5 RAB aspects
26.4543GPPCodec for Enhanced Voice Services (EVS)Interface to Iu, Uu, Nb and MbRelease 17TS
3GPP TS 26.103 [20] specifies all allowed EVS Configurations, EVS (Set x), for UMTS_EVS. All these EVS Configurations are multi-mode Configurations. One of these EVS Configurations is selected by the MSC for a given call and the corresponding parameters for the "Transport Format Combination Set" (TFCS) are sent in RAB Assignment Request to the RNC. The RNC may accept the RAB Assignment Request as a whole or reject it as a whole. The RNC may, however, select also a subset of the requested TFCS for the Uu interface, as long as these are TrFO-compatible to the requested TFCS. Example: instead of EVS (Set 2), the RNC may select EVS (Set 1) or even EVS (Set 0).
UMTS_EVS is applied with Equal Error Protection (EEP) on the radio interface. Only class A bits are defined. Class B and Class C bits are not present.
During the RAB Assignment procedure, initiated by the CN to establish the RAB for EVS, the RAB parameters are defined. The EVS RAB is established with one RAB sub-flow with predefined sizes and QoS parameters.
Some of the QoS parameters in the RAB assignment procedure are determined from the Bearer Capability Information Element used at call set up. These QoS parameters as defined in TS 23.231 [3] may be set as follows:
Table 5-1: Example of mapping of BC IE into QoS parameters for UMTS AMR
|
RAB service attribute |
RAB service attribute value |
Comments |
||
|---|---|---|---|---|
|
Traffic Class |
Conversational |
|||
|
RAB Asymmetry Indicator |
Symmetric, bidirectional |
Symmetric RABs are used for uplink and downlink |
||
|
Maximum bit rate |
24.75 (Config-EVS-Code 2) or |
This value depends on the highest rate in the RFCS |
||
|
Guaranteed bit rate (GBR) |
24.75 or |
One of the values is chosen, depending on the lowest rate-controllable SDU format (note 2) |
||
|
Delivery Order |
Yes |
(note 1) |
||
|
Maximum SDU size |
495 (Config-EVS-Code 2) or 271 (Config-EVS-Code 1 and 3) or |
Maximum size of payload field in Iu UP, according to the highest mode rate in the RFCS |
||
|
Traffic Handling Priority |
Not applicable |
Parameter not applicable for the conversational traffic class. (note 1) |
||
|
Source statistics descriptor |
Speech |
(note 1) |
||
|
SDU Parameters |
RAB sub-flow 1 (Class A bits) |
The number of SDU, their number of RAB sub-flow and their relative sub-flow size is subject to operator tuning (note 3) |
||
|
SDU error ratio |
[7 * 10-3] |
(note 3) |
||
|
Residual bit error ratio |
[10-5] |
(note 3) |
||
|
Delivery of erroneous SDUs |
yes |
All bits are delivered with Frame Quality Classification (FQC) |
||
|
SDU format information |
(note 4) |
|||
|
Sub-flow SDU size |
(note 5) |
|||
|
NOTE 1: These parameters apply to all UMTS speech codec types. NOTE 2: The guaranteed bit rate (GBR) depends on the periodicity and the lowest rate-controllable SDU size. NOTE 3: These parameters are subject to operator tuning. The values in brackets [] are for further study, see also TS 26.114 [21], Annex E, clauses E.31 to E.34. NOTE 4: SDU format information has to be specified for each EVS payload size (i.e. with Speech bits and SID bits) included in the RFCS as defined in TS 26.453 [19]. NOTE 5: The sub-flow SDU size corresponding to an EVS core frame type indicates the number of bits in the class A fields. |
||||
The RAB parameters shall be set so that DTX (SCR) is always supported in uplink and downlink.
The conversational traffic class shall be used for the speech service. The parameters traffic class, transfer delay, traffic handling priority and source statistics descriptor shall be the same for all speech codec types applicable for UMTS.