Cisco Cisco IOS Software Release 12.4(22)XR

In many mobile services and applications, the payload size of an IP packet is smaller than the IP header. 
These services and applications include VoIP, interactive games, and text messaging.

A full size IP header is required to successfully route a packet through a complex network. However, the 
full size header is not required for the packet to travel a single link in that journey. You can compress the 
header for travel across the one link. This can reduce the size of the header by 90% or more. The smaller 
header size saves bandwidth and uses network resources more efficiently. Header compression also 
reduces packet loss and improves the interactive response time.

PDSN uses Robust Header Compression (ROHC) for compressing and decompressing the SO 67(Aux 
A10) traffic between MN and PDSN. ROHC is an efficient and robust compression scheme. This is 
required due to the high BER and long RTT common on 2.5G and 3G links.ROHC compresses excess 
protocol headers before transmitting them across a link. It uncompresses them at the other end of the 
link. The redundant header fields of the packet allow compression. You can also compress consecutive 
packets in the same packet stream. ROHC uses an extendible framework of packet stream profiles. The 
profiles include IP/UDP/RTP, IP/ESP, IP/UDP and Uncompressed

The ROHC standard is detailed in IETF RFC 3095 and related RFCs.