Mobile Originated/Terminated call in WCDMA(MO/MT call)
Introduction
This article covers mobile originated and mobile(UE) terminated call flow between Mobile(UE) and network compatible with WCDMA standard. It covers messages exchanged between Layer 3 entities at both side. It include channels used at layer 1 to carry these messages over the air. This article assumes that initial frequency and time synchronization is done between UE and Network as per WCDMA specifications.
The figure describes message sequences between WCDMA UE and network for MO call(Mobile originated call). In Mobile terminated(MT) CS(circuit switched) voice call, once RRC connection is established, Mobile terminated UE gets call setup requirement from the network and replies with a call confirm message.
For further details on PHY(layer 1), MAC(layer 2),RLC(layer 2),RRC(layer 3) and various modules in these layers refer our tutorial on UMTS in tutorials section. The UMTS tutorial also covers WCDMA logical/transport/physical channels.
Call Control(CC) Messages exchanged between CC entity of UE and CC entity of network are summarized below for MO call establishment:
(UE) SETUP >>>(NETWORK)
(UE)<<< CALL PROCESSING (NETWORK)
(UE)<<< ALERTING (NETWORK)
(UE)<<< CONNECT (NETWORK)
(UE) CONNECT ACK >>>(NETWORK)
Call Control(CC) Messages exchanged between CC entity of UE and CC entity of network are summarized below for MT call establishment:
(UE)<<< SETUP (NETWORK)
(UE) CALL CONFIRMED >>> (NETWORK)
(UE) ALERTING >>> (NETWORK)
(UE) CONNECT >>> (NETWORK)
(UE)<<< CONNECT ACK (NETWORK)
Fields(IEs-Information Elements)of MO CC SETUP Message
CC protocol discriminator
TI
Message type
Bearer capability(RI,1,2)
Facility
Calling party subaddress
called party binary coded decimal (BCD) number
called party subaddress
Low layer compatibility (RI,1,2)
High layer compatibility (RI,1,2)
User to user
SS version
CLIR suppression
CLIR invocation
CC capabilities
SI
Fields(IEs-Information Elements)of CALL PROCESSING Message
CC protocol discriminator,TI,Message type,Bearer capability(RI,1,2),Facility, Progress Indicator,Priority granted,network call control capabilities.
Fields(IEs-Information Elements)of ALERTING Message
CC protocol discriminator,TI,Message type,Facility,Progress Indicator,user-user (information)
MO MT CS PS call flow in GSM related links
Mobile Terminated Call
GSM downlink PS data call flow
GSM uplink PS data call flow
Circuit Switching vs Packet Switching