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10. The UE responds to the SRNC with the RRC connection setup complete message,
but now it can use the DCCH that has been established. The parameters here are
UE capability information, such as integrity and ciphering information. There is
now a signalling connection between the UE and SRNC but data transfer cannot
take place just yet.

Note that in the following sections, some of the involved procedures described above,
such as the L1 synchronization and the downlink/uplink synchronization, do still take place
but are omitted from the descriptions for simplicity.
The decision to allocate a user a dedicated signalling connection as shown above is
made in the RNC through its admission control policy. Alternatively, as illustrated in
Figure 6.130, the RRC connection could be established on the RACH/FACH common
transport channels.

1. As before, the UE initiates an RRC connection request on the CCCH/RACH/PRACH.
Notice that this is a much simpler procedure with NBAP and ALCAP signalling not
being required. This is because the CCCH channels will be set up already when the
cell was ¬rst established or reset.
2. After performing admission control, the SRNC decides to use the FACH/RACH for
this RRC connection, and allocates the UE both a U-RNTI and a C-RNTI identi¬er.
The RRC connection setup message is sent on CCCH, including the same parameters
as before with the addition of the C-RNTI. The C-RNTI is required since the CCCH
is now being used for signalling as well as data transfer; the signalling will be
destined for the controlling RNC of this BTS. At this point the CRNC MAC-c/sh will
be able to determine if this is signalling or user data; the user data will be forwarded
to the MAC-d of the SRNC, which may or may not be in the same physical RNC.


UE BTS SRNC


RRC Connection Request
RRC RRC 1

RRC Connection Setup
RRC RRC 2

RRC Connection Setup Complete
RRC RRC 3



Figure 6.130 RRC connection on FACH/RACH
6.22 UMTS CALL LIFE CYCLE 405


3. The UE responds with the RRC connection setup complete message on a DCCH
logical channel, which is mapped to the RACH transport channel.


6.22.2 Location updating
Once the connection to the circuit core has been established, the UE proceeds to perform
a location update (Figure 6.131).

1. The L3 location updating request is carried to the 3G MSC using the RRC initial
direct transfer message and the RANAP and initial UE message. As was discussed
in Section 6.19.7, at the lower SCCP layer, this initial UE message will establish a
RANAP unique signalling link between the SRNC and the 3G MSC. Since this is
carried over AAL5 there is no need to set up an AAL2 connection as was required
over the Iub. The UE will identify itself in the location updating request by its IMSI
or TMSI.
2. Then the core network will invoke the authentication procedure, during which there
is mutual authentication between the UE and network, keys for encryption and
integrity protection are generated, and suitable algorithms are selected. Please refer to
Section 6.21 for full details of these procedures.
3. After the authentication procedure has successfully completed, the 3G MSC sends
the UE a location updating accept message.
4. This now completes the transaction, so the connection is no longer required. The 3G
MSC thus sends the Iu release message to release this connection, and the RNC
replies with the Iu release complete.


UE BTS SRNC 3G MSC

initial direct transfer
RRC RRC
L3 location updating request initial UE message
RANAP RANAP 1
L3 location updating request
authentication and security control procedures 2
direct transfer
RANAP RANAP
3
downlink direct transfer L3 location updating accept
RRC RRC
L3 location updating accept
Iu release
RANAP RANAP
4
Iu release complete
RANAP RANAP
connection release
RRC RRC
5
connection release complete
RRC RRC
RL deletion request
NBAP NBAP
6
RL deletion response
NBAP NBAP
REL
A2SIG A2SIG
7
RLC
A2SIG A2SIG



Figure 6.131 UMTS location update
406 UNIVERSAL MOBILE TELECOMMUNICATIONS SYSTEM


5. In turn, the RRC connection may also be released, and the UE may return to idle
mode. The layer 3 signalling actually has a follow-on parameter, which may be set
by the UE if it is going to send another message, such as make a phone call,
immediately after the location updating request. In this situation the RRC connection
may not be released. This, however, is not the case in this particular scenario.
6. The RNC then instructs the BTS to delete the radio link.
7. The AAL2 transport channel for that radio link is also deleted.



6.22.3 Paging
As previously discussed, there are two types of paging used in UMTS. For type 1, the UE
has no connection to the network so needs to be paged on a paging channel. For type 2,
the UE has a connection on the FACH or DCH and can be paged along that connection.

Paging type 1
This is the paging for a UE with no FACH/DCH connection. This applies to a UE in
RRC idle mode and RRC connected mode for both CELL-PCH and URA-PCH states.
In this example, shown in Figure 6.132, the paging is performed for a UE in RRC idle
mode. The core network domain could be the CS or PS domain, and in idle mode, the
RAN knows nothing about the user. The UE is only known to a CN location, either an
LA for CS or an RA for PS. Therefore, the paging message must be distributed across
that whole LA/RA to reach the user. The example shows that the area spans two RNCs,
so the paging message must be sent to both.

1. The CN initiates the paging of a UE across an LA, which spans two RNCs. The
paging is performed using the RANAP paging message and contains the following
parameters: CN domain indicator (CS or PS), permanent NAS UE identity (e.g.
IMSI, TMSI or P-TMSI) and the paging cause.
2. Paging of the UE is then performed by the RNCs. This is done by sending a paging
message, type 1, across the Iub interface using the Iub common channel frame


UE BTS2 BTS1 RNC2 RNC1 CN


Paging
RANAP RANAP
1
Paging
RANAP RANAP
CCCH/PCH/SCPCH Paging type 1
FP FP
2
CCCH/PCH/ Paging type 1
FP FP
SCPCH



Figure 6.132 Paging in idle mode
6.22 UMTS CALL LIFE CYCLE 407


protocol. This is then carried on the air interface on the PCH, carried in the physical
secondary CPCH. The page is sent across all the cells in the LA (only two are shown
in the diagram). The UE will answer the page in whichever cell it is currently in, and
will then reinitiate an RRC connection.

This procedure described for RRC idle mode also applies to RRC connected mode for
CELL-PCH and URA-PCH states. The difference here is that the RNC will only page
on the PCH across either one cell or one URA. Also, in these states, the paging message
will identify the user using the U-RNTI, rather than the IMSI/TMSI/P-TMSI.

Paging type 2
Paging type 2 is used when an RRC connection has already been established for this
particular mobile device, i.e. it has an RRC connection (DCH or FACH). In this case, the
mobile device is paged directly over the established RRC signalling link rather than the
paging channel. The SRNC determines that an RRC has already been established for this
mobile device since the RRC connection is associated with the IMSI within the RNC. The
following example shows how paging is performed for a UE in RRC connected mode
(CELL-DCH and CELL-FACH states) when the UTRAN coordinates the paging request
with the existing RRC connection using DCCH (Figure 6.133). The scenario set out in
the section will not use paging type 2 since the RRC connection was released after the
location update; however, it is presented here for a comparison.

1. As before, the CN initiates the paging of a UE via the RANAP paging message. The
parameters are CN domain indicator, IMSI/TMSI/P-TMSI and the paging cause.
2. The SRNC sends the RRC paging type 2 message. This is on the established logical
DCCH, which can be transported over a DCH, the FACH or DSCH.


6.22.4 Connection establishment: circuit core
Once the UE has detected the paging message, it will answer the call and reinitiate a
connection to the network (Figure 6.134). It should be noted that although there is no
signalling connection to the network, the CN still retains information about the UE.


CN
UE RNC2


Paging
1
RANAP RANAP

Paging type 2
2
RRC RRC



Figure 6.133 UE paging using dedicated channel
408 UNIVERSAL MOBILE TELECOMMUNICATIONS SYSTEM


UE BTS SRNC 3G MSC

Paging Procedure

Signalling Connection Establishment 1
Initial Direct Transfer
RRC RRC
Paging Response 2
initial UE message
RANAP
RANAP
Paging Response
Common ID Update
RANAP RANAP 3
Direct Transfer
RANAP RANAP
Setup 4
Downlink Direct Transfer
RRC RRC
Setup
Uplink Direct Transfer
RRC RRC
Call Confirmed Direct Transfer
RANAP RANAP
Call Confirmed
RAB Assignment
RANAP RANAP 5
Request
ERQ
A2SIG A2SIG
6
ECF
A2SIG A2SIG
RL Reconfig Prepare
NBAP NBAP
7
RL Reconfig Ready
NBAP NBAP
ERQ
A2SIG A2SIG
8
ECF
A2SIG A2SIG
RL Reconfig Commit
NBAP NBAP 9
Radio Bearer Setup
RRC RRC
10
Radio Bearer Setup Complete
RRC RRC
RAB Assignment

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