Shared RAN deployment scenarios are an excellent opportunity for mobile network operators to lower their investments on both, network hardware and operational costs by sharing resources.
The MORAN approach where each operator continues to have its dedicated spectrum (= radio network cells) is easy to understand.
However, the Multi-Operator Core Network (MOCN) is a bit more complex, especially if one of the involved operators asks for service assurance KPIs that apply to its - and only its - subscribers. In this case it is a prerequisite to find out which "call" belongs to which core network operator to enable further KPI correlation and aggregation.
The figure below illustrates how this works:
(click on picture for larger version)
In the System Information Block (SIB) 1 of the cell a list of PLMN-IDs is broadcasted followed by a single Tracking Area Code (which can be combined each of the PLMN-IDs to get multiple TAIs) and a single Cell Identity.
Encoding is specified in 3GPP 36.331 (RRC) as follows:
SystemInformationBlockType1 ::= SEQUENCE {
cellAccessRelatedInfo SEQUENCE {
plmn-IdentityList PLMN-IdentityList,
trackingAreaCode TrackingAreaCode,
cellIdentity CellIdentity,
The spec further defines that the ECGI is the CellIdentiy combined with the first (!!!) PLMN-ID from the PLMN-ID List:
CellGlobalIdEUTRA field descriptions |
cellIdentity Identity of the cell within the context of the PLMN. |
plmn-Identity Identifies the PLMN of the cell as given by the first PLMN entry in the plmn-IdentityList in SystemInformationBlockType1. |
So there is one and only 1 ECGI per radio cell in the network, but multiple PLMN-IDs and hence, multiple TAI, one fore each core network operator, are broadcasted.
During RRC establishement a particular UE signals on behalf on the selected PLMN-ID information element in the RRC Connection Setup Complete message to which core network operator shall be used.
This information is "translated" by the eNB into ECGI and TAI with different PLMN-IDs. While the ECGI displays the PLMN-ID of the operator that owns the RAN equipment the TAI shows the selected PLMN-ID of the UE's core network operator.
