5 TFO Frame Structure

28.0623GPPInband Tandem Free Operation (TFO) of speech codecsService descriptionStage 3TS

5.1 General

TFO Frame formats are defined for the following Speech Codec Types:

– GSM Full Rate (GSM_FR);

– GSM Half Rate (GSM_HR);

– GSM Enhanced Full Rate (GSM_EFR);

– Adaptive Multi Rate Family (FR_AMR, HR_AMR,UMTS_AMR, UMTS_AMR_2, OHR_AMR);

– WB Adaptive Multi Rate Family (UMTS_AMR-WB, FR_AMR-WB, OFR_AMR-WB, OHR_AMR-WB)

TFO Frame formats for 8 kbit/s, 16kbit/s and 32 kbit/s sub-multiplexing are defined in the following clauses.

5.2 TFO Frames for 16 kbit/s sub-multiplexing

5.2.1 TFO Frames for GSM Full Rate and GSM Enhanced Full Rate

The TFO Frames for GSM_FR and GSM_EFR are derived from the uplink TRAU Frames as defined in the 3GPP TS 48.060. Table 5.2.1-1 defines the coding of the Control Bits for these TFO Frames.

Table 5.2.1-1: Control Bits in TFO Frames for GSM_FR and GSM_EFR

Control Bit	Description	Comment
C1 – C4 0.0.0.1 1.1.0.1	Frame Type GSM_FR GSM_EFR	copied from uplink TRAU Frames 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) set to Spare by TRAU
C12	BFI	Copied from the uplink TRAU Frame
C13 – C14	SID	Copied from the uplink TRAU Frame
C15	TAF	Copied from the uplink TRAU Frame
C16	Spare	set to Spare by TRAU
C17	DTXd	Copied from the uplink TRAU Frame
C18 – C21	Spare	set to Spare by TRAU

Any spare control bit shall be coded as binary "1". They are reserved for future use and may change.

The Synchronisation Pattern is similar to the Synchronisation Pattern in the 3GPP TS 48.060, with some exceptions depending on the value of the EMBED Bit:

EMBED equal "0": the Synchronisation Pattern is exactly as described in the 3GPP TS 48.060;
EMBED equal "1": the Synchronisation Pattern contains an embedded TFO Message.

For the coding of the Data Bits see 3GPP TS 48.060.

For the coding of the Time Alignment Bits (T_Bits, T1.. T4) see 3GPP TS 48.060. The T_Bits normally correspond to the T_Bits received in the up-link TRAU Frame.

5.2.2 TFO Frames for the Adaptive Multi Rate Family

The TFO Frames for any narrow-band AMR Codec Type use always 16 kbit/s sub-multiplexing on the A-Interface, regardless which sub-multiplexing is used on the Abis-Interfaces. Two different AMR_TFO Frame formats exist. One, called AMR_TFO_16k, is based on the TRAU Frame format for 16 kBit/s sub-multiplexing, as described in 3GPP TS 48.060. The other one, called AMR_TFO_8+8k, is based on the TRAU Frame format for 8 kbit/s sub-multiplexing, as described in 3GPP TS 48.061, with an added synchronisation pattern, to improve transmission and synchronisation quality on the A-Interface.

Optionally the TRAU frame format AMR_TRAU_8+8k may be used on the Abis-Interface for 16 kBit/s sub-multiplexing, when a TFO connection with HR_AMR on the distant side is established.

Additionally, a frame format using 16 kbit/s sub-multiplexing is defined for wide band AMR codec types, called AMR_WB_TFO_16k. It is based on the TRAU frame format for 16 kBit/s sub-multiplexing, as described in 3GPP TS 48.060.

5.2.2.1 TFO Frame Format AMR_TFO_16k

TFO Frames with format AMR_TFO_16k are derived from the TRAU Frames for Adaptive Multi Rate as defined in the 3GPP TS 48.060. The AMR_TFO_16k Frame structure is illustrated in Figure 5.2.2.1-1, using the same notations as in 3GPP TS 48.060. Table 5.2.2-1 defines the coding of the Control Bits for AMR TFO Frames. Note that additional TFO Configuration Parameters may be carried by the Data Bits of the TFO Frames, as defined in annex C.

			Bit number
Octet no.	1	2	3	4	5	6	7	8
0	0	0	0	0	0	0	0	0
1	0	0	0	0	0	0	0	0
2	1	C1	C2	C3	C4	C5	C6	C7
3	C8	C9	C10	C11	C12	C13	C14	C15
4	1	C16	C17	C18	C19	C20	C21	C22
5	C23	C24	C25	D1	D2	D3	D4	D5
6	1	D6	D7	D8	D9	D10	D11	D12
7	D13	D14	D15	D16	D17	D18	D19	D20
8..36
37	D238	D239	D240	D241	D242	D243	D244	D245
38	1	D246	D247	D248	D249	D250	D251	D252
39	D253	D254	D255	D256	T1	T2	T3	T4

Figure 5.2.2.1-1: Structure of AMR_TFO_16k Frames

Table 5.2.2.1-2: Coding of the Control Bits for AMR_TFO_16k Frames

Control Bits	Description		Comment
	FR_AMR, HR_AMR, UMTS_AMR_2, OHR_AMR	UMTS_AMR	FR_AMR, HR_AMR, OHR_AMR	UMTS_AMR, UMTS_AMR_2
C1 – C4 (0.0.0.1) 0.0.1.1 0.1.0.0 0.1.0.1 0.1.1.0 (1.0.0.1) (1.0.1.0) 1.0.1.1 (1.1.0.0) (0.0.1.0) (1.1.0.1)	Frame_Type / Codec Type (GSM_FR) FR_AMR HR_AMR UMTS_AMR UMTS_AMR_2 (FR_AMR-WB) (UMTS_AMR-WB) OHR_AMR (OFR_AMR-WB) (OHR_AMR-WB) (GSM_EFR)		The coding is different from the coding in TFO Messages. It is also not identical to the coding on Abis/Ater. The TRAU shall translate the coding between TRAU and TFO Frames. Codec Types in (brackets) are not supported by this TFO Frame format. They are listed to show their coding for convenience.
C5 0 1	EMBED No TFO Message embedded A TFO Message is embedded		Indicates the presence of an embedded TFO Message. Set by the TRAU.
C6 – C8	Set to "1.1.1"(see note)	Codec Mode Request (CMR))	In GSM TRAU Frames, these bits carry part of the Time Alignment. They are set to 1.1.1 by the TRAU.	Coding as defined in 3GPP TS 48.060
C9 – C11 0.0.0 0.0.1 0.1.0 0.1.1 1.0.0 1.0.1 1.1.0 1.1.1	TFO and Handover_Notifications TFO_On TFO_Soon TFO_Off Handover_Soon Handover_Complete undefined undefined undefined		In GSM TRAU Frames these bits are part of the Time Alignment field. These bits are copied from TRAU frames to TFO Frames and vice versa. TFO_On is the default value in TFO Frames.
C12	RIF (Request or Indication Flag)	set to 0	Copied from the uplink TRAU Frame in GSM Generated by the Transcoder in 3G systems for FR_AMR and HR_AMR: The changes of the uplink Codec Mode, as received via the Iu Frames, are monitored. Whenever the Codec Mode changes, the RIF bit is set to "0". The next frames are then alternatingly marked with RIF = "1", "0", "1" and so on.
C13	Spare (set to 1)		C13 is spare in UL TRAU frames.
C14 – C16	Config_Prot		Coding defined in Annex C.
C17 C18	Mess No		Coding defined in Annex C.
C19	DTXd (see note)		Copied from uplink TRAU Frame in GSM
C20 0 1	TFOE TFO Disable TFO Enable		Copied from the uplink TRAU Frame in GSM Generated by the Transcoder in 3G systems with the same coding as in the 3GPP TS 48.060
C21 – C22 1 1 1 0 0 1 0 0	Frame_Classification "Speech_Good" "Speech_Degraded" "Speech_Bad" "No_Speech"		Copied from the uplink TRAU Frame in GSM Derived from the Frame Quality Indicator and Frame Type for 3G systems (see Table 5.2.2.1-3 below)
C23 – C25	(see 3GPP TS 48.060) CMI (if RIF == 0) or CMR (if RIF == 1) or 0.0.0 (if Frame_Classification == 0.0)	Codec Mode Indication (CMI); (RIF ==0 is always the case in UMTS_AMR)	Carry CMI or CMR depending of the value of RIF, if the Frame Classification bits are different from "0 0" (No_Speech), and set to "000" otherwise. Copied from the uplink TRAU Frame in GSM Derived from the Frame Quality Indicator and Frame Type for 3G systems (see Table 5.2.2.1-3)	Coding as defined in 3GPP TS 48.060
T1 – T4	Time Alignment Bits		In GSM copied from the uplink TRAU Frame In 3G, generated by the TC (UMTS) based on Iu Frame arrival time(s)

NOTE 0: Any spare control bits shall be coded as binary "1". They are reserved for future use and may change.

The CRC1 covering also the control bits C1..C25 shall be recomputed in the transcoders.

The coding of the Data Bits is described in 3GPP TS 48.060.

In 3G systems, the Frame_Classification Bits must be derived from the Frame Quality Indicator (FQI) and Frame Type Index as defined in the 3GPP TS 26.101. Table 5.2.2.1-3 provides the conversion rules between the generic AMR Frames (as defined in 3GPP TS 26.101) and TFO Frames. In this table, the arrows in the fourth column indicate the direction for which the conversion applies.

NOTE 1: A one-to-one relationship between Generic AMR Frames and TFO Frames does not always exist, but the conversion is always possible.

NOTE 2: In the generic AMR Frames (3GPP TS 26.101), the differentiation between SID_FIRST and SID_UPDATE is done in the Data bits (SID Type Indicator). The Codec Mode Indication (CMI) is carried in 3G systems within the SID payload.

For the FR_AMR, HR_AMR, UMTS_AMR_2 and OHR_AMR Codec Types, bits C23 – C25 shall carry either the Codec Mode Request (CMR) or the Codec Mode Indication (CMI), depending on the value of RIF, if the Frame_Classification bits are different from "0.0". If the Frame_Classification bits are equal to "0.0" (SID_First and SID_Update Frames), C23 – C25 are set to 0.0.0, and the CMI and CMR are carried in the data bits D35 – D40.

For 3G systems using the UMTS_AMR_2 Codec Types, the TC shall monitor the changes of the uplink Codec Mode, as received in the Iu Frames. Every time the Codec Mode changes in the Iu Frames the TC shall set RIF = "0" in the corresponding TFO Frame. The next TFO Frames are alternatively marked with RIF = "1", "0", "1" and so on.

NOTE 3: Per definition for UMTS_AMR_2 the UE shall select the phase of potential Codec Mode changes in uplink once at call set-up and shall not alter this later on. At call set-up TFO is not active and the TC has enough time to find the phase of the RIF by the proposed implicit method, before the first TFO Frame has to be sent.

Table 5.2.2.1-3: Conversion between Generic AMR Frames and AMR_TFO_16k Frames

Generic AMR Frame				AMR_TFO_16k Frame
Frame Quality Indicator	Frame Type Index	TX_TYPE or RX_TYPE (see 3GPP TS 26.101)		Frame_ Classification C21 – C22	CMI or CMR C23 – C25	Data bits in No_Speech frames D32 .. D34	Equivalent Frame Type in 3GPP TS 48.060)
1	0-7	SPEECH_GOOD	< >	1 1	0-7	–	Speech_Good
1	0-7	SPEECH_GOOD	<	1 0	0-7	–	Speech_Degraded
0	0-7	SPEECH_BAD	< >	0 1	0-7	–	Speech_Bad
1	8	SID_FIRST	< >	0 0	0 0 0	SID_First	No_Speech
1	15	NO_DATA	<	0 0	0 0 0	Onset	No_Speech
1	8	SID_UPDATE	< >	0 0	0 0 0	SID_Update	No_Speech
0	8	SID_BAD	< >	0 0	0 0 0	SID_Bad	No_Speech
1	15	NO_DATA	< >	0 0	0 0 0	No_Data	No_Speech

The Synchronisation Pattern is similar to the Synchronisation Pattern in 3GPP TS 48.060, with some exceptions related to the value of the EMBED Bit:

EMBED equal "0": the Synchronisation Pattern is exactly as described in the 3GPP TS 48.060;
EMBED equal "1": the Synchronisation Pattern contains an embedded TFO Message.

For the coding of the Data Bits see 3GPP TS 48.060 and Annex C for the bits reserved for TFO Configuration Parameters.

For the coding of the Time Alignment Bits (T_Bits, T1 .. T4) see 3GPP TS 48.060 and Annex C. When the TFO Frame is generated by a GSM Network, the T_Bits normally correspond to the T_Bits received in the up-link TRAU Frame.

5.2.2.2 TFO Frame Format AMR_TFO_8+8k

The AMR_TFO_8+8k Frame formats are derived from the GSM Adaptive Multi-Rate 8 kbit/s TRAU Frame formats defined in 3GPP TS 48.061. AMR Codec Modes with rates up to 7,40 kbit/s can be used with these AMR_TFO_8+8k Frame formats. The AMR_TFO_8+8k is described in an 8 kbit/s frame structure for the second LSB of the PCM samples and an 8 kbit/s synchronisation pattern for the LSB. The TFO Frame structures for the second LSB are illustrated in Figures 5.2.2.2-1 to 5.2.2.2-3, using the same notations as in 3GPP TS 48.061. Figure 5.2.2.2-4 defines the additional Synchronisation pattern for the LSB. Both frames shall be exactly synchronised on the A-Interface. This additional Synchronisation Pattern is sometimes modified by embedding of TFO Messages, indicated by the value of the EMBED bit:

EMBED equal "0": the Synchronisation Pattern is exactly as described in Figure 5.2.2.2-4;
EMBED equal "1": the Synchronisation Pattern contains an embedded TFO Message.

	Bit number
Octet no	1	2	3	4	5	6	7	8
1	0	0	0	0	0	0	0	0
2	1	D1	D2	D3	D4	D5	D6	D7
3	1	C1	C2	C3	C4	C5	D8	D9
4	0	1	D10	D11	D12	D13	D14	D15
5…19	1
20	1	D121	D122	D123	D124	D125	D126	T

Figure 5.2.2.2-1: AMR_TFO_8+8k Frame Structure, second LSB:
NO_SPEECH frames and SPEECH frames for Codec Modes 4,75, 5,15 and 5,90 kbit/s

	Bit number
Octet no	1	2	3	4	5	6	7	8
1	0	0	0	0	0	0	0	0
2	1	D1	D2	D3	D4	D5	D5	D7
3	1	C1	C2	C3	D8	D9	D10	D11
4…19
20	D130	D	D	D	D	D	D	D137

Figure 5.2.2.2-2: AMR_TFO_8+8k Frame Structure, second LSB:
Speech frame for Codec Mode 6,70 kbit/s

	Bit number
Octet no	1	2	3	4	5	6	7	8
1	0	0	1	D1	D2	D3	D4	D5
2	0	D6	D7	D8	D9	D10	D11	D12
3	1	C1	C2	C3	D13	D14	D15	D16
4	0	D17	D18	D19	D20	D21	D22	D23
5	D24	D	D	D	D	D	D	D31
6 … 19
20	D144	D145	D146	D147	D148	D149	D150	D151

Figure 5.2.2.2-3: AMR_TFO_8+8k Frame Structure, second LSB:
Speech frame for Codec Mode 7,40 kbit/s

	Bit number
Octet no	1	2	3	4	5	6	7	8
1	0	0	0	0	0	0	0	0
2	1	EMBED	EXTEND
3…6	1							1
7	0	1
8 … 19	1
20	1						1	1

Figure 5.2.2.2-4: AMR_TFO_8+8k Frame Structure, LSB:
Additional Synchronisation Pattern

EXTEND equal "0": The bits not defined in the Synchronisation Pattern described in Figure
5.2.2.2-4 are "spare" (equal 1). In AMR_TFO_8+8k frames these undefined bit positions shall leave the original bits of the PCM coded speech unaltered.
In TRAU_8+8k frames these undefined bits shall be set to "1" (spare).

EXTEND equal "1": The bits not defined in the Synchronisation Pattern described in Figure
5.2.2.2-4 transport other parameters (tbd).

Table 5.2.2.2-1 defines the coding of the Control Bits for AMR TFO Frames. Note that additional TFO Configuration Parameters may be carried by the Data Bits of the TFO Frames, as defined in Annex C.

Table 5.2.2.2-1: The coding of the Control Bits (C1 .. C5) for AMR_TFO_8+8k Frames

Control Bit	Description	No_Speech frames and Speech frames for 4,75, 5,15 and 5,9 kbit/s Codec Modes	6,7 + 7,4 kbit/s Codec Mode
C1 – C3	see 3GPP TS 48.061	– For the low rates frame types, these bits jointly define the CMI, CMR and RIF. – For the No_Speech frame type, they define the RIF. – Copied from the uplink TRAU Frame in GSM. – Derived from the Frame Quality Indicator and Frame Type for 3G systems (see Table 5.2.2.2-2 below)	– For the 6,70 and 7,40 kbit/s speech frame, these bits jointly provide the CMR, RIF, and the Frame Classification. – Copied from the uplink TRAU Frame in GSM. – Derived from the Frame Quality Indicator and Frame Type for 3G systems (see Table 5.2.2.2-2 below)
C4 – C5 1 1 1 0 0 1 0 0	Frame_Classification (No_Speech and low rates modes only) "Speech_Good" "Speech_Degraded" "Speech_Bad" "No_Speech"	– Copied from the uplink TRAU Frame in GSM – Derived from the Frame Quality Indicator and Frame Type for 3G systems (see Table 5.3.2-2 below)	The Frame_Classification is defined by bits C1-C3 in 6,70 and 7,40 kbit/s TFO Frames C4..C5 are not existent for this codec modes

The CRC1 covering also the control bits shall be recomputed in the transcoders.

The coding of the Data Bits is described in 3GPP TS 48.061 [4].

For 3G systems, Table 5.2.2.2-2 provides the conversion rules between the generic AMR Frames as defined in 3GPP TS 26.101 and the AMR_TFO_8+8k Frames. In this table, the arrows in the fourth column indicate the direction for which the conversion applies. The Transcoder shall autonomously and internally generate a RIF alternating between the binary "0" and "1" values (see Annex D).

Table 5.2.2.2-2: Conversion between Generic AMR Frames and AMR_TFO_8+8k Frames

Generic AMR Frame					TFO Frame for 8 kbit/s submultiplexing
Frame Quality Indicator	Frame Type Index	TX_TYPE or RX_TYPE (see 3GPP TS 26.101)			Bits C1 .. C3	Bits C4 – C5	Data bits in No_Speech frames D8 .. D10	Equivalent Frame Type in 3GPP TS 48.061	Frame Type
1	0-2	SPEECH_GOOD	< >		as 3GPP TS 48.061	1 1	–	Speech_Good	4,75 kbit/s, 5,15 kbit/s, 5,90 kbit/s Modes
1	0-2	SPEECH_GOOD	<		as 3GPP TS 48.061	1 0	–	Speech_Degraded
0	0-2	SPEECH_BAD	< >		as 3GPP TS 48.061	0 1	–	Speech_Bad
1	3-4	SPEECH_GOOD	< >		as 3GPP TS 48.061	Speech bits	–	Speech_Good	6,70 kbit/s, 7,40 kbit/s Modes
1	3-4	SPEECH_GOOD	<		as 3GPP TS 48.061	Speech bits	–	Speech_Degraded
0	3-4	SPEECH_BAD	< >		as 3GPP TS 48.061	Speech bits	–	Speech_Bad
1	8	SID_FIRST	< >		as 3GPP TS 48.061	0 0	SID_First	No_Speech	No Speech
1	15	NO_DATA	<		as 3GPP TS 48.061	0 0	Onset	No_Speech
1	8	SID_UPDATE	< >		as 3GPP TS 48.061	0 0	SID_Update	No_Speech
0	8	SID_BAD	< >		as 3GPP TS 48.061	0 0	SID_Bad	No_Speech
1	15	NO_DATA	< >		as 3GPP TS 48.061	0 0	No_Data	No_Speech

The Synchronisation Pattern in the second LSB of the PCM samples is identical to the Synchronisation Pattern in 3GPP TS 48.061. Embedding of TFO Messages has no influence on this synchronisation pattern.

For the coding of the Time Alignment Bit (T Bit) for all modes below 5,9 kbit/s and the No_Seech Frame, see 3GPP TS 48.061.The T-Bit in a TFO Frame normally corresponds to the T_Bit received in the up-link TRAU Frame.

5.2.2.3 TFO Frame Format AMR_WB_TFO_16k and AMR_WB_TFO_32k

TFO Frames with format AMR_WB_TFO_16k and AMR_WB_TFO_32k are derived from the TRAU Frames for Adaptive Multi-Rate Wide Band as defined in the 3GPP TS 48.060. The AMR_WB_TFO_16k Frame structure is illustrated in Table 5.2.2.3-1 below, using the same notations as in 3GPP TS 48.060.

For AMR_WB_TFO_32k Frames the identical frame structure is used twice, once in the lower 16k main part (identical to the AMR_WB_TFO_16k) and in the upper 16k extension part (carrying some data bits, but no synchhronisation and no control bits, see Table 5.2.2.3-2). The unspecified bits in Table 5.2.2.3-2 shall not alter the bits of the PCM samples on the 64 kbit/s A interface.

Table 5.2.2.3-3 defines the coding of the Control Bits for the Frame Type (== Codec Type) field (C1..C4) in AMR_WB_TFO_16k and AMR_WB_TFO_32k frames. For the remaining control bits (C5…C25) the definition is as for AMR_TFO_16k frames for FR_AMR.

Table 5.2.2.3-1: Structure of AMR_WB_TFO_16k Frames
and the lower 16k main part of AMR_WB_TFO_32k Frames

			Bit number
Octet no.	1	2	3	4	5	6	7	8
0a	0	0	0	0	0	0	0	0
1a	0	0	0	0	0	0	0	0
2a	1	C1	C2	C3	C4	C5	C6	C7
3a	C8	C9	C10	C11	C12	C13	C14	C15
4a	1	C16	C17	C18	C19	C20	C21	C22
5a	C23	C24	C25	D1	D2	D3	D4	D5
6a	1	D6	D7	D8	D9	D10	D11	D12
7a	D13	D14	D15	D16	D17	D18	D19	D20
8a..36a
37a	D238	D239	D240	D241	D242	D243	D244	D245
38a	1	D246	D247	D248	D249	D250	D251	D252
39a	D253	D254	D255	D256	T1	T2	T3	T4

Table 5.2.2.3-2: Structure of the upper 16k extension part in AMR_WB_TFO_32k Frames

			Bit number
Octet no.	1	2	3	4	5	6	7	8
0b
1b
2b
3b
4b
5b				D1	D2	D3	D4	D5
6b		D6	D7	D8	D9	D10	D11	D12
7b	D13	D14	D15	D16	D17	D18	D19	D20
8b..36b
37b	D238	D239	D240	D241	D242	D243	D244	D245
38b	1	D246	D247	D248	D249	D250	D251	D252
39b	D253	D254	D255	D256

Table 5.2.2.3-3: Coding of the Frame Type for AMR_WB_TFO_16k Frames
and AMR_WB_TFO_32k Frames

Control Bits	Description	Comment
C1 – C4 (0.0.0.1) (0.0.1.1) (0.1.0.0) (0.1.0.1) (0.1.1.0) 1.0.0.1 1.0.1.0 (1.0.1.1) 1.1.0.0 0.0.1.0 (1.1.0.1)	Frame_Type / Codec Type (GSM_FR) (FR_AMR) (HR_AMR) (UMTS_AMR) (UMTS_AMR_2) FR_AMR-WB UMTS_AMR-WB (OHR_AMR) OFR_AMR-WB OHR_AMR-WB (GSM_EFR)	The coding is different from the coding in TFO Messages. It is also not identical to the coding on Abis/Ater. The TRAU shall translate the coding between TRAU and TFO Frames. Note: Codec Types in (brackets) are not supported by this TFO Frame format. They are listed to show their coding for convenience. Note: By definition FR_AMR-WB and OHR_AMR-WB do only use the AMR_WB_TFO_16k Frame, because they never use a Codec Mode higher than 12.65 kbit/s. UMTS_AMR-WB and OFR_AMR-WB use the AMR_WB_TFO_32k Frame when at least one Codec Mode is above 12.65 kbit/s.

NOTE: Any spare control bits shall be coded as binary "1". They are reserved for future use and may change.

The CRC covering also the control bits C1..C25 shall be recomputed in the transcoder, because some control bits change between TRAU Frames and TFO Frames, e.g. the coding of the Frame Type.

The coding of the Data Bits is described in 3GPP TS 48.060. In AMR_WB_TFO_32k Frames the data bits in the upper 16k extension part shall be set as defined in TS 48.060. But in all unused bit positions of this upper extension part the bits of the PCM samples shall not be altered in order to minimise the audible effect.

In 3G systems, the Frame_Classification Bits must be derived from the Frame Quality Indicator (FQI) and Frame Type Index as defined in the 3GPP TS 26.201. The conversion rules are the same as for the FR_AMR.

NOTE 1: A one-to-one relationship between Generic WB AMR Frames and TFO Frames does not always exist, but the conversion is always possible.

NOTE 2: In the generic WB AMR Frames (3GPP TS 26.201), the differentiation between SID_FIRST and SID_UPDATE is done in the Data bits (SID Type Indicator). The Codec Mode Indication (CMI) is carried in 3G systems within the SID payload.

3G systems using the UMTS_AMR-WB Codec Type, the TC shall monitor the changes of the uplink Codec Mode, as received in the Iu Frames. Every time the Codec Mode changes in the Iu Frames the TC shall set RIF = "0" in the corresponding TFO Frame. The next TFO Frames are alternatively marked with RIF = "1", "0", "1" and so on.

NOTE 3: Per definition for UMTS_AMR-WB the UE selects the phase of potential Codec Mode changes in uplink once at call set-up and does not alter this later on. At call set-up TFO is not active and the TC has enough time to find the phase of the RIF by the proposed implicit method, before the first TFO Frame has to be sent.

The Synchronisation Pattern is similar to the Synchronisation Pattern in 3GPP TS 48.060, with some exceptions related to the value of the EMBED Bit:

EMBED equal "0": the Synchronisation Pattern is exactly as described in the 3GPP TS 48.060;
EMBED equal "1": the Synchronisation Pattern contains an embedded TFO Message.

For the coding of the Data Bits see 3GPP TS 48.060.

For the coding of the Time Alignment Bits (T_Bits, T1 .. T4) see 3GPP TS 48.060. When the TFO Frame is generated by a GSM Network, the T_Bits normally correspond to the T_Bits received in the up-link TRAU Frame.

5.2.3 Transmission of the bits of 16 kbit/s TFO Frames

For the purpose of this description the 320 bits of one TFO Frame are arranged in 40 rows (0..39), with 8 bit each (1..8: one octet) as in 3GPP TS 48.060.

The bits of 16 kbit/s TFO Frames 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 TFO Frame, which follows the received uplink TRAU frame with a small delay (Tultfo), as described in clause 8, see figure 8.1.2-1.

5.2.3a Transmission of the bits of 32 kbit/s TFO Frames

For the purpose of this description the 640 bits of one TFO Frame are arranged in 2 x 40 rows (0a..39a, 0b…39b), with 8 bit each (1..8: one octet) as in 3GPP TS 48.060, see also Table 5.2.2.3-1and Table 5.2.2.3-2.

The bits of 32 kbit/s TFO Frames 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 = (0a…39a).

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 = (0a..39a).

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

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

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

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

PCM sample (k=1) is the first PCM sample of the TFO Frame, which follows the received uplink TRAU frame with a small delay (Tultfo), as described in clause 8, see figure 8.1.2-1.

It is important that the lower main 16k part and the upper 16k extension part are exactly synchronised as described above, see also clause 8.

5.2.4 Transmission of the bits of AMR_TFO_8+8k Frames

For the purpose of this description the 160+160 bits of one AMR_TFO_8+8k frame are arranged in 20 rows (1..20), with 8 bit each (1..8: one octet) as shown in Figures 5.2.2.2-1 to 5.2.2.2-4.

The bits of AMR_TFO_8+8k frames are transmitted in the following order:

Bit m of octet n of the additional synchronisation pattern described in Figure 5.2.2.2-4 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).

Bit m of octet n of the No_Speech and Speech frames as described in Figures 5.2.2.2-1 to 5.2.2.2-3 shall be transmitted in the Second 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 TFO Frame, which follows the received uplink TRAU frame with a small delay (Tultfo), as described in clause 8, see figure 8.1.2-1.

5.2.5 Optional AMR_TRAU_8+8k Frames

For TFO Connections with FR_AMR on the local side and HR_AMR on the distant side the local side may use the AMR_TRAU_8+8k frame format after TFO has been established. The AMR_TRAU_8+8k Frame is based on the TRAU Frame formats for the AMR for 8 kBit/s sub-multiplexing as defined in 3GPP TS 48.061 (TRAU_8k), with the additional Synchronisation pattern as defined in Figure 5.2.2.2-4. The differences to AMR_TFO_8+8k frames are:

– the additional synchronisation pattern shall be transmitted in the Second LSBs of the 16 kbit/s sub-multiplexed channel, while the TRAU_8k frames shall be transmitted in the LSBs;

– no embedded TFO Messages shall exist in TRAU_8+8k frames;

– the EMBED bit shall be set to "0";

– the EXTEND bit shall be set to "0";

– undefined bits in Figure 5.2.2.2-4 shall be set to "1" (spare) in TRAU_8+8k frames.

The potential transition from regular TRAU_16k frames to AMR_TRAU_8+8k frames shall be triggered by the FR_TRAU with TFO_Soon and Dis_Req (including the distant Codec Type: HR_AMR) in downlink direction.

If the BTS applies the optional AMR_TRAU_8+8k format, then the BTS shall respond with the acknowledging TFO_Soon in the first AMR_TRAU_8+8k frame in uplink. This will result in a small additional delay for the decoded PCM samples, which the TRAU shall handle by proper concealment techniques. The delay for TFO Messages and TFO Frames is, however, not increased: since no format conversion is necessary in the TRAU the delay for AMR_TFO_8+8k frames is minimised. After TFO has been established the TRAU shall change from TRAU_16k to AMR_TRAU_8+8k in downlink with the reception of the first AMR_TFO_8+8k frame.

If the BTS does not apply the AMR_TRAU_8+8k frame format in uplink, the TRAU shall also not use this in downlink. The TRAU shall perform format conversion in uplink from TRAU_16k format to AMR_TFO_8+8k format and in downlink from AMR_TFO_8+8k format to TRAU_16k format. This will cause an additional delay of TFO Messages and TFO Frames, which shall be handled by inserting the necessary number of T_Bits. This format conversion causes also an additional delay in downlink, which the BTS shall handle by proper buffering technique.

5.3 TFO Frames for 8 kbit/s sub-multiplexing

5.3.1 TFO Frame for the GSM Half Rate

The GSM Half Rate (GSM_HR) TFO Frames are always based on the uplink GSM Half Rate TRAU Frames for 8 kbit/s submultiplexing scheme, as defined in the 3GPP TS 48.061.

If GSM_HR 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.

The coding of the Control Bits (C1 .. C9) is defined by the following Table 5.3.1-1:

Table 5.3.1-1: Coding of the Control Bits (C1 .. C9) for the GSM_HR

Control Bit	Description	Comment
C1 – C4 0.0.0.1	Frame Type GSM_HR	All other code words are reserved.
C5	EMBED	Indicates the presence of an embedded TFO Message
C7 – C8	spare
C9	DTXd	Copied from the uplink TRAU Frame

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

The Synchronisation Pattern is similar to the Synchronisation Pattern in the 3GPP TS 48.061, with some exceptions depending on the value of the EMBED Bit:

EMBED equal "0": the Synchronisation Pattern is exactly as described in the 3GPP TS 48.061;
EMBED equal "1": the Synchronisation Pattern contains an embedded TFO Message.

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.
All other codes are reserved.

For the coding of the Data Bits see 3GPP TS 48.061.

For the coding of the Time Alignment Bits see 3GPP TS 48.061. The T_Bits normally correspond to the T_Bits received in the up-link TRAU Frame.

5.3.2 Transmission of the bits of 8 kbit/s TFO frames

For the purpose of this description the 160 bits of one frame are arranged in 20 rows (1..20), with 8 bit each (1..8: one octet) as in 3GPP TS 48.061.

The bits of 8 kbit/s TFO Frames 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 TFO frame which follows the received uplink TRAU frame with a small delay (Tultfo), as described in clause 8, see figure 8.1.2-1.

5.4 Void

5.5 Determination of the TFO Frame format

The TFO Frame format is depending on the Codec Types at both ends of the TFO connection.

For the GSM FR and GSM EFR Speech Codec Types, the TFO Frame format shall be 16 kbit/s (see clause 5.2.1).

For the GSM HR Speech Codec Type, the TFO Frame format shall be 8 kbit/s (see clause 5.3.1).

For any TFO connection with at least one side using the HR_AMR with a configuration not including the mode 7.95 kBit/s the TFO frame format shall be AMR_TFO_8+8k (see clause 5.2.2.2).

For all other AMR TFO connections, including HR_AMR with 7.95 kBit/s in the ACSes on both sides, the TFO Frame format shall be AMR_TFO_16k (see clause 5.2.2.1).

For any AMR-WB TFO connection not supporting codec modes higher than 12,65 kbit/s, the TFO frame format shall be AMR_WB_TFO_16k.

For all other AMR WB TFO connections, the TFO frame format shall be AMR_WB_TFO_32k.

5.6 Codec Types in TFO Frames

The Codec Type in TFO Frames shall always be the Local Used Codec of the sender of the TFO Frames, exactly as used in TFO Messages.

In cases where compatible, but different Codec Types are used on both sides of the TFO connection (e.g. in calls involving HR_AMR and FR_AMR) each side shall use its own Codec Type in its transmitted TFO Frames. Consequently the Codec Types inside the TFO Frames may be different in both directions of the TFO-link. The TRAU shall always use the Local Used Codec on Ater/Abis interface and therefore translate between Codec Types in TFO and TRAU frames if necessary.