Implementation of Header Compression in 3GPP LTE

Header compression is the process of reducing protocol header overhead in order to improve link efficiency while maintaining the end-to-end transparency. Robust header compression (ROHC) is a scheme for IMS (IP multimedia subsystem) and MBMS (multimedia broadcast multicast service). ROHC is defined for 2.5 Gm (GPRS) and according to 3Gpp2 next generation network, in CDMA2000 1x EV-DO and 1x EV-DV (Release B and onwards) system. ROHC specifies compression of IP headers including IPv4, IPv6, RTP and ESP on a per hop basis. The compressed header size is reduced to around 1-3 bytes. This header compression can be implemented in mobile handsets and all of the wireless infrastructure equipment upstream BTS/NodeB. Header compression basically includes generation of IP context to send on wireless device and each IP context is given a sequence number which is encoded before sending the information. The audio-video streams is first encapsulated in RTP (real time transport protocol) packet, which is then included under UDP packet, and finally IP packet carries this whole UDP & RTP data. The compression takes place at the radio layer defined at PDCP link layer. ROHC is very robust against bit errors on the link and also against errors introduced due to long RTT. In addition, it results in very high compression ratios, which increase effective link bandwidth and decrease packet processing requirements in power sensitive downstream devices.