If the eNB cannot access any MME, then all cells of the eNB will be barred. When Cell is Barred eNB doesn't transmit anything or transmits the RS with a very low value, so UE doesn't receive anything. eNB can also inform UE that Cell is in Barred state through SIB1 as Salil Agrawal mentioned
SystemInformationBlockType1 ::= SEQUENCE {
cellAccessRelatedInfo SEQUENCE {
plmn-IdentityList PLMN-IdentityList,
trackingAreaCode TrackingAreaCode,
cellIdentity CellIdentity,
**cellBarred ENUMERATED {barred, notBarred},**
intraFreqReselection ENUMERATED {allowed, notAllowed},
csg-Indication BOOLEAN,
csg-Identity CSG-Identity OPTIONAL -- Need OR
},
As per Spec 36.331
Essential system information missing The UE shall:
If in RRC_IDLE or in RRC_CONNECTED while T311 is running:
¤ If the UE is unable to acquire the MasterInformationBlock or the SystemInformationBlockType1:
- consider the cell as barred in accordance with TS 36.304; and
- perform barring as if intraFreqReselection is set to allowed, and as if the csg-Indication is set to FALSE;
else if the UE is unable to acquire the SystemInformationBlockType2:
¤ Treat the cell as barred in accordance with TS 36.304;