What is BSIC?

Hi Nguyen,
Thank you for the information about inter-PLMN handover. When performing inter-PLMN handover MS gets registered in VPLMN first, doesn’t it? Does it imply that core-MSC changes at the inter-PLMN handover?

Hello!!
This is a nice place for discussion. Lot of technical interaction going on. Was searching thru Google on AXE810 and found this forum. Just been thru the “Switch Planning for GSM” thread and then going thru this one.
I think the GSM specifications do not describe the handovers between cells of different PLMNs. Please correct me if I am wrong. If it exists, it should be similar to Inter-MSC handover except for the fact that roaming check feature of the visiting MS would have to be done which need not be done for Inter-MSC handover because here it is generally assumed that both the MSCs would be of the same PLMN.
Nguyen>>> What Diampl probably means is that if MSC A(core MSC) of HPLMN was handling the call and then Inter-PLMN handover takes place to MSC B of VPLMN. Would MSC A be completely out of picture now ? Well, in case of Inter MSC handovers, that’s how it happens.
Diampl >>> I feel if Inter-PLMN handovers do exist then the same should be the case here too. Core MSC A should be out of picture. But could you please tell me what happens to CDRs during the Inter MSC handovers. Would both the MSCs generate CDRs for their portion of call handling.
One more silly doubt now after going thru this thread. Let us consider a scenerio where a MS in speech phase moves to an area with a different LAC but within the same MSC area. Handover takes place. It is said that handover would be done first and then LU would take place. Will the LU be done during the speech phase over FACCH or will it happen after call termination.

Regards.

Hi Nguyen,
It was a pleasure.
I quickly went thru the GSM Rec 03.09 version 7.0.0 release 1998 on Handover procedures. It says, after Handover from MSC-A to MSC-B, the connection between MSC-A and MSC-B is released. I think anchor and relay MSCs are the names given for understanding the scenerios.
When you say LU will be executed after the end of call, I assume you are meaning after the speech phase is over.
Main components of LU are TMSI and LAI. VLR-B, HLR and SIM card of MS must be updated and VLR-A cleared. While the call is in speech phase and the handover has been completed, I think VLR-B should be updated with the LAI,HLR of MS must have the VLR-B number. I feel this is necessary coz if a call lands on MS while he has moved from MSC-A to MSC-B and is still in speech phase and the LU has not yet been done then the HLR of MS will show the presence of MS in VLR-A and VLR-A will have the old LAI and the response to the calling party would be that the MS is not answering the call(this would also be improper utilization of PCH in VLR-A area). Whereas, actually he is busy in VLR-B area. But if the VLR-B and HLR of MS are updated during speech phase immediately after handover, any caller to this MS will hear the announcement that the subscriber is busy. But don’t know what the GSM recs say.
Another thing is updating the SIM of MS. New TMSI and LAI should be given to MS. When will this be done? I feel this info can be exchanged over FACCH during speech phase but not sure. Any member familiar with this scenerio may please contribute.
And yes, roaming subscription checks of MS for Inter PLMN(even if it exists) shouldn’t be an issue. The handover request would first have been received by MSC-A of HPLMN. Right at this moment before communicating with MSC-B of VPLMN, the MSC-A can find out from HLR of MS(or may be keeping such records already within VLR-A) whether the MS has Inter PLMN roaming subscription(MSC-A by now knows the area/operator where the MS is heading to). If yes then it proceeds to call MSC-B. Now if roaming agreements are in place between MSC-A and MSC-B of different PLMNs, then MSC-B will accept the handover request of MSC-A. Well, I have just tried to apply logic to the above scenerio, not read these in GSM Recs. In case of error, please correct me.
Regards.

You are right Nguyen!!
Actually, I had read thru the GSM specs very quickly(one should never do that) and missed out the most important part. It clearly says, “MSC-A shall retain overall call control until the call is cleared by the fixed subscriber or the MS and there is no further
call control functions to be performed (e.g. servicing waiting calls, echo cancellers)”.
I knew LU takes place over SDCCH but my above misconception was causing the confusion in my mind.
Many many thanks for clarification.
Regards.

Nguyen, thanks for the specs reference for Inter PLMN Handover. Will go thru them and get back. But I think HPLMN1 MSC-A would anyway come to know of the handover request and can check the Inter PLMN roaming subscription of the MS. VPLMN2 MSC-B would just check whether handover request from MSC-A is to be entertained or not.
Could you pl elaborate, what is the issue/concern you see here?
Are you interested in knowing the exact sequence of operations or you find an issue coz of which you see it not happening.
Regards.

Hi all,
Shall we get back to inter-PLMN handover? Nguyen, thank you for the reference on inter-PLMN handover that you’ve given before. I went quickly throu it. (3GPP TS 22.129 version 5.2.0 Release 5) The spec leaves many issues open but it states (Annex A ) that if handover request is accepted by target PLMN and the call continues in adjacent PLMN, subscriber location information in HLR remains unchanged. After inter-PLMN handover, anchor MSC located in previous PLMN continues to control a call. When the call is over, LU takes place.

During inter-MSC handover, the serving BSC sends handover required message to the serving MSC (MSC-A), then MSC-A sends handover request message to the target MSC (MSC-B). MSC-A takes control over all connection of the MS. If A losses control, the call will drop immediately. The MS then register itself to the MSC-B by location updating procedure.

When the MS moves from one country to another one in the idle mode, this is not a handover procedure. This is called roaming procedure.

The MS will request location updating as usually. The visited network will check for roaming subscription of the MS, and if it is permitted, the location updating procedure will be processed as normally.