View Full Version : 3G/UMTS Complete Mobile Originated Circuit Switched Call Setup

2008-10-03, 10:51 AM
<h3>A Complete Mobile Originated Circuit Switched Call Setup is shown in the MSC below. </h3><table>
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1. System Information (BCCH)
The UE reads the System Information that is
broadcast on BCCH. The information is not read continuously. It is only
read if the information changes

2. RRC: RRC Connection Request (CCCH)
The Mobile user decides to initiate a voice
call. The first message the UE will send on CCCH is RRC Connection
Request. This will contain among other things, Initial UE Identity and
Establishment Cause

3. NBAP: Radio Link Setup Request
The SRNC sends this message to Node B. It will pass the Cell Id, TFS, TFCS, frequency, UL Scrambling code, etc to Node B.<br>

4. NBAP: Radio Link Setup Response
Node B allocates the resources and starts PHY
Reception. While transmitting the response it includes the Transport
layer addressing information that includes the Binding Identity of the
AAL2 for Iub data transport bearer<br>

5. ALCAP: Establish REQ
The AAL2 binding identity (Iub Data Transport
Bearer Id) is passed to ALCAP protocol in Node B. The Iub Data
Transport bearer is now bounf to DCH. <br>

6. ALCAP: Establish CNF
Establish confirm from ALCAP in Node B<br>

7: DCH-FP: Downlink Synchronisation
The Node B and SRNC establishes synchronisation
for the Iub Data Transport bearer by means of exchange of the
appropriate DCH Frame Protocol frames.<br>

8: DCH-FP: Uplink Synchronisation
Once the UL synchronisation is acheived, Node B starts DL transmission.<br>

9: RRC: RRC Connection Setup (CCCH)
RRC Connection Setup message is sent on CCCH
with the parameters required to establish DCH. Also the state indicator
will be set to DCH for the voice (or CS) call.<br>

10: NBAP: Radio Link Restore Indication
Once the UE establishes Radio Link, Node B will send RL Restore indication to the SRNC.<br>

11: RRC: RRC Connection Setup Complete (DCCH)
RRC Connection Setup complete will be sent on
DCCH. Integrity and Ciphering related paarmeters and UE capability
information will be sent back to SRNC<br>

12: RRC: Initial Direct Transfer [CM Service Request]
First NAS message is now sent by the UE. It
indicates that a UE orginated Voice call is required. The UE identity
(TMSI) will also be passed in this message<br>

13: RANAP: Initial UE Message [CM Service Request]
The NAS message will be forwarded to appropriate
CN Domain (CS Domain in this case). Along with the CM service request,
it will also include LAI and SAI.<br>

14: RANAP: Direct Transfer [Authentication Request]
MSC/VLR needs to perform authentication to make
sure that the UE is genuine. For this reason it will challenge the UE
with a Authentication token and RAND (random number)<br>

15: RRC: Downlink Direct Transfer [Authentication Request]
SRNC transfers the NAS message to the UE<br>

16: RRC: Uplink Direct Transfer [Authentication Response]
UE computes the response (RES) and sends it back in the NAS message<br>

17: RANAP: Direct Transfer [Authentication Response]
SRNC relays the response to the MSC/VLR. The
MSC/VLR will compare the response RES with the expected response XRES.
If they are the same then the procedure will continue.<br>

18: RANAP: Security Mode Command
MSC/VLR sends the Security Mode Command to start
Ciphering and Integrity Protection. Ciphering is optional while
Integrity Protection is mandatory. The Algorithms, etc are known to the
MSC/VLR and the UE and only the ones that are common between them are

19: RRC: Security Mode Command
RRC Forwards the Security Mode command received from MSC/VLR to the UE.<br>

20: RRC: Security Mode Complete
The UE configures the Ciphering and Integity
Protection and responds back to the network. The response message is
Integrity Protected for further safety. Ciphering is started at
Ciphering activation time. Since this is a Circuit switched call, the
Ciphering will be started in MAC. In case of AM and UM bearers it is
started in RLC.<br>

21: RANAP: Security Mode COmplete
The network forwards the Security Mode Complete message to MSC/VLR.<br>

22: RANAP: Direct Transfer [TMSI Reallocation Command]
The network may decide to re-allocate the TMSI
to the UE. It sends a DT message which includes the NAS TMSI
Reallocation Command.<br>

23: RRC: DL Direct Transfer [TMSI Reallocation Command]
The RNC relays the DT message to the UE.<br>

24: RRC: UL Direct TRansfer [TMSI Reallocation Complete]
The UE takes the new TMSI and responds with the Complete message<br>

25: RANAP: Direct Transfer [TMSI Reallocation Complete]
The RNC relays the message to the CN domain<br>


2009-03-18, 01:15 AM