ion. As in LTE, the configuration of integrity protection is mandatory for signaling radio bearers (SRBs) and for emergency calls of UEs in a limited service state, the NULL algorithm is configured. Unlike in LTE, though, integrity protection is not limited to SRBs (see Section 7.7); it can also be configured for DRBs, albeit up to a bit rate given by the UE capabilities. The integrity protection function of PDCP includes integrity protection in the transmitter and integrity verification in the receiver. Integrity protection results in a 32-bit MAC-I, which is appended at the end of the PDCP PDU. The integrity protection algorithms and their inputs are defined in 3GPP TS 33.501. The ciphering function of PDCP includes ciphering in the transmitter and decipher- ing in the receiver. Only the data portion of the SDAP PDU is ciphered, together with the MAC-I when present. Leaving the SDAP header un-ciphered allows data routing to take place in the receiver before de-ciphering. If the SDAP header were also ciphered, this would have imposed certain hardware architecture restrictions on both the UE and the network by precluding such routing. The ciphering algorithms and their inputs are defined in 3GPP TS 33.501. Figure 7.7 below summarizes security in PDCP and to which portion of the PDCP PDU integrity protection and ciphering apply. When after deciphering, integrity verification fails in the receiver for a radio bearer, only the corresponding PDU is discarded and RRC is notified. If this happens on an SRB, RRC then triggers a reestablishment. Not triggering a reestablishment when integrity verification fails on a DRB limits the impacts of packet injection and reduces the chances of Denial of Service (DoS). 7.4.4 Header Compression Header compression in PDCP is based on the Robust Header Compression (RoHC) framework defined in RFC 5795, which defines multiple header compression algorithms Integrity Protected Ciphered PDCP Header SDAP Header SDAP SDU MAC I PDCP SDU PDCP PDU Figure 7.7 Security in PDCP. 7 5G Radio Protoc