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.
For the purposes of the present document, the terms and definitions given in TR 21.905 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.
For the purposes of the present document, the abbreviations given in TR 21.905 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.
The X2 user plane (X2 UP) protocol is located in the User Plane of the Radio Network layer over the X2 interface.
The X2 UP protocol is used to convey control information related to the user data flow management of E-RABs.
Each X2 UP protocol instance is associated to one E-RAB only.
This version of the present document defines the X2 UP protocol in the context of dual connectivity only, more specifically, only for X2 user data bearers setup for E-RABs configured with the split bearer option.
If configured, X2 UP protocol instances exist at the eNBs between which the X2 user data bearers are setup, specifically for dual connectivity between the MeNB and the SeNB.
In this version of the present document, X2 UP protocol data is conveyed by GTP-U protocol means, more specifically, by means of the "RAN Container" GTP-U extension header as defined in TS 29.281.