6.7 Handling of unknown, unforeseen and erroneous protocol data
25.4153GPPRelease 17TSUTRAN Iu interface user plane protocols
6.7.1 General
Error handling in Iu UP protocol is applicable only for Iu UP in Support mode.
The Handling of Error Event procedure is the procedure handling error reporting. The Handling of Error Event procedure in the Iu UP can be triggered by:
– An error detected by the Iu UP functions (by receiving an erroneous frame or by receiving a frame with unknown or unexpected data);
– A request by the upper layers;
– An ERROR EVENT control frame over the Iu UP protocol.
The error can be reported either by:
– An ERROR EVENT control frame over the Iu UP protocol;
– An Iu UP Status Indication to upper layers (e.g. to be used by O&M).
When an Error event is reported, either by an Iu-UP-Status-Indication, or by an ERROR EVENT control frame the following information shall be included:
– Type of the error (syntactical error, semantical error or other error);
– Error distance, i.e. information where the error occurred.
6.7.2 Error detected by Iu UP functions
When an error is detected within the Iu UP functions (by receiving a frame containing erroneous, unknown or unexpected data) one of the following actions is taken depending on the type of the error:
1. Error indicated to upper layers by sending a Iu-UP-Status-Indication primitive;
2. ERROR EVENT control frame sent;
3. ERROR EVENT control frame sent and error indicated to upper layers by sending a Iu-UP-Status-Indication primitive;
4. No action.
6.7.3 Request by upper layers
When the IU UP receives an Iu-UP-Status-Request indicating Error event then an ERROR EVENT control frame should be sent over the Iu UP protocol indicating the appropriate error type.
6.7.4 Error event frame over the Iu UP protocol
When an ERROR EVENT control frame is received over the Iu UP protocol an Iu-UP-Status-Indication with ‘Error event’ information indicating the error type should be made to the upper layers. The Error event report contains a ‘Cause value’ that tells the type of the error. The Error event report also contains a field ‘Error distance’ that tells the distance to the entity reporting the error event. The ‘Error distance’ is "0" when the error is originally sent. When an Error event report is forwarded the ‘Error distance’ is incremented by one.
6.7.5 Handling of error reports
6.7.5.1 General
Figure 28 shows the external error case when the Handling of Error Event procedure is originally triggered by an Iu-UP-Status-Request. As an action on this the Handling of Error Event procedure sends an ERROR EVENT control frame over the Iu UP. On the other side the reception of ERROR EVENT control frame triggers the Handling of Error Event procedure , and an Iu-UP-Status-Indication is sent to upper layers. The handling is symmetrical over the Iu UP protocol.
Figure 28: External error
Figure 29 shows the internal error case when the Handling of Error Event procedure is originally triggered by the Iu UP functions. As an action on this the Handling of Error Event procedure sends an ERROR EVENT control frame over the Iu UP. On the other side the reception of ERROR EVENT control frame triggers the Handling of Error Event procedure, and an Iu-UP-Status-Indication is sent to the upper layers. The handling is symmetrical over the Iu UP protocol.
Figure 29: Internal error
6.7.5.2 Error distance
In an ERROR EVENT control frame the error distance has the following meaning:
0: Error report relates to an Iu UP function error at the other side.
1: Error report relates to an error at the other side reported by the upper layers.
In an Iu UP-Status indication the error distance has the following meaning:
0: Error report relates to an local Iu UP function error.
1: Error report relates to an Iu UP function error at the other side.
2: Error report relates to an error at the other side reported by the upper layers.
6.7.6 List of errors in Iu UP
Table 0: List of errors in Iu UP
|
Error Type |
Error Cause |
Recommended action by Handling of Error Event procedure |
Possibly detected by function |
Comment |
|---|---|---|---|---|
|
Syntactical |
CRC error of Frame payload (CRC check) |
No action |
NAS Data Streams specific functions |
Handled by Frame Quality Classification, when applied |
|
CRC error of Frame Header (CRC check) |
Iu-UP-Status-Indication(Error event) |
Frame Handler functions |
Frame discarded |
|
|
Unexpected Frame Number |
Iu-UP-Status-Indication(Error event) |
Frame Handler functions |
See 6.6.3.3 |
|
|
Frame loss |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Frame Handler functions |
See 6.6.3.3 |
|
|
PDU type Unknown |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Frame Handler functions |
Used when PDU type is not 0, 1, or 14 |
|
|
Unknown procedure |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Frame Handler functions |
Used when procedure value is neither 0, 1, 2, or 3 |
|
|
Unknown reserved value |
See 8.1.1 |
|||
|
Unknown field |
This error cause shall not be sent. |
|||
|
Frame too short |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Frame Handler functions |
Used when: – the length of the entire received PDU is less than the expected (calculated) PDU header length, or – the length of the payload (entire received PDU minus PDU header length) is less than the expected (calculated) payload length |
|
|
Missing fields |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Frame Handler functions |
This error cause shall not be sent. |
|
|
Semantical |
Unexpected PDU type |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Frame Handler functions |
|
|
Unexpected procedure |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Frame Handler functions |
||
|
Unexpected RFCI |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
NAS Data Streams specific functions |
||
|
Unexpected value |
Iu-UP-Status-Indication(Error event) and ERROR EVENT control frame |
Procedure Control functions |
||
|
Other error |
Initialisation failure (outside Iu UP) |
ERROR EVENT control frame |
Function outside Iu UP |
|
|
Initialisation failure (network error, timer expiry) |
Iu-UP-Status-Indication(Error event) |
Procedure Control functions |
||
|
Initialisation failure (Iu UP function error, repeated NACK) |
Iu-UP-Status-Indication(Error event) |
Procedure Control functions |
||
|
Rate control failure |
Iu-UP-Status-Indication(Error event) |
Procedure Control functions |
||
|
Error event failure |
Iu-UP-Status-Indication(Error event) |
Procedure Control functions |
||
|
Time Alignment not supported |
Iu-UP-Status-Indication(Error event) |
Procedure Control functions |
||
|
Requested Time Alignment not possible |
Iu-UP-Status-Indication(Error event) |
Function outside Iu UP |
||
|
Iu UP version not supported |
Iu-UP-Status-Indication(Error event) |
Procedure Control functions |
6.7.7 Error detection
6.7.7.1 General
Error detection is provided on frames through a Cyclic Redundancy Check. The CRC for the payload is 10 bits and for the header it is 6 bits.
6.7.7.2 CRC Calculation
The parity bits are generated by one of the following cyclic generator polynomials:
gCRC6(D) = D6 + D5 + D3 + D2 + D1 + 1;
gCRC10(D) = D10 + D9 + D5 + D4 + D1 + 1.
Denote the bits to be protected of a frame by 
(
being the bit with the highest bit position in the first octet), and the parity bits by 
. Ai is the length of the protected data and Li is 6 or 10 depending on the CRC length.
The encoding is performed in a systematic form, which means that in GF(2), the polynomial
yields a remainder equal to 0 when divided by gCRC6(D) and the polynomial
yields a remainder equal to 0 when divided by gCRC10(D). If 
, 
.
6.7.7.3 Relation between input and output of the Cyclic Redundancy Check
The protected bits are left unchanged in the frame. The parity bits for the Header CRC are put in the Header CRC field with
being the highest bit position of the first octet of the Header CRC field. The parity bits for the Payload CRC are put in the Payload CRC field with
being the highest bit position of the first octet of the Payload CRC field.