9. PDCP layer

The PDCP (Packet Data Convergence Protocol) layer is used for both user data transfer and signaling transmission . It incorporates the ROHC (RObust Header Compression) mechanism, which enables header compression and decompression. Indeed, applications such as voice over IP involve a large protocol stack: a voice block, typically 30 bytes, is placed in an RTP (Real Time Protocol) block adding a header of typically 12 bytes; the RTP block is transported in a UDP segment with an 8-byte header, itself placed in an IP packet with a 40-byte header (in IPv6). The total header size is 60 bytes for a payload of 30 bytes.