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RRC Connection Setup Complete

Figure 6.66 RRC connection establishment

Table 6.16 CPICH Ec/Io values
Value of Actual value range (dB)
CPICH Ec/Io < ’24
’24 = CPICH Ec/Io < ’23.5
’23.5 = CPICH Ec/Io < ’23
. .
. .
. .
’0.5 = CPICH Ec/Io < 0
0 = CPICH Ec/Io

Table 6.17 RRC connection setup elements
Information Element Explanation
Initial UE identity IMSI, TMSI or P-TMSI number
RRC transaction ID Unique identi¬er for this transaction
New U-RNTI or C-RNTI Allocation of a U-RNTI/C-RNTI to the user
For a FACH connection, C-RNTI is allocated
RRC state indicator The connected state, e.g. CELL-DCH for a dedicated
DRX cycle length coef¬cient Used by the UE to calculate the frame numbers in
which it should check the PICH for an incoming
Signalling radio bearer information Information on the signalling bearers being
established (see Section 6.16.4)
UL/DL transport channel information Information regarding the uplink and downlink
transport channels, such as transport formats

For establishment of a dedicated channel, the RRC connection setup message will
contain the key information elements listed in Table 6.17. Note that this connection is
only through as far as the RNC. If and when a connection through to the core network is
required, this must be established also.

6.16.4 Signalling radio bearers
The 3GPP de¬nes four radio bearers for use as signalling bearers for RRC messages.
Signalling radio bearer 0 (SRB0) is used for all messages sent on the CCCH. In the
uplink direction, this uses RLC transparent mode and in the downlink unacknowledged
mode. SRB1 is for messages sent on the DCCH using unacknowledged mode. SRB2
is for messages on the DCCH using acknowledged mode, and SRB3 is for transport of
non-access stratum messages, such as mobility management messages, on the DCCH in
acknowledged mode. Providing two separate acknowledged-mode signalling radio bearers
allows for the prioritization of RAN-related RRC messages over those for the non-access
stratum. There is an optional ¬fth bearer, SRB4, which is also an acknowledged-mode
bearer for NAS signalling. This allows for two priorities of NAS signalling, with SRB3
deemed ˜high priority™ and SRB4 ˜low priority™. High priority is used for NAS signalling

that uses service access point identi¬er 0 (SAPI 0), and low priority for signalling using
SAPI 3, which is de¬ned for SMS traf¬c. These different radio bearers are distinguished
as different logical channels at the MAC layer using the C/T ¬eld.
For conformance, the speci¬cations require that all UEs must be able to support stan-
dalone signalling radio bearers of 1.7 kbps, 3.4 kbps and 13.6 kbps. For signalling radio
bearers associated with data radio bearers, for example voice and signalling, the rate is
usually de¬ned at a bit rate of 3.4 kbps; however, for lower rates such as AMR 4.75 kbps,
the 1.7 kbps rate can be used. The 3.4 kbps channel is established at the transport layer
with a transport block size of 148 bits and a TTI of 40 ms. It assumes an RLC/MAC
overhead of 12 bits (RLC-UM: 8 bits, MAC C/T ¬eld: 4 bits). The RLC-AM signalling
radio bearers will be slightly less than 3.4 kbps due to the extra overhead imposed by
the RLC layer. It is the RNC that will decide, according to its admission control policy,
which standalone signalling bearer rate the user is allocated. The RRC connection setup
complete message provides the RNC with the core network domain it wishes to connect
to, and the capabilities of the UE. This information element covers a whole range of UE
capabilities such as for RLC, security and RF capabilities.

6.16.5 RRC security mode control
User authentication in UMTS differs from GSM in that the procedure validates not only
the UE to the network, but also the network to the UE. During the NAS security authenti-
cation procedures, two keys are generated for ciphering (CK) and integrity checking (IK).
The security mode procedure starts (or recon¬gures) the security process (Figure 6.67).
Subsequently, all signalling messages may be checked for integrity to verify that they
have not been altered en route. The UE and RNC will discard any messages for which
the integrity check fails.
The procedure for integrity checking is described in further detail in Section 6.21.

6.16.6 RRC paging
The RRC protocol is responsible for delivering paging messages to the UE. Two types of
paging mode exist, and the method employed is dependent on the state of the UE:


Security Mode Command

Security Mode Complete

Figure 6.67 Security procedure

• Paging type 1: this is used where there is no longer a dedicated connection between
the UE and the network. It is applicable to idle, CELL-PCH and URA-PCH modes.
A paging type 1 message is transferred on the paging control channel (PCCH). In
idle mode, the paging message will be sent to all cells in the location/routing area. In
CELL-PCH and URA-PCH, the RNC knows the location of the user to a cell or URA,
and can transmit the message on the PCCH just in that cell or URA.
• Paging type 2: this is used to transmit paging information to the UE when the RNC
has an established connection to the network, i.e. the UE is in CELL-FACH or CELL-
DCH mode. In this instant, the paging message is delivered along the FACH or DCH,

6.16.7 Radio bearer establishment
Another RRC procedure is the establishment of radio bearers. This is required if the
UE wishes to send or receive data. If the UE already has a suitable bearer established,
it may recon¬gure that bearer for the new traf¬c. It is the job of the RNC to perform
the radio bearer setup in response to Layer 3 signalling. Figure 6.68 shows the general
procedure ¬‚ow.
The contents of the radio bearer setup and setup complete are much the same as those
outlined for the RRC connection and will de¬ne which RLC mode each bearer should use,
and relevant parameters for this, the transport block sizes and formats, and the physical
layer parameters. Prior to this establishment, the RNC will either set up a new radio link,
or recon¬gure the existing radio link to support this new bearer.
Table 6.18 shows some examples of the recommended bearers and bearer combinations
expected to be supported in the system, with their relevant parameters. For this table, the
transport format for the 3.4 kbps signalling bearer when included with a data bearer is
the same as described for the standalone. Notice that for the last case of a simultaneous
packet and circuit connection, the voice call does not add to the physical layer resource
usage, and the same SF for UL/DL is used. For further details, please refer to TS34.108.


NBAP Radio Link

Radio Bearer Setup/Reconfiguration

Radio Bearer Setup/Reconfiguration

Figure 6.68 Radio bearer setup or recon¬guration

Table 6.18 Example data bearer con¬gurations

Description Bit rate Transport format SF
Standalone signalling 1.7 TB size: 148 bits 256 512
bearers TTI: 80 ms
1/3 rate CC, 16-bit CRC
3.4 TB size: 148 bits 256 256
TTI: 40 ms
1/3 rate CC, 16-bit CRC
13.6 TB size: 148 bits 64 128
TTI: 10 ms
1/3 rate CC, 16-bit CRC
Speech + signalling 12.2 + 3.4 TB size: 244 bits (refer to 64 128
Section 6.13)
TTI: 20 ms
1/3 rate + 1/2 rate CC, 16-bit
CRC + no CRC
28.8 + 3.4 TB size: 1 — 576, 2 — 576 bits
Circuit switched 32 64
non-transparent TTI: 40 ms
data + signalling TC, 16-bit CRC
64 + 3.4 TB size: 1 — 320, 2 — 320,
Circuit switched 16 32
transparent data + 4 — 320, 8 — 320 bits
signalling TTI: 40 ms
TC, 16-bit CRC
16 + 3.4 TB size: 1 — 336, 2 — 336 bits
Packet switched data 32 64
+ signalling TTI: 40 ms
TC, 16-bit CRC
64 + 3.4 TB size: 1 — 336, 2 — 336,
Packet switched data 16 32
+ signalling 3 — 336, 4 — 336 bits
TTI: 20 ms
TC, 16-bit CRC
UL: TB size: 1 — 336, 2 — 336,
Asymmetric packet 64 UL/ 384 16
switched data + DL + 3.4 3 — 336, 4 — 336 bits
signalling TTI: 20 ms
TC, 16-bit CRC
DL: TB size: 1 — 336, 2 — 336, 8
4 — 336, 8 — 336, 12 — 336,
16 — 336, 20 — 336,
24 — 336 bits
TTI: 20 ms
TC, 16-bit CRC
UL: TB size: 1 — 336, 2 — 336,
Asymmetric packet 64 UL/ 16
switched data + 3 — 336, 4 — 336 bits
2048 DL
+ 3.4
signalling TTI: 20 ms
TC, 16-bit CRC
DL: TB size: 1 — 656, 2 — 656, 4—3
4 — 656, 8 — 656, 12 — 656, DPDCH
16 — 656, 20 — 656,
24 — 656, 28 — 656,
32 — 656 bits
TTI: 10 ms
TC, 16-bit CRC

Table 6.18 (continued)

Description Bit rate Transport format SF
64 + 12.2 + As above for ˜Speech +
Packet switched data 16 32
+ circuit switched 3.4 signalling™ and ˜Packet
voice call + switched data + signalling™

CC, Convolution coding; TC, turbo coding

6.16.8 Transfer of NAS messages
RRC also offers procedures for transferring non-access stratum messages between the UE
and the core network. For this, the direct transfer messages are used. There are three
types of direct transfer message, as explained in Table 6.19. The direct transfer message
transparently transports the NAS message, providing only an indication of which core
network domain (CS or PS) is being used. The direct transfer message is transported to
the core network across the Iu interface transparent to UTRAN by RANAP. For example,
an MM location update request message from the UE will be transferred to the RNC
using RRC intial direct transfer, and then from the RNC to the CN using the RANAP
initial ue Message.

6.16.9 Cell/URA update
For a location or routing area update, the UE must establish a dedicated RRC connection
(CELL-FACH/CELL-DCH), and transfer the signalling using the direct transfer message
over a DCCH. However, for UTRAN mobility, there is no need to do this, but rather,
in CELL-PCH/URA-PCH, the UE can send an update message across the CCCH to the
RNC. The format of this is shown in Figure 6.69.

Table 6.19 Direct transfer messages
Message Explanation RANAP
Initial direct This is used to establish a Initial UE


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