How ROHC works at LTE PDCP layer ?

Question

I heard a term "ROHC" at PDCP. But how it works for data plane ? Is it works for control plane messages too ?

Comments

ROHC is called Robost Header compression which does IP/UDP/RTP IP/TCP etc header compression. Basically it operates on DRBs which has IP data but not on SRB data which are RRC messages.

Answer 1

ROHC is an optional feature in PDCP.

For down link data packet PDCP performs the ROHC operation first and process further for cyphering (if configured).

During Voice traffic (VoIP), the size of the packets flowing through PDCP are very small with relatively big IP header and less data (32 bytes of payload and 60/40 bytes of header for IPv6/IPv4 respectively). To achieve big gain in bandwidth, PDCP uses RoHC to reduce the IP header size significantly, which in turn helps in carrying more payload data.

Answer 2

LTE network gives service to its user's through IP. IP header has significance when IP TCP/IP protocol is being used between nodes. Over the air interface there is no use do IP header. So to optimize radio resource. This header compression need to be done. ROHC at PDCP layer involve for this compression/decompression.
Please check:
RoHC is described in RFC 3095