ETSI TS 136 420 V10.0.0 (2011-01) Technical Specification LTE; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 general aspects and principles (3GPP TS 36.420 version 10.0.0 Release 10) 3GPP TS 36.420 version 10.0.0 Release 10 1 ETSI TS 136 420 V10.0.0 (2011-01) Reference RTS/TSGR-0336420va00 Keywords LTE ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16 Siret N° 348 623 562 00017 - NAF 742 C Association à but non lucratif enregistrée à la Sous-Préfecture de Grasse (06) N° 7803/88 Important notice Individual copies of the present document can be downloaded from: http://www.etsi.org The present document may be made available in more than one electronic version or in print. In any case of existing or perceived difference in contents between such versions, the reference version is the Portable Document Format (PDF). 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ETSI 3GPP TS 36.420 version 10.0.0 Release 10 3 ETSI TS 136 420 V10.0.0 (2011-01) Contents Intellectual Property Rights ................................................................................................................................ 2 Foreword ............................................................................................................................................................. 2 Foreword ............................................................................................................................................................. 4 1 Scope. ....................................................................................................................................................... 5 2 References ................................................................................................................................................ 5 3 Definitions, symbols and abbreviations ................................................................................................... 5 3.1 Definitions .......................................................................................................................................................... 5 3.2 Symbols .............................................................................................................................................................. 5 3.3 Abbreviations ..................................................................................................................................................... 5 4 General aspects ......................................................................................................................................... 6 4.1 Introduction ........................................................................................................................................................ 6 4.2 X2 interface general principles ........................................................................................................................... 6 4.3 X2 interface specification objectives .................................................................................................................. 6 4.3.1 General .......................................................................................................................................................... 6 4.3.2 Addressing of eNBs over the X2 interface ................................................................................................... 6 4.4 X2 interface capabilities ..................................................................................................................................... 6 4.4.1 Radio application related signalling .............................................................................................................. 6 4.4.2 X2 tunnels ..................................................................................................................................................... 7 4.5 X2 interface characteristics ................................................................................................................................ 7 4.5.1 Uses of SCTP ................................................................................................................................................ 7 4.5.1.1 General .................................................................................................................................................... 7 5 Functions of the X2 interface ................................................................................................................... 7 5.1 Function list ........................................................................................................................................................ 7 5.2 Function description ..................................................................................................................................... 7 5.2.1 Intra LTE-Access-System mobility support for ECM-CONNECTED UE ................................................... 7 5.2.1.1 Context transfer from source eNB to target eNB .................................................................................... 8 5.2.1.2 Control of user plane transport bearers between source eNB and target eNB ........................................ 8 5.2.1.3 Handover cancellation ............................................................................................................................. 8 5.2.1.4 UE context release in source eNB ........................................................................................................... 8 5.2.2 Load management ......................................................................................................................................... 8 5.2.3 Inter-cell interference coordination ............................................................................................................... 8 5.2.3.1 Uplink interference load management .................................................................................................... 8 5.2.3.2 Downlink interference avoidance ............................................................................................................ 8 5.2.4 General X2 management and error handling functions ................................................................................ 8 5.2.4.1 Error indication ....................................................................................................................................... 8 5.2.4.2 Reset ........................................................................................................................................................ 8 5.2.5 Trace functions ............................................................................................................................................. 9 5.2.6 Application level data exchange between eNBs ........................................................................................... 9 6 X2 interface protocols and protocol structure .......................................................................................... 9 6.1 General ............................................................................................................................................................... 9 6.2 Radio signalling protocols .................................................................................................................................. 9 6.2.1 X2AP protocol .............................................................................................................................................. 9 6.3 User plane protocol ............................................................................................................................................ 9 6.3.1 Tunnelling protocol GTP-U .......................................................................................................................... 9 7 Other X2 interface specifications ........................................................................................................... 10 7.1 E-UTRAN X2 interface: X2 layer 1 (TS 36.421)............................................................................................. 10 7.2 E-UTRAN X2 interface: X2 signaling transport (TS 36.422) ......................................................................... 10 7.3 E-UTRAN X2 interface: X2 application protocol (X2AP) (TS 36.423) .......................................................... 10 7.4 E-UTRAN X2 interface: X2 data transport (TS 36.424) .................................................................................. 10 7.5 Summary of E-UTRAN X2 interface Technical Specifications ....................................................................... 11 Annex A (informative): Change history ............................................................................................... 12 History .............................................................................................................................................................. 13 ETSI 3GPP TS 36.420 version 10.0.0 Release 10 4 ETSI TS 136 420 V10.0.0 (2011-01) Foreword This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP). The contents of the present document are subject to continuing work within the TSG and may change following formal TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an identifying change of release date and an increase in version number as follows: Version x.y.z where: x the first digit: 1 presented to TSG for information; 2 presented to TSG for approval; 3 or greater indicates TSG approved document under change control. y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections, updates, etc. z the third digit is incremented when editorial only changes have been incorporated in the document. ETSI 3GPP TS 36.420 version 10.0.0 Release 10 5 ETSI TS 136 420 V10.0.0 (2011-01) 1 Scope. The present document is an introduction to the TSG RAN TS 36.42x series of UMTS Technical Specifications that define the X2 interface. It is an interface for the interconnection of two E-UTRAN NodeB (eNB) components within the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) architecture [2]. 2 References The following documents contain provisions which, through reference in this text, constitute provisions of the present document. • References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific. • For a specific reference, subsequent revisions do not apply. • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document. [1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications". [2] 3GPP TS 36.401: "E-UTRAN architecture description". [3] 3GPP TS 36.421: "X2 layer 1". [4] 3GPP TS 36.422: "X2 signaling transport". [5] 3GPP TS 36.423: "X2 application protocol (X2AP)". [6] 3GPP TS 36.424: "X2 data transport". 3 Definitions, symbols and abbreviations 3.1 Definitions For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1]. E-RAB: Defined in [2]. 3.2 Symbols For the purposes of the present document, the following symbols apply: 3.3 Abbreviations For the purposes of the present document, the abbreviations given in TR 21.905 [x] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1]. ECM EPS Connection Management E-RAB E-UTRAN Radio Access Bearer ETSI 3GPP TS 36.420 version 10.0.0 Release 10 6 ETSI TS 136 420 V10.0.0 (2011-01) X2-C X2 Control plane 4 General aspects 4.1 Introduction The interface allowing to interconnect eNBs with each other is referred to as the X2 interface. 4.2 X2 interface general principles The general principles for the specification of the X2 interface are as follows: - the X2 interface should be open; - the X2 interface shall support the exchange of signalling information between two eNBs, in addition the interface shall support the forwarding of PDUs to the respective tunnel endpoints; - from a logical standpoint, the X2 is a point-to-point interface between two eNBs within the E-UTRAN. A point- to-point logical interface should be feasible even in the absence of a physical direct connection between the two eNBs. 4.3 X2 interface specification objectives 4.3.1 General The X2 interface specifications shall facilitate the following: - inter-connection of eNBs supplied by different manufacturers; - support of continuation between eNBs of the E-UTRAN services offered via the S1 interface; - separation of X2 interface Radio Network functionality and Transport Network functionality to facilitate introduction of future technology. 4.3.2 Addressing of eNBs over the X2 interface - 4.4 X2 interface capabilities 4.4.1 Radio application related signalling The X2 interface provides capability to support radio interface mobility between eNBs, of UEs having a connection with E-UTRAN. ETSI 3GPP TS 36.420 version 10.0.0 Release 10 7 ETSI TS 136 420 V10.0.0 (2011-01) 4.4.2 X2 tunnels 4.5 X2 interface characteristics 4.5.1 Uses of SCTP 4.5.1.1 General The SCTP is used to support the exchange of X2 Application Protocol (X2AP) signalling messages between two eNBs A single SCTP association per X2-C interface instance shall be used with one pair of stream identifiers for X2-C common procedures. Only a few pairs of stream identifiers should be used for X2-C dedicated procedures. The upper limit for the number of stream identifiers for dedicated procedures is FFS. Source-eNB communication context identifiers that are assigned by the source-eNB for X2-C dedicated procedures, and target-eNB communication context identifiers that are assigned by the target-eNB for X2-C dedicated procedures, shall be used to distinguish UE specific X2-C signalling transport bearers. The communication context identifiers are conveyed in the respective X2AP messages. 5 Functions of the X2 interface 5.1 Function list The list of functions on the X2 interface is the following: - Intra LTE-Access-System Mobility Support for ECM-CONNECTED UE: - Context transfer from source eNB to target eNB; - Control of user plane transport bearers between source eNB and target eNB; - Handover cancellation; - UE context release in source eNB. - Load Management - Inter-cell Interference Coordination - Uplink Interference Load Management; - General X2 management and error handling functions: - Error indication; - Reset. - Application level data exchange between eNBs - Trace functions 5.2 Function description 5.2.1 Intra LTE-Access-System mobility support for ECM-CONNECTED UE This function allows the eNB to handover the control of a certain UE to another eNB. ETSI 3GPP TS 36.420 version 10.0.0 Release 10 8 ETSI TS 136 420 V10.0.0 (2011-01) 5.2.1.1 Context transfer from source eNB to target eNB This function allows transferring information required to maintain the E-UTRAN services for an UE in ECM- CONNECTED from source to target eNB. 5.2.1.2 Control of user plane transport bearers between source eNB and target eNB This function allows establishing and releasing transport bearers between source and target eNB to allow for data forwarding. At most one user plane transport bearer per E-RAB allocated to the UE may be established for relaying DL data received from the EPC from the source eNB to the target eNB. At most one user plane transport bearer per E-RAB allocated to the UE may be established for relaying the UL data received from the UE from the source eNB to the target eNB. 5.2.1.3 Handover cancellation This function allows informing an already prepared target eNB that a prepared handover will not take place. It allows releasing the resources allocated during a preparation. 5.2.1.4 UE context release in source eNB This function allows the target eNB to trigger the release of the resources allocated to the UE in the source eNB. 5.2.2 Load management This function allows exchanging overload and traffic load information between eNBs, such that the eNBs can control the traffic load appropriately. This information may be spontaneously sent to selected neighbour eNBs, or reported as configured by a neighbour eNB. 5.2.3 Inter-cell interference coordination This function allows keeping inter-cell interference under control. For this neighbouring eNBs exchange appropriate information allowing that eNBs make radio resource assignments such that interference is mitigated. 5.2.3.1 Uplink interference load management This function allows indicating an uplink interference overload and resource blocks especially sensitive to inter-cell interference between neighbouring eNBs, such that neighbour eNBs can co-ordinate with each other such that the mutual interference caused by their uplink radio resource allocations is mitigated. 5.2.3.2 Downlink interference avoidance This function allows an eNB to inform its neighbour eNBs about downlink power restrictions in its own cells, per resource block for interference aware scheduling by the neighbour eNBs. 5.2.4 General X2 management and error handling functions These functions allow for managing of signalling associations between eNBs, surveying X2 interface and recovering from errors. 5.2.4.1 Error indication This function allows the reporting of general error situations on application level. 5.2.4.2 Reset This function allows an eNB to inform another eNB that it has recovered from an abnormal failure and that all the 1 2 contexts (except the application level data – see section 5.2.6) related to eNB and stored in eNB shall be deleted, and 1 2 the associated resources released. ETSI 3GPP TS 36.420 version 10.0.0 Release 10 9 ETSI TS 136 420 V10.0.0 (2011-01) 5.2.5 Trace functions Trace recoding sessions on E-UTRAN interfaces for a particular UE is initiated by the EPC. The trace initiation information is also propagated to the Target eNB during handover, attached to certain handover messages on X2. 5.2.6 Application level data exchange between eNBs This function allows two eNBs to exchange application level data when an X2 connection is setup, and to update this information at any time. 6 X2 interface protocols and protocol structure 6.1 General There shall exist a clear separation between the Radio Network Layer and the Transport Layer. Therefore, the radio network signaling and X2 data streams are separated from the data transport resource and traffic handling as shown in Figure 6.1.1. Radio Radio User Plane Network Signalling PDUs layer Protocols Transport layer Signalling Data Bearer Transport Figure 6.1.1: Separation of Radio Network Protocols and transport over X2 6.2 Radio signalling protocols 6.2.1 X2AP protocol The protocol responsible for providing signalling information across the X2 interface is called the X2 Application Protocol (X2AP). The X2AP is terminated by the two eNBs inter-connected via the X2 interface X2AP Procedure Modules. 6.3 User plane protocol 6.3.1 Tunnelling protocol GTP-U 6.4 X2 interface protocol structure The X2 interface protocol architecture consists of two functional layers: ETSI