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Content for  TS 23.401  Word version:  16.7.0

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K  Isolated E-UTRAN Operation for Public Safety |R13|Word‑p. 420

K.1  General description of the IOPS concept

Isolated E-UTRAN Operation for Public Safety (IOPS) provides the ability to maintain a level of communications for public safety users, via an IOPS-capable eNB (or set of connected IOPS-capable eNBs), following the loss of backhaul communications.
The Isolated E-UTRAN mode of operation is also applicable to the formation of a Nomadic EPS deployment, i.e. a deployment of one or more standalone IOPS-capable eNBs, creating a serving radio access network without backhaul communications and also providing local connectivity (e.g. for IP or Ethernet) and services to public safety users in the absence of normal EPS infrastructure availability.
This annex provides implementation and deployment guidelines for the operation of public safety networks in the no backhaul (to Macro EPC) scenario using a Local EPC approach.
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K.2  Operation of isolated public safety networks using a Local EPC

K.2.1  General Description

This approach to the provision of isolated operation (e.g. when there is no S1 connectivity to the macro EPC) assumes that the IOPS-capable eNB is co-sited with, or can reach, a Local EPC instance which is used in IOPS mode. The Local EPC instance includes at least MME, SGW/PDN GW and HSS functionality.
A PLMN identity is dedicated to IOPS mode of operation and is broadcast in System Information by the eNB when IOPS mode is in operation. Only authorized IOPS-enabled UEs can access a PLMN indicated as an IOPS PLMN.
Support of application services over the IOPS network will be based upon the LTE-Uu radio interface and EPS bearer services supported by the Local EPC. An IOPS network will provide local connectivity services, i.e. for an IP PDN type, IP address assignment and local routing in the IOPS network. For an IP PDN type, During the attachment procedure to the local EPC a local IP address is assigned to the UE as per the standard procedure when attaching to a Macro EPC. The Local EPC acts as a router among the UEs locally attached to the same IOPS network. When operating in IOPS mode IOPS-enabled UEs only use the appropriate USIM credentials defined in the UICC, i.e. those defined exclusively for use in an IOPS PLMN.
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K.2.2  UE configuration

An IOPS-enabled UE has the dedicated IOPS PLMN identity configured in a separate dedicated USIM application as an HPLMN along with the Access Class status of 11 or 15, subject to regional/national regulatory requirements and operator policy.
An IOPS-enabled UE can display information on available PLMNs, including the IOPS PLMN, assisting the user to activate an appropriate USIM application. Subject to user preferences, e.g. to maintain a group communication, the user can perform a manual USIM application switch at any time.
When an authorized IOPS-enabled UE, with the dedicated IOPS USIM application activated, selects an IOPS-mode cell, it selects the dedicated IOPS PLMN identity, attaches to the IOPS PLMN (supported by the Local EPC) and is authenticated using security procedures as specified in TS 33.401 and the security credentials from the active IOPS USIM application.
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K.2.3  IOPS network configurationWord‑p. 421
An IOPS network can comprise either:
  • a Local EPC and a single isolated IOPS-capable eNB, which may be co-located or have connectivity to the Local EPC; or
  • a Local EPC and two or more IOPS-capable eNBs, which have connectity to a single Local EPC.
Existing procedures described in TS 36.300 can be used to achieve dynamic configuration of the S1-MME interface. An IOPS-capable eNB can be pre-provisioned with IP endpoint information, relating to the MMEs of one or more candidate Local EPC instances. For each local MME in turn the eNB can try to initialize a SCTP association. Once SCTP connectivity has been established, the eNB and local MME exchange application level configuration data over the S1-MME application protocol with the S1 Setup Procedure (see TS 36.413). In line with local operator policies the eNB can be provisioned with the IP endpoint of a preferred Local EPC MME instance and the IP endpoints of one or more alternative Local EPC MME instances. The alternative Local EPC instances will be used if an S1-MME path cannot be established with the local MME of the preferred Local EPC instance.
All Local EPCs deployed by a public safety authority / operator assume the same PLMN-Id. In order to achieve the broadcast of different TAIs on separate IOPS networks the TACs broadcast by the cells of eNBs connected to different Local EPCs are distinct to ensure the required UE mobility behaviour (see clause K.2.5). Therefore, the TAC broadcast by the cells of an eNB operating in IOPS mode will be dependent upon the Local EPC to which the eNB has established an S1-MME connection.
If the scope of service of a Local EPC is a single eNB, then all cells served by the eNB share the same TAC (assigned for use in IOPS mode) and neighbouring eNBs that are also operating in IOPS mode with the same dedicated PLMN-Id are assigned different TACs (resulting in different TAIs) so a TAU attempt is triggered upon mobility.
If multiple eNBs are configured to be served by a single Local EPC, configuration of TAIs for IOPS can be done according to local operator policies in such a way that a reselection to a cell operating a PLMN in normal mode always triggers an attach request.
If sharing the same PLMN-Id, it is assumed the TAC assigned to cells in a Nomadic EPS would be different from the TACs assigned to infrastructure eNBs operating in IOPS mode, so as to trigger a TAU between these systems.
The support by IOPS network entities of S1-flex and/or eMBMS is up to local operator policy and configuration.
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K.2.4  IOPS network establishment/termination

The decision by an IOPS-capable eNB to enter IOPS mode of operation is made in accordance with the local policies of the RAN operator. Such policies can be affected by any RAN sharing agreements that are in place.
In situations when the backhaul to the Macro EPC is lost and an eNB can start IOPS mode of operation based on local policies, or an eNB is deployed as part of a Nomadic EPS, the following eNB behaviour is expected:
  • If the eNB can reach a Local EPC for IOPS mode of operation, the eNB uses the Local EPC.
  • If the eNB cannot reach a Local EPC, then the eNB enters a state where UEs do not attempt to select the cells under its control.
In this release of the specification IOPS networks will be established by the independent actions of each eNB entering IOPS mode of operation. An IOPS network comprising two or more eNBs will be established as a result of multiple eNBs entering IOPS mode of operation and establishing S1-MME paths to the local MME of the same Local EPC instance.
An eNB in IOPS mode of operation, indicates/broadcasts the IOPS PLMN cell(s) as "Not Barred" & "Reserved for Operator Use", for the IOPS PLMN identity, as defined in TS 36.304. This "Cell Reserved for Operator Use" feature will allow the IOPS-enabled UEs to get access to the IOPS network while barring other non-IOPS-enabled UEs in the same area. The dedicated IOPS USIM application configuration (clause K.2.2) is restricted to use only by users authorised to access a network in IOPS mode of operation.
When a backhaul to the Macro EPC is re-established, the S1 connections to the Local EPC are released according to the local IOPS network policies, to move the UEs to Idle mode, and IOPS mode of operation ceases. The PLMN identity of the Macro EPC is announced by the eNB so that UEs reselect the normal PLMN and attach afresh to the Macro EPC.
Figure K.2.4-1 provides an example of the basic steps involved in IOPS network establishment, access and termination.
Reproduction of 3GPP TS 23.401, Figure K.2.4-1: Example of Local EPC based IOPS operation
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Step 1.
The UE is attached to the Macro EPC accessing normal application (e.g. MCPTT) services.
Step 2.
The eNB detects loss of the backhaul to the Macro EPC and in accordance with local operator policies decides to activate IOPS mode of operation. The eNB prevents any UEs from selecting the cell, using a suitable mechanism such as cell barring, until step 3 and step 4 are completed.
Step 3.
Local EPC is activated.
Step 4.
The eNB establishes an S1 link to the Local EPC.
Step 5.
The eNB broadcasts the PLMN identity for IOPS operation with the Local EPC and indicates the IOPS PLMN cell(s) as "Not Barred" & "reserved" for operator use.
Step 6.
The UE detects the IOPS PLMN-Id and a decision is made to switch USIM application and the UE activates the IOPS USIM application.
Step 7.
The UE selects the IOPS PLMN-Id.
Step 8.
The UE attaches to the Local EPC and, for an IP PDN type, obtains a local IP address, if authorised.
Step 9.
Public safety services supported by the IOPS network can be accessed at this time.
Step 10.
At some point in time the eNB detects that the backhaul to the Macro EPC has been restored.
Step 11.
S1 connections to the Local EPC are released according to the IOPS network policies to move the UEs to idle mode.
Step 12.
The eNB stops its IOPS mode of operation and the Local EPC is de-activated.
Step 13.
The eNB establishes an S1 link to the Macro EPC.
Step 14.
The PLMN-Id of the Macro EPC is announced and the normal TAIs of the Macro EPC are advertised by the eNB so that UEs reselect the normal PLMN.
Step 15.
The UE detects the PLMN-Id of the Macro EPC and a decision is made to switch USIM application and the UE activates the normal USIM application.
Step 16.
The UE selects the normal PLMN-Id.
Step 17.
The UE attaches as normal to the Macro EPC, if authorised.
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K.2.5  UE mobilityWord‑p. 424
A number of distinct UE mobility scenarios can be identified given the following assumptions:
  • multiple eNBs can be configured to be served by a single Local EPC;
  • a single dedicated PLMN-Id will be advertised by all eNBs operating in IOPS mode (of a given public safety authority/operator);
  • the TACs broadcast by cells (eNBs) served by different Local EPCs will be different.
The mobility scenarios that can be distinguished are:
Step 1.
UE transitions from a cell controlled by the normal macro EPC to a cell operating in IOPS mode;
Step 2.
UE transitions from a cell operating in IOPS mode to a cell controlled by the normal macro EPC;
Step 3.
UE transitions from a cell operating in IOPS mode whose eNB is served by one Local EPC to a cell also operating in IOPS mode whose eNB is served by a different Local EPC (Inter-IOPS network cell transition);
Step 4.
UE transitions between cells operating in IOPS mode whose eNB(s) are served by the same Local EPC (Intra-IOPS network cell transition).
The expected mobility behaviour in each of these scenarios is summarised in Table K.2.5-1.
MOBILITY ECM STATE: TRANSITION
IDLE MODE
ECM STATE: CONNECTED MODE

Normal mode cell to IOPS mode cell
Cell re-selection and USIM application switch:
- UE performs cell re-selection based upon radio measurements and no suitable cell is found.
- UE switches USIM application.
- UE performs cell selection and a suitable cell is found.
- UE initiates Attach procedure towards Local/Normal EPC.
Radio link failure followed by cell re-selection:
- UE performs radio measurements but source and target cells are on different
IOPS mode cell to Normal mode cell networks. The PLMN-Id of the target cell is not supported by the subscription details in the currently selected USIM application. Handover does not occur.
- Radio link failure occurs and UE returns to Idle Mode.
- UE proceeds as per behaviour for Idle Mode.
Intra-IOPS network cell transition
Idle Mode mobility as per normal EPC mobility.
As per normal EPC Connected mode mobility procedures.
Inter-IOPS network cell transition
Idle Mode mobility as per normal EPC mobility.
As per normal EPC Connected mode mobility procedures.

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