TSG-SA Working Group 2 (Architecture ) meeting #4	TSGS2#3(99)180
19 - 22 April 1999	
Yokohama

3GPP TSG-CN WG2	 Tdoc 3GPP N2-99264 
ETSI SMG3 Working Party ‘C’
Joint Meeting
Issy-les-Moulineau, France
22 - 26 March, 1999
To:	TSG-SA2
Source:	NEC
Title:	Proposed LS on out-of-band transcoder control

TSG-CN2 would like to inform TSG SA2 that TSG CN2 is currently studying the feasibility of out-of-band transcoder control in the UMTS/CN. A copy of the 1st draft of the TR on out-of-band transcoder control is attached to this LS.

3GPP TSG-CN WG2	 Tdoc 3GPP N2-99235
ETSI SMG3 Working Party ‘C’
Joint Meeting
Issy-les-Moulineau, France
22 - 26 March, 1999

Source:		NEC
Title:		Technical Report on out-of-band transcoder control 
Version:		0.0.1

This is the first draft of the technical report on out-of-band transcoder control in the UMTS CN. This report is made based on the N2-99153 report (Summary report of TSG-N plenary meeting) such as presented in the 3GPP TSG-CN WG2 meeting held in 22nd of March 1999.

1.	Intellectual Property Rights
[Editor’s note: TBD]

2.	Foreword
[Editor’s note: TBD]

3.	Introduction
In order to improve voice quality for mobile-to-mobile calls (MS-MS calls) in GSM Phase 2+ networks, Tandem Free Operation (TFO) using in-band signalling has been specified. The TFO mode of operation could also be used to reduce the transmission bandwidth between Mobile services Switching Centres (MSC). The equivalent function in Japan's PDC (Personal Digital Cellular) network is known as Transcoder Bypass. But, this function is created based on the out-of-band signalling (i.e. by the PDC-MAP protocol).

On the other hand, the UMTS may be going to provide many transcoder types. In order to accommodate to this enhancement, the in-band transcoder control may have a limit to handle multiple transcoder types since this method uses the limited unused spare area in PCM coded form. 

This TR introduces the out-of-band transcoder control to be supported for UMTS.

The UMTS Phase 1 network operator should have the option to implement the Transcoder Control by In-band control, out-of-band control or both.

4.	Scope
This TR provides the procedure of out-of-band transcoder control and the expected benefits and expected complexities in order to provide this function for the UMTS/IMT-2000.

5.	Reference
GSM 02.53 ver.7.0.0	Digital cellular telecommunications system (Phase 2+); Tandem Free Operation (TFO); Service description; Stage1
GSM 03.53 ver.7.0.0	Digital cellular telecommunications system (Phase 2+); Tandem Free Operation (TFO); Service description; Stage 2

6.	Definitions and Abbreviations
Transcoder:  The equipment to convert the signal format between radio related signalling (mobile side) and general signalling format used in the PLMN. An example of the transcoder is voice codec equipment.

Transcoder Control:	In case of mobile to mobile call, two transcoders intervened in the PLMN may be freed or may be needed depending on a call situation. The method for both freeing the transcoders and inserting the transcoders in the PLMN network is defined as the transcoder control.

7.	The capabilities required for out-of-band transcoder control 
The following three items are required to support out-of-band transcoder control;

1.	Negotiation
In case of mobile to mobile call, the negotiation executed between two MSCs to exchange transcoder type information being used. Generally, This negotiation is executed during the call establishment phase.
2.	Transcoder freeing
In accordance with the negotiation (described above), the action in the MSCs to free two intervened transcoders in a call and configures through connection between two mobiles. Generally, This procedure is executed after the negotiation procedure.
3.	Transcoder insertion
After a call has been configured the transcoder through connection by transcoder freeing, the transcoders in the two MSCs are inserted in a call and configure the two transcoder intervened connection. This procedure is executed in case the communication environment has been changed by any reasons and encountered with difficulties to continue the transcoder through connection service. (Ex. Call interruption caused by supplementary service) 

8.	Procedure of out-of-band transcoder control
[Editor’s note: Under studying.]

9.	The cost benefits 
[Editor’s note: The cost benefits with comparing to the in-band transcoder control on the following views will be included.

 -Advantage to accommodate with further transcoder type expansion.
 -Other possible cost benefits. ]

10.	Modification of the 3GPP specification
[Editor’s note: Under studying]