1 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Signalling Flow:
PS Call
Establishment
2 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Introduction• This slide set provides a detailed illustration of the message
flow observed for an PS call
• The message flow is focused upon communication with the packet switched core and does not include communication with the circuit switched core.
• The UE starts by searching for candidate cells by correlating the RSSI with the code defining the primary SCH
• The UE then achieves radio frame synchronisation and reads the BCCH logical channel
• The BCCH provides system information including the cell selection criteria
• If the cell passes the cell selection criteria then the UE establishes an RRC connection and registers with the core network
• Having registered the UE activates the PDP context with the CN using the existing CN (assumption is that follow on request pending is set)
• In case of no activity (no data nor signalling data transmitted between the UE and CN) the dedicated channel between the UE and the RNC is released and UE is moved to Cell_FACH or Cell_PCH cell state
UE is powered up
Read BCCH
Cell selection
Register with core network
Cell State Transitions
Radio frame synchronisation
Cell search
Originating PS Call
3 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Protocol Stacks• Communication between the UE, RNC and packet core makes use of
• Uu interface protocol stack
• Iub interface protocol stack
• Iu,ps interface protocol stack
Iub Iu,ps
Uu
Node B RNC SGSN
4 © Nokia Siemens Networks Presentation / Author / DateFor internal use
PS Radio Interface Control Plane
• The radio interface protocol control plane allows RRC signalling between the RNC and UE
• RRC signalling is communicated across the Iub using the Iub user plane protocol stack i.e. using Frame protocol and AAL2 based ATM
• Acknowledged or unacknowledged mode RLC is used between the UE and RNC
WCDMA L1
RRC
WCDMA L1
AAL2
FP
ATM
Phy
MAC
RLC-C
AAL2
FP
ATM
Phy
MAC
RLC-C
UE
Node B
RNC
Uu Iub
RRC
5 © Nokia Siemens Networks Presentation / Author / DateFor internal use
PS User Plane
• The SGSN provides connectivity to the packet switched core and applications
• Acknowledged mode RLC (or unacknowledged) is used between the UE and RNC
• AAL2 based ATM is used to transfer user plane data across the Iub and AAL5 based ATM across Iu,ps interface
WCDMA L1
WCDMA L1
AAL2
FP
ATM
Phy
MAC
RLC-U
AAL2
FP
ATM
Phy
MAC
RLC-U
AAL5
ATM
Phy
GTP-U
AAL5
ATM
Phy
UE
Node B
RNC SGSN
Uu Iub Iu,ps
UDP
IP
GTP-U
UDP
IP
6 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Read BCCH• The BCCH encapsulates the System Information message
which includes the Master Information Block (MIB), Scheduling Blocks (SB) and System Information Blocks (SIB)
UE is powered up
Read BCCH
Cell selection
Register with core network
Cell State Transitions
Radio frame synchronisation
Cell search
Originating PS Call
7 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Cell Selection • Cell selection is based upon the S-criteria
• UE extracts the S-criteria parameters from SIB 3
• QqualMin
• QrxlevMin
• UE_TXPWR_MAX_RACH
UE is powered up
Read BCCH
Cell selection
Register with core network
Cell State Transitions
Radio frame synchronisation
Cell search
Originating PS Call
8 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Register with the Core Network
• The UE registers with the PS core domain (the UE also registers with the CS core domain but this slide set concerns only the PS domain)
• PS domain registering is a GPRS attach procedure
• Registering is achieved by establishing an RRC connection and sending non-access stratum messages to the 3G SGSN
• RRC Connection Establishment
• GPRS Attach
UE is powered up
Read BCCH
Cell selection
Register with core network
Cell State Transitions
Radio frame synchronisation
Cell search
Originating PS Call
9 © Nokia Siemens Networks Presentation / Author / DateFor internal use
UTRAN Specific Signalling Protocols
3G-MSC/VLR
3G-SGSN
UE Node BRNC
RNC
RNS
RNS
RRC
Iur: RNSAP
Iu-PS: RANAP
Iu-CS: RANAP
Iub: NBAP
10 © Nokia Siemens Networks Presentation / Author / DateFor internal use
RRC Connection Setup UE Node-B RNC CN
RRC Connection Setup Request ( CCCH on RACH)
Radio Link Setup Request NBAPNBAP
Radio Link Setup Response
NBAPNBAP
RRC Connection Setup Complete (DCCH on DCH)
RRC Connection Setup (CCCH on FACH)
Establish RequestALCAPALCAP
Establish ResponseALCAPALCAP
RRC RRC
RRCRRC
RRC RRC
Signalling Bearer
establishment
11 © Nokia Siemens Networks Presentation / Author / DateFor internal use
GPRS Attach
UEATTACH REQUEST ( )
(Identification Procedure)
Authentication and Ciphering Procedure
ATTACH ACCEPT ( )
e.g. new TMSIor P-TMSI
ATTACH COMPLETE ( )
3G-SGSN
13 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Initial Direct Transfer
UE RNC MSC
RRC Connection Setup
Initial Direct Transfer
CM Service RequestRRC RRC
Node-B
UE RNC SGSN Node-B
Initial UE Message
CM Service RequestRANAPRANAP
Initial Direct Transfer
Attach Request GMMRRC RRC
Initial UE Message
Attach Request GMMRANAPRANAP
RRC Connection Setup
14 © Nokia Siemens Networks Presentation / Author / DateFor internal use
PS CallUE is powered up
Read BCCH
Cell selection
Register with core network
Cell State Transitions
Radio frame synchronisation
Cell search
Originating PS Call
• The PS call can be either mobile originated or mobile terminated
• The following slides present a mobile originated call
• The first step is to establish an RRC connection, however if the “follow on request” is SET in NAS Message – ‘GPRS Attach Request’ -> there is no Iu release as CN is waiting for additional signalling using the same RRC (e.g. PDP context Activation)
• This means that RRC Connections for PS calls are initiated with cause : registration
15 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Activate PDP Context Request
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH)
• Having attached with the PS Core NW, UE sends Activate PDP context request DCCH ->DCH -> DPCH
• By sending this message UE requests a service for the packet switched connection establishment
• DCCH contains the RRC: Uplink Direct Transfer message
• Message is sent using acknowledged mode RLC
Direct Transfer : Activate PDP context request
GPRS Attach
16 © Nokia Siemens Networks Presentation / Author / DateFor internal use
IEI Information Element Type/Reference Presence Format Length Protocol discriminator Protocol discriminator
10.2 M V 1/2
Transaction identifier
Transaction identifier 10.3.2
M V 1/2– 3/2
Activate PDP context request message identity
Message type 10.4
M V 1
Requested NSAPI Network service access point identifier 10.5.6.2
M V 1
Requested LLC SAPI LLC service access point identifier 10.5.6.9
M V 1
Requested QoS Quality of service 10.5.6.5
M LV 12
Requested PDP address Packet data protocol address 10.5.6.4
M LV 3 - 19
28 Access point name Access point name 10.5.6.1
O TLV 3 - 102
27 Protocol configuration options Protocol configuration options 10.5.6.3
O TLV 3 - 253
NAS: Activate PDP Context Request
17 © Nokia Siemens Networks Presentation / Author / DateFor internal use
RAB Assignment Request
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RAB Assignment Request
• Having received the Activate PDP Context Request message the PS core sends the RANAP: RAB Assignment Resuest message to the RNC
• The RANAP: RAB Assignment Resuest message requests the RNC to establish a RAB with a specified set of QoS parameters
• The PS core requests these QoS parameters based upon the subscription and the service being requested (as seen from Activate PDP Context Request message the QoS is based entirely on the subscription)
GPRS Attach
18 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Bearer Setup
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
• Once the RANAP: RAB Assignment Request message has been received from PS CN and RNC has resources to setup the 0/0 kbps RB the RNC sends a RRC: Radio Bearer Setup message to the UE
GPRS Attach
19 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Bearer Setup Complete
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
• The UE acknowledges the RRC: Radio Bearer Setup message with a RRC: Radio Bearer Setup Complete message
GPRS Attach
20 © Nokia Siemens Networks Presentation / Author / DateFor internal use
RAB Assignment Response
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
• Once the radio bearer establishment has been acknowledged, the RNC indicates to the PS core that the RAB has been established using the RANAP: RAB Assignment Response message
RAB Assignment Response
GPRS Attach
21 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Measurement Control
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
RAB Assignment ResponseMeasurement Control
• Once the RAB has been established the RNC sends a measurement control messages
•For traffic volume measurements (UE internal)
•For intra and inter frequency measurements
• Prior to receiving this message, the UE uses the measurement control information from the SIBs (inter and intra freq. Measurements – traffic volume measurements are not performed prior to measurement control)
• Measurement control defines the reporting thresholds for traffic volume measurements which are used for the UL capacity requests
Measurement Control
GPRS Attach
22 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Activate PDP Context Accept
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
• Once the radio access bearer establishment has been acknowledged, (measurement control messages can be sent before or after the Activate PDP Context Accept) the PS CN indicates to the UE that the PDP Context Ativation has been successfully established using the RANAP: Activate PDP Context Accept message
• RNC receives the Direct Transfer : Activate PDP Context Accept message and forwards it as Downlink Direct Transfer : Activate PDP Context Accept message to the UE
RAB Assignment Response
Direct Transfer: Activate PDP Context AcceptDownlink Direct Transfer : Activate PDP Context Accept (DCH)
Measurement Control
Measurement Control
GPRS Attach
23 © Nokia Siemens Networks Presentation / Author / DateFor internal use
PS call established
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
•PS data call Established, but 0/0 kbps RB
RAB Assignment Response
Direct Transfer: Activate PDP Context AcceptDownlink Direct Transfer : Activate PDP Context Accept (DCH)
Call Established
Measurement Control
Measurement Control
GPRS Attach
24 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Bearer Setup
UE Initiated PDP Context Activation
UE
3G-SGSN
GGSNACTIVATE PDP CONTEXT REQUEST ( )
ACTIVATE PDP CONTEXT ACCEPT ( )
CREATE PDP CONTEXT REQUEST
CREATE PDP CONTEXT RESPONSE
UPDATE PDP CONTEXT REQUEST
UPDATE PDP CONTEXT RESPONSE
26 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Reporting event:4A: Transport Channel Traffic Volume becomes larger than an absolute threshold4B: Transport Channel Traffic Volume becomes smaller than an absolute threshold
time
TransportChannelTrafficVolume(TCTV)
Threshold
4B
4A
4B 4B
4A4A
Traffic Volume Measurements
27 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Reporting Event 4a
UE RNC SGSNNode B
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
RAB Assignment Response
Direct Transfer: Activate PDP Context AcceptDownlink Direct Transfer : Activate PDP Context Accept (DCH)
Packet Call Established
Measurement Control
Measurement Control
Measurement Report : e4a
• Once the UE determines that an event 4a has occurred it sends a measurement report to the RNC. This is done using the RRC: Measurement Report message
• As instructed, the UE sends measurement report when the RLC buffer absolute payload exceeds the threshold
• The measurement identity reflects that provided within the measurement control message
GPRS Attach
28 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Link Reconfigure Ready
UE RNC SGSNNode B
NBAP: Radio Link Reconfigure Prepare
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
RAB Assignment Response
Direct Transfer: Activate PDP Context AcceptDownlink Direct Transfer : Activate PDP Context Accept (DCH)
Call Established
Measurement Control
Measurement Control
Measurement Report : e4a
Radio Bearer Reconfiguration
• Once the reconfiguration of radio link at Node-B is done the RNC sends a RRC: RRC: Radio Bearer Reconfiguration message to UE
RRC: Radio Bearer Reconfiguration (DCH)
GPRS Attach
29 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Link Reconfigure Ready
UE RNC SGSNNode B
NBAP: Radio Link Reconfigure Prepare
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
RAB Assignment Response
Direct Transfer: Activate PDP Context AcceptDownlink Direct Transfer : Activate PDP Context Accept (DCH)
Call Established
Measurement Control
Measurement Control
Measurement Report : e4a
Radio Bearer Reconfiguration Complete
• The UE acknowledges the RRC: Radio Bearer Reconfiguration message with a RRC: Radio Bearer Reconfiguration Complete message
RRC: Radio Bearer Reconfiguration (DCH)RRC: Radio Bearer Reconfiguration Complete (DCH)
GPRS Attach
30 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Link Reconfigure Ready
UE RNC SGSNNode B
NBAP: Radio Link Reconfigure Prepare
Uplink Direct Transfer : Activate PDP context request (DCH) Direct Transfer : Activate PDP context request
RANAP: RAB Assignment RequestRRC: Radio Bearer Setup
Radio Bearer Setup Complete
RAB Assignment Response
Direct Transfer: Activate PDP Context AcceptDownlink Direct Transfer : Activate PDP Context Accept (DCH)
Call Established
Measurement Control
Measurement Control
Measurement Report : e4a
UL: 64kbps DL: 64 kbps Connection Established
RRC: Radio Bearer Reconfiguration (DCH)RRC: Radio Bearer Reconfiguration Complete (DCH)
GPRS Attach
64 kbps service established
31 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Cell State Transitions
• When the RNC notices that there is nothing being transmitted between UE and RNC, inactivity timers will start to run and in case of expiry of those timers the UE is moved to use common channels i.e. cell state transition from Cell_DCH to Cell_FACH occurs
• In order to save some UE battery power (as in Cell_FACH the UE has to read FACH channel all the time) in case of further inactivity i.e. no capacity requests from UE nor RNC the UE is further moved to Cell_PCH where the UE only listens to PCH (paging channel)
UE is powered up
Read BCCH
Cell selection
Register with core network
Cell State Transitions
Radio frame synchronisation
Cell search
Originating PS Call
32 © Nokia Siemens Networks Presentation / Author / DateFor internal use
AAL2SIG:ECFAAL2SIG:ERQ
Radio Link Reconfigure Ready
UE RNC SGSNNode B
NBAP: Radio Link Reconfigure Prepare
Call Established
Measurement Report : e4a
FP: Downlink Sync
FP: Uplink SyncRadio Link Reconfiguration Commit
Radio Bearer Reconfiguration
RRC: Radio Bearer Reconfiguration (DCH)RRC: Radio Bearer Reconfiguration Complete (DCH)
Measurement Control
RRC: Radio Bearer Reconfiguration (DCH)
Data Flow
• In case the RNC decides to move the UE to Cell_FACH state it sends RRC: Radio Bearer Reconfiguration
GPRS Attach
33 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Bearer Reconfiguration Complete
• The UE acknowledges the RRC: Radio Bearer Reconfiguration message with a RRC: Radio Bearer Reconfiguration Complete message on RACH
AAL2SIG:ECFAAL2SIG:ERQ
Radio Link Reconfigure Ready
UE RNC SGSNNode B
NBAP: Radio Link Reconfigure Prepare
Call Established
Measurement Report : e4a
FP: Downlink Sync
FP: Uplink SyncRadio Link Reconfiguration Commit
RRC: Radio Bearer Reconfiguration (DCH)RRC: Radio Bearer Reconfiguration Complete (DCH)
Measurement Control
RRC: Radio Bearer Reconfiguration (DCH)
Data Flow
RRC: Radio Bearer Reconfiguration Complete (RACH)
GPRS Attach
34 © Nokia Siemens Networks Presentation / Author / DateFor internal use
UE in Cell_FACH
Measurement Control (FACH)
AAL2SIG:ECFAAL2SIG:ERQ
Radio Link Reconfigure Ready
UE RNC SGSNNode B
NBAP: Radio Link Reconfigure Prepare
GPRS Attach
Call Established
Measurement Report : e4a
FP: Downlink Sync
FP: Uplink SyncRadio Link Reconfiguration Commit
RRC: Radio Bearer Reconfiguration (DCH)RRC: Radio Bearer Reconfiguration Complete (DCH)
Measurement Control
RRC: Radio Bearer Reconfiguration (DCH)
Data Flow
RRC: Radio Bearer Reconfiguration Complete (RACH)
NBAP: Radio Link Deletion Response
NBAP: Radio Link Deletion Request
ALCAP: Release Request
ALCAP: Release Confirm
UE in Cell_FACH, PDP Context Active and GPRS Attached
35 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Physical Channel Reconfiguration
Measurement Control (FACH)
UE RNC SGSNNode B
GPRS Attach
Call Established
RRC: Radio Bearer Reconfiguration (DCH)
Data Flow
RRC: Radio Bearer Reconfiguration Complete (RACH)
NBAP: Radio Link Deletion Response
NBAP: Radio Link Deletion Request
ALCAP: Release Request
ALCAP: Release Confirm
UE in Cell_FACH, PDP Context Active and GPRS Attached
RRC: Physical Channel Reconfiguration (FACH)
RRC: Physical Channel Reconfiguration Complete (RACH)
• RNC sends RRC: Physical Channel Reconfiguration message to the UE to move the UE to Cell_PCH state
36 © Nokia Siemens Networks Presentation / Author / DateFor internal use
UE in Cell_PCH
Measurement Control (FACH)
UE RNC SGSNNode B
GPRS Attach
Call Established
RRC: Radio Bearer Reconfiguration (DCH)
Data Flow
RRC: Radio Bearer Reconfiguration Complete (RACH)
NBAP: Radio Link Deletion Response
NBAP: Radio Link Deletion Request
ALCAP: Release Request
ALCAP: Release Confirm
UE in Cell_FACH, PDP Context Active and GPRS Attached
RRC: Physical Channel Reconfiguration (FACH)
RRC: Physical Channel Reconfiguration Complete (RACH)
UE in Cell_PCH, PDP Context Active and GPRS Attached
37 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Cell Update
Measurement Control (FACH)
UE RNC SGSNNode B
GPRS Attach
Call Established
RRC: Radio Bearer Reconfiguration (DCH)
Data Flow
RRC: Radio Bearer Reconfiguration Complete (RACH)
NBAP: Radio Link Deletion Response
NBAP: Radio Link Deletion Request
ALCAP: Release Request
ALCAP: Release Confirm
UE in Cell_FACH, PDP Context Active and GPRS Attached
RRC: Physical Channel Reconfiguration (FACH)
RRC: Physical Channel Reconfiguration Complete (RACH)
UE in Cell_PCH, PDP Context Active and GPRS Attached
RRC: Cell Update (RACH)
• In case the UE has something to send it has to send RRC: Cell Update message to the RNC to move the UE to Cell_FACH state to get dedicated resources
38 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Cell Update Confirm
Measurement Control (FACH)
UE RNC SGSNNode B
GPRS Attach
Call Established
RRC: Radio Bearer Reconfiguration (DCH)
Data Flow
RRC: Radio Bearer Reconfiguration Complete (RACH)
NBAP: Radio Link Deletion Response
NBAP: Radio Link Deletion Request
ALCAP: Release Request
ALCAP: Release Confirm
UE in Cell_FACH, PDP Context Active and GPRS Attached
RRC: Physical Channel Reconfiguration (FACH)
RRC: Physical Channel Reconfiguration Complete (RACH)
UE in Cell_PCH, PDP Context Active and GPRS Attached
RRC: Cell Update (RACH)
• RNC acknowledges the UE message RRC: Cell Update with RRC: Cell Update Confirm message and instructs UE to move to Cell_FACH state
RRC: Cell Update Confirm (FACH)
39 © Nokia Siemens Networks Presentation / Author / DateFor internal use
UE RNC SGSNNode B
GPRS Attach
Call Established
Data Flow
UE in Cell_DCH, PDP Context Active and GPRS Attached
Deactivate PDP Context Request
UpLink Direct Transfer : Deactivate PDP Context Request (DCH) Direct Transfer : Deactivate PDP Context Request (DCH)
• The UE requests deactivation of PDP context by sending the Deactivate PDP Context Request towards the PS core encapsulated within RRC: Uplink Direct Transfer
40 © Nokia Siemens Networks Presentation / Author / DateFor internal use
UE RNC SGSNNode B
GPRS Attach
Call Established
Data Flow
UE in Cell_DCH, PDP Context Active and GPRS Attached
Deactivate PDP Context Accept
UpLink Direct Transfer : Deactivate PDP Context Request (DCH) Direct Transfer : Deactivate PDP Context Request
Direct Transfer : Deactivate PDP Context AcceptDownlink Direct Transfer : Deactivate PDP Context Accept (DCH)
• The PS CN acknowledges the deactivation of PDP context by sending Deactivate PDP Context Accept to the UE encapsulated within RRC: Downlink Direct Transfer
41 © Nokia Siemens Networks Presentation / Author / DateFor internal use
Radio Bearer Release
RANAP: RAB Assignment Request
RANAP: RAB Assignment Response
UE RNC SGSNNode B
GPRS Attach
Call Established
Data Flow
UE in Cell_DCH, PDP Context Active and GPRS Attached
UpLink Direct Transfer : Deactivate PDP Context Request (DCH) Direct Transfer : Deactivate PDP Context Request
Direct Transfer : Deactivate PDP Context AcceptDownlink Direct Transfer : Deactivate PDP Context Accept (DCH)
NBAP: Radio Link Reconfiguration Prepare
NBAP: Radio Link Reconfiguration Ready
NBAP: Radio Link Reconfiguration Commit
RRC: Radio Bearer Release (DCH)
• Then the RNC is ready to inform the UE about the changes in the RB by sending RRC: Radio Bearer Release
• After this there is only signalling link active between the UE and PS CN and the UE can be moved to Cell_FACH and to Cell_PCH still maintaining the signalling link or the signalling link can be deactivated by doing GPRS detach or by releasing the RRC connection (and Iu) but still GPRS Attached
RRC: Radio Bearer Release Complete (DCH)