A Performance Study on ROHC for Wireless VoIP Environments

A Voice over Internet Protocol (VoIP) packet is encapsulated by Internet Protocol (IP), User Datagram Protocol (UDP) and Real-time Transport Protocol (RTP) headers. In IEEE 802.11b wireless environments, the 802.11 data-link layer (i.e. Media Access Control) header and a checksum field should be added to the VoIP packet. Take G.711 as an example, the total length of IPv4 voice packet is 234 bytes, including 74 bytes (31%) header fields, and the total length of IPv6 voice packet is 254 bytes, including 94 bytes (37%) header fields. The header overhead occupies more than 30% wireless bandwidth. To reduce header overhead of the IPv4 or IPv6 voice packets, we designs a VoIP compression method which integrates Robust Header Compression (ROHC) with Session Initiation Protocol (SIP). Then, we evaluate the improvement of the proposed method compared to the original header format for both IPv4 and IPv6.