OEA000210 LTE Signaling and Protocols ISSUE1.04

LTE Signaling and Protocols

Confidential Information of Huawei. No Spreading Without Permission

The above architecture is applied for both FDD and TDD LTE.

In addition to the new air interface, a new base station has also be specified by the 3GPP and is referred to as an eNB (Evolved Node B). These, along with their associated interfaces form the E-UTRAN and in so doing, are responsible for:

RRM (Radio Resource Management) - this involves the allocation to the UE of the physical resources on the uplink and downlink, access control and mobility control.

Date Compression - is performed in both the eNB and the UE in order to maximize the amount of user data that can be transferred on the allocated resource. This process is undertaken by PDCP.

Data Protection - is performed at the eNB and the UE in order to encrypt and integrity protect RRC signaling and encrypt user data on the air interface.

Routing - this involves the forwarding of Control Plane signaling to the MME and User Plane traffic to the S-GW (Serving - Gateway).

Packet Classification and QoS Policy Enforcement - this involves the marking of uplink packets based upon subscription information or local service provider policy. QoS (Quality of Service) policy enforcement is then responsible for ensuring such policy is enforced at the network edge.



The MME is the Control Plane entity within the EPC and as such is responsible for the following functions:

NAS Signaling and Security - this incorporates both EMM (Evolved Mobility Management) and ESM (Evolved Session Management) and thus includes procedures such as Tracking Area Updates and EPS Bearer Management. The MME is also responsible for NAS security.

S-GW and PDN-GW Selection - upon receipt of a request from the UE to allocate a bearer resource, the MME will select the most appropriate S-GW and PDN-GW. This selection criterion is based on the location of the UE in addition to current load conditions within the network.

Tracking Area List Management and Paging - whilst in the LTE Idle state, the UE is tracked by the MME to the granularity of a Tracking Area. Whilst UEs remain within the Tracking Areas provided to them in the form of a Tracking Area List, there is no requirement for them to notify the MME. The MME is also responsible for initiating the paging procedure.

Inter MME Mobility - if a handover involves changing the point of attachment within the EPC, it may be necessary to involve an inter MME handover. In this situation, the serving MME will select a target MME with which to conduct this process.

Authentication - this involves interworking with the subscribers HSS (Home Subscriber Server) in order to obtain AAA (Access Authorization and Accounting) information with which to authenticate the subscriber. Like that of other 3GPP system, authentication is based on AKA (Authentication and Key Agreement).

The S-GW terminates the S1-U Interface from the E-UTRAN and in so doing, provides the following main functions:

Downlink Packet Buffering - when traffic arrives for a UE at the S-GW, it may need to be buffered in order to allow time for the MME to page the UE and for it to enter the LTE Active state.

Packet Routing and Forwarding - traffic must be routed to the correct eNB on the downlink and the specified PDN-GW on the uplink.



The PDN-GW is the network element which terminates the SGi Interface towards the PDN (Packet Data Network). If a UE is accessing multiple PDNs, there may be a requirement for multiple PDN-GWs to be involved. Functions associated with the PDN-GW include:

Packet Filtering - this incorporates the deep packet inspection of IP datagrams arriving from the PDN in order to determine which TFT (Traffic Flow Template) they are to be associated with.

IP Address Allocation - IP addresses may be allocated to the UE by the PDN-GW. This is included as part of the initial bearer establishment phase or when UEs roam between different access technologies.

Transport Level Packet Marking - this involves the marking of uplink and downlink packets with the appropriate tag e.g. DSCP (Differentiated Services Code Point) based on the QCI (QoS Class Identifier) of the associated EPS bearer.

Accounting - through interaction with a PCRF (Policy Rules and Charging Function), the PDN-GW will monitor traffic volumes and types.

HSS (Home Subscriber Server) - this can be considered a master database within the PLMN. Although logically it is considered as one entity, the HSS in practice is made up of several physical databases depending upon subscriber numbers and redundancy requirements. The HSS holds variables and identities for the support, establishment and maintenance of calls and sessions made by subscribers. It is connected to the MME via the S6a Interface which uses the protocol Diameter.

PCRF (Policy and Charging Rules Function) - this supports functionality for policy control through the PDF (Policy Decision Function) and charging control through the CRF (Charging Rules Function). As such, it provides bearer network control in terms of QoS and the allocation of the associated charging vectors. The PCRF downloads this information over the Gx Interface using the Diameter protocol.



Control plane provides the signaling processing function for both RRC(Radio Resource Control) and NAS (Non-Access Stratum).

RRC signaling is responsible for the radio resource management. Its terminated between UE and eNodeB.

NAS signaling is terminated between UE and MME forwarded by eNodeB through S1 interface. Its encapsulated into RRC signaling on the air interface transmission.



User plane provides tunnels for data communication between UE and P-GW, and no service is terminated in E-UTRAN or EPC. E-UTRAN and EPC only forward the data to internet or other elements ( such as IMS for VoIP ).



AP: Application Part



Before UE read PDSCH and PUSCH, it should first decoding PDCCH which is scrambled by the specific UE ID in eNodeB called RNTI. Above table shows all kinds of RNTI and corresponding scenarios.

P-RNTI and SI-RNTI are common IDs used in all the cells for every UE.



A unique International Mobile Subscriber Identity (IMSI) shall be allocated to each mobile subscriber in the GSM/UMTS/EPS system.

MCC: Mobile Country Code

MNC: Mobile Network Code

MSIN: Mobile Subscriber Identification Number

NMSI: National Mobile Subscriber Identity There is a one-to-one mapping between TMSIs and IMSIs within a VLR. The TMSI is

allocated by the MSC or VLR, and will be reallocated if routing information is updated. The TMSI consists of 4 octets. The P-TMSI is allocated by the SGSN, and is valid only within a routing area. It will be

reallocated during an RAU. The P-TMSI consists of 3 octets. The S-TMSI is a simple expression of the GUTI, thereby improving the efficiency in

radio signaling processes, such as paging and serving requesting processes. The MME uses the S-TMSI for paging. =

The M-TMSI identifies a UE between the UE and MME. The mapping between the M-TMSI and IMSI is known only to the associated UE and MME.



MCC

Not more than 15 digits

3 digits 2 or 3

MNC MSINNMSI

IMSI

The purpose of the GUTI is to provide an unambiguous identification of the UE that does not reveal the UE or the user's permanent identity in the Evolved Packet System (EPS). It also allows the identification of the MME and network. It can be used by the network and the UE to establish the UE's identity during signalling between them in the EPS.

The GUTI has two main components:

one that uniquely identifies the MME which allocated the GUTI;

one that uniquely identifies the UE within the MME that allocated the GUTI.

Within the MME, the mobile shall be identified by the M-TMSI.

The Globally Unique MME Identifier (GUMMEI) shall be constructed from the MCC, MNC and MME Identifier (MMEI).

The MMEI shall be constructed from an MME Group ID (MMEGI) and an MME Code (MMEC).

The GUTI shall be constructed from the GUMMEI and the M-TMSI.



Note: Upon receiving a PLMN selection request from the NAS, the RRC layer responds only after the UE camps on a cell.



Invisible: Untraced by network tracing software.

Partial visible: traced at layer 2 of Uu interface which cant be traced by Huawei LMT ( ocal maintenance terminal ).

Visible: traced at layer 3 of Uu interface, which can be traced by Huawei LMT.



The following PLMN lists are maintained by UE:

RPLMN: The RPLMN is the PLMN on which the UE has performed a location registration successfully by TA update.

EPLMN: The Equivalent PLMN (EPLMN) list is a list of PLMNs considered as equivalents to Registered PLMNs (RPLMNs) in terms of service provisioning. During PLMN selection, a UE preferentially selects a PLMN from the list. The EPLMN list plus RPLMN is sent from the EPC and stored in the UE during an Attach procedure and TA update. An EPLMN list can contain more than one EPLMN.

EHPLMN: An Equivalent Home PLMN (EHPLMN) is an equivalent to the HPLMN, and takes precedence over the HPLMN.

HPLMN: The Home PLMN (HPLMN) is the PLMN in which the UE is defined. Each UE belongs to only one HPLMN.

UPLMN: User controlled PLMN list, it is a file stored in USIM.



Background: When a UE moves to a different country, two VPLMNs are available for GSM and LTE services. In addition, roaming is available between the HPLMN and these VPLMNs.

Q1: Which PLMN does the UE register with? Q2: What role does the CN play in PLMN selection?

Answer to Q1: There is no relationship between PLMN selection and roaming. After being powered on, the UE selects a PLMN in the following order: RPLMN > HPLMN > User controlled PLMN (UPLMN) > Operator controlled PLMN (OPLMN) > VPLMN

The RPLMN is a PLMN with which the UE registered during the latest network access. RPLMN lists are stored in the UE. The UE is responsible for synchronizing the RPLMN list with the RPLMN list stored in the USIM or SIM card. The information about RPLMN access technologies (ACTs) is also stored in the UE. Information about UPLMN and OPLMN lists and the related ACTs is stored in separate dedicated data files of the USIM/SIM card. UEs identify and parse these files from the USIM/SIM card for PLMN selection. Information about the HPMN and its actions is stored in another dedicated data file of the USIM/SIM card. A UE selects a VPLMN using the related VPLMN selection mechanism. Each PLMN type corresponds to an ACT, except for the VPLMN.

Answer to question 2:The CN nodes, such as the MME/SGW and HSS, are not involved in PLMN selection. After a UE selects a PLMN, the EPC performs mobility management, authentication, and encryption when the UE attempts to register with the PLMN.



The cell search is associated with PLMN selection, we can treat those two as one integrated step after UE power-on. Our slide split them into two parts in order to detail each of them.



Cell search is a procedure in which a UE achieves time and frequency synchronization with a cell, obtains the physical cell identifier (PCI), and learns the RX signal quality and other information about the cell based on the PCI.

The detailed cell search procedure is as following:

The UE monitors the P-SCH to achieve clock synchronization with a maximum synchronization error of 5 ms. The UE determines the cell identity in a cell identity group based on the mapping between cell identities and primary synchronization signals.

The UE monitors the S-SCH to achieve frame synchronization, that is, time synchronization with the cell. Cell identity groups have a one-to-one relationship with secondary synchronization signals. Therefore, the UE acquires the number of the cell identity group to which the cell identity belongs by monitoring the S-SCH.

The UE monitors the Broadcast Channel (BCH) to acquire other information about the cell

The UE determines the PCI based on the cell identity and the cell identity group number.

The UE monitors the downlink reference signal to acquire the RX signal quality in the cell



During the cell search process, the UE performs time and frequency synchronization with a cell and obtains the PCI of the cell. Based on the PCI, the UE obtains signal quality in the cell and other cell information. During cell selection and reselection, a UE searches for cells on all the available frequencies.

In the LTE system, SCHs are specially used for cell search. There are two types of SCH: P-SCH and S-SCH. The UE searches for a suitable cell on SCHs using the following steps:

The UE monitors the P-SCH for clock synchronization with a maximum synchronization offset of 5 ms. By monitoring the P-SH, the UE obtains the PCI. There is one-to-one mapping between PCIs and PSSs.

The UE monitors the S-SCH for time synchronization with the cell. By monitoring the S-SCH, the UE obtains the cell identity group ID of the PCI. There is one-to-one mapping between cell identity group IDs and SSSs.

The UE detects downlink reference signals to obtain the signal quality in the cell.

The UE obtains other cell information by monitoring the BCH.




LTE SAE System Overview

11 SIBs are defined in 3GPP Release 8 and 13 SIBs in 3GPP Release 9.

Mandatory SIB: SIB1 and SIB2.



ETWS: Earthquake and Tsunami Warning System

CMAS: Commercial Mobile Alert System (CMAS), also known as the Personal Localized Alerting Network (PLAN), is an alerting network designed to disseminate emergency alerts to mobile devices such as cell phones and pagers.

MBMS: Multimedia Broadcast Multicast Service



Please list the type of system message One MIB and 13 SIBs.

What are the major information included in each message?

Which message delivers system downlink and uplink bandwidth?MIB and SIB2.



MIB system frame number, DL bandwidth and PHICH configuration

SIB1 Cell selection and camp related parametersSI period for other SIBs

SIB2 Common physical channel configuration, UE timer, uplink bandwidth

SIB3 Common parameters for cell reselection

SIB4 Intra-frequency neighbor list; Neighbor reselection parameters; Neighbor black list

SIB5

Inter-frequency list and corresponding cell reselection parameters

Inter-frequency neighbor list and corresponding cell reselection parameters

Inter-frequency black list

SIB6 UMTS frequency list and neighbor list

SIB7 GSM frequency list and neighbor list

SIB8 CDMA2000 frequency list and neighbor list

SIB9 Home eNodeB information

SIB10 ETWS primary notification

SIB11 ETWS secondary notification

SIB12 CMAS notification

SIB13 MBMS control information

When a UE transits from the connected mode to the idle mode or after it selects a PLMN, the UE must select a cell to camp on. When the UE transits from the connected mode to the idle mode, it first attempts to select the last cell that it camped on in connected mode or select a suitable cell on the frequency that is allocated through the RRC Connection Release message. If such a cell is not available, the UE attempts to find a suitable cell by performing the Stored Information Cell Selection procedure. If the UE fails to find a suitable cell, the UE performs the Initial Cell Selection procedure.

Stored information cell selection:

The Stored Information Cell Selection procedure requires stored information on carrier frequencies and information on cell parameters. The information is obtained from previously received measurement control information elements or from previously detected SI messages of cells. This information can help speed up cell selection.

The Stored Information Cell Selection procedure is as follows: On the known carrier frequency, the UE searches for a suitable cell. If the UE finds a suitable cell, it selects that cell to camp on. If the UE fails to find a suitable cell, it initiates the Initial Cell Selection procedure.

Initial Cell Selection:

The Initial Cell Selection procedure is as follows: The UE scans all RF channels in the E-UTRAN bands according to its capabilities in order to find a suitable cell. On each carrier frequency, the UE searches for the strongest cell only. If the UE finds a suitable cell, it selects that cell to camp on. If the UE fails to find a suitable cell, it selects an acceptable cell to camp on.



A UE considers an E-UTRAN cell as a suitable cell only when the measured RSRP and reference signal received quality (RSRQ) values of the cell are greater than the receive (RX) level threshold and the RX signal quality threshold for the cell, respectively.

An E-UTRAN cell becomes a suitable cell when both the following conditions are met:

Srxlev > 0 Squal > 0

Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminoffset) Pcompensation

Squal = Qqualmeas - (QQualMin + QQualMinOffset)

Parameter Description

Qrxlevmeas Measured RSRP value

Qrxlevmin Minimal Required Rx level (dBm) in SIB1

Qrxlevminoffset Offset to Srxlev, relative with PLMN priority ,.QrxlevminOffset is only applied when a cell is evaluated for cell selection as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN in SIB1

Pcompensation max (PMaximum allowed power PUE MAX Output Power, 0), where PMaximum allowed power is sent in SIB1

Qqualmeas measured RX signal quality (RSRQ value) of the cell, expressed in units of dB.

Qqualmin Minimal required signal quality

QQualMinOffset Offset to Qqualmin, relative with PLMN priority ,.QrxlevminOffset is only applied when a cell is evaluated for cell selection as a result of a periodic search for a higher priority PLMN while camped normally in a VPLMN in SIB1



Case 1: initial RRC connection establishment. When a UE is changed from RRC_IDLE mode to RRC_CONNECTED mode, the UE initiates RA.

Case 2: RRC connection reestablishment. When a radio link fails, the UE needs to reestablish RRC connection. In this case, the UE initiates RA.

Case 3: handover. When a UE performs handover, the UE initiates RA in the target cell.

Case 4: downlink data arrival. When an eNodeB needs to transmit downlink data to a UE in RRC_CONNECTED mode and finds that the UE is in the uplink synchronization loss state, the eNodeB instructs the UE to initiate RA.

Case 5: uplink data arrival. When a UE in RRC_CONNECTED mode needs to transmit uplink data to an eNodeB and finds that it is in the uplink synchronization loss state, the UE initiates RA.

Case 6: When UE initiates location service, it trigger RA.



The RA-RNTI associated with the PRACH in which the Random Access Preamble is transmitted, is computed as:

RA-RNTI = 1 + t_id + 10 * f_id

Where t_id is the index of the first subframe of the specified PRACH (0 t_id

RRC_IDLE

The upper layer configures DRX for a specific UE.

The eNodeB performs UE controlled mobility management.

In RRC_IDLE mode, the UE performs the following operations:

Monitors a paging channel for incoming calls, system information updates, and ETWS notifications (only available to ETWS-capable UEs).

Performs neighboring cell measurements and cell reselection.

Detects system information.

RRC_CONNECTED

Transmits data sent from the UE.

In the lower layer, the UE can be configured with dedicated DRX.

eNodeB controlled mobility management, including handover and NACC to GERAN

In RRC_CONNECTED mode, the UE performs the following operations:

Detects the paging channel and SIB1 for system information updates as well as ETWS notifications (available only for ETWS-capable UEs)

Monitors control channels associated with shared channels.

Provides channel quality and feedback information.

Measures neighboring cells and sends measurement reports to eNodeBs.

Detects system information.



The NAS enables the UE and MME to exchange signaling between each other.

In E-UTRAN, NAS messages can be encapsulated in RRC messages.

NAS protocols include the EMM and EPS protocols. EPS Mobility Management (EMM) protocol

Processes signaling related to UE mobility and encryption. EPS Session Management (ESM) protocol

Processes signaling related to default bearers and dedicated user-plane bearers.

The EMM states indicate the mobility management states in different mobility management procedures, such as attach and TAU.

Both the MME and UE store the NAS states of the UE. The UE stores its EMM state assumed by the UE itself and the MME stores the EMM state of the UE assumed by the MME. In most cases, the EMM state stored in a UE is consistent with that stored in the MME. This does not apply in some temporary occasions, for example, when the MME performs implicit detach.

The ECM states indicate the NAS connectivity between a UE and the EPC.

ECM and EMM states are independent from each other. UEs can switch from the EMM-REGISTERED state to the EMM-DEREGISTERED state at any time, regardless of the ECM state. However,the ECM state is valid only after a UE switches from the EMM-DEREGISTERED state to the EMM-REGISTERED state.

ECM ( EPS Connection Management )



NAS states indicate the connectivity between a UE and an MME. Based on UE registration states and states of dedicated S1 connections, NAS states are classified into the following states:

EMM-DEREGISTERED

When a UE is in the EMM-DEREGISTERED state, the MME does not have the UE context or location and routing information and cannot provide services for the UE, that is to say, the MME cannotmanage the UE in this state. A UE is working in the EMM-DEREGISTERED state when being powered off.

UE contexts can be stored in the UE and MME, preventing authentication from being performed every time the UE attaches to the network.

EMM-REGISTERED

UEs enter this state after successfully attaching to the network. When a UE is in the EMM-REGISTERED state, the MME creates and stores the UE context, then in this state, the MME knows about the UE location or TA and can provide services to the UE.

ECM-IDLE

When a UE is in the ECM-IDLE state, no NAS connection is established between the UE and the MME. In addition, no UE context is stored on the eNodeB and no S1-MME or S1-U connection is available.

ECM-CONNECTED

When a UE is in the ECM-CONNECTED state, a NAS connection is established between the UE and the MME and the eNodeB creates and stores the UE context. The MME informs a UE in this state of the serving eNodeB ID.




EMM procedures:

Attach - this is used by the UE to attach to an EPC (Evolved Packet Core) for packet services in the EPS (Evolved Packet System).

Tracking Area Updating - this procedure is always initiated by the UE and is used for the various purposes. The most common include normal and periodic tracking area updating

Detach - this is used by the UE to detach from EPS services. In addition, it can also be used for other procedures such as disconnecting from non-EPS services

Identification - this is used by the network to request a particular UE to provide specific identification parameters, e.g. the IMSI (International Mobile Subscriber Identity) or the IMEI (International Mobile Equipment Identity).

Authentication - this is used for AKA (Authentication and Key Agreement) between the user and the network.

Security Mode Control - this is used to take an EPS security context into use, and initialize and start NAS signaling security between the UE and the MME with the corresponding NAS keys and security algorithms.

GUTI Reallocation - this is used to allocate a GUTI (Globally Unique Temporary Identifier) and optionally to provide a new TAI (Tracking Area Identity) list to a particular UE. Service Request - this is used by the UE to get connected and establish the radio and S1 bearers when uplink user data or signaling is to be sent.



Extended Service Request - this is used by the UE to initiate a Circuit Switched fallback call or respond to a mobile terminated Circuit Switched fallback request from the network.

Paging - this is used by the network to request the establishment of a NAS signaling connection to the UE. Is also includes the Circuit Switched Service Notification

EMM Status - this is sent by the UE or by the network at any time to report certain error conditions.

EMM Information - this allows the network to provide information to the UE.

ESM Procedures:

Default EPS Bearer Context Activation - this is used to establish a default EPS bearer context between the UE and the EPC.

Dedicated EPS Bearer Context Activation - this is to establish an EPS bearer context with specific QoS (Quality of Service) and TFT (Traffic Flow Template) between the UE and the EPC. The dedicated EPS bearer context activation procedure is initiated by the network, but may be requested by the UE by means of the UE requested bearer resource allocation procedure.

EPS Bearer Context Modification - this is used to modify an EPS bearer context with a specific QoS and TFT.

EPS Bearer Context Deactivation - this is used to deactivate an EPS bearer context or disconnect from a PDN by deactivating all EPS bearer contexts to the PDN.


UE Requested PDN Connectivity - this is used by the UE to request the setup of a default EPS bearer to a PDN.

UE Requested PDN Disconnect - this is used by the UE to request disconnection from one PDN. The UE can initiate this procedure to disconnect from any PDN as long as it is connected to at least one other PDN.

UE Requested Bearer Resource Allocation - this is used by the UE to request an allocation of bearer resources for a traffic flow aggregate.

UE Requested Bearer Resource Modification - this is used by the UE to request a modification or release of bearer resources for a traffic flow aggregate or modification of a traffic flow aggregate by replacing a packet filter.

ESM Information Request - this is used by the network to retrieve ESM information, i.e. protocol configuration options, APN (Access Point Name), or both from the UE during the attach procedure.

ESM Status - this is used to report at any time certain error conditions detected upon receipt of ESM protocol data.



The preceding figure shows the connection management process. When a UE requests services, performs TAUs, or is paged, it performs random access to the network. After the random access process is complete, control-plane connections, including the RRC connection and dedicated S1 connection, are set up between the UE and the MME. The RRC connection is routed between the UE and the eNodeB, and the dedicated S1 connection is routed between the eNodeB and the MME. If the control-plane connections are set up due to service requests, the MME instructs the eNodeB to set up the E-RAB. Then, the eNodeB performs the radio bearer management function to set up, modify, or release control-plane connections.

UE connections include signaling connections and radio bearers.

Signaling connection

In signaling connection setup, signaling connections, including RRC and dedicated S1 connections, have been set up before the security control mode is activated.

Signaling connection setup starts with the RRC connection setup under UE requests. After the RRC connection is set up, the eNodeB sets up a dedicated S1 connection to the MME over the S1 interface. After the dedicated S1 connection is set up, the UE can exchange signaling with the MME.



During the signaling connection release process, the MME releases the E-RAB and dedicated S1 connection in sequence. The signaling connection release is typically initiated by the MME. The MME can also release the dedicated S1 connection to release all S1 resources.

Radio bearer

Radio bearer management involves E-RAB setup and release after the security control mode is activated, including the setup, modification, and release of the DRB and the setup and modification of SRB2. Note that radio bearer management does not involve the SRB2 release. The SRB2 and SRB1 are released simultaneously in the signaling connection release process.



Signaling connection procedures involve setting up a signaling connection between the UE and the MME, releasing the signaling connection and service bearers, and processing NAS messages between the UE and the MME.




Functions of RRC

Broadcast of system information:

Common NAS information

Information applicable to UEs in RRC_IDLE mode, such as cell selection and reselection parameters, and neighboring cell information

Information applicable to UEs in RRC_CONNECTED mode, such as common channel configuration information

ETWS notifications

RRC connection control

Paging

Setup, modification, and release of RRC connections, allocation and modification of UE identifiers (C-RNTI), setup, modification, and release of SRB1 and SRB2, and access barring types

Initial security activation, including initial configuration of AS integrity protection (SRBs) and AS encryption (SRBs and DRBs)

Mobility in RRC connected mode, including intra- and inter-frequency handovers, security processing, cipher key and algorithm changes, and RRC context information transmitted between nodes

DRB setup, modification, and release


Radio configuration control, including assignment and modification of ARQ, HARQ, and DRX configurations

QoS control, including assignment and modification of the following items: Allocation and modification of semi-persistent scheduling (SPS) configurations in the downlink and uplink, and allocation of the priority and a prioritized bit rate (PBR) for each resource bearer in the uplink

Rectification of radio link failures

Inter-RAT mobility, including security activation and transfer of RRC context information

Measurement configuration and reporting

Setup, modification, and release of measurements, such as intra-frequency, inter-frequency, and inter-RAT measurements

Setup and release of measurement gaps

Measurement reporting

Other functions, such as the transport of dedicated NAS information and non-3GPP information, transport of radio access performance information, and support of E-UTRAN sharing

Universal protocol-compliant error processing

Self-configuration and self-optimization

Resource bearers are classified into SRBs and DRBs according to carried information.

SRBs carry signaling in the control plane. There are three types of SRBs:

SRB0: Carries RRC signaling on a common control channel (CCCH) in transparent mode (TM) at the Radio Link Control (RLC) layer before the RRC connection is set up.

SRB1: Carries RRC signaling (which may include NAS messages) and pre-SRB2-setup non-access stratum (NAS) messages on a dedicated control channel (DCCH) in acknowledged mode (AM) at the RLC layer.

SRB2: Carries NAS signaling on a DCCH in AM mode at the RLC layer. SRB2 has a lower priority than SRB1, and SRB2 can be set up only after the security mode is activated.

DRBs carry data in the user plane. A maximum of eight DRBs can be set up between a UE and the eNodeB.



In physical layer, all the RRC signalings except system information block are carried by PDSCH and PUSCH. This is the biggest differences with legacy network, and it simplifies the channel classification.



SRB0: Bears RRC signaling before the RRC connection is set up.

SRB2 is set up after AS encryption.



SRB1: Bears RRC signaling (that may include NAS signaling messages) and NAS signaling transmitted before SRB2 is set up, which means before AS encryption.



NAS messages is transmitted via four RRC messages in Radio Bearer.

RRC Connection Setup Complete.

RRC Connection Reconfiguration.

UL Information Transfer.

DL Information Transfer.



After a UE is powered on, it attempts to register with the EPC. The UE can run services only when it successfully registers with the EPC and attaches to the network. During network attach, the MME obtains information about UE location and capability. In addition, a default bearer is set up to enable always-online connectivity and an IP address is assigned to the UE. If dynamic PCC is deployed, the P-GW obtains the PCC rule of the default bearer from the PCRF or in preconfigured mode.

PCC (Policy and Charging Control )



The RRC connection is a layer 3 connection between the UE and eNodeB, and its setup is initiated by the UE. During RRC connection setup, SRB1 is set up.

Before an S1 connection is established, the eNodeB cannot obtain the UE context from the EPC. Therefore, the security mode does not need to be activated during the RRC connection setup and encryption or integrity protection is not applied to SRB1. During RRC connection setup, the UE can be configured to perform measurements. However, the UE can receive handover commands only after the security mode is activated.

An RRC connection setup procedure is as follows:1. The UE sends the eNodeB an RRC Connection Request message containing an

RRC connection setup cause value on the CCCH. For details about the RRC connection setup cause values, see the preceding table. Note: The RRC Connection Request message contains the UE ID. If the upper layer provides the S-TMSI, the UE signals the S-TMSI to the eNodeB. If no S-TMSI is available, the UE signals a random value ranging from 0 to 240-1 to the eNodeB. In the LTE system, the UE's IMSI information is unknown to the eNodeB.

2. The eNodeB setup an RRC connection. 3. The eNodeB performs admission control and resource allocation for SRB1.

If resource allocation fails, the eNodeB sends an RRC Connection Reject message to the UE. If resource allocation succeeds, go to the next step.

4. The eNodeB sends an RRC Connection Setup message to the UE over the CCCH. The message contains SRB1 resource configuration.

5. The UE performs radio resource configurations and then sends the eNodeB an RRC Connection Setup Complete message containing NAS messages.

6. After the eNodeB receives the RRC Connection Setup Complete message, the RRC connection is setup.



IE added within the release 10 version of the specifications:

The Globally Unique MME Identity (GUMMEI) Type information was added within the release 10 version of the specifications. This can be signalled using values of native or mapped. The native value indicates that the GUMMEI has been assigned by the Evolved Packet Core (EPC), whereas the mapped value indicates that the GUMMEI has been derived from 2G/3G identifiers. This information can impact the selection of an MME for the UE.

The Radio Link Failure Information Available flag was added within the release 10 version of the specifications. This flag can be used for the mobility robustness optimisation component of Self Organising Networks (SON).

The Logged Measurements Available flag was added within the release 10 version of the specifications. This flag can be used to indicate that information is available to be reported for the Minimisation of Drive Tests (MDT).

The Relay Node Subframe Configuration Requested information element was also added within the release 10 version of the specifications. It is used to indicate that the RRC connection establishment is for a relay node. It is also used to indicate whether or not the relay node would like a subframe configuration to be allocated, i.e. when included, it can be signalled using values of required or not required.



UE Identity

The UE identity is signalled using the SAE Temporary Mobile Subscriber Identity (S-TMSI) if the UE is registered with the Tracking Area to which the current cell belongs. Otherwise, the UE selects a random number in the range from 0 to 240 - 1 to represent the UE identity.

Establishment Cause

Emergency

TheEmergency cause value is used if the EPS Attach Type within the Attach Request message is set to EPS Emergency Attach. The Emergency cause value can also be used if the higher layers within the UE indicate the requirement to establish emergency bearer services, even when the EPS Attach Type is not set to EPS Emergency Attach.

High Priority Access

For these NAS procedures initiated by UEs of access class 12, 13 or 14 in their home country, the RRC establishment cause will be set to "High priority access AC 11 15". For this purpose the home country is defined as the country of the MCC part of the IMSI, see 3GPP TS 22.011 [1A].



For these NAS procedures initiated by UE of access class 11 or 15 in their HPLMN (if the EHPLMN list is not present or is empty) or EHPLMN (if the EHPLMN list is present), the RRC establishment cause will be set to "High priority access AC 11 15".

Delay Tolerant Access (3GPP release 10)

TheDelay Tolerant Access cause value is used if the UE has been configured for low priority NAS signaling. This RRC establishment cause was introduced within the release 10 version of the 3GPP specifications. The concept of low priority NAS signaling is intended to provide a mechanism for congestion control, i.e. low priority signaling is dropped prior to higher priority signaling during periods of congestion. The NAS Signaling Priority Tag within the USIM defines whether or not the device has been configured for low priority NAS signaling. This priority can also be used to impact charging, i.e. devices using low priority signaling could be charged less. Machine to machine type communications could use low priority signaling if their traffic is primarily background and best effort.



In the case of the Attach procedure, theMobile Originating Signaling cause value is used by default.

In the case of the Detach procedure, the Mobile Originating Signaling cause value is used.

In the case of the Tracking Area Update procedure:

The Mobile Originating Signaling cause value is used by default

The Delay Tolerant Access cause value is used if the UE has been configured for low priority NAS signaling

The Emergency cause value is used if the UE already has a Packet Data Network (PDN) connection established for emergency bearer services, or if the UE is establishing a PDN connection for emergency bearer services

In the case of the Service Request procedure:

The Mobile Originating Signaling cause value is used by default when the Service Request is used to request either user plane radio resources or uplink signaling resources

The Delay Tolerant Access cause value is used when the Service Request is used to request either user plane radio resources or uplink signaling resources, and the UE has been configured for low priority NAS signaling.

The Mobile Terminating Access cause value is used when the Service Request is a response to paging where the core network domain indicator is set to Packet Switched (PS).



The Emergency cause value is used if the Service Request is being used to request user plane radio resources for emergency bearer services, or if the Service Request is triggered by a PDN connectivity request with an emergency cause value.

In the case of the Extended Service Request procedure:

The Mobile Originating Data cause value is used by default if the Extended Service Request is used for mobile originating CS fallback.

The Delay Tolerant Access cause value is used for mobile originating CS fallback and packet services via the S1 when the UE has been configured for low priority NAS signaling.

The Mobile Terminating Access cause value is used by default if the Extended Service Request is used for packet services via S1. It is also used when the Extended Service Request is used for mobile terminating CS fallback.

The Emergency cause value is used if the Extended Service Request is being used for a mobile originating CS fallback emergency call. It is also used if the Extended Service Request is being used for packet services via S1 when requesting radio resources for emergency bearer services.

In all cases, the RRC establishment cause is set to High Priority Access if the UE uses Access Class (AC) 11 to 15 within its home PLMN.

The UE starts the T300 timer after transmitting the RRC Connection Request message. The value of T300 is broadcast within SIB 2.UMTS uses T300 in combination with N300 to manage retransmissions of the RRC Connection Request message. LTE does not have an N300 parameter and the RRC layer sends the RRC Connection Request message only once per establishment procedure. HARQ retransmissions from the MAC layer can be used to improve the reliability of transferring the RRC Connection Request and RRC Connection Setup messages. LTE uses the T300 timer to define how long the UE waits for a response to the RRC Connection Request message. The establishment procedure fails if T300 expires before receiving an RRC Connection Setup message. The procedure also fails if the UE completes a cell re-selection prior to receiving the RRC Connection Setup message.



Authentication and NAS-specific security mode are performed as follows:

1. The MME sends the UE an AUTH REQ message containing RAND and AUTN fields.

2. The UE responds with an AUTH RES message containing RES parameters.

3. The MME initiates the security mode procedure upon receiving the AUTH RES message. If the MME does not receive the AUTH RES message, it responds with an AUTH REJ message.

4. Upon receiving a NAS SMC message, the UE:

(1) Uses the Selected NAS security algorithms IE in the NAS SMC message to calculate KnasEnc and KnasInt cipher keys.

(2) Checks whether the UE security capabilities and KSI IEs are valid. If they are valid, the UE responds with a Security Mode Complete message to the MME. If they are invalid, the UE responds with a SECURITY MODE REJECT message.



When NAS or non-3GPP indication information is to be transferred, the UE in RRC_CONNECTED mode initiates the uplink information transfer process by sending a UL Information Transfer message, except in the RRC connection setup process with the RRC Connection Setup Complete message containing NAS information. When CDMA2000 information is to be delivered, the UE initiates the uplink information transfer process only after SRB2 has been set up.

The dedicatedInfoType IE in a UL Information Transfer message is set as follows:

If NAS information is to be transferred, the dedicatedInfoType IE contains dedicatedInfoNAS.

If CDMA2000 1xRTT information is to be transferred, the dedicatedInfoType IE contains dedicatedInfoCDMA2000-1XRTT.

If CDMA2000 HRPD information is to be transferred, the dedicatedInfoType IE contains dedicatedInfoCDMA2000-HRPD.

Then, the UL Information Transfer message is delivered to the lower layer for transmission.



Multiple E-RABs, including the default bearer, are set up during the UE context setup. Besides, UE context information related to security, handover policies, and UE capability are specified. With the initial UE contexts set up, the UE RRC mode switches from RRC_IDLE mode to RRC_CONNECTED mode and the UE ECM mode switches from ECM_IDLE mode to ECM_REGISTERED mode. In addition, the security mode configuration for the UE is completed.

The EPC must be prepared to receive user-plane data on an E-RAB before the MME receives a Context Setup Response message from an eNodeB.

Upon receiving an Initial Context Setup Request message, the eNodeB:

Attempts to configure the E-RAB as required by the EPC.

Saves the UE aggregate maximum bit rate in the UE context and adopts the UE aggregate maximum bit rate on non-GBR bearers.

Saves the handover restriction list in the UE context.

Saves UE capability information in the UE context.



MME UE S1AP ID and eNB UE S1AP ID is used to identify the unique S1 dedicated signaling connection.



The RRC_SECUR_MODE_CMD and RRC_SECUR_MODE_CMP messages are used for encryption on the AS. While the identity, authentication, and security procedures are used for encryption on the NAS.

SRB1 and SRB2 use the same integrity protection algorithm, and all RBs use the same encryption algorithm. SRB0 is not subject to integrity protection or encryption.

During RRC signaling handling, some security configurations are applied, including the integrity protection algorithm, encryption algorithm, and fields keyChangeIndicator and nextHopChainingCount. Fields keyChangeIndicator and nextHopChainingCount are used to determine the cipher key on the AS when the UE is handed over or an RRC connection is reestablished.

Integrity protection and encryption of RRC signaling are activated simultaneously. The null encryption algorithm eea0 may also be used.

The null integrity protection algorithm eia0 applies only to UEs running limited services. The null integrity protection algorithm requires the null encryption algorithm.

Note: If an RRC message fails the integrity check, the bottom layer discards the RRC message and reports this check failure to the RRC layer.



Three cipher keys derived from the KeNodeB algorithm are used on the AS: KRRCint for integrity protection of RRC signaling, KRRCenc for encryption of RRC signaling, and KUPenc for encryption of user data. The KeNodeB algorithm is based on the KASME algorithm and is processed by the upper layer.

During RRC connection setup, a new AS cipher key is derived without AS parameters being used.

In a handover, the source eNodeB applies integrity protection and encryption on the RRC messages used for handover execution based on the pre-handover security settings.

The integrity protection and encryption algorithms are changed only when a handover is performed. The four cipher keys, including KeNodeB, KRRCint, KRRCenc, and KUPenc, are changed every time a handover is performed or an RRC connection is reestablished. The keyChangeIndicator field is used in a handover to indicate whether the UE should use a cipher key related to the KASME key used recently. When a new key KeNodeB is derived to create the KRRCint, KRRCenc, and KUPenc keys, the UE uses nextHopChainingCount in the handover or RRC connection reestablishment.

nextHopChainingCount is reserved for each RB separately in the uplink and downlink. For details, see 3GPP TS 36.323. For each DRB, the count is used as the input of the encryption algorithm. For each SRB, the count is used as the input of the encryption and integrity protection algorithm. The same counter value cannot be used for multiple times for an given cipher key. To prevent null signaling, some messages or data packets contain the PDCP SN. For details, see 3GPP TS 36.323. In addition, HFN (TX_HFN and RX_HFN) is used as the overflow counter mechanism. For details, see 3GPP TS 36.323. The HFN must be synchronized between the UE and eNodeB. The eNodeB prevents the repeated use of the count configured with the same resource bearer ID and KeNodeB. When a large amount of data is to be transmitted, the eNodeB sets up or releases new radio bearers. If resource bearers are consecutively set up, the eNodeB uses different IDs to identify these resource bearers and to trigger switching from the RRC_CONNECTED mode to the RRC_IDLE mode and back to the RRC_CONNECTED mode.

AES: Advanced Encryption Standard, The algorithm described by AES is a symmetric-key algorithm, meaning the same key is used for both encrypting and decrypting the data.

SNOW 3G is word-based synchronous stream ciphers

Following descriptions are from Protocol 33401



Each EPS Integrity Algorithm (EIA) will be assigned a 4-bit identifier. Currently, the following values have been defined:

"00002" EIA0 Null Integrity Protection algorithm

"00012" 128-EIA1 SNOW 3G

"00102" 128-EIA2 AES

The remaining values have been reserved for future use.

UEs and eNBs shall implement 128-EIA1 and 128-EIA2 for RRC signalling integrity protection.

UEs and MMEs shall implement 128-EIA1 and 128-EIA2 for NAS signalling integrity protection.

Each EPS Encryption Algorithm (EEA) will be assigned a 4-bit identifier. Currently, the following values have been defined for NAS, RRC and UP ciphering:

"00002" EEA0 Null ciphering algorithm

"00012" 128-EEA1 SNOW 3G based algorithm

"00102" 128-EEA2 AES based algorithm

The remaining values have been reserved for future use.

UEs and eNBs shall implement EEA0, 128-EEA1 and 128-EEA2 for both RRC signalling ciphering and UP ciphering.

UEs and MMEs shall implement EEA0, 128-EEA1 and 128-EEA2 for NAS signalling ciphering.



When a UE attaches to the network, the eNodeB requests UE capability information from the UE. Then, the eNodeB reports the UE capability information received from the UE to the EPC for storage over the S1 interface using the UE capability indication procedure. The S1AP_INITIAL_CONTEXT_SETUP_REQ message delivered by the EPC does not contain UE capability information.

When a UE switches from the RRC idle mode to the RRC connected mode, the EPC informs the eNodeB of UE capability information using an S1AP_INITIAL_CONTEXT_SETUP_REQ message. In this scenario, the eNodeBdoes not need to request UE capability information from the UE, reducing resource usage over the radio interface.

During network attach, the E-RAB cannot be set up if the UE capability query procedure fails.

Function of the UE capability query procedure

This procedure enables the UE to transfer UE capability information to the eNodeB.

Initiated by

The eNodeB initiates the UE capability query procedure. Upon receiving a UE capability query request from the eNodeB, the UE reports the supported RAT types to the eNodeB. In 3GPP specifications released in 2009 Q1, the group features function is added to query the function list supported by a UE.



If the E-UTRAN access capability of a UE is changed, the UE requests the upper layer to initialize some specified NAS procedures, which enables the eNodeB to update information about the UE capability when an RRC connection is set up. For details about the initialization of some specified NAS procedures, see 3GPP TS 23.401.

Reception of the UE Capability Enquiry message by the UE The UE sets the contents of the UE Capability Information message as follows:

If ue-CapabilityRequest includes eutra, the UE includes UE-EUTRA-CapabilityRAT-Container within ue-CapabilityRAT-Container and sets rat-Type to eutra.

If ue-CapabilityRequest includes geran-ps and the UE supports the GERAN PS domain, the UE includes the UE radio access capabilities for GERAN PS within ue-CapabilityRAT-Container and sets rat-Type to geran-ps.

If ue-CapabilityRequest includes geran-ps and the UE supports the GERAN PS domain, the UE includes the UE radio access capabilities for GERAN PS within ue-CapabilityRAT-Container and sets rat-Type to geran-ps.

If ue-CapabilityRequest includes utra and if the UE supports UTRA, the UE includes the UE radio access capabilities for UTRA within ue-CapabilityRAT-Container and sets rat-Type to utra.

If ue-CapabilityRequest includes cdma2000-1XRTT and the UE supports CDMA2000 1xRTT, the UE includes the UE radio access capabilities for CDMA2000 within ue-CapabilityRAT-Container and sets rat-Type set to cdma2000-1XRTT.



The following table describes UE categories.

UECategory

Total DL-SCH bits received per TTI

DL max. No. of layers for spatial mux.

Total UL-SCH bits transmitted

per TTI

Uplink Support for

64QAM

Total L2 buffer size

(bytes)

1 10296 1 5160 No 150 000

2 51024 2 25456 No 700 000

3 102048 2 51024 No 1 400 000

4 150752 2 51024 No 1 900 000

5 299552 4 75376 Yes 3 500 000

6 [R10] 301504 2 or 4 51024 No 3 300 000

7 [R10] 301504 2 or 4 102048 No 3 800 000

8 [R10] 2998560 8 1497760 Yes 42 200 000



RRC connections are reconfigured to, for example, set up, modify, or release radio bearers, to perform handovers, and to prepare for, modify, or abort measurements. In this procedure, NAS dedicated information can be transmitted from E-UTRAN to the UE.

Initiation E-UTRAN initiates the RRC connection reconfiguration process towards a UE

in RRC_CONNECTED mode. The RRC Connection Reconfiguration message contains mobilityControlInfo

only when AS security has been activated. In this process, SRB2 and at least one DRB are set up and not suspended.

The RRC connection procedure involves RB setup only when AS security has been activated. SRB1 is set up during RRC connection setup.)

Reconfiguration failure If the UE cannot reconfigure RRC connections in compliance with parameter

settings in the RRC Connection Reconfiguration message, the RRC connections with original parameter settings are retained. If security control is not activated, the UE exits the RRC_CONNECTED mode with the cause value "other". If the UE reconfigures RRC connections in compliance with parameter settings in the RRC Connection Reconfiguration message, new RRC connections are set up.

Radio bearer management is performed after encryption and integrity protection start. Radio bearer management involves setting up and modifying SRB2 and DRBs, and releasing DRBs. SRB2 is released during the signaling connection release process.



After AS security mode setup, eNodeB initials RRC reconfiguration procedure to setup SRB2. In the message, eNodeB also send the NAS PDU to instruct UE to activate EPS bearer, so we can also find default DRB setup in this procedure.



This reconfiguration procedure delivers intra-frequency measurement parameters for handover. The following IEs (Information Element) are included inside:

Measurement object, indicate the object with unique frequency and ID

Report configuration, indicate the related event to period report parameters. A1/A2/A3 could be included.

Measurement ID, bind the ID with object and report configuration, thus eNodeB can understand the purpose of each report.

Quantity configuration, including the measurement filter parameters



The signaling connection release process can be initiated by the MME or eNodeB. When services are complete on the NAS between the UE and MME or the UE requests the MME to terminate services, the MME sends the eNodeB a UE Context Release Command message to initiate the signaling connection release process. When an eNodeB detects an abnormal event, the eNodeB sends a UE Context Release Request message to the MME.

The signaling connection release process is described as follows: The eNodeB releases transmission resources and initiates an RRC connection

release process over the Uu interface. The eNodeB sends the UE an RRC Connection Release message to release

radio resources, without requiring the UE to respond to this message. The eNodeB releases radio resources. The eNodeB sends a UE Context Release Complete message to the MME,

indicating that resources are released. Then, the eNodeB releases UE context. After the eNodeB releases the UE context,

the UE switches from RRC_CONNECTED mode to RRC_IDLE mode. After the dedicated S1 connection is released, all the S1 resources, including service

bearer resources, are released. The eNodeB keeps checking whether a UE transmits or receives data within the time

specified by the UeInactiveTimer parameter. If the time eclipses and the UE does not transmit or receive data, the eNodeB sends a UE Context Release Request message to the MME.

When the MME initiates load balancing, the MME reconfigures its relative capacity and then sends the reconfiguration result to the eNodeB. Upon receive the reconfiguration result, the eNodeB does not select the MME for RRC connection establishment. If an RRC connection is released due to load balancing initiated by the MME, the eNodeB redirects the UE to another cell in the LTE system or in another RAT system.



1. Upon detecting that an S1 connection needs to be released, the eNodeB sends the MME an S1 UE Context Release Request message to trigger the S1 connection release process. The cause value can be O&M intervention, unspecified failure, user inactivity, repeated integrity checking failure, or release due to UE-generated signaling connection release.

Note: Step 1 is applicable only when the eNodeB initiates the S1 connection release process. The S1 connection release process initiated by the MME begins with step 2.

2. The MME sends a Release Access Bearers Request message, requesting the S-GW to release all S1-U bearers related to the UE. Upon receiving the message, the S-GW deletes information only about eNodeB IP address and TEID related to the S1-U bearers. and then responds with a Release Access Bearers Response message.

3. Upon receiving the Release Access Bearers Response message from the S-GW, the MME sends an S1 UE Context Release Command message containing a specific cause value to the eNodeB.

4. If the RRC connection still exists, it needs to be released. Upon receiving an acknowledgement from the UE, the eNodeB releases the UE context.

5. The eNodeB sends an S1 UE Context Release Complete message to the MME, confirming that the S1 connection has been released.



When a UE attaches to the target network, a default bearer is set up. In the EPS, many default bearers exist. If no data is transmitted on these default bearers, resources allocated to these default bearers, especially radio resources, need to be released using the S1 connection release process.

In the S1 connection release process, all the user-plane bearers and the control-plane S1 connections between eNodeB and MME are released. Then, the UE switches from RRC_CONNECTED mode to RRC_IDLE mode and disconnects from the EPC, and the eNodeB releases all UE context information.

After the S1 connection release process is complete, all radio resources and S1-U connections are released. If the UE needs to transmit data to the PDN, it initiates the service request process. If the PDN needs to transmit data to the UE, the MME initiates the paging procedure.



Please review the major step for initial attachment.

What is the relevant ID for control plane and user plane on each interface?



interface Control Plane User Plane

S1 S1 AP UE ID TEID

X2 X2 AP UE ID TEID

Uu RA-RNTI, TC-RNTI, C-RNTI, SPS-CRNTI, P-RNTI, SI-RNTI

C-RNTI, SPS-CRNTI

In the EPS, bearers are the basic QoS control unit.

The EPS bearer is used to transmit all the service flows associated with the same QoS policy between UE and an S-GW. All the service flows transmitted on the same EPS bearer are subject to the same data transmission treatment related to scheduling, queue management, transmission rate restrictions, and RLC configurations. If two service data flow require different QoS policies, different EPS bearers need to be set up for these service data flows.



Dedicated bearer setup Dedicated bearers are required between a UE and the EPC when the UE

needs to run services. Dedicated bearers can be set up only upon the request of the MME. UEs

can request the MME to set up dedicated bearers. During network attach, only one default bearer can be set up for each data card while

for VoIP-capable LG terminals and some smart terminals provided by suppliers such as HTC, dedicated bearers are also set up.

The EPS bearer traffic flow template (TFT) is the set of all packet filters associated with that EPS bearer.For detail, please refer to protocol 23401.

An UpLink Traffic Flow Template (UL TFT) is the set of uplink packet filters in a TFT.

A DownLink Traffic Flow Template (DL TFT) is the set of downlink packet filters in a TFT.

Every dedicated EPS bearer is associated with a TFT. The UE uses the UL TFT for mapping traffic to an EPS bearer in the uplink direction. The PCEF (for GTP-based S5/S8) or the BBERF (for PMIP-based S5/S8) uses the DL TFT for mapping traffic to an EPS bearer in the downlink direction.



EPS bearers are classified into the following types based on bit rate guarantee:

Non-GBR(Guaranteed Bit Rate) bearers

Non-GBR bearers are not permanently allocated dedicated network resources to ensure the bit rate.

GBR bearers

GBR bearers are permanently allocated dedicated network resources to ensure the bit rate.

EPS bearers are classified into the following types based on the setup time:

Default bearer

A user bearer for data and signalings with the default QoS class. It provides best-effort IP connectivity.

According to 3GPP TS 23.401, when the UE initially accesses the PDN, the MME sets up a default bearer between the UE and the P-GW in the initial UE context setup process. The default bearer remains established until the UE exits the PDN, providing always-on IP connectivity for the UE and ensuring a low delay when the UE attempts to run services.

The default bearer is a non-GBR bearer.



Dedicated bearer

Dedicated bearers are SAE bearers used for specific services. In most cases, dedicated bearers have higher QoS requirements than default bearers.

Apart from the default bearer, all other bearers between the UE and the same PDN are dedicated bearers. When a UE requests a service and the default bearer does not meet QoS requirements, a dedicated bearer is required.

Dedicated bearers can be GBR or non-GBR bearers.



Meaning of always-online: From the E2E point of view, after a UE registers with an MME, the MME stores valid routing information of the UE, which enables connections to the UE can be set up at any time. If no data is transmitted over the radio interface for a long time, radio connections are released but the connection between the UE and the EPC remains established and the latest valid routing information is stored. When data needs to be transmitted, only radio connections need to be established, quickening the switchover from RRC_IDLE mode to RRC_CONNECTED mode. "Always-on" does not mean that the entire E2E connection between UEs or between the UE and the P-GW remains established at any time.

The always-online characteristic applies to UMTS and EPS, but has different meanings, which can be observed in the network attach procedure.

For UMTS, when the UE attaches to the network in the PS domain and is authenticated, the UE context is established on the SGSN and UE location information is stored in the HSS. Though the UE has attached to the network, the GGSN does not assign an IP address to the UE, and the UE is working in PMM-connected mode and SM-inactive mode. If the UE attempts to run services, it initiates the PDP context activation procedure by sending a PDP context activation message containing the target APN and other necessary IP parameters. The SGSN selects the serving GGSN for the UE based on the resolved APN, and then the GGSN assigns an IP address to the UE. When the IP address is assigned, an IP connection is set up to transmit and receive data, as shown in Figure "Switchover between PMM states and SM states (for 3G networks)". If the UE attempts to run services with different QoS policies or wants to set up service connections using other APNs, it needs to activate more PDP contexts.



To optimize UE access to the network, the network attach process in the EPS can be regarded as the combination of UMTS network attach and PDP context activation. It also involves the set up of an IP connection (default bearer). To some extent, the default bearer has similar functions as the PDP context used in UMTS. After the UE attaches to the EPS network, the UE enters EMM-REGISTERED mode, the default bearer has been set up, and the S-GW and P-GW have been selected for the UE. During network attach, the P-GW assigns an IP address to the UE when or after the default bearer is set up, as shown in the preceding figure.

If the UE needs to transmit data to the same PDN and the default bearer meets the QoS requirements, the UE uses the default bearer for data transmission, avoiding PDP context activation.

The default bearer remains established for always-on PDN connectivity after the UE registers with the EPS, even when all the radio and S1 bearers are released. The default bearer is released only when the UE detaches from the network.

The default bearer is a non-GBR bearer and meets the default QoS requirements.



The EPS provides various PS services, such as videophone, voice, video, web browsing, and email services.

Different service types have different QoS requirements.

For the EPS, QoS parameters include the QCI and ARP.

Each QCI is characterized by priority, packet delay budget, and acceptable packet loss rate.

Bearers can be classified into GBR and non-GBR bearers based on the QoS that these bearer provide.

For GBR bearers, the GBR and MBR are used to control the bit rate.

For non-GBR bearers, the AMBR is used to control the bit rate.

The ARP of a bearer is used to decide whether the requested bearer can be established or modified in case of radio congestion.



QoS parameters related to the EPS bearer

QoS Parameter Description

QCI

3GPP specifications define nine QCIs for services to standardize QoS requirements. Each QCI specifies a set of requirements for the resource type, priority, delay, and packet loss rate of a service type. QCIs are transmitted among EPS nodes, thereby eliminating the need for negotiation and delivery of a large number of QoS parameters. The EPS performs QoS control by using QCIs.

Service data flows with different QCIs are transported on different EPS bearers.

ARP

ARP indicates an EPS bearer's priority for resource allocation and retention. Based on the ARP, the eNodeB decides whether the requested bearer should be set up or modified when network resources are limited and whether a bearer should be released when the network is congested.

GBR

MBR

The GBR specifies the bit rate that can be ensured on a bearer and the MBR specifies the maximum bit rate that can be provided on the bearer.

The GBR and MBR are used for bandwidth management on GBR bearers. By using methods such as resource reservation, the eNodeB transports data flows when the bit rate is lower than or equal to the GBR, and discards data flows when the bit rate exceeds the MBR. When the bit rate is higher than the GBR but is lower than the MBR, the eNodeB processes the data flow based on network conditions. If the network is congested, the eNodeB discards the data flow. If the network is not congested, the eNodeB transports the data flow.

UE-AMBR

APN-AMBR

The eNodeB does not allow the aggregate bit rate of a data stream group to exceed the AMBR using traffic limitation. Multiple EPS bearers can use the same AMBR. AMBRs are categorized as follows:

APN-AMBR: The APN-AMBR limits the aggregate bit rate that can be provided across all non-GBR bearers of the same APN.

UE-AMBR: The UE-AMBR limits the aggregate bit rate that can be provided across all Non-GBR bearers of a UE.



The QCI is characterized by the priority, packet delay budget, and packet error loss rate.

QCI specifies the bearer-level packet forwarding priority.

The preceding table describes the standardized QCIs.



The ARP shall contain information about the priority level (scalar), the pre-emption capability (flag) and the pre-emption vulnerability (flag). The primary purpose of ARP is to decide whether a bearer establishment / modification request can be accepted or needs to be rejected due to resource limitations (typically available radio capacity for GBR bearers). For details, see 3GPP TS 25.413.



GBR bearers are applicable to realtime services, such as voice, video, realtime gaming services. GBR bearers are dedicated bearers. For a GBR bearer, a fixed amount of bandwidth resources are preserved, regardless of whether the resources are used or not. Each GBR bearer is associated with a GBR and MBR. The MBR is the maximum bit rate that can be achieved by GBR bearers. The data flows with a bit rate higher than the MBR are discarded. Currently, the MBR equals the GBR.

Non-GBR bearers are applicable to non-realtime services, such as email, FTP, and HTTP services. For a non-GBR bearer, no fixed amount of bandwidth resources are preserved, and therefore traffic is not ensured. Non-GBR bearers may experience packet losses when the network is congested. No transmission bandwidth resources can be preserved for non-GBR bearers. Non-GBR bearers are associated only with the AMBR and operators can use the AMBR for bandwidth resource allocation control. When no data is transmitted on the other EPS bearer, data flows on a non-GBR bearer can be transmitted at the associated AMBR. The AMBR limits the total bit rate of all the bearers associated with an AMBR. The APN-AMBR is provided on the P-GW and UE. The UE-AMBR is provided on the eNodeB.



The AMBR mechanism helps improve the bearer resource efficiency. When multiple non-GBR bearers are set up for a UE or APN and some of these non-GBR bearers do not carry services, the other non-GBR bearers share the entire AMBR resources.

The APN-AMBR limits the aggregate bit rate that can be provided across all non-GBR bearers related to all PDN connections on the same APN.

The UE-AMBR is the aggregate maximum bit rate that are expected on all the non-GBR bearers related to a UE.

Different AMBRs are defined in the uplink and downlink, including the uplink APN-AMBR, downlink APN-AMBR, uplink UE-AMBR, and DL UE-AMBR.



In GPRS/UTRAN, QoS is subscribed in HLR. For each PDP context, separated QoSshould be assigned. That is, you need to set different values like bit rate, delay etc. for each PDP context in each APN.

In EPS, the QoS is subscribed in HSS and PCRF.

The HSS only contains QoS profile for default bearer that established while users attach the network.

If the QoS for default bearers can not meet the requirement for a certain service (for example, the default bearer can not satisfy the delay need for VoIP service), UE may request to establish a dedicated bearer. The PDN GW that determines the QoS of the dedicated bearer based on the authorized QoSreceived from the PCRF. So there is no need to have specific subscription parameters for dedicated bearers in the HSS.



UE request the MME to setup a dedicated bearer, the UE NAS sends an RRC_MM_DATA_REQ message containing the Bearer Resource Modification message to the UE RRC layer. Upon receiving the RRC_MM_DATA_REQ message, the UE RRC layer sends the Bearer Resource Modification message to the MME transparently through the eNodeB.

Upon receiving the Bearer Resource Modification message from the UE, the MME sends a Bearer Setup Request message to the eNodeB, which then sends the UE an RRC Connection Reconfiguration message containing the Active Dedicate Bearer Request message. Then, the UE RRC sends the UE NAS an RRC_MM_DATA_IND message containing the Active Dedicate Bearer Request message.

After internal processing, the UE NAS sends the UE RRC layer an RRC_MM_DATA_REQ message containing an Active Dedicate Bearer Accept message. The UE RRC layer sends the eNodeB an RRC Connection Reconfiguration Complete message to the eNodeB, and then sends the eNodeB an UL Information Transfer message containing an Activated Dedicated EPS Bearer Context Accept message.



The E-RAB setup procedure is used to establish the UE dedicated bearer. If new servicesare required after the completion of the UE context access, the E-RAB setup is initiated.NAS signaling is exchanged in the E-RAB setup process. During the NAS signalingexchange, service parameters are negotiated on the NAS for AS resource allocation.

Several E-RABs are set up during the E-RAB setup procedure. The E-RAB setup processcan be initiated by the UE or the MME. When a UE attempts to run new services or theMME needs to set up new services for the UE, an E-RAB can be set up using thededicated bearer activation process on the NAS. In the dedicated bearer activationprocess, the UE and MME negotiate QoS information with each other. Based on the QoSinformation, the eNodeB allocates resources to the UE and completes the E-RAB setupprocess.

The E-RAB setup process is described as follows: If new services are required after the initial UE context setup, the UE applies for the

dedicated bearers through the NAS signaling from the MME. In response to the Uplink NAS Transport message, the MME allocates dedicated bearers

to the UE based on the NAS signaling and sends an E-RAB Setup Request message tothe eNodeB. The E-RAB Setup Request message contains the E-RAB setup list,including the E-RAB ID, QoS information of the bearers, the configuration information ofthe transport layer, and NAS information.

In response to the E-RAB Setup Request message, the eNodeB allocates resources tothe UE based on the RRM algorithm. The resources include transmission, radio,scheduling, power, and antenna resources. Then, the eNodeB sends an RRC ConnectionReconfiguration message to the UE.

The UE configures parameters based on the allocated resources and sends an RRCConnection Reconfiguration Complete message, informing the eNodeB that theconfiguration is complete.

The eNodeB sends the MME an E-RAB Setup Response message, indicating that the E-RAB setup process is complete.



Several E-RABs can be modified in an E-RAB modification process initiated by the UE or MME. If service attributes need to be modified, the eNodeB allocates bearer resources to the UE based on the new QoS information negotiated between the UE and MME, and modifies the E-RAB.

The E-RAB setup process is described as follows: If new services are required after the initial UE context and E-RABs are set up, the UE

requests the MME to set up dedicated bearers by sending NAS signaling. The MME allocates dedicated bearers to the UE based on the service modification

information delivered in the Uplink NAS Transport message, and delivers the E-RAB Modify Request message to the eNodeB. The E-RAB Setup Request message contains the E-RAB setup list, including the E-RAB ID, QoS information of the bearers, the configur

OEA000210 LTE Signaling and Protocols ISSUE1.04

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