3GPP TSG-CN WG1 	Tdoc 3GPP N1-99580
Sophia Antipolis, FRANCE
1 – 4 June 1999

Source:	TSG-N1
To:	TSG-S1, Multicall ad hoc Gr, TSG CN, TSG-T2, TSG-CN-SS ad hoc, N2

Liaison Statement on the requirements for Multicall
The TSG-N1 have discussed the LS from N2 in N1-99-510 (which is N2-99-685) which relates to specification 22.135, Version 1.0.0, Service Aspects of Multicall. 

TSG-N1 would like to add the following information to N2’s questions.

1.	Limiting the number of multicall
N1 notes N2’s comment.

2.	Upper limit of the maximum number
The upper limit of the maximum number of active calls or sessions simultaneously will be important issue for the design of the call control and session management protocols. 

With respect to MSC based Call Control, the transaction identifiers in GSM 04.08 currently impose a maximum limit of 7 uplink plus 7 downlink calls. Although this number could be increased, this would require substantial extra effort. (Note that one transaction ID is needed for each active call, each held call, each waiting call and each CCBS recall).

With respect to the number of SGSN based PDP contexts, GSM transaction identifiers limit the number of Mobile originated PDP contexts to 7 and the number of network initiated PDP contexts to 7. The GTP protocol imposes a maximum number of simultaneous GTP tunnels of 15. The SNDCP protocol has a limit of 11 ‘connections’ between mobile and SGSN (SNDCP is needed when PS-Multicall is used in GSM radio coverage). All these restrictions can be removed but this would require substantial effort.

N1 note that use of one PDP context (with one IP address) can still permit multiple TCP/IP connections to be established. This can be used to establish an almost unlimited number of ‘IP sessions’ in the PS domain. N1 note that the number of these “IP sessions” is not visible to the SGSN and probably not visible at the GGSN.

The TSG-N1 request  TSG-S1 to set the upper limit of the maximum number of simultaneous calls/sessions bearing in mind the likely work that will result in TSG-N1.

3.	Busy definition
From the N1 perspective, the multicall work item will require changes to the way the mobile handles call setup attempts while an existing call is active or is being established. Such changes mean that reducing the number of conditions which lead to NDUB will have little impact on mobiles.