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].
CSG Cell: an E-UTRAN cell broadcasting a CSG Identifier.
Elementary Procedure: S1AP consists of Elementary Procedures (EPs). An Elementary Procedure is a unit of interaction between eNBs and the EPC. These Elementary Procedures are defined separately and are intended to be used to build up complete sequences in a flexible manner. If the independence between some EPs is restricted, it is described under the relevant EP description. Unless otherwise stated by the restrictions, the EPs may be invoked independently of each other as stand alone procedures, which can be active in parallel. Examples on using several S1AP EPs together with each other and EPs from other interfaces can be found in reference [FFS].
An EP consists of an initiating message and possibly a response message. Two kinds of EPs are used:
- Class 1: Elementary Procedures with response (success and/or failure).
- Class 2: Elementary Procedures without response.
For Class 1 EPs, the types of responses can be as follows:
Successful:
- A signalling message explicitly indicates that the elementary procedure successfully completed with the receipt of the response.
Unsuccessful:
- A signalling message explicitly indicates that the EP failed.
- On time supervision expiry (i.e. absence of expected response).
Successful and Unsuccessful:
- One signalling message reports both successful and unsuccessful outcome for the different included requests. The response message used is the one defined for successful outcome.
Class 2 EPs are considered always successful.
eNB UE S1AP ID: according to definition in 23.401.
[Note (to be removed once captured in another TS): The eNB UE S1AP ID shall be allocated so as to uniquely identify the UE over the S1 interface within the eNB. When MME receives eNB UE S1AP ID it shall store it for the duration of the UE-associated logical S1-connection for this UE. Once known to MME his IE is included in all UE associated S1-AP signalling (UL as well as DL).]
MME UE S1AP ID: according to definition in 23.401.
[Note (to be removed once captured in another TS): The MME UE S1AP ID shall be allocated so as to uniquely identify the UE over the S1 interface within the MME. When eNB receives MME UE S1AP ID it shall store it for the duration of the UE-associated logical S1-connection for this UE. Once known to eNB this IE is included in all UE associated S1-AP signalling (UL as well as DL).]
E-RAB: as defined in [2].
Note: The E-RAB is either a default E-RAB or a dedicated E-RAB.
E-RAB identity: the E-RABidentity uniquely identifies an E-RABfor one UE.
Note: The E-RAB identity remains unique for the UE even if the UE-associated logical S1-connection is released during periods of user inactivity.
Data Radio Bearer: the Data Radio bearer transports the packets of an E-RAB between a UE and an eNB. There is an one-to-one mapping between the E-RAB and the Data Radio Bearer.
UE-associated signalling: When S1-AP messages associated to one UE uses the UE-associated logical S1-connection for association of the message to the UE in eNB and EPC.
UE-associated logical S1-connection: The UE-associated logical S1-connection uses the identities MME UE S1AP ID and eNB UE S1AP ID according to definition in [23.401]. For a received UE associated S1-AP message the MME identifies the associated UE based on the MME UE S1AP ID IE and the eNB identifies the associated UE based on the eNB UE S1AP ID IE. The UE-associated logical S1-connection may exist before the S1 UE context is setup in eNB.
3.2 Symbols
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3.3 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] 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].
CDMA Code Division Multiple Access
CS Circuit Switched
CSG Closed Subscriber Group
CN Core Network
DL Downlink
ECGI E-UTRAN Cell Global Identifier
E-RAB E-UTRAN Radio Access Bearer
eNB E-UTRAN NodeB
EP Elementary Procedure
EPC Evolved Packet Core
E-UTRAN Evolved UTRAN
GBR Guaranteed Bit Rate
GUMMEI Globally Unique MME Identifier
GTP GTP Tunneling Protocol
HFN Hyper Frame Number
HRPD High Rate Packet Data
IE Information Element
MME Mobility Management Entity
NAS Non Access Stratum
PS Packet Switched
PDCP Packet Data Convergence Protocol
PLMN Public Land Mobile Network
PS Packet Switched
RRC Radio Resource Control
RIM RAN Information Management
SN Sequence Number
S-TMSI S-Temporary Mobile Subscriber Identity
TAI Tracking Area Identity
TEID Tunnel Endpoint Identifier
UE User Equipment
UE-AMBR UE-Aggregate Maximum Bitrate
UL Uplink
4 General
Editor’s Note: Section captures procedure specification principles, forward/backward compatibility issue and specification notations.
4.1 Procedure Specification Principles
The principle for specifying the procedure logic is to specify the functional behaviour of the terminating node exactly and completely. Any rule that specifies the behaviour of the originating node shall be possible to be verified with information that is visible within the system.
The following specification principles have been applied for the procedure text in clause 8:
- The procedure text discriminates between:
1) Functionality which "shall" be executed
The procedure text indicates that the receiving node "shall" perform a certain function Y under a certain condition. If the receiving node supports procedure X but cannot perform functionality Y requested in the REQUEST message of a Class 1 EP, the receiving node shall respond with the message used to report unsuccessful outcome for this procedure, containing an appropriate cause value.
2) Functionality which "shall, if supported" be executed
The procedure text indicates that the receiving node "shall, if supported," perform a certain function Y under a certain condition. If the receiving node supports procedure X, but does not support functionality Y, the receiving node shall proceed with the execution of the EP, possibly informing the requesting node about the not supported functionality.
- Any required inclusion of an optional IE in a response message is explicitly indicated in the procedure text. If the procedure text does not explicitly indicate that an optional IE shall be included in a response message, the optional IE shall not be included. For requirements on including Criticality Diagnostics IE, see section 10. For examples on how to use the Criticality Diagnostics IE, see Annex A.2.
4.2 Forwards and Backwards Compatibility
The forwards and backwards compatibility of the protocol is assured by mechanism where all current and future messages, and IEs or groups of related IEs, include ID and criticality fields that are coded in a standard format that will not be changed in the future. These parts can always be decoded regardless of the standard version.
4.3 Specification Notations
For the purposes of the present document, the following notations apply:
Procedure When referring to an elementary procedure in the specification the Procedure Name is written with the first letters in each word in upper case characters followed by the word "procedure", e.g. E-RAB procedure.
Message When referring to a message in the specification the MESSAGE NAME is written with all letters in upper case characters followed by the word "message", e.g. MESSAGE NAME message.
IE When referring to an information element (IE) in the specification the Information Element Name is written with the first letters in each word in upper case characters and all letters in Italic font followed by the abbreviation "IE", e.g. Information Element IE.
Value of an IE When referring to the value of an information element (IE) in the specification the "Value" is written as it is specified in subclause 9.2 enclosed by quotation marks, e.g. "Value".
5 S1AP Services
S1AP provides the signalling service between E-UTRAN and the evolved packet core (EPC) that is required to fulfil the S1AP functions described in clause 7. S1AP services are divided into two groups:
1. Non UE-associated services: They are related to the whole S1 interface instance between the eNB and MME utilising a non UE-associated signalling connection.
2. UE-associated services: They are related to one UE. S1AP functions that provide these services are associated with a UE-associated signalling connection that is maintained for the UE in question.
6 Services Expected from Signalling Transport
The signalling connection shall provide in sequence delivery of S1AP messages. S1AP shall be notified if the signalling connection breaks.
7 Functions of S1AP
Editor’s Note: Description of S1AP functions.
S1AP protocol has the following functions:
- E-RAB management function: This overall functionality is responsible for setting up, modifying and releasing E-RABs, which are triggered by the MME The release of E-RABs may be triggered by the eNB as well.
- Initial Context Transfer function: This functionality is used to establish an S1UE context in the eNB, to setup the default IP connectivity, to setup one or more E-RAB(s) if requested by the MME, and to transfer NAS signalling related information to the eNB if needed.
- UE Capability Info Indication function: This functionality is used to provide the UE Capability Info when received from the UE to the MME.
- Mobility Functions for UEs in LTE_ACTIVE in order to enable
- a change of eNBs within SAE/LTE (Inter MME/Serving SAE-GW Handovers) via the S1 interface (with EPC involvement).
- a change of RAN nodes between different RATs (Inter-3GPP-RAT Handovers) via the S1 interface (with EPC involvement).
- Paging: This functionality provides the EPC the capability to page the UE.
- S1 interface management functions comprise the:
- Reset functionality to ensure a well defined initialisation on the S1 interface.
- Error Indication functionality to allow a proper error reporting/handling in cases where no failure messages are defined.
- Overload function to indicate the load situation in the control plane of the S1 interface.
- Load balancing function to ensure equally loaded MMEs within an MME pool area
- S1 Setup functionality for initial S1 interface setup for providing configuration information
- eNB and MME Configuration Update functions are to update application level configuration data needed for the eNB and MME to interoperate correctly on the S1 interface.
- NAS Signalling transport function between the UE and the MME is used:
- to transfer NAS signalling related information and to establish the S1 UE context in the eNB.
- to transfer NAS signalling related information when the S1 UE context in the eNB is already established.
- S1 UE context Release function: This functionality is responsible to manage the release of UE specific context in the eNB and the MME.
- UE Context Modification function: This functionality allows to modify the established UE Context partly.
- Status Transfer: This functionality transfers PDCP SN Status information from source eNB to target eNB in support of in-sequence delivery and duplication avoidance for intra LTE handover.
- Trace function: This functionality is to control a trace recording for a UE in ECM_CONNECTED.
- Location Reporting: This functionality allows MME to be aware of the UE’s current location.
- S1 CDMA2000 Tunneling function: This functionality is to carry CDMA2000 signalling between UE and CDMA2000 RAT over the S1 Interface.
- Warning message transmission function:
This functionality provides the means to start and overwrite the broadcasting of warning message
