MO Voice Call [Under UMTS]
Let us take a look at example of Mobile Originated Voice Call
(CS-domain). MSC stand for MSC/VLR.
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| UE/RRC in idle mode. User makes a call. Protocol stack receive AT command ATD. |
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CM Service Request thru RRC IDT message |
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SCCP connection req/cnf |
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| Iu signaling connection establishment |
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CC - CM Service Request over RANAP |
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| CM Service request contain cause for request (voice call, SMS etc.), identity (IMSI, TMSI) etc. MSC/MM may trigger authentication & ciphering procedure at this time. |
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CC - SETUP |
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| CC/SETUP message contain called number, bearer capability info, AMR speech capability info etc. |
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| MSC validate SETUP request and start resource assignment for carrying user data (in this case it would be voice data) at Iu interface. MSC may also acknowledge UE with CC/Call proceeding message |
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CC - Call Proceeding |
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| RNC does Iu bearer setup with ALCAP signaling (as shown in Iu interface article, ALCAP is needed for setting up Iu bearer for CS data. For PS data, ALCAP is not needed). RNC invokes radio bearer setup. |
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RANAP - RAB Assignment Request |
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RAB Assignment Response |
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| While RAB setup is in progress, MSC may have already started network side signaling (like talking to HLR to get routable number for dialed mobile number and ISUP call establishment with target MSC, or ISUP call establishment if the dialed number belong to PSTN or another non-GSM/UMTS number). |
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ISUP - IAM |
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ISUP - ACM |
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| ISUP trunk establishment (two way or one way from GMSC to MSC). |
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CC - Call Proceeding (alert) |
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| Called party answered the call. |
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ISUP - ANM |
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| ISUP trunk connected both ways if not connected earlier. |
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CC - CONNECT |
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CC - CONNECT Ack |
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| UE/RRC in connected/CELL_DCH state (doing measurements and reporting to RNC; this may result in HO). For PS call, RRC would be in CELL_DCH (large amount of data) or CELL_FACH (small amount of data) state. |
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1: Serving RNC (SRNC) is that one which
provide Iu connection for the UE. The terminology comes in UMTS
due to presence of Iur interface between RNCs. Drift RNC is the
one which has radio connection with UE. Drift RNC (DRNC) act as
relay between UE and SRNC. When register to the network, RNC which
it registers to becomes SRNC. Later it may drift to another RNC
(during active CS or PS connection) and that RNC becomes DRNC if
new RNC has Iur connection with SRNC. If Iur connection is not
present, the configuration become similar to GSM; hard handover is
to be performed in such case.
References: UMTS
by Sanchez and Thioune, and WCDMA
for UMTS by Holma and Toskala.
| Copyright © Samir Amberkar 2010 | § |
