6.7.1 Mobile-originated
Call Setup
To
initiate a call, the UE needs to establish communication with the network via
radio interface signaling and send a message that contains the called
subscriber number, i.e. the SETUP message on the Iu interface. The CN will
establish a communication channel to the UE and use the obtained called party
UERN to create an IAM/IAI message before sending the message to the called
party. Note that the IAM/IAI message is not involved in the intra-office calls
and it only exists on the E interface.
1)
The UE sends a CHANNEL REQUEST
message to the network over the random access channel.
2)
The network responds with an
IMMEDIATE ASSIGNMENT message so that the UE can occupy the specified dedicated
channel.
3)
The UE sends a CM SERVICE
REQUEST message to the CN.
4)
The network initiates the
authentication and ciphering procedures.
5)
After sending the SECURITY MODE
COMPLETE message, the UE sends the SETUP message to the CN to initiate the call
setup procedure.
6)
The CN responds with a CALL
PROCEEDING message.
7)
In the case of immediate assignment,
a communication channel must be assigned to the UE before the CN initiates the
call setup procedure to the fixed network.
8)
When the called party rings,
the network must send an ALERTING message to the calling UE upon receipt of the
ALERTING message from the called party. Meanwhile, it also needs to send a
ringback tone to the calling party.
9)
When the called party answers,
it will send a CONNECT message to the network and the network will forward this
message to the calling party.
10)
When the calling UE returns a
CONNECT ACKNOWLEDGE message, the call setup procedure is complete.
6.7.2 Mobile-terminated
Call Setup
A
mobile-terminated call procedure is executed when the mobile subscriber is called.
And the call setup procedure is initiated by the network.
If the
incoming call is allowed for setup after CN receives the IAM/IAI message or
gets the MSRN from within the local office, the CN must page the UE via radio
interface signaling. When the UE responds with the PAGING RESPONSE message, the
CN will establish a communication channel to the UE upon receipt of this
message.
1)
The CN sends a PAGING message
to the RNS and the RNS broadcasts this PAGING message over the paging channel.
For details, refer to the paging procedure described in Section 6.6.4 .
2)
The called UE detects this
paging and sends a channel request to the RNS. The RNS returns an immediate
assignment command to indicate the UE to use the specified signaling channel.
3) The UE sends a PAGING RESPONSE message on the signaling channel.
Upon receipt of the PAGING RESPONSE message from the UE, the CN initiates the
authentication and ciphering procedures (these two security procedures are
optional and can be configured through the MAP function procedure).
4)
The CN sends a SETUP message to
the RNS. The SETUP message carries the bearer capability of the call and the
calling number.
5)
Upon receipt of the SETUP
message from the RNS, the UE returns a CALL CONFIRMED message. If the
negotiated bearer capability parameter changes, the CALL CONFIRMED message
shall carry the bearer capability information.
6)
Upon receipt of the CALL
CONFIRMED message from the RNS, the CN sends an RAB ASSIGNMENT REQ message to
the RNS to request for radio channel assignment while the RNS sends an
assignment message to the UE so as to switch the UE to a specified
communication channel. After the UE is switched to the specified communication
channel, it sends the RB ASSIGNMENT COMPLETE message to the RNS.
7) The RNS sends a RAB ASSIGNMENT RESPONSE message to the CN.
8) The UE sends an ALERTING message to indicate that the called
subscriber should ring now.
9) When the called party answers, the called UE sends a CONNECT message
via the RNS to the CN.
10)
The CN returns a CONNECT
ACKNOWLEDGE message to the UE to end the call setup procedure.
6.7.3 RAB
Procedure
1. RAB
management
It is
defined that the RAB (Radio Access Bearer) shall be established between the UE
and the CN. Different RABs are used for the different subscriber data, CN
service capabilities and QoS requirements in the service request of the UE.
The RAB
ID is related to the NAS binding information. For example, the RAB ID in the
RANAP layer of the CS domain is numerically the same as the SI in the CC
sublayer. The SI is allocated by the UE and the CN corresponds with the SIs to
the RAB IDs one by one during the allocation of RAB IDs. In the point of view
of a UE, the RAB ID is global in terms of RB (Radio Bearer) and Iu bearer and
one RAB ID corresponds to a unique connection instance in the user plane (an Iu
UP instance).
The CN
controls the establishment, modification and release of RABs. It initiates the
establishment, modification and release procedures of RABs, while the UTRAN
executes the establishment, modification and release procedures of RABs. It is
one function of the UTRAN to initiate the RAB release request (this function is
triggered when the UTRAN cannot maintain the RAB with the UE).
During
RAB establishment, the CN maps the RABs to the Uu interface bearers while the
UTRAN maps the RABs to the Uu interface transport bearers and the Iu interface
transport bearers.
If the
AAL2 bearer is to be used in the CS domain, the UTRAN will initiate the setup
and release of AAL2 connections.
The
priority of RABs are determined by the CN according to the subscription and QoS
information. The CN specifies the priority, preempt capability and queuing
feature of an RAB during the RAB establishment and modification messages. The
UTRAN executes the RAB queuing and resource preemption.
2. RAB access control
Upon
receipt of an RAB establishment or modification request (the RAB QoS is mapped
via the BC IE according to the R99 CS specification), the CS verifies if the
subscriber is allowed to use the RAB in the request parameter. If yes, the CN
will accept the request; otherwise it will reject the request.
When the
UTRAN receives an RAB establishment or modification request from the CN, the
admission control entity will judge if the request should be accepted or
rejected according to the current radio resource conditions.
3. RAB establishment, release and modification procedures
The
purpose of the RAB Assignment procedure is to modify and/or release the
established RAB, and/or establish a new RAB. The procedure is
connection-oriented.
The CN first sends an RAB Assignment
Request message to the RNC and the CN then starts the timer TRABAssgt. In an
RAB Assignment Request message, the CN may request the UTRAN to
establish/modify/release one or several RABs. The message contains the
following information:
The list of RABs to be established or
modified, along with the bearer feature;
The list of RABs to be released.
The RAB ID is unique in each Iu connection.
If the message received by the RNC includes an existing RAB ID, the RNC will
regard that the RAB is to be modified (except release).
The RNC
will receive RAB release messages at any time and will always respond. If the
RNC receives a message to release an RAB while it is establishing or modifying
this RAB, it will stop the RAB configuration procedure, release all resources
related to this RAB and return a response.
Upon
receipt of the message, the UTRAN will execute the requested RAB configuration
and then send an RAB Assignment Response message to the CN to report the result
of request. One RAB Assignment Response message may contain the information of
one or more RABs as follows:
The RABs that have been successfully
established, modified or released;
The RABs that fail to be established,
modified or released;
The RABs in queuing.
If no RABs are queued, the CN will strop
the timer TRABAssgt and then the RAB Assignment procedure will end on the UTRAN
side.
When the
RABs to be established or modified are queued, the UTRAN will start the timer
TQUEUING that specifies the maximum queuing time before establishment and
modification of the RABs and will monitor all the queued RABs. The queued RABs
may have the following results:
Establishment or modification success;
Establishment or modification failure;
Failure due to expiry of the TQUEUING timer.
In the
first RAB Assignment Response message, the UTRAN reports the state of all the
RABs involved in the RAB ASSIGNMENT REQUEST message. The UTRAN then reports the
state of the queued RABs in the following RAB Assignment Response message,
except the RABs with TQUEUING expiry. When knowing that the modification or
establishment of all the queued RABs has succeeded or failed, the UTRAN stops
the timer TQUEUING and the RAB Assignment procedure ends at the CN and the
UTRAN simultaneously.
When the
CN receives a response indicating that the RABs are queued, it hopes that the
UTRAN can provide the result of RABs queuing before expiry of the timer TRABAssgt;
otherwise, it will regard that the RAB Assignment procedure has ended and the
configuration of those RABs not reported has failed.
Upon
expiry of the timer TQUEUING, all the queued RABs in the UTRAN will end the
procedure of queuing and the UTRAN will use an RAB Assignment Response message
to report the states of all the queued RABs. At the same time, the whole
procedure is stopped on the CN side.
4. RAB
establishment procedure
The
following figure depicts the procedure of RAB establishment via UTRAN between
the CN and the UE.
The
above example shows the procedure of establishing an RAB (DCH) in the DCH RRC
state after the RRC connection has been established.
l Time
In the
CS domain, upon receipt of a service request from the UE (Caller SETUP, called
CALL CONFIRM and CONNECT messages, etc.), the CN sends an RAB Assignment
Request message to indicate that a new AS bearer channel is needed to bear the
NAS subscriber data and thus initiates the procedure of bearer channel
establishment.
l Procedure
1)
The CN decides what kind of
RABs are to be used according to the subscriber data, CN service capability and
QoS requirements in the service request of the UE. It sends an RANAP message,
i.e. the Radio Access Bearer Assignment Request (Setup) message, to request the
RAB establishment. In the message, the RAB ID is filled with the SI value. The
key parameters of the CS domain include the RAB parameter, the user plane mode,
the ATM address of the local user plane and the IU BINDING ID.
2) The Serving RNC uses the ALCAP protocol to initialize the Iu
interface data transport bearer establishment.
In the
case of using the AAL2 bearer in the CS domain (this procedure is not needed in
the case of the PS domain), the SUGR parameter will be used in the AAL2
connection establishment request message to transparently transmit the BINDING
ID to the CN, so as to complete the binding between the RABs and the data
transport bearers. This request message also contains the following key
parameters:
Peer ATM
address, path ID, Channel ID (CID), path feature and channel feature.
3)
After the Serving RNC
reconfigures the radio links with such equipment as Node B and completes the
uplink-downlink synchronization, it uses an RRC message (i.e. Radio Access
Bearer Setup) to carry the subflow and subflow combination parameters among the
RAB parameters as well as the RAB ID before sending the message to the UE.
4) Upon receipt of the success acknowledgement RRC message (i.e. Radio
Bearer Setup Complete) from the UE and the establishment success information of
the ALCAP procedure, the Serving RNC acknowledges the RAB establishment success
to the CN. It sends an RANAP message (Radio Bearer Assignment Response) to the
CN.
5)
If the user plane is in the
support mode, the UTRAN initializes the Iu interface user plane via the
Initialization message after the result is reported.
Note:
The procedures of
interaction with the Drift RNC and the Drift Node B are not indicated in the
above figure.
For the RACH/FACH – DCH, RACH/FACH -
RACH/FACH and PS domain non-synchronous modes, the procedures are similar.
5. RAB release procedure
l Trigger time
This
procedure is initiated in the CS domain when all the transactions over the RAB
in the CC layer end or the RNC requests to release the RAB.
l Procedure
1)
The CN sends an RANAP message,
i.e. Radio Access Bearer Assignment Request (Release), to initiate the RAB
release procedure together with the RAB ID specified.
2)
The Serving RNC acknowledges
the request message with another RANAP message, i.e. Radio Access Bearer
Assignment Response.
3)
The Serving RNC uses the ALCAP
protocol. In the case of the AAL2 bearer, it uses the AAL2 release message to
initiate the release procedure of the Iu data transport bearer between itself
and the CN (this procedure is not needed in the PS domain).
4)
The Serving RNC sends an RRC
message (Radio Bearer Release) to the UE to initiate the bearer release
procedure after releasing the link with such equipment as Node B.
5)
The Serving RNC receives the
acknowledgement RRC message (Radio Bearer Release Complete) from the UE and the
whole release procedure thus ends.
6. RAB modification procedure
l Trigger condition
When the
UE is handed over or the UE rate changes, the CN reconfigures the traffic
channel to support the service attribute change.
l Procedure
1) The CN sends an RANAP message, i.e. the Radio Access Bearer
Assignment Request (Modify), to request the RAB modification. The request
message contains the RAB ID that indicates which RAB is to be modified and such
key parameters of the CS domain as RAB parameters.
2)
The Serving RNC selects which
parameters are to be modified and which programs are to be initiated.
3)
The SRNC uses the ALCAP
protocol to modify the channel characteristics of the Iu interface data
transport bearers.
4) Upon successful modification procedure of the Iu interface transport control plane, the Serving RNC modifies the radio links together with such equipment as Node B. It then sends the subflow and subflow combination parameters among the RAB parameters as well as RAB ID in the RRC message (Radio Bearer Reconfiguration) to the UE.
5, 6) Upon receipt of the success acknowledgement RRC message (i.e. Radio Bearer Setup Complete) from the UE, the Serving RNC acknowledges the RAB modification success to the CN. It sends an RANAP message (Radio Bearer Assignment Response) to the CN.
7) If the user plane is in the support mode, the UTRAN initializes the Iu interface user plane via the Initialization message after the result is reported.
6.7.4 Paging
Procedure
The
paging procedure is a procedure of paging initiated from the CN to the called
party. When the CN needs to set up a connection with the called subscriber, it
first needs to find the called subscriber via the paging procedure. The purpose
of the paging procedure is just to enable the CN to page the called subscriber.
The paging procedure is set up via connectionless signaling.
The CN
sends the PAGING message to the called subscriber to initiate the paging
procedure. The PAGING message should contain sufficient information so that the
RNC can find the called subscriber. If the called subscriber is unreachable in
one paging, the CN will repeat the paging procedure via the Iu interface.
Generally, the number of paging retries and the paging interval can be
controlled by the CN.
1. Paging
procedure
After
the call request information from the caller is processed by the CN, the paging
procedure starts if the called subscriber information has been successfully
obtained. The CN needs to know the location area information of the called
subscriber and get the sufficient paging information parameters before it can
initiate the paging procedure to the called subscriber.
If the
CN does not get the location area information of the called subscriber, it
needs to send the PAGING message through the broadcast procedure to all the
RNCs under its control.
The CN
sends the PAGING message via the RANAP interface, which processes the PAGING
message from the CN. The PAGING message includes such parameters as whether the
paging request comes from the CS domain or the PS domain, what reason caused
the paging and the specific location area information of the called subscriber.
The RANAP sends the PAGING message to the RNC where the location area of the
called subscriber resides.
When the
PAGING message reaches the RNC, the RNC analyzes the parameters of the PAGING
message to get the location area information of the called subscriber and then
transmits via PCCH the PAGING information to the UE in that location area. If
the called UE detects the PAGING message from the RNC, it starts to execute the
NAS signaling procedure.
If the
paging is successful, the CN will get the paging response message; otherwise
the CN needs to repeat sending the PAGING message via the Iu interface.
2. Paging procedure of the UE in
the RRC idle state
When the
RRC is idle, the UE may receive paging from the CS or PS domain. Because the UE
is now in the idle state, the CN can learn the Location Area Identification
(LAI) information of the UE. The paging will be sent via this location area and
the LA in this example crosses two RNCs.
1)
The CN initiates the paging
information and sends it after passing two RNCs to the called UE. At this time
it can be see from the Iu interface that two PAGING messages are continuously
send by the CN, they carry the same LAI, except that the DPCs are the two RNCs.
2)
Cell 1 initiates the paging
procedure via the Paging Type 1 message.
3)
Cell 2 initiates the paging
procedure via the Paging Type 1 message.
The PAGING message reaches RNC1 and RNC2 via RANAP, and the two RNCs
transmit the PAGING message to the UE in the specified location area over the
PCCH. If the called UE detects the PAGING message from RNC1 or RNC2, it then
starts executing the NAS signaling procedure.
3. Paging
procedure of the UE in the RRC connected state
When the
RRC is in the connected state, the paging procedure of the UE may fall into two
cases: The CS domain or the PS domain of the CN. Due to the independency of
mobility management, there are two possible solutions:
1)
The UTRAN coordinates the
paging request over the existing RRC connection;
2)
The UE coordinates the paging
request over the existing RRC connection.
The
following example shows the paging procedure of the UE in the RRC connected
state (CELL_DCH and CELL_FACH), where the UTRAN coordinates the paging request
over the DCCH in the RRC connected state.
1)
The CN sends the PAGING message
via RANAP to UE to page the UE.
2) The Serving RNC sends the Paging Type 2 to the RRC (UE).
& Note:
Paging Type 1 is sent over
the PCCH when the UE is idle while Paging Type 2 is sent over the DCCH when the
UE is in the RRC connected state. The typical case is that the UE uses the
Paging Type 2 to send the PAGING message of the CS domain in the PS service
procedure. However, the Paging Type is controlled by the RNC and the CN does
not need to know it.
6.7.5 Call
Release Procedure
When the mobile subscriber ends the
conversation, the calling party or the called onhook message shall be notified
to the network side to initiate the call release procedure. The network
releases the call by terminating the CS connection between the PLMNs or between
the PLMN and other networks.
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