ROHC

ROHC in the TCP / IP protocol stack :

application	HTTP	SIP	RTP	...		ROHC
transport	TCP		UDP
Internet	IP ( IPv4 , IPv6 )
Network access	Ethernet		Token ring	FDDI		...

Robust Header Compression (ROHC) is a method for compressing IP , TCP , UDP and RTP headers, which is described in RFC 3095 of the IETF from 2001.

It is mainly used in wireless connections, which are characterized by a high bit error rate of up to 10 ⁻² and round trip times of up to 100–200 ms. ROHC is used in UMTS and LTE mobile radio networks in the Packet Data Convergence Protocol (PDCP) . While the compression of the payload in multimedia and VoIP streaming is done by the application layer, the header data of each packet occupy a lot of bandwidth. Without compression, the overhead of IP (20 bytes or 40 bytes), UDP (8 bytes) and RTP (12 bytes) adds up to 40 bytes per packet for IPv4 and 60 bytes for IPv6 for typical Voice over IP applications. depending on the codec used, only 15 to 20 bytes of user data are transported per packet. This imbalance is intolerable in mobile use, where bandwidth is expensive and scarce.

ROHC typically compresses these 40 or 60 bytes into a few bytes (depending on the description of the technology, the achievable size is between 2 and 5 bytes) by using a compressor in front of the transmission channel with limited bandwidth and a decompressor behind it. For the compression, the similarities between the header data of several packets of the same connection and the predictability of the header data of the different protocols are used. A large part of the header data can be viewed as static or quasi-static.

ROHC can be understood as a compression framework that can be expanded using packet flow profiles for new protocol combinations and is located in the ISO / OSI model between the IP-based network level and the link level.

See also

• TCP / IP reference model
• CSLIP
• Packet Data Convergence Protocol

Web links

• Official charter of the ROHC IETF working group
• RFC 3095 - "ROHC Framework and four profiles: RTP, UDP, ESP, and uncompressed"
• RFC 3096 - "Requirements for robust IP / UDP / RTP header compression"
• RFC 4815 - "Corrections and Clarifications to RFC 3095 "
• RFC 3843 - "RObust Header Compression (ROHC): A Compression Profile for IP"
• RFC 4019 - "RObust Header Compression (ROHC): Profiles for User Datagram Protocol (UDP) Lite"
• RFC 4995 - "The RObust Header Compression (ROHC) Framework"
• RFC 5225 - "RObust Header Compression Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and UDP-Lite"
• A free implementation of ROHC on sourceforge.net
• A free and efficient library implementing the ROHC standard

Footnotes

1. ↑ Header Compression Schemes for Wireless Internet Access ( Memento of the original from September 10, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
2. ↑ The concept of robust header compression, ROHC (PDF; 399 kB)