4.4 Network elements

23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.4.1 E-UTRAN

E-UTRAN is described in more detail in TS 36.300 [5].

In addition to the E-UTRAN functions described in TS 36.300 [5], E-UTRAN functions include:

– Header compression and user plane ciphering and integrity protection (for user plane data sent across S1-U);

– MME selection when no routing to an MME can be determined from the information provided by the UE;

– UL bearer level rate enforcement based on UE-AMBR and MBR via means of uplink scheduling
(e.g. by limiting the amount of UL resources granted per UE over time);

– DL bearer level rate enforcement based on UE-AMBR;

– UL and DL bearer level admission control;

– Transport level packet marking in the uplink, e.g. setting the DiffServ Code Point, based on the QCI, and optionally the ARP priority level, of the associated EPS bearer;

– ECN-based congestion control.

4.4.2 MME

MME functions include:

– NAS signalling;

– NAS signalling security;

– Inter CN node signalling for mobility between 3GPP access networks (terminating S3);

– UE Reachability in ECM-IDLE state (including control, execution of paging retransmission and optionally Paging Policy Differentiation);

– Tracking Area list management;

– Mapping from UE location (e.g. TAI) to time zone, and signalling a UE time zone change associated with mobility,

– PDN GW and Serving GW selection;

– MME selection for handovers with MME change;

– SGSN selection for handovers to 2G or 3G 3GPP access networks;

– Roaming (S6a towards home HSS);

– Authentication;

– Authorization;

– Bearer management functions including dedicated bearer establishment;

– Lawful Interception of signalling traffic;

– Warning message transfer function (including selection of appropriate eNodeB);

– UE Reachability procedures;

– Support Relaying function (RN Attach/Detach);

– Change of UE presence in Presence Reporting Area reporting upon PCC request,

– in the case of Change of UE presence in Presence Reporting Area reporting, management of Core Network pre-configured Presence Reporting Areas.

– For the Control Plane CIoT EPS Optimisation:

a) transport of user data (IP, Non-IP and Ethernet));

b) local Mobility Anchor point;

c) header compression (for IP user data);

d) ciphering and integrity protection of user data;

e) Lawful Interception of user traffic not transported via the Serving GW (e.g. traffic using T6a).

NOTE: The Serving GW and the MME may be implemented in one physical node or separated physical nodes. For CIoT EPS Optimisation, the Serving GW and the MME can be implemented in one physical node (e.g. C-SGN) or separated physical nodes. The C-SGN can also encompass the PDN GW function.

The MME shall signal a change in UE Time Zone only in the case of mobility and in the case of UE triggered Service Request, PDN Disconnection and UE Detach. If the MME cannot determine whether the UE Time Zone has changed (e.g. the UE Time Zone is not sent by the old MME during MME relocation), the MME should not signal a change in UE Time Zone. A change in UE Time Zone caused by a regulatory mandated time change (e.g. daylight saving time or summer time change) shall not trigger the MME to initiate signalling procedures due to the actual change. Instead the MME shall wait for the UE’s next mobility event or Service Request procedure and then use these procedures to update the UE Time Zone information in the PDN GW.

4.4.3 Gateway

4.4.3.1 General

Two logical Gateways exist:

– Serving GW (S‑GW);

– PDN GW (P‑GW).

NOTE: The PDN GW and the Serving GW may be implemented in one physical node or separated physical nodes.

4.4.3.2 Serving GW

The Serving GW is the gateway which terminates the user plane interface towards E-UTRAN (except when user data is transported using the Control Plane CIoT EPS Optimisation).

For each UE associated with the EPS, at a given point of time, there is a single Serving GW.

The functions of the Serving GW, for both the GTP-based and the PMIP-based S5/S8, include:

– the local Mobility Anchor point for inter-eNodeB handover (except when user data is transported using the Control Plane CIoT EPS Optimisation);

– sending of one or more "end marker" to the source eNodeB, source SGSN or source RNC immediately after the Serving GW switches the path during inter-eNodeB and inter-RAT handover, especially to assist the reordering function in eNodeB.

– Mobility anchoring for inter-3GPP mobility (terminating S4 and relaying the traffic between 2G/3G system and PDN GW);

– ECM-IDLE mode downlink packet buffering and initiation of network triggered service request procedure and optionally Paging Policy Differentiation;

– Lawful Interception;

– Packet routing and forwarding;

– Transport level packet marking in the uplink and the downlink, e.g. setting the DiffServ Code Point, based on the QCI, and optionally the ARP priority level, of the associated EPS bearer;

– Accounting for inter-operator charging. For GTP-based S5/S8, the Serving GW generates accounting data per UE and bearer;

– Interfacing OFCS according to charging principles and through reference points specified in TS 32.240 [51];

– Forwarding of "end marker" to the source eNodeB, source SGSN or source RNC when the "end marker" is received from PDN GW and the Serving GW has downlink user plane established. Upon reception of "end marker", the Serving GW shall not send Downlink Data Notification.

Additional Serving GW functions for the PMIP-based S5/S8 are captured in TS 23.402 [2].

Connectivity to a GGSN is not supported.

4.4.3.3 PDN GW

The PDN GW is the gateway which terminates the SGi interface towards the PDN.

If a UE is accessing multiple PDNs, there may be more than one PDN GW for that UE, however a mix of S5/S8 connectivity and Gn/Gp connectivity is not supported for that UE simultaneously.

PDN GW functions include for both the GTP-based and the PMIP-based S5/S8:

– Per-user based packet filtering (by e.g. deep packet inspection);

– Lawful Interception;

– UE IP address allocation;

– Transport level packet marking in the uplink and downlink, e.g. setting the DiffServ Code Point, based on the QCI, and optionally the ARP priority level, of the associated EPS bearer;

– Accounting for inter-operator charging: for home routed roaming, the P-GW shall collect and report the uplink and downlink data volume (per EPS bearer) as received from and sent to the serving node;

– UL and DL service level charging as defined in TS 23.203 [6]
(e.g. based on SDFs defined by the PCRF, or based on deep packet inspection defined by local policy);

– Interfacing OFCS through according to charging principles and through reference points specified in TS 32.240 [51].

– UL and DL service level gating control as defined in TS 23.203 [6];

– UL and DL service level rate enforcement as defined in TS 23.203 [6]
(e.g. by rate policing/shaping per SDF);

– UL and DL rate enforcement based on APN-AMBR
(e.g. by rate policing/shaping per aggregate of traffic of all SDFs of the same APN that are associated with Non-GBR QCIs);

– DL rate enforcement based on the accumulated MBRs of the aggregate of SDFs with the same GBR QCI
(e.g. by rate policing/shaping);

– DHCPv4 (server and client) and DHCPv6 (client and server) functions;

– The network does not support PPP bearer type in this version of the specification. Pre-Release 8 PPP functionality of a GGSN may be implemented in the PDN GW;

– The PDN GW may support Non-IP data transfer (e.g. with CIoT EPS Optimisations);

– The PDN GW (when acting as a combined PDN GW+SMF as specified in TS 23.501 [83]) may support Ethernet data transfer;

– packet screening;

– sending of one or more "end marker" to the source SGW immediately after switching the path during SGW change;

– PCC related features (e.g. involving PCRF and OCS) as described in TS 23.203 [6].

Additionally the PDN GW includes the following functions for the GTP-based S5/S8:

– UL and DL bearer binding as defined in TS 23.203 [6];

– UL bearer binding verification as defined in TS 23.203 [6];

– Functionality as defined in RFC 4861 [32];

– Accounting per UE and bearer.

The P‑GW provides PDN connectivity to both GERAN/UTRAN only UEs and E‑UTRAN capable UEs using any of E‑UTRAN, GERAN or UTRAN. The P‑GW provides PDN connectivity to E‑UTRAN capable UEs using E‑UTRAN only over the S5/S8 interface.

4.4.4 SGSN

In addition to the functions described in TS 23.060 [7], SGSN functions include:

– Inter EPC node signalling for mobility between 2G/3G and E-UTRAN 3GPP access networks;

– PDN and Serving GW selection: the selection of S‑GW/P‑GW by the SGSN is as specified for the MME;

– Handling UE Time Zone as specified for the MME;

– MME selection for handovers to E-UTRAN 3GPP access network.

4.4.5 GERAN

GERAN is described in more detail in TS 43.051 [15].

4.4.6 UTRAN

UTRAN is described in more detail in TS 25.401 [16].

4.4.7 PCRF

4.4.7.1 General

PCRF is the policy and charging control element. PCRF functions are described in more detail in TS 23.203 [6].

In non-roaming scenario, there is only a single PCRF in the HPLMN associated with one UE’s IP-CAN session. The PCRF terminates the Rx interface and the Gx interface.

In a roaming scenario with local breakout of traffic there may be two PCRFs associated with one UE’s IP-CAN session:

– H-PCRF that resides within the H-PLMN;

– V-PCRF that resides within the V-PLMN.

4.4.7.2 Home PCRF (H-PCRF)

The functions of the H-PCRF include:

– terminates the Rx reference point for home network services;

– terminates the S9 reference point for roaming with local breakout;

– associates the sessions established over the multiple reference points (S9, Rx), for the same UE’s IP-CAN session (PCC session binding).

The functionality of H-PCRF is described in TS 23.203 [6].

4.4.7.3 Visited PCRF (V-PCRF)

The functions of the V-PCRF include:

– terminates the Gx and S9 reference points for roaming with local breakout;

– terminates Rx for roaming with local breakout and visited operator’s Application Function.

The functionality of V-PCRF is described in TS 23.203 [6].

4.4.8 PDN GW’s associated AAA Server

The PDN Gateway may interact with a AAA server over the SGi interface. This AAA Server may maintain information associated with UE access to the EPC and provide authorization and other network services. This AAA Server could be a RADIUS or Diameter Server in an external PDN network, as defined in TS 29.061 [38]. This AAA Server is logically separate from the HSS and the 3GPP AAA Server.

4.4.9 HeNB subsystem

A HeNB subsystem consists of a HeNB, optionally a HeNB GW and optionally a Local GW.

The Local IP Access and SIPTO at the Local Network with L-GW function collocated with the HeNB functions are achieved using a Local GW (L-GW) collocated with the HeNB.

Figure 4.4.9-1 illustrates the architecture for LIPA and/or SIPTO at the Local Network with L-GW function collocated with the HeNB.

Figure 4.4.9-1: Architecture for LIPA or SIPTO at the Local Network with L-GW collocated with the HeNB

NOTE 1: The optional HeNB GW is not shown in the figure for simplicity.

The HeNB subsystem is connected by means of the standard S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME interface and to the Serving Gateway (S-GW) by means of the S1-U interface. When LIPA or SIPTO at the Local Network with L-GW function collocated with the HeNB is activated, the L-GW has a S5 interface with the S-GW.

NOTE 2: In this specification and for simplification the term eNodeB refers to the HeNB subsystem if the UE accesses the network via a HeNB unless stated otherwise.

NOTE 3: Detailed functions of HeNB and HeNB GW are described in TS 36.300 [5].

NOTE 4: An L-GW collocated with a HeNB may support LIPA, or SIPTO@LN, or both.

The Local GW is the gateway towards the IP networks (e.g. residential/enterprise networks, Internet) associated with the HeNB. The Local GW has the following PDN GW functions:

– UE IP address allocation;

– DHCPv4 (server and client) and DHCPv6 (client and server) functions;

– Packet screening;

– Functionality as defined in RFC 4861 [32].

Additionally, the Local GW has the following functions:

– ECM-IDLE mode downlink packet buffering;

– ECM-CONNECTED mode direct tunnelling towards the HeNB.

NOTE 5: The architecture for SIPTO at the Local Network with L-GW function collocated with a HeNB depicted in Figure 4.4.9-1 also applies to SIPTO at the Local Network with L-GW function collocated with an eNodeB.

4.4.10 DeNB

DeNB function is described in more detail in TS 36.300 [5].

DeNB provides the necessary S/P‑GW functions for the operation of RNs connected to the DeNB.

In order to provide the Relay Function the DeNB shall support the following P-GW functions:

– IP address allocation for the UE functionality of the RN;

– Downlink transport level packet mapping between the DSCP value used over S1-U of the UE (which is the SGi interface of the PDN GW function in the DeNB) and the EPS bearers with an appropriate QCI value and optionally ARP priority level value, established between the PDN GW function in the DeNB and the UE function of the RN;

– Uplink transport level packet mapping between QCI value and optionally ARP priority level value, of the EPS bearers (established between the PDN GW function in the DeNB and the UE function of the RN) and the DSCP value used over S1-U of the UE (which is the SGi interface of the PDN GW function in the DeNB).

In order to provide the Relay Function the DeNB shall support the following S-GW functions:

– Termination the S11 session of the MME(RN).

S-GW functions related to ECM-IDLE are not required.

S-GW functions related to mobility management are not supported.

4.4.11 CSG Subscriber Server

CSG Subscriber Server (CSS) is an optional element that stores CSG subscription data for roaming subscribers. The CSS stores and provides VPLMN specific CSG subscription information to the MME. The CSS is accessible from the MME via the S7a interface. The CSS is always in the same PLMN as the current MME.

If the same CSG ID exists in both CSS subscription data and HSS subscription data, the CSG subscription data from the HSS shall take precedence over the data from CSS.

Figure 4.4.11-1 illustrates CSS connected to MME.

Figure 4.4.11-1: CSS connected to MME

4.4.12 RAN Congestion Awareness Function

The RAN Congestion Awareness Function (RCAF) is an element that provides RAN User Plane Congestion Information (RUCI) to the PCRF to enable the PCRF to take the RAN user plane congestion status into account for policy decisions.

The RCAF collects information related to user plane congestion from the RAN’s OAM system based on which the RCAF determines the congestion level (and the identifier) of an eNodeB or E-UTRAN cell.

Via the Nq interface the RCAF determines the UEs served by a congested eNodeB or congested E-UTRAN cell and retrieves the APNs of the active PDN connections of those UEs. The decision whether the RCAF operates on eNodeB or E-UTRAN cell level is up to operator configuration.

Via the Np reference point, the RCAF sends the RUCI to the PCRFs serving the UEs’ PDN connections.

NOTE 1: The details of congestion reporting to the PCRF and the Np reference point are specified in TS 23.203 [6].

NOTE 2: In the case of roaming or RAN sharing as specified in TS 23.251 [24], Np is an inter-operator reference point. Whether Np applies in the case of roaming and RAN sharing is subject to inter-operator agreements.

Figure 4.4.12-1 illustrates the RCAF connected to the MME. The RCAF is located in the same PLMN as the serving MME except in network sharing scenarios where the RCAF belongs to the RAN operator.

Figure 4.4.12-1: RCAF connected to MME

4.4.13 UCMF

The UCMF is used for storage of dictionary entries corresponding to either PLMN-assigned or UE manufacturer-assigned UE Radio Capability IDs. An MME may subscribe with the UCMF to obtain from the UCMF new values of UE Radio Capability ID that the UCMF assigns for the purpose of caching them locally.

Provisioning of UE manufacturer-assigned UE Radio Capability ID entries in the UCMF is performed from an AS that interacts with the UCMF either directly or via the SCEF (or via Network Management) (see TS 23.682 [74] for further information). A UCMF that serves both EPS and 5GS shall require provisioning the UE Radio Capability ID with the TS 38.331 [89] format or the TS 36.331 [37] format or both the formats of the UE radio capabilities.

For PLMN-assigned UE Radio Capability ID the UCMF also is the entity that assigns the UE Radio Capability ID values.

Figure 4.4.13-1: UCMF connected to MME

Each PLMN-assigned UE Radio Capability ID is also associated to the IMEI/TAC of the UE model(s) that it is related to. When an MME requests the UCMF to assign a UE Radio Capability ID for a set of UE radio capabilities, it indicates the IMEI/TAC of the UE that the UE Radio Capability information is related to.

The UCMF may be provisioned with a dictionary of UE manufacturer-assigned UE Radio Capability IDs which include a "Vendor ID" that applies to the Manufacturers of these UE, and a list of IMEI/TACs for which the PLMN has obtained UE manufacturer-assigned UE Radio Capability IDs.

A PLMN-assigned UE Radio Capability IDs is kept in the UCMF storage as long as it is associated with at least a IMEI/TAC value. When a IMEI/TAC value is related to a UE model that is earmarked for operation based on UE manufacturer-assigned UE Radio Capability IDs, this IMEI/TAC value is disassociated in the UCMF from any PLMN assigned UE Radio Capability IDs.

For the case the PLMN is configured to store PLMN assigned IDs in the UE manufacturer-assigned operation requested list defined in clause 5.11.3a, the UCMF does not remove from UE manufacturer-assigned operation requested list any PLMN assigned UE Radio Capability ID no longer used, and rather quarantines it to avoid any future reassignment.

The UCMF stores a Version ID value for the PLMN assigned UE Radio Capability IDs so it is included in the PLMN assigned UE Radio Capability IDs it assigns. This shall be configured in the UCMF.

A UCMF dictionary entry shall include also the related UE Radio Capability for Paging for each RAT.