Basic Signaling Procedures
1) MS sends a Channel Request message to BTS on the access channel of Um interface (The message contains the access cause value "Location update"). 2) BTS sends a Channel Request message to BSC. 3) Upon receipt of the Channel Request message, BSC allocates signaling channels, and sends a Channel Activation message to BTS. 4) If the channel type is correct, upon receipt of the Channel Activation message, BTS opens the power amplifier on the specified channel, and sends a Channel Activation Acknowledge message to BSC. 5) BSC sends an Immediate Assignment Command message to MS via BTS. 6) MS sends an SABM (Set Asynchronous Balanced Mode) frame for establishing link with BTS. 7) BTS returns a UA (Unnumbered Acknowledgement) frame for acknowledgement. 8) BTS sends an Establishment Indication message to BSC, which contains the content of the location Update Request message. 9) BSC establishes SCCP link connection on A interface, and sends a Location Update Request message to MSC. The parameter including the CGI of the current cell. 10) MSC returns a link acknowledge message to BSC. 11) MSC sends a Location Updating Accept message to BSC, indicating that location updating has succeeded. 12) The network shall deliver a Location Updating Reject message to MS if it rejects the location updating request. 13) If "Allocate TMSI upon location updating" is set to "No" in MSC, MS shall not report the TMSI Reallocation Complete message in the location updating procedure. 14) The network shall initiate the channel release procedure if no further transactions are scheduled.
N.B> T3210 used by MS till getting successful location update, and T3211, T3212 for BSC. Page 1 of 16
Authentication The network initiates the authentication procedure by transferring an Authentication. Request message to MS and starts timer T3260. Upon receipt of the Authentication Response message, the network stops timer.T3260 and checks the validity of the response.
Mobile Originating Call Establishment Procedure
As per assignment type, the mobile originating call establishment procedure can be classified into 3 types, early assignment, late assignment and very early assignment. The selection of early assignment and late assignment is determined by MSC. The selection of very early assignment is determined by BSS as per the status of radio resources.
OACSU denotes "Off-Air-Call-Set-Up".
1) MS sends a Channel Request message to BTS on the access channel (RACH) of Um interface. The message contains the cause value "MOC", but that value is not completely accurate, because it is indicated both in the mobile originating call Establishment procedure and IMSI detach procedure.
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2) BTS sends a Channel required message to BSC. 3) Upon receipt of the Channel required message, BSC allocates a signaling channel and sends a Channel Activation message to BTS. 4) If the channel type is correct, upon receipt of the Channel Activation message, BTS opens the power amplifier on the specified channel, and sends a Channel Activation Acknowledge message to BSC. 5) BSC sends an Immediate Assignment Command message to MS via BTS. The message is sent on AGCH on Um interface. 6) MS sends an SABM frame on SDCCH to BTS to access the network. 7) BTS returns a UA frame on SDCCH for acknowledgement. 8) BTS sends an Establishment Indication message to BSC (This message contains the accurate causes for MS's access. For example, different cause values are indicated in the mobile originating call establishment procedure and IMSI detach procedure). This message contains the contents of the CM Service Request message. 9) BSC establishes the SCCP link connection on A interface, and sends a CM Service Request message to MSC. 10) MSC returns a message to BSC to acknowledge the link connection. 11) MSC sends a CM Service Accepted message to MS. The message is sent on SDCCH on Um interface. 12) The calling MS sends a Setup message on SDCCH. 13) MSC sends a Call Proceeding message to the calling MS. The message is sent on SDCCH on Um interface. 14) MSC sends an Assignment Request message to BSC, which contains the CIC allocated to A interface. 15) BSC allocates a TCH, and sends a Channel Activation message to BTS. 16) If the channel type is correct, upon receipt of the Channel Activation message, BTS opens the power amplifier on the specified channel, starts to receive the uplink information and sends a Channel Activation Acknowledge message toBSC. 17) BSC sends an Assignment Command message to MS via BTS on SDCCH. 18) MS sends an SABM frame to BTS, to access the network on FACCH indicated in the Assignment Command message. 19) BTS sends a UA frame for acknowledgement on FACCH. 20) BTS sends an Establishment Indication message to BSC. 21) After accessing the TCH, MS sends an Assignment Complete message to BSC on FACCH. 22) After the radio traffic channel and terrestrial circuit are both successfully connected, BSC sends an Assignment complete message to MSC, and regards this call in session state. 23) MSC sends an Altering message to the calling MS. The calling MS will hear the ringback. The message is sent on FACCH on Um interface. 24) MSC sends a Connect message to MS. The message is sent on FACCH on Um interface. 25) The calling MS returns a Connect Acknowledge message on FACCH to MSC. 26) The calling MS and called MS enters the session state. 27) After the conversation is over, the calling MS hangs up and sends a Disconnect message on FACCH. 28) MSC sends a Release message to MS. The message is sent on FACCH on Um interface.
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29) MS returns a Release Complete message. The message is sent on FACCH on Um interface. 30) MSC sends a Clear Command message to BSC. Upon receipt of the message, BSC initiates the release procedure. See Chapter 5 for the description of the subsequent release procedure. 31) BSC sends a Channel Release message to MS through BTS, The message is sent on FACCH on Um interface. 32) MS sends DISC frame on FACCH. 33) BTS returns UA frame on FACCH. ==============================================================================
Late Assignment 1) The difference between Figure 7-1 and Figure 7-2 is that late assignment takes place after the Alerting indication is sent. 2) The advantage of late assignment lays in that it can save the seizure time of TCHs. 3) The disadvantage of late assignment is that if the subsequent assignment is unsuccessful, the called MS can only hear the ring but cannot establish a connection, thus leading to user complaints. Therefore, in actual application, this procedure is generally not adopted. Instead, the procedure in Figure 7-1 is adopted.
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1) The difference between Figure 7-1 and Figure 7-3 is that the TCH allocated during the immediate assignment in Figure 7-3 serves as a signaling channel. Therefore, no TCH need be reallocated during the assignment procedure. Instead, the TCH allocated in the immediate assignment procedure is adjusted as a TCH by using the Mode Modify message. 2) Very early assignment generally takes place if there is no free SDCCH for allocation during immediate assignment, but there are free TCHs and immediate assignment of TCHs is allowed in BSC data configuration.
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Handover Procedure A handover procedure can be divided into 3 types according to different ranges involved in handover: intra-BSC handover procedure, inter-BSC handover procedure and inter-MSC handover procedure.
In case of asynchronous handover, i.e., when BTS1 and BTS2 are located in different BTSs, BTS2 will send PHY INFO on FACCH to MS while sending Handover Detect to BSC. The PHY INFO includes such contents as the synchronous information for correct access of MS. In case of synchronous handover, i.e., when BTS1 and BTS2 are located in the same BTS, the PHY INFO message will not be delivered.
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Ciphering Mode Setting Procedure The ciphering mode setting procedure is generally used in service requests such as location update, service access, interoffice handover, etc. It requires the support from GSM network equipment, especially BTS, and also depends on the encryption support capabilities of MS.
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Short Message Procedure Short messages can be transmitted either through SDCCH, SACCH. Short message procedure can classify short message calling procedure and called procedure.
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