RRC Signalling Procedure.xlsx

Mapping of UE state to 3GPP Specifications

RRC Tasks and Functions

After UE switch on, there are two basic operational modes of a UE, idle mode and connected mode.The connected mode can be further divided into 4 service states,which define what kind of physical channels a UE is using. The mapping of UE state to 3GPP speciafication is shown below:

The RRC protocol is the application part for the UMTS radio access technology. This means all controlling radio tasks are in the responsibility of RRC. The RRC has following functions:-broadcasting of system information for NAS stratum-establishment,maintenance and release of RRC signaling between UE and UTRAN connections-establishment,reconfiguration and release of radio bearers-RRC connection mobility functions-Quality of Service (QOS) control-UE measurement reports-outer loop power control-security control-paging-Initial cell selection and reselection-transport of NAS stratum control messages

With all these tasks the RRC protocol belongs to the access stratum when the radio oriented control tasks are performed and it belongs to the transport stratum,because it carriers the higher layer control plane protocol messages.

UE Switch on

UE Idle3GPP TS 25.304

UE Connected3GPP TS 25.331

GSM ConnectedGSM TS 04.18

GSM Packet Transfer

GSM TS 04.50

GSM IdleGSM TS 05.08

UE Idle3GPP TS 25.3043GPP TS 25.331

Cell_DCH3GPP TS 25.331

Cell_PCH3GPP TS 25.3043GPP TS 25.331

Cell_FACH3GPP TS 25.3043GPP TS 25.331

URA_PCH3GPP TS 25.3043GPP TS 25.331

RRC Modes and State Transitions including GSM

Usage of Radio Bearer by the RRC protocolThe RRC protocol uses the radio bearer service provided by the layer 1 and layer 2 of the UMTS radio interface. The radio bearers in an UE will be numbered from 0 to 31. The radio bearers 0,1,2,3,4 are pre-assigned for exclusive RRC usage. The following is speified:-RB0 : The radio bearer 0 shall be used for all CCCHs. The CCH in the uplink is mapped to the RACH with RLC transparent mode, the downlink CCCH is mapped to the FACH with RLC unacknowledged mode.-RB1 : The radio bearer 1 is for all DCCH messages with RLC unacknowledged mode-RB2 : The radio bearer 2 is used for all DCCH messages in RLC acknowledged mode, but not for RRC messages that transport NAS messages inside.-RB3 and optional RB4 : These two radio bearers shall be used for RRC messages carrying NAS messages on DCCH in RLC acknowledged mode.

The radio bearers 5,...,31 can be used with explicit radio bearer set up for all purposes, e.g. traffic channels or control channels.For RRC messages the protocol specified which RLC mode and with this which radio bearer can be chosen for transport of this message.

The RRC protocol is an application part (Radio Resource Management) and transport protocol (NAS message transport). Therefore the RRC protocol requires state definition with transitions between states.The RRC state definiton describes the RRC protocol behavior as a nested set of stated. Two main states are defined:1. UTRA Idle Mode : In UTRA idle mode, the UE has no signaling relationship with the UTRAN. In this case the idle mode procedures have to be applied. This means as soon as the UE is switched on, it searches for PLMNs and cells and listen to the broadcasted system information of selected cells

2. UTRA RRC Connected Mode : In the connected mode the UE has a signaling connection with the UTRAN. The setup of this signaling conenction is done by a RRC procedure (RRCconnection set up). This procedure is the transistion from idle to connected mode. When the RRC connection is released, the connected mode is left and the idle more is entered.

For multi-mode mobile phones (e.g. UMTS,GSM/GPRS) the RRC states can be combined with the radio resource management states of GSM/GPRS. In GSM/GPRS the states of a mobile phone can be:1. Idle Mode : The idle mode of GSM/GPRS has the same meaning as the idle mode of UMTS. The only difference is, that the UE is camped on a GSM/GPRS cell2. GSM conected mode : In GSM the RR (Radio Resource Layer) performs the radio management. This protocol can setup a RR connection between network and mobile equipment.When such a connection exist,the UE is in GSM connected mode. A GSM-DCCH is allocated for the UE in this case.3. GPRS packet transfer mode : In GPRS the radio resources are allocated for a mobile temporary only. Such a temporary resource is called a temporary block flow (TBF). When a mobile is granted a temporary block flow ,the mobile is in GPRS packet transfer mode (GPRS-RLC state)

With a multi-mode UE it shall be possible to perform in-service-transitions between the different Radio Access Technology (RAT).Therefore it is possible to make a inter-system handover from UTRA connected mode to GSM connected mode and vice versa. A transistion from UTRA connected mode to GPRS packet transfer mode is simply done by stoppint thepacket transfer in UMTS, making a cell reselection to a GPRS cell and getting a GPRS temporary block flow.

Release RRCConnection

Release RRCConnection

Establish RRCConnection

Establish RRCConnection

CellReselection

Releaseof a TBF

URA_PCH

CELL_DCH CELL_FACH

CELL_PCH

UTRA RRC Connected Mode

Idle Mode

(UE camps on UTRAN cell)

GSM-UMTS Handover

UTRA: Inter-RAT Handover

(MS in GPRS Packet Idle Mode)

(MS camps on a GSM/GPRS cell)

GPRS PacketTransfer

Mode

RRC Mode DescriptionRRC Idle Mode

RRC Connected Mode

The RRC protocol is an application part (Radio Resource Management) and transport protocol (NAS message transport). Therefore the RRC protocol requires state definition with transitions between states.The RRC state definiton describes the RRC protocol behavior as a nested set of stated. Two main states are defined:1. UTRA Idle Mode : In UTRA idle mode, the UE has no signaling relationship with the UTRAN. In this case the idle mode procedures have to be applied. This means as soon as the UE is switched on, it searches for PLMNs and cells and listen to the broadcasted system information of selected cells

2. UTRA RRC Connected Mode : In the connected mode the UE has a signaling connection with the UTRAN. The setup of this signaling conenction is done by a RRC procedure (RRCconnection set up). This procedure is the transistion from idle to connected mode. When the RRC connection is released, the connected mode is left and the idle more is entered.

For multi-mode mobile phones (e.g. UMTS,GSM/GPRS) the RRC states can be combined with the radio resource management states of GSM/GPRS. In GSM/GPRS the states of a mobile phone can be:1. Idle Mode : The idle mode of GSM/GPRS has the same meaning as the idle mode of UMTS. The only difference is, that the UE is camped on a GSM/GPRS cell2. GSM conected mode : In GSM the RR (Radio Resource Layer) performs the radio management. This protocol can setup a RR connection between network and mobile equipment.When such a connection exist,the UE is in GSM connected mode. A GSM-DCCH is allocated for the UE in this case.3. GPRS packet transfer mode : In GPRS the radio resources are allocated for a mobile temporary only. Such a temporary resource is called a temporary block flow (TBF). When a mobile is granted a temporary block flow ,the mobile is in GPRS packet transfer mode (GPRS-RLC state)


When a UE is switched on, it enters the RRC idle mode. In the RRC idle mode, there is no connection on the access stratum level between the UE and UTRAN. UTRAN has no information about UEs in the RRC idle mode. If UTRAN wants to address the UE, it must use non-access stratum identifiers, such as IMSI or TMSI and LAI.

In the RRC idle mode, the UE monitors the BCCH, and when it is registered to the CN, it also listens to paging occasions on its PICH.

The transition from the RRC idle mode to the RRC connected mode can only be initiated by the UE by sending the "RRC Connection Request" message to UTRAN. If common transport channels used to exchange messages and data between the UE and UTRAN, the UE is identified by a Radio Network Temporary Identity (RNTI). As can be seen in thefigure above, the UE can be in one of four sub-states, when it is in the RRC connected mode. The sub-states depend on the connectivity level between the UE and UTRAN. The set of usable transport channels depend also on the sub-states. For instance, the DCHs are not available in the sub-states CELL_PCH and CELL_URA. The UE leaves the RRC idle mode when sending the RRC Connection Request message to UTRAN. When UTRAN accepts the UE‘s request, the UE enters either the sub-state CELL_DCH or CELL_FACH.

The RRC connected Mode can be further decomposed into four different states. These four sub-states describe, on which level the UE is known by UTRAN and which resources are allocated by the UE. UTRAN can know any UE either on cell level (cell state) or on URA level (URA state). On the other hand any UE can have a DCH or a FACH or no transport channel for control message exchange. Therefore the four connected states are introduced:

CELL_DCHIn this sub-state, dedicated physical channels are allocated to the UE. DCCH and – if configured – DTCH information can be transmitted. There no need to identify the UE on a dedicated channel, because the physical channels are exclusively allocated to this UE. UTRAN knows the active set cells for the radio links and thus the location of the the UE. Also downlink shared channels can be allocated to the UE. In this state, the UE is capable to receive RRC messages on the DCCH (and BCCH, if it owns specific capabilities). The cell system information is broadcasted on the FACH. The UE reads the cell system information and acts accordingly. For instance, it determines the measurement quality and the reporting events from the cell system information. This state can only be entered from Cell_FACH by setting up a DCH. When the last DCH is released the UE enters Cell_FACH,Cell_PCH,URA_PCH or idle mode

In the CELL_DCH state the UE shall perform the following actions:if DCCH and DTCH are available:- read system information broadcast on FACH (applicable only to UEs with certain capabilities and camping on FDD cells);- perform measurements process according to measurement control information

CELL_FACHThis state was introduced for traffic situations, where only small amounts of data have to be transmitted. This is the case when only higher layer signalling information (NAS signalling) or small amount of user data (e.g. SMS messages) have to be transmitted. In this case, an exclusive allocation of one physical channel to the UE would result in a waste of resources. Only common transport channel FACH can be used by the UE to transmit higher layer data, which it has to share with other UEs. Each UE must be explicitly addressed, for instance by the RNTI. It has to monitor the FACH permanently in the downlink, not to miss user data for it. The UE‘s FACH is mapped on one S-CCPCH.

In the uplink, it uses the shared transport channels for user data transfer, such as the RACH. The UE is only connected to one cell, and this is the location information, known within UTRAN. No soft handover takes place in this sub-state. The UE is responsible for cell re-selection. By listening to the cell system information from the BCCH, it gains all relevant measurement qualities, threshold values, neighbourhood lists to perform the cell re-selection process. Other relevant information is also learned from the BCCH. The UE receives RRC messages on the BCCH, CCCH and DCCH channels. Due to the discontinuous type of traffic, UTRAN can command the UE to perform periodic cell updates.

In the CELL_FACH state the UE shall perform the following actions:if the UE is "in service area":- DCCH and DTCH are available- perform cell reselection process- perform measurements process according to measurement control information- run timer T305 (periodical cell update)- listen to all FACH transport channels mapped on S-CCPCH assigned to this UEif the UE is "out of service area":- perform cell reselection process- run timers T305 (periodical cell update), and T317 (cell update when re-entering "in service") or T307 (transition to Idle mode)

RRC Connection Mobility Management and RRC Modes

CELL_FACHThis state was introduced for traffic situations, where only small amounts of data have to be transmitted. This is the case when only higher layer signalling information (NAS signalling) or small amount of user data (e.g. SMS messages) have to be transmitted. In this case, an exclusive allocation of one physical channel to the UE would result in a waste of resources. Only common transport channel FACH can be used by the UE to transmit higher layer data, which it has to share with other UEs. Each UE must be explicitly addressed, for instance by the RNTI. It has to monitor the FACH permanently in the downlink, not to miss user data for it. The UE‘s FACH is mapped on one S-CCPCH.

In the uplink, it uses the shared transport channels for user data transfer, such as the RACH. The UE is only connected to one cell, and this is the location information, known within UTRAN. No soft handover takes place in this sub-state. The UE is responsible for cell re-selection. By listening to the cell system information from the BCCH, it gains all relevant measurement qualities, threshold values, neighbourhood lists to perform the cell re-selection process. Other relevant information is also learned from the BCCH. The UE receives RRC messages on the BCCH, CCCH and DCCH channels. Due to the discontinuous type of traffic, UTRAN can command the UE to perform periodic cell updates.

In the CELL_FACH state the UE shall perform the following actions:if the UE is "in service area":- DCCH and DTCH are available- perform cell reselection process- perform measurements process according to measurement control information- run timer T305 (periodical cell update)- listen to all FACH transport channels mapped on S-CCPCH assigned to this UEif the UE is "out of service area":- perform cell reselection process- run timers T305 (periodical cell update), and T317 (cell update when re-entering "in service") or T307 (transition to Idle mode)

CELL_PCH and URA_PCHThe remaining two sub-states – CELL_PCH and URA_PCH – were introduced to cope with inactive data users. Just think about users, who surf in the Internet. After downloading some files, they work with the data, and for a longer time, no transmission takes place. If this is the case, access stratum resources can be released when moving in one of the two states. In both states, no DCCH nor DTCH is allocated to the UE. No exchange of data is possible between the UE and UTRAN. If the UE wants to transmit something, it must move first internally to the sub-state CELL_FACH.

The UE listens to the cell system information, broadcasted on the BCCH. It performs measurements accordingly, and is responsible for cell-reselection. In addition to that, it periodically looks for a PLMN with a higher priority. When UTRAN wants to transmit data to the UE, it must be paged first. Therefore, the UE has to monitor paging occasions on its PICH, i.e. it receives RRC messages both on the BCCH and the PCCH.

CELL_PCH In this sub-state, the UE‘s current cell is known to the RNC. If the RNC wants to exchange data with the UE, it only needs to page the UE there. If the UE changes the cell, itmust perform a cell update. Also periodical cell updates can be requested by UTRAN. To perform updates, the UE must change to the CELL_FACH sub-state. (Please note, that no uplink transmission is allowed in CELL_PCH/URA_PCH.)

URA_PCH URA stands for UTRAN Registration Area. This state is comparable to the Cell_PCH,only that the UTRAN knows the UE on URA level. If the UE is in the CELL_PCH and moving fast, a lot of cell updates have to be performed. URAs are a combination of one or several cells under one S-RNC. URAs may overlap, i.e. a cell may belong to several URAs. If UTRAN wants to transmit something to the UE, it must page the UE within the URA. The UE is responsible for URA updates – when it changes theURA – and periodic URA updates – when required by UTRAN.

In the URA_PCH or CELL_PCH state the UE shall perform the following actions:if the UE is "in service area":- maintain up-to-date system information as broadcast by the serving cell - perform cell reselection process- perform a periodic search for higher priority PLMNs- monitor the paging occasions according to the DRX cycle and receive paging information on the PCH- perform measurements process according to measurement control information- maintain up-to-date BMC data if it supports Cell Broadcast Service (CBS)- run timer T305 for periodical URA update if the UE is in URA_PCH or for periodical cell update if the UE is in CELL_PCHif the UE is "out of service area":- perform cell reselection process- run timer T316;- run timer T305

If the UE is in the RRC connected mode, but not in the CELL_DCH sub-state, it is responsible to inform UTRAN about a detected change of location. The UE then moves (or is) in the CELL_FACH state and send the RRC message Cell Update or URA Update.

Depending on the UE‘s RRC message, UTRAN returns the RRC message Cell Update Confirm or URA Update Confirm – if it accepts the UE‘s update request. Otherwise, it return the RRC Connection Release message.

The cell or URA update are conducted for several reasons:1. The UE is in the CELL_PCH or URA_PCH sub-state and re-entering the UMTS service area. Then the UE moves to the CELL_FACH state and notifies UTRAN.2. Periodical updates can be enforced by the operator for UEs in the sub-states CELL_FACH, CELL_PCH and URA_PCH. 3. There is an unrecoverable error at the UE‘s RLC-entity, used for acknowledge mode of operation. 4. A cell update is additionally triggered for several reasons:- The UE has performed cell-reselection. It is camping on a new cell, and UTRAN must be notified about it. - The UE was paged in the sub-states URA_PCH or CELL_PCH. - The UE informs UTRAN about its transition to the CELL_FACH state. Another reason for a CELL_FACH transition is an indication by the UE‘s higher layers, that data has to be transmitted uplink.- The UE is in the CELL_DCH and a radio link failed. - The UE was not capable to transmit the RRC message UE Capability Information.

If a cell update takes place, the UE may be requested to modify its RB configuration, TrCH configuration, etc. This must be confirmed by the UE. It may also include a re-establishments of RLC-entities in the acknowledged mode as figures below.

URA Update is conducted – next to re-entering the UMTS service area, due to an RRC acknowledged mode unrecoverable error and because of an periodic URA update – when the UE performs cell re-selection, and the „new“ cell does not belong the the UE‘s URA. An URA Update is then triggered by the UE to get a new URA assigned.

When a UE transmits a Cell Update or URA Update message, it starts the timer T302. It waits for the T302 period to get the Cell Update Confirm resp. URA Update confirm messageIf no confirmation message arrived within this time period, the UE retransmits the original message. The number of Cell Update or URA Update messages, the UE is allowed to send, it hereby limited to N302. The retransmission is of course only possible, when the UE is in the service area; if not, it must continue to search a service area.

If the UE is in the RRC connected mode, but not in the CELL_DCH sub-state, it is responsible to inform UTRAN about a detected change of location. The UE then moves (or is) in the CELL_FACH state and send the RRC message Cell Update or URA Update.

Depending on the UE‘s RRC message, UTRAN returns the RRC message Cell Update Confirm or URA Update Confirm – if it accepts the UE‘s update request. Otherwise, it return the RRC Connection Release message.

The cell or URA update are conducted for several reasons:1. The UE is in the CELL_PCH or URA_PCH sub-state and re-entering the UMTS service area. Then the UE moves to the CELL_FACH state and notifies UTRAN.2. Periodical updates can be enforced by the operator for UEs in the sub-states CELL_FACH, CELL_PCH and URA_PCH. 3. There is an unrecoverable error at the UE‘s RLC-entity, used for acknowledge mode of operation. 4. A cell update is additionally triggered for several reasons:- The UE has performed cell-reselection. It is camping on a new cell, and UTRAN must be notified about it. - The UE was paged in the sub-states URA_PCH or CELL_PCH. - The UE informs UTRAN about its transition to the CELL_FACH state. Another reason for a CELL_FACH transition is an indication by the UE‘s higher layers, that data has to be transmitted uplink.- The UE is in the CELL_DCH and a radio link failed. - The UE was not capable to transmit the RRC message UE Capability Information.

If a cell update takes place, the UE may be requested to modify its RB configuration, TrCH configuration, etc. This must be confirmed by the UE. It may also include a re-establishments of RLC-entities in the acknowledged mode as figures below.



Cell and URA updates performed according to the causes in the figure below. As you can see, a periodic update can be done not only, when the UE is in the CELL_PCH or URA_PCH sub-state, but also, when the UE is in the CELL_FACH sub-state. A periodic update is a supervision mechanism, which can be used by the mobile operator to keep track of the UE. If a cell or URA update was performed, a UE in the CELL_FACH sub-state may transit to the sub-states CELL_DCH, CELL_PCH or URA_PCH, or in the RRC mode idle.

UE Tasks in the CELL_FACH Sub-stateIn the CELL_FACH, but also in the CELL_PCH and URA_PCH, the timer T305 is used for periodical cell or URA updates. It is still active, when the UE is out of the service area. What happens, if this timer expires? The timer T307 is activated, and the UE starts the cell selection process. If the timer T307 expires, the UE moves into the idle mode and releases all resources.

The timers can be broadcasted with the System Information Block 1 (or as part of the UTRAN Mobility Information message):

Out-of-Service Area TimingIf the UE is out of service area, it runs the cell selection process. It keeps the timers T305 running and starts timer T316. The UE attempts to find a serving cell again. If it is successful,and the UE is in the service area again, the UE stops timer T316. It also stops timer T307, in case this timer is active. Being back in the service area can mean, that the UE is served by the same cell or URA, and no update is required. If the UE is in the service area, but the cell or URA has changed, the cell or URA update has to be initiated by the UE. But what happens, if the timer T316 expires? If the UE is still out of service area, it moves to the sub-state CELL_FACH and starts timer T317. If the UE is back in the service area, it performs the Cell Update with cause „re-entering service area.

In the CELL_FACH state, the UE acts like this: If the UE is in the service area and the timer T305 has expired, it performs a periodical cell update.

If the UE is out of service area, it performs the cell selection process. The timers T305 is still active, and the UE starts timer T317, if it was not yet active. If the UE enters the service area again, the timer T317 is stopped. Also timer T307 is stopped, when it was active. The UE has to transmit the RRC Cell Update message to UTRAN, indicating the cause of the cell update: re-entering service area. If the timer T317 expires, the UE moves to the idle mode. It releases all dedicated resources.

Mapping of UE state to 3GPP Specifications

RRC Tasks and Functions

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After UE switch on, there are two basic operational modes of a UE, idle mode and connected mode.The connected mode can be further divided into 4 service states,which define what kind of physical channels a UE is using. The mapping of UE state to 3GPP

The RRC protocol is the application part for the UMTS radio access technology. This means all controlling radio tasks are in the responsibility of RRC. The RRC has following functions:

With all these tasks the RRC protocol belongs to the access stratum when the radio oriented control tasks are performed and it belongs to the transport stratum,because it carriers the

GSM Packet Transfer

GSM TS 04.50

RRC Modes and State Transitions including GSM

The RRC protocol uses the radio bearer service provided by the layer 1 and layer 2 of the UMTS radio interface. The radio bearers in an UE will be numbered from 0 to 31. The radio bearers 0,1,2,3,4 are pre-assigned for exclusive RRC usage. The following is speified:

The radio bearer 0 shall be used for all CCCHs. The CCH in the uplink is mapped to the RACH with RLC transparent mode, the downlink CCCH is mapped to the

The radio bearer 2 is used for all DCCH messages in RLC acknowledged mode, but not for RRC messages that transport NAS messages inside. These two radio bearers shall be used for RRC messages carrying NAS messages on DCCH in RLC acknowledged mode.

The radio bearers 5,...,31 can be used with explicit radio bearer set up for all purposes, e.g. traffic channels or control channels.For RRC messages the protocol specified which RLC mode and with this which radio bearer can be chosen for transport of this message.

The RRC protocol is an application part (Radio Resource Management) and transport protocol (NAS message transport). Therefore the RRC protocol requires state definition with transitions

The RRC state definiton describes the RRC protocol behavior as a nested set of stated. Two main states are defined: In UTRA idle mode, the UE has no signaling relationship with the UTRAN. In this case the idle mode procedures have to be applied. This means as soon as the

UE is switched on, it searches for PLMNs and cells and listen to the broadcasted system information of selected cells

In the connected mode the UE has a signaling connection with the UTRAN. The setup of this signaling conenction is done by a RRC procedure (RRCconnection set up). This procedure is the transistion from idle to connected mode. When the RRC connection is released, the connected mode is left and the idle more is entered.

For multi-mode mobile phones (e.g. UMTS,GSM/GPRS) the RRC states can be combined with the radio resource management states of GSM/GPRS. In GSM/GPRS the states of a mobile

The idle mode of GSM/GPRS has the same meaning as the idle mode of UMTS. The only difference is, that the UE is camped on a GSM/GPRS cell In GSM the RR (Radio Resource Layer) performs the radio management. This protocol can setup a RR connection between network and mobile equipment.

When such a connection exist,the UE is in GSM connected mode. A GSM-DCCH is allocated for the UE in this case. In GPRS the radio resources are allocated for a mobile temporary only. Such a temporary resource is called a temporary block flow (TBF). When a


Release RRConnection

Establish RRConnection

Initiationof a TBF

Releaseof a TBF

GSMConnected

Mode

GSM-UMTS Handover

UTRA: Inter-RAT Handover

(MS in GPRS Packet Idle Mode)

(MS camps on a GSM/GPRS cell)

GPRS PacketTransfer

Mode

RRC Mode Description

The RRC protocol is an application part (Radio Resource Management) and transport protocol (NAS message transport). Therefore the RRC protocol requires state definition with transitions

The RRC state definiton describes the RRC protocol behavior as a nested set of stated. Two main states are defined: In UTRA idle mode, the UE has no signaling relationship with the UTRAN. In this case the idle mode procedures have to be applied. This means as soon as the

UE is switched on, it searches for PLMNs and cells and listen to the broadcasted system information of selected cells

In the connected mode the UE has a signaling connection with the UTRAN. The setup of this signaling conenction is done by a RRC procedure (RRCconnection set up). This procedure is the transistion from idle to connected mode. When the RRC connection is released, the connected mode is left and the idle more is entered.

For multi-mode mobile phones (e.g. UMTS,GSM/GPRS) the RRC states can be combined with the radio resource management states of GSM/GPRS. In GSM/GPRS the states of a mobile

The idle mode of GSM/GPRS has the same meaning as the idle mode of UMTS. The only difference is, that the UE is camped on a GSM/GPRS cell In GSM the RR (Radio Resource Layer) performs the radio management. This protocol can setup a RR connection between network and mobile equipment.

When such a connection exist,the UE is in GSM connected mode. A GSM-DCCH is allocated for the UE in this case. In GPRS the radio resources are allocated for a mobile temporary only. Such a temporary resource is called a temporary block flow (TBF). When a


When a UE is switched on, it enters the RRC idle mode. In the RRC idle mode, there is no connection on the access stratum level between the UE and UTRAN. UTRAN has no information about UEs in the RRC idle mode. If UTRAN wants to address the UE, it must use non-access stratum identifiers, such as IMSI or TMSI and LAI.

In the RRC idle mode, the UE monitors the BCCH, and when it is registered to the CN, it also listens to paging occasions on its PICH.

The transition from the RRC idle mode to the RRC connected mode can only be initiated by the UE by sending the "RRC Connection Request" message to UTRAN. If common transport channels used to exchange messages and data between the UE and UTRAN, the UE is identified by a Radio Network Temporary Identity (RNTI). As can be seen in thefigure above, the UE can be in one of four sub-states, when it is in the RRC connected mode. The sub-states depend on the connectivity level between the UE and UTRAN. The set of usable transport channels depend also on the sub-states. For instance, the DCHs are not available in the sub-states CELL_PCH and CELL_URA. The UE leaves the RRC idle mode when sending the RRC Connection Request message to UTRAN. When UTRAN accepts the UE‘s request, the UE enters either the sub-state CELL_DCH or CELL_FACH.

The RRC connected Mode can be further decomposed into four different states. These four sub-states describe, on which level the UE is known by UTRAN and which resources are allocated by the UE. UTRAN can know any UE either on cell level (cell state) or on URA level (URA state). On the other hand any UE can have a DCH or a FACH or no transport channel for control message

In this sub-state, dedicated physical channels are allocated to the UE. DCCH and – if configured – DTCH information can be transmitted. There no need to identify the UE on a dedicated channel, because the physical channels are exclusively allocated to this UE. UTRAN knows the active set cells for the radio links and thus the location of the the UE. Also downlink shared channels can be allocated to the UE. In this state, the UE is capable to receive RRC messages on the DCCH (and BCCH, if it owns specific capabilities). The cell system information is broadcasted on the FACH. The UE reads the cell system information and acts accordingly. For instance, it determines the measurement quality and the reporting events from the cell system information. This state can only be entered from Cell_FACH by setting up a DCH. When the last DCH is released the UE enters Cell_FACH,Cell_PCH,URA_PCH or idle mode

- read system information broadcast on FACH (applicable only to UEs with certain capabilities and camping on FDD cells);

This state was introduced for traffic situations, where only small amounts of data have to be transmitted. This is the case when only higher layer signalling information (NAS signalling) or small amount of user data (e.g. SMS messages) have to be transmitted. In this case, an exclusive allocation of one physical channel to the UE would result in a waste of resources. Only common transport

can be used by the UE to transmit higher layer data, which it has to share with other UEs. Each UE must be explicitly addressed, for instance by the RNTI. It has to monitor the FACH

. The UE is only connected to one cell, and this is the location information, known within UTRAN. No soft handover takes place in this sub-state. The UE is responsible for cell re-selection. By listening to the cell system information from the BCCH, it gains all relevant measurement qualities, threshold values, neighbourhood lists to perform the cell re-selection process. Other relevant information is also learned from the BCCH. The UE receives RRC messages on the BCCH, CCCH and DCCH channels. Due to the discontinuous type of traffic, UTRAN can command the UE to perform periodic cell updates.

- run timers T305 (periodical cell update), and T317 (cell update when re-entering "in service") or T307 (transition to Idle mode)

RRC Connection Mobility Management and RRC Modes

This state was introduced for traffic situations, where only small amounts of data have to be transmitted. This is the case when only higher layer signalling information (NAS signalling) or small amount of user data (e.g. SMS messages) have to be transmitted. In this case, an exclusive allocation of one physical channel to the UE would result in a waste of resources. Only common transport

can be used by the UE to transmit higher layer data, which it has to share with other UEs. Each UE must be explicitly addressed, for instance by the RNTI. It has to monitor the FACH

. The UE is only connected to one cell, and this is the location information, known within UTRAN. No soft handover takes place in this sub-state. The UE is responsible for cell re-selection. By listening to the cell system information from the BCCH, it gains all relevant measurement qualities, threshold values, neighbourhood lists to perform the cell re-selection process. Other relevant information is also learned from the BCCH. The UE receives RRC messages on the BCCH, CCCH and DCCH channels. Due to the discontinuous type of traffic, UTRAN can command the UE to perform periodic cell updates.

- run timers T305 (periodical cell update), and T317 (cell update when re-entering "in service") or T307 (transition to Idle mode)

The remaining two sub-states – CELL_PCH and URA_PCH – were introduced to cope with inactive data users. Just think about users, who surf in the Internet. After downloading some files, they work with the data, and for a longer time, no transmission takes place. If this is the case, access stratum resources can be released when moving in one of the two states. In both states, no DCCH nor DTCH is allocated to the UE. No exchange of data is possible between the UE and UTRAN. If the UE wants to transmit something, it must move first internally to the sub-state CELL_FACH.

The UE listens to the cell system information, broadcasted on the BCCH. It performs measurements accordingly, and is responsible for cell-reselection. In addition to that, it periodically looks for a PLMN with a higher priority. When UTRAN wants to transmit data to the UE, it must be paged first. Therefore, the UE has to monitor paging occasions on its PICH, i.e. it receives RRC messages

In this sub-state, the UE‘s current cell is known to the RNC. If the RNC wants to exchange data with the UE, it only needs to page the UE there. If the UE changes the cell, itmust perform a cell update. Also periodical cell updates can be requested by UTRAN. To perform updates, the UE must change to the CELL_FACH sub-state. (Please note, that no

This state is comparable to the Cell_PCH,only that the UTRAN knows the UE on URA level. If the UE is in the CELL_PCH and moving fast, a lot of cell updates have to be performed. URAs are a combination of one or several cells under one S-RNC. URAs may overlap, i.e. a cell may belong to several URAs. If UTRAN wants to transmit something to the UE, it must page the UE within the URA. The UE is responsible for URA updates – when it changes the

- run timer T305 for periodical URA update if the UE is in URA_PCH or for periodical cell update if the UE is in CELL_PCH

If the UE is in the RRC connected mode, but not in the CELL_DCH sub-state, it is responsible to inform UTRAN about a detected change of location. The UE then moves (or is) in the CELL_FACH

URA Update Confirm – if it accepts the UE‘s update request. Otherwise, it return the RRC

1. The UE is in the CELL_PCH or URA_PCH sub-state and re-entering the UMTS service area. Then the UE moves to the CELL_FACH state and notifies UTRAN.2. Periodical updates can be enforced by the operator for UEs in the sub-states CELL_FACH, CELL_PCH and URA_PCH.

- The UE has performed cell-reselection. It is camping on a new cell, and UTRAN must be notified about it.

- The UE informs UTRAN about its transition to the CELL_FACH state. Another reason for a CELL_FACH transition is an indication by the UE‘s higher layers, that data has to be

If a cell update takes place, the UE may be requested to modify its RB configuration, TrCH configuration, etc. This must be confirmed by the UE. It may also include a re-



If the UE is in the RRC connected mode, but not in the CELL_DCH sub-state, it is responsible to inform UTRAN about a detected change of location. The UE then moves (or is) in the CELL_FACH

URA Update Confirm – if it accepts the UE‘s update request. Otherwise, it return the RRC

1. The UE is in the CELL_PCH or URA_PCH sub-state and re-entering the UMTS service area. Then the UE moves to the CELL_FACH state and notifies UTRAN.2. Periodical updates can be enforced by the operator for UEs in the sub-states CELL_FACH, CELL_PCH and URA_PCH.

- The UE has performed cell-reselection. It is camping on a new cell, and UTRAN must be notified about it.

- The UE informs UTRAN about its transition to the CELL_FACH state. Another reason for a CELL_FACH transition is an indication by the UE‘s higher layers, that data has to be

If a cell update takes place, the UE may be requested to modify its RB configuration, TrCH configuration, etc. This must be confirmed by the UE. It may also include a re-



Cell and URA updates performed according to the causes in the figure below. As you can see, a periodic update can be done not only, when the UE is in the CELL_PCH or URA_PCH sub-state, but also, when the UE is in the CELL_FACH sub-state. A periodic update is a supervision mechanism, which can be used by the mobile operator to keep track of the UE. If a cell or URA update was performed, a UE in the CELL_FACH sub-state may transit to the sub-states CELL_DCH, CELL_PCH or URA_PCH, or in the RRC mode idle.

periodical cell or URA updates. timer T307 is activated, and the UE starts the cell selection process. If the timer T307 expires, the UE

The timers can be broadcasted with the System Information Block 1 (or as part of the UTRAN Mobility Information message):

If the UE is out of service area, it runs the cell selection process. It keeps the timers T305 running and starts timer T316. The UE attempts to find a serving cell again. If it is successful,It also stops timer T307, in case this timer is active. Being back in the service area can mean, that the UE is served

by the same cell or URA, and no update is required. If the UE is in the service area, but the cell or URA has changed, the cell or URA update has to be initiated by the UE. But what CELL_FACH and starts timer T317. If the UE is back in the service area, it performs

If the UE is out of service area, it performs the cell selection process. The timers T305 is still active, and the UE starts timer T317, if it was not yet active. If the UE enters the service area again, the timer T317 is stopped. Also timer T307 is stopped, when it was active. The UE has to transmit the RRC Cell Update message to UTRAN, indicating the cause of the cell update: re-entering service area. If the timer T317 expires, the UE moves to the idle mode. It releases all dedicated resources.


>>State Transistions Parameters Description (Module II)




>>UE&NodeB Timer and constant Parameters Description (Module II)


Documents

RRC Signalling Procedure.xlsx