15 Support of non-transparent bearer services in A/Gb mode
3GPP48.020Rate adaption on the Base Station System - Mobile-services Switching Centre (BSS - MSC) interfaceRelease 17TS
15.1 TCH/F9.6 and TCH/F4.8 kbit/s channel codings
In the case of non-transparent services the RA1/RA1′ function shall perform the same mapping as that described for transparent services, using 12 and 6 kbit/s radio interface data rates, with the following modification.
The E2 and E3 bits in the modified ITU-T V.110 80 bit frames shown in Figure 3 (derived from the standard ITU-T V.110 frame shown in Figure 2) are used to indicate each consecutive sequence of ITU-T V.110 80 bit frames corresponding to the four modified ITU-T V.110 60 bit frames (Figure 4) received/transmitted in one radio interface frame. This allows 240 bit Radio Link Protocol frames to/from the MSC to be aligned with the 4×60 bit frames encoded by the radio subsystem channel coder as a single unit (see 3GPP TS 45.003). The 8 bits consisting of the E2 and E3 bits in one of the above sequences is referred to as the Frame Start Identifier. The FSI value is 00 01 10 11. This value is assigned to the E2 and E3 bits as shown in Table7.
Table 7
|
E2 |
E3 |
|
|
First Modified ITU-T V.110 80 bit frame |
0 |
0 |
|
Second |
0 |
1 |
|
Third |
1 |
0 |
|
Fourth |
1 |
1 |
As each RLP frame is transported between the BSS and MSC in four modified ITU-T V.110 80 bit frames, it is necessary following a transmission break and at start up, to determine which modified ITU-T V.110 80 bit frame of the stream is the first for a particular RLP frame. This is needed so that correct alignment with the radio subsystem can be achieved.
Modified V.110 80 bit frames can slip in time during re-routing, and whilst sync exists within the modified ITU-T V.110 80 bit frame to determine the modified ITU-T V.110 80 bit frame boundaries, the FSI is required to determine which quarter of an RLP frame each modified ITU-T V.110 80 bit frame contains.
Table 8: Relationship between FNUR, AIUR, substream rate, number of substreams and intermediate rate
|
FNUR |
AIUR |
Number of Channels x Substream Rate |
Channel Coding |
Multislot Intermediate Rate |
|
2,4 kbit/s |
2,4 kbit/s |
2-8 times duplication of each bit to reach 2,4 kbit/s |
TCH/F4.8 |
8 kbit/s |
|
4,8 kbit/s |
4,8 kbit/s |
4,8 kbit/s |
TCH/F4.8 |
8 kbit/s |
|
4,8 kbit/s |
9,6 kbit/s |
9,6 kbit/s |
TCH/F9.6 |
16 kbit/s |
|
9,6 kbit/s |
9,6 kbit/s |
2×4,8 kbit/s |
2XTCH/F4.8 |
8 kbit/s |
|
9,6 kbit/s |
9,6 kbit/s |
9,6 kbit/s |
TCH/F9.6 |
16 kbit/s |
|
14,4 kbit/s |
14,4 kbit/s |
3X4,8 kbit/s |
3XTCH/F4.8 |
8 kbit/s |
|
14,4 kbit/s |
19,2 kbit/s |
2X9,6 kbit/s |
2XTCH/F9.6 |
16 kbit/s |
|
19,2 kbit/s |
19,2 kbit/s |
4X4,8 kbit/s |
4XTCH/F4.8 |
8 kbit/s |
|
19,2 kbit/s |
19,2 kbit/s |
2X9,6 kbit/s |
2XTCH/F9.6 |
16 kbit/s |
|
28,8 kbit/s |
28,8 kbit/s |
3X9,6 kbit/s |
3XTCH/F9.6 |
16 kbit/s |
|
38,4 |
38,4 kbit/s |
4X9,6 kbit/s |
4XTCH/F9.6 |
16 kbit/s |
|
NOTE: The table gives the relation between the FNUR, AIUR, Substream Rate, Channel Coding and Intermediate Rate. As an example: the wanted FNUR is 14,4 kbit/s and the selected channel coding is TCH/F9.6. The data stream is split into two substreams of 9,6 kbit/s yielding an AIUR of 19,2 kbit/s. |
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15.1.1 Alignment
An alignment window spanning four modified ITU-T V.110 80 bit frames shall be used to search for the pattern of 8 bits described above in order to identify alignment with an RLP frame.
In the event of failure to detect the 8 bit pattern, the alignment window is shifted one complete modified V.110 80 bit frame, discarding the contents of the most historical frame and then checking the new 8 bit pattern.
15.1.2 Support of Discontinuous Transmission (DTX)
The E1 bit in the modified ITU-T V.110 80 bit frame shown in Figure 3 shall be used in the direction MSC-BSS to indicate that DTX may be invoked (see 3GPP TS 24.022). The E1 bit in all of the four consecutive frames relating to the RLP frame to which DTX may be applied shall be set to 1. If DTX is not to be applied, the E1 bit shall be set to 0.
In the direction BSS-MSC the E1 bit shall always be set to 0.
15.1.3 Order of Transmission
The first bit of each quarter of an RLP frame to be transmitted shall correspond to bit D1 of a modified V.110 frame (figures 3 and 4). The remaining 59 bits of each quarter of an RLP frame shall correspond to the D and D’ bits , D2 – D’12, in order left to right and top to bottom as shown in figures 3 and 4.
The first quarter of an RLP frame to be transmitted shall contain the E2 and E3 bit code 00 as shown in Table 1. The second quarter contains the code 01, etc.
15.2 TCH/F14.4, TCH/F28.8, and TCH/F43.2 channel codings
In case of non-transparent service, a 576 bit RLP frame shall be mapped over two consecutive A-TRAU frames.
Because of that mapping, it is required, following a transmission break and at start up, to determine which A-TRAU frame of the stream is the first for a particular RLP frame. This is needed so that correct alignment with the radio subsystem can be achieved.
The two consecutive M1 bits are referred to as the Frame Start Identifier. The FSI value is 01. This value is assigned to the M1 bits as shown in Table 9.
Table 9
|
M1 bit |
|
|---|---|
|
First A-TRAU frame |
0 |
|
Second A-TRAU frame |
1 |
A-TRAU frames can slip in time during re-routing, and whilst A-TRAU frame synchronisation exists, the FSI is required to determine which half of an RLP frame each A-TRAU frame contains.
Table 10: Relationship between AIUR, substream rate, number of substreams and intermediate rate
|
AIUR |
Number of substreams x |
Channel Coding |
Multislot intermediate Rate |
|
|
14,4 kbit/s |
14,4 kbit/s |
TCH/F14.4 |
16 kbit/s |
|
|
28,8 kbit/s |
2X14,4 kbit/s |
2XTCH/F14.4 1XTCH/F28,8 |
16 kbit/s |
|
|
43,2 kbit/s |
3X14,4 kbit/s |
3XTCH/F14.4 1XTCH/F43,2 |
16 kbit/s |
|
|
57,6 kbit/s |
4X14,4 kbit/s |
4XTCH/F14.4 |
16 kbit/s |
|
|
57,6 kbit/s |
4X14,4 kbit/s |
4XTCH/F14.4 2XTCH/F28,8 |
16 kbit/s |
|
|
NOTE: The table gives the relation between AIUR, Substream Rate, Channel Coding and Intermediate Rate. As an example: the AIUR is 28,8 kbit/s and the selected channel coding is 14,5 kbit/s. The data stream is split into two substreams of 14,5 kbit/s yielding an AIUR of 28,8 kbit/s The same number of substreams is used in each direction, even if the AIURs in each direction differ. Superfluous substreams are filled with idle frames. These are inserted at the BTS or IWF and are discarded at the IWF or BTS respectively. At the IWF, the down link AIUR is determined by the out of band signalling (Assignment Complete, Handover Performed), whereas the up link AIUR is determined inband by examining the possible substream positions on the A interface. |
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15.2.1 Alignment
An alignment window spanning two 290 bit blocks in case of TCH/F14.4 channel shall be used to search for the pattern of 2 bits ’01’ described in subclause 15.2, in order to identify alignment with an RLP frame.
In the event of failure to detect the 2 bits pattern the alignment window is shifted one 290 bit block, discarding the contents of the most historical frame and then checking the new 2 bits pattern.
15.2.2 Support of Discontinuous Transmission (DTX)
The M2 bit in the A-TRAU frame shown in Figure 5 shall be used in the direction MSC to BSS to indicate that DTX may be invoked (see 3GPP TS 24.022). The M2 bit in all of the two consecutive A-TRAU frames relating to the RLP frame to which DTX may be applied shall be set to 1. If DTX is not to be applied, the M2 bit shall be set to 0.
In the direction BSS to MSC the M2 bit shall always be set to 0.