Full configuration

In LTE, there's this thing called full configuration. I guess it's usually used in handovers. During a handover, the source eNodeB informs the target eNodeB about the source eNodeB's enabled features. For instance, the source eNodeB may inform the target eNodeB that it was performing 256QAM with the UE.

Sometimes, however, the target eNodeB does not support the features the source eNodeB was using with the UE. For instance, the source eNodeB may have been previously using 256QAM with the UE, but the target eNodeB may not have support for this feature. When this happens, the target eNodeB may issue a full configuration to the UE. It does this by sending an RRC Connection Reconfiguration message to the UE. This message is first sent to the source eNodeB, then passed as is (without modification) to the UE.

The target eNodeB informs the UE that a full configuration is in progress by sending the fullConfig-r9 information element. During full configuration, the target eNodeB has to resend all information related to bearer setup (as if these bearers were being set up from scratch or for the first time).

In the case of DRB bearers, the DRB-ToAddMod message has to have the following elements present during full configuration:

1. eps-BearerIdentity
2. pdcp-Config
1. discardTimer
2. rlc-AM or rlc-UM (one of them, but not both, has to be present)
3. rlc-Config
4. logicalChannelIdentity
5. logicalChannelConfig