0 ms 244 bits every 20 ms 12 bytes 8 bytes 4 bytes 20 bytes 28.2 kbps 13.8 kbps 564 bits every 20 ms 276 bits every 20 ms Figure 8.5. Header compression. AMR: Adaptive Multi-Rate The ROHC decompressor uses the PDCP Feedback control message to inform the ROHC compressor that the decompression is successful or that the synchronization between compression and decompression has been lost. 8.2.1.2. Loss of frames during handover The PDCP allows the recovery of frames that had been lost during handover, but only if the Radio Link Control (RLC) protocol uses the acknowledgement mode. For the downlink direction, during the handover procedure, the source gNB entity sends the target gNB entity an Xn-AP SN STATUS NUMBER message which it provides, on the one hand, the PDCP frames transmitted to the mobile and unacknowledged with their Sequence Number (SN) and, on the other hand, the Sequence Numbers (SN) of non-received PDCP frames from the mobile for the uplink direction. When the mobile connects to the target gNB entity, the recovery of lost frames is performed by the following exchanges: - the mobile sends the target gNB entity the PDCP Status Report message which mentions the missing PDCP frames for the downlink direction; - the target gNB entity sends the PDCP Status Report message to the mobile which mentions the missing PDCP frames for the uplink direction. 212 NG-RAN and 5G-NR 8.2.1.3. Packet removal (PDCP discard) During the handover or when the radio link is not good enough, the maximum data rate reached at the radio interface is lower than the rate desired by the application. Buffering PDCP packets is used to resolve the jitter issue. Buffering data can also temporarily compensate the reduction in data rate. Deleting packets at the transmitter allows the transmission buffer to be emptied, especially in the case of real-time applications. A frame drop timer is activated for each PDCP SDU frame. When the timer expires, if the PDCP frame is not transmitted, the latter frame is deleted. 8.2.1.4. Split bearer The split