RLC SDUs which need support of PDCP SN/SFN, Integrity, Ciphering or Integrity & Ciphering both mapped to PDCP layer. But there are some other types of RRC data that passes through RLC layer which doesn't need any support of the PDCP layer. These different types of data are carried over using different logical channels.
These are following logical channels supported in LTE technology.
- BCCH (RLC SDU maps with RRC)
- PCCH (RLC SDU maps with RRC)
- CCCH (RLC SDU maps with RRC)
- DCCH (RLC SDU maps with RRC, PDCP)
- DTCH (RLC SDU maps with PDCP)
There are another set of logical channels that are used to support eMBMS features.
I am not sure about these two channels and their mapping to PDCP.