: Reset Flag information element
The "Reset-bit" is coded as shown below:
0 Do not reset.
1 Reset.
10.3.8 (void)
10.3.9 NS SDU Control Bits
This IE is used to indicate additional information about the NS-SDU to the user of the NS entity. All unused bits are spare.
|
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
spare |
C-bit |
R-bit |
|||||
Figure 10.3.9.1: NS SDU Control Bits information element
The "R-bit" is coded as shown below:
0 No request for change flow;
1 Request change flow.
The "C-bit" is coded as shown below:
0 No confirmation for change flow;
1 Confirm change flow.
10.3.10 Transaction ID
This IE provides an identifier for SNS PDUs.
|
8 |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
|
|
octet 1 |
Value |
|||||||
Figure 10.3.10.1: Transaction ID information element