Protocol

6. UE states and state transitions
RRC supports the following three states:
RRC_IDLE:
- Cell re-selection mobility;
- Paging is initiated by CN;
- Paging area is managed by CN.
RRC_INACTIVE:
- Cell re-selection mobility;
- CN – NR RAN connection (both C/U-planes) has been established for
UE;
- The UE AS context is stored in at least one gNB and the UE;
- Paging is initiated by NR RAN;
- RAN-based notification area is managed by NR RAN;
- NR RAN knows the RAN-based notification area which the UE belongs
to;
RRC_CONNECTED:
- The UE has an NR RRC connection;
- The UE has an AS context in NR;
- NR RAN knows the cell which the UE belongs to;
- Transfer of unicast data to/from the UE;
- Network controlled mobility, i.e. handover within NR and to/from E-UTRAN.

56. NBIOT

58. Downlink Channels & Signals
1) Narrowband Primary Synchronization Signal (NPSS)
2) Narrowband Secondary Synchronization Signal (NSSS)
3) Narrowband Reference Signal (NRS)
4) Narrowband Physical Broadcast Channel (NPBCH)
5) Narrowband Physical Downlink Shared Channel (NPDSCH)
6) Narrowband Physical Downlink Control Channel (NPDCCH)

59. Uplink Channels & Signals
1) Narrowband Physical Random Access Channel (NPRACH)
2) Narrowband Physical Uplink Shared Channel (NPUSCH)
3) Demodulation Reference Signal (DMRS)

60. SRVCC from E-UTRAN to GERAN or UTRAN
SRVCC impacts the eNodeB, the MME and the MSC Server and
requires service continuity support in the IMS.
A new interface, Sv, has been specified between the MME and
the MSC to execute the actual handover.
Prerequisites for SRVCC are that both the UE and the EPS are
SRVCC capable and that the session is anchored in a Service
Centralization and Continuity Application Server (SCC AS) in the
IMS.
To illustrate the SRVCC functionality, we will examine an
example of a call between two UE’s where UE-A will experience
an SRVCC.

61. SRVCC from E-UTRAN to GERAN or UTRAN

62. SRVCC from E-UTRAN to GERAN or UTRAN
 For example, the UE-A and UE-B are using IMS voice telephony to
communicate.
 The IMS signaling traverses the IMS control nodes and is anchored in an SCC
AS in UE-A’s network.
 The IMS voice packets are sent end-to-end between the UEs using the EPS IP
connectivity through eNodeB and Serving/PDN GW (the details on how the
IMS voice packets are sent to UE-B are note relevant for this discussion).
 When UE-A moves in the network, it may reach a point where there the LTE
coverage will diminish and an SRVCC handover must be performed to
GERAN CS or UTRAN CS.
 When the LTE signal strength decreases, the UE will measure on neighbour
cell to discover suitable HO candidates and report the measurements to the
eNodeB.
 Based on the bearer QCI and configured knowledge of to which cells SRVCC
is necessary, the eNodeB can trigger an SR VCC HO if PS handover is not
possible.

63. SRVCC from E-UTRAN to GERAN or UTRAN
 The MME is informed by the eNodeB that SRVCC HO is needed via the hand-
over request from eNodeB with the indication that this is for SRVCC handling.
 The MME then triggers the SRVCC procedure with the MSC Server via the Sv
interface (the address of the MSC is provisioned to the MME).
 The MME also passes a special routing number that allows the MSC Server to
establish a session with the IMS SCC AS.
 The MSC Server initiates the session transfer procedure to IMS and
coordinates it with the CS handover procedure to the target cell.
 The MSC Server sends a response to the MME, which includes the necessary
CS HO command information for the UE to access the target UTRAN/GERAN
cell.
 The MME sends a handover command to the eNodeB that passes it to the UE.
 After, the UE tunes into the GERAN/UTRAN cell and in principle experience a
CS HO in the target cell where the UE will receive a CS telephony bearer.
 After the HO, the UE-A will be connected with CS telephony to the MSC
Server.

64. SRVCC from E-UTRAN to GERAN or UTRAN