Bsc Description

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GSM_BSC Interfaces (Intra MSC Handover Call Flow) Highway GSM Coverage GSM Mobile Mobile Bethesda Bethesda Cell Bethesda BSC

GSM Equipment Rockville MSC VLRs Rockville Cell Rockville BSC Maryland MSC VLR

EventHelix.com/EventStudio 2.5

31-Dec-04 08:05 (Page 1)

This call flow was generated with EventStudio 2.5 (http://www.EventHelix.com/EventStudio). How does a GSM mobile phone maintain a calleven when moving from one cell to another? The calls are maintained by handing over a call from one cell to another. This call flow covers a simple case of call handover in GSM. Here a user has an active call and is moving from the Rockville Cell to the Bethesda Cell. As the user moves, the call will be handed over by the Rockville Cell to the Bethesda Cell. Copyright © 2000-2004 EventHelix.comInc. All Rights Reserved. The GSM Mobile has an active call in the Rockville Cell. 1:RR MEASUREMENT REPORT
Signal Quality = GOOD

The mobile is reporting good signal quality, so no further action is taken.

The user reaches the boundary between the Rocville Cell and Bethesda cell. The Rockville BSC decides to initiate a handover as the mobile will be better served by another cell. The BSC analysesthe measurement reports Check if handover is needed to determine that the mobile will be best served by the Bethesda Cell. 3:BSSMAP HANDOVER REQUIREDThe BSC decides to request a handover. A list of target cells is provided to the MSC. Target Cells, Origin Cell The Bethesda Cell is included in the list of target cells. 4:T7 The T7 timer is started to wait for the handover command from the MSC.5:BSSMAP HANDOVER REQUEST The MSC passes on the handover request to the Bethesda BSC. (The Rockville BSC Target Cells, Origin Cell identified this BSC as as a target cell for handover.) The handover request is treated as a new Allocate TCH call. A traffic channel (TCH) is allocated for the call that will be handed-in. At this point the Bethesda BSC prepares the Build RR HANDOVER COMMAND messagehandover command that needs to be sent to the mobile. This message contains all the information the mobile will need to handover to this cell. 6:BSSMAP HANDOVER REQUEST ACKNOWLEDGE The Bethesda BSC includes the RR HANDOVER COMMAND message as a RR HANDOVER COMMAND payload in the HANDOVER REQUEST ACK that is sent back to the MSC. The RR HANDOVER COMMAND will be delivered to the mobile via the RockvilleBSC. 7:BSSMAP HANDOVER COMMANDThe MSC delivers the handover command to the Rockville BSC. This command RR HANDOVER COMMAND encapsulates the RR HANDOVER COMMAND from the destination BSC. 8:T7 The handover command has been received. So the T7 timer can now be stopped. 9:RR HANDOVER COMMAND The Rockville BSC extracts the RR HANDOVER COMMAND message from the Handover Reference, TCH BSSMAP message andsends it to the mobile. 10:T8 T8 is started to await the clear of this call from the MSC. If the handover to the target cell is successful, the MSC will initiate a
Signal Quality = POOR

2:RR MEASUREMENT REPORT

GSM_BSC Interfaces (Intra MSC Handover Call Flow) Highway GSM Coverage GSM Mobile Mobile Bethesda Bethesda Cell Bethesda BSC

GSM Equipment Rockville MSC VLRs Rockville Cell Rockville BSCMaryland MSC VLR

EventHelix.com/EventStudio 2.5

31-Dec-04 08:05 (Page 2)

11:RR HANDOVER ACCEPT
Access Burst, Handover Reference

12:BSSMAP HANDOVER DETECTED 13:RR PHYSICAL INFORMATION
Handover Reference

14:T3105 15:RR SABM 16:T3105 17:RR UA 18:RR HANDOVER COMPLETE 19:BSSMAP HANDOVER COMPLETE Release call resources in Rockville BSC.

resource release to the source BSC. The BSC receives theHANDOVER ACCEPT from the terminal. The actual call is identified using the handover reference. (The handover reference was send in the encapsulated HANDOVER COMMAND message. ) The BSC informs the MSC that the handover has been detected. At this point the MSC can switch the voice path. The BSC sends the PHYSICAL INFORMATION message to the mobile. This message contains a time and frequency correction....
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