5 TFO Frame Structure

08.623GPPInband Tandem Free Operation (TFO) of speech codecsService descriptionStage 3TS

5.1 TFO Frames for Full Rate and Enhanced Full Rate

Full Rate (Enhanced Full Rate) TFO Frames are structured similar to uplink Full Rate (Enhanced Full Rate) TRAU Frames.

Table 1: The coding of the Control Bits (C1 .. C21) for Full Rate TFO Frames

Control Bit

Description

Comment

C1 – C4

Frame Type

FR

EFR

C1 C2 C3 C4

0 . 0 . 0 . 1

1 . 1 . 0 . 1 All other code words are reserved.

C5

EMBED

Indicates the presence of an embedded TFO Message

C6 – C11

spare

(is Time Alignment in TRAU frame)

C12

BFI

Copied from uplink TRAU frame

C13 – C14

SID

Copied from uplink TRAU frame

C15

TAF

Copied from uplink TRAU frame

C16

spare

C17

DTXd

Copied from uplink TRAU frame

C18 – C21

spare

Any spare control bits should be coded binary "1". They are reserved for future use and may change.

The Synchronisation Pattern is similar to the Synchronisation Pattern in 08.60, with some exceptions:

EMBED: C5 equal "0": the Synchronisation Pattern is exactly as described in 08.60;

C5 equal ”1”: the Synchronization Pattern is changed by embedding a TFO Message.

For the coding of the Data Bits see GSM 08.60.

For the coding of the Time Alignment Bits (T_Bits, T1.. T4) see GSM 08.60.

The T_Bits correspond normally to the T_Bits received in the up-link TRAU Frame.

For the purpose of this description the 320 bits of one TFO Frame are arranged in 40 rows (0..39),

with 8 bit (1..8: one octet) each (see GSM 08.60).

The bits of a Full Rate (Enhanced Full Rate) TFO Frame are transmitted in the following order:

Bit m of octet n, shall be transmitted in the Least Significant Bit of the

PCM sample k = n*4 + (m+1)/2 for m = (1, 3, 5, 7) and n = (0..39).

Bit m of octet n shall be transmitted in the second Least Significant Bit of the

PCM sample k = n*4 + m/2 for m = (2, 4, 6, 8) and n = (0..39).

PCM sample (k=1) is the first PCM sample of the corresponding decoded speech frame (k=(1..160)).

5.2 TFO Frame for Half Rate

Half Rate TFO Frames are always structured similar to uplink Half Rate TRAU Frames for 8 kBit/s submultiplexing, see GSM 08.61 subclauses 5.2.1 and 5.2.4.1.

If Half Rate TRAU Frames with 16 kBit/s submultiplexing are used on the Abis/Ater interface, then the Control and Extended Control Bits for the 8 kBit/s TFO Frame need to be generated on basis of the received Control Bits from the TRAU Frame.

Table 2: Void

The coding of the Control Bits (C1 .. C9) is according to the following table 3:

Table 3: The coding of the Control Bits (C1 .. C9)

Control Bit

Description

Comment

C1 – C4

Frame Type

HR

C1 . C2 . C3 . C4

0 . 0 . 0 . 1 All other code words are reserved.

C5

EMBED

Indicates the presence of an embedded TFO Message

C7 – C8

spare

C9

DTXd

Copied from uplink TRAU frame

Any spare control bits should be coded binary "1". They are reserved for future use and may change.

The Synchronisation Pattern is similar to the Synchronisation Pattern in 08.61, with some exceptions:

EMBED: C5 equal "0": the Synchronisation Pattern is exactly as described in 08.61;

C5 equal ”1”: the Synchronization Pattern is changed by embedding a TFO Message.

The coding of the Extended Control Bits (XC1.. XC6):

XC1 is copied from the uplink TRAU Frame.

XC2 .. XC6: These bits are normally copied from the 8 kBit/s TRAU frame corresponding to this TFO Frame.

All other codes are reserved.

For the coding of the Data Bits see GSM 08.61.

For the coding of the Time Alignment Bits see GSM 08.61.

The T_Bits correspond normally to the T_Bits received in the up-link TRAU Frame.

For the purpose of this description the 160 bits of one frame are arranged in 20 rows (1..20), with 8 bit (1..8: one octet) each (see GSM 08.61).

The bits of a Half Rate TFO Frame are transmitted in the following order:

Bit m of octet n shall be transmitted in the Least Significant Bit of the

PCM sample k = (n-1)*8+m; with m = (1..8) and n = (1..20).

PCM sample (k=1) is the first PCM sample of the corresponding decoded speech frame (k=(1..160)).