Control Plane CIoT EPS optimization

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Hi Guys today we are learning about  Control Plane CIoT EPS optimization in detail for NB-IoT, For more update Please visit our NB-IoT page.


Control Plane CIoT EPS optimization:


In order to reduce the total number of control plane messages when handling a short data transaction, user data or SMS messages is conveyed to the IOT services via MME by encapsulating them in NAS messages.

There are two paths through which, user data or SMS can be transmitted on the Control Plane CIoT EPS optimization:
  • UL data are transferred from the eNB (CIoT RAN) >> the MME >> the Serving Gateway (SGW) >> the Packet Data Network Gateway (PGW) >> IOT Services


  • UL data are transferred from the eNB (CIoT RAN) >> the MME >> the Service Capability Exposure Function (SCEF)(only for non-IP data packets) >> IOT Services.



In both the cases mentioned above, DL data is transmitted over the same paths but in the reverse direction.

In these cases, since data packets are sent on the signaling radio bearer (SRB), there is no need for data radio bearer (DRB) set up.

For small data transmission between the MME and S-GW, a new interface named S11-U is introduced as a part of control plane CIoT EPS optimization.

The SCEF, a new node designed especially for machine type data, is used for delivery of non-IP data over control plane and also provides an abstract interface for the network services like authorization and authentication, discovery and access network capabilities.

Data transfer of both IP and non-IP data follows the conventional path in Control Plane CIoT optimization. It is transmitted over data radio bearers through the SGW and PGW, to the CIoT application services.Structure-wise the access network in NB-IoT is the same as LTE.

In the Control Plane CIoT EPS optimisation, the exchange of data between the UE and the eNB is done on RRC level. Here the DL data packets can be piggybacked in the RRCConnectionSetup message or in the RRCConnectionSetupComplete message for UL. If this is not enough, DLInformationTransfer and ULInformationTransfer can also be used for data transfer.

All these messages contain a byte array which has NAS information, which corresponds to the NB-IoT data packets in this case. The dedicatedInfoNAS between the eNB and the MME is exchanged via the S1-MME interface. As a result, it is transparent to the eNB, and the UE's RRC directly forwards the content of the received DLInformationTransfer to its upper layer. For the data delivery method, Security on AS level is not applied. As data is transferred via NAS messages, there is no RRC connection reconfiguration. It may either start immediately after or during the RRC connection setup or RRC Connection resume procedure, respectively due to termination of the RRC connection after RRC connection release.

If the operator supports SCEF, then MME uses SCEF based delivery mechanism for Non-IP data.First a PDN connection is established towards the selected SCEF which is also known as an "SCEF Connection".

Note: For SCEF based delivery, the APN used is an FQDN, which either resolves to an SCEF hostname or to an SCEF IP address.


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