Effnet licenses header compression algorithm

Effnet licenses header compression algorithm
By Patrick Mannion, EE Times
January 4, 2002 (10:39 p.m. EST)
URL: http://www.eetimes.com/story/OEG20011120S0046

MANHASSET, N.Y. — Effnet Inc. says its EffnetEdge Header Compression Suite is the first commercial implementation of the Robust Header Compression Protocol, or RFC 3095, defined by the Internet Engineering Task Force. Intended for wireless links using the Internet Protocol, RFC 3095 is designed to shrink packet size, thereby increasing spectral efficiency and interactivity in wireless networks while reducing latencies and packet loss.

Wireless links suffer from a number of conditions that don't apply to wireline networks, said Rich Stamm, marketing director at Effnet, based in Mountain View, Calif. "As a result, they have very high error rates — as high as one in a hundred bits," he said. At that rate, according to Stamm, most headers will contain errors, resulting in lost packets.

The problem is exacerbated by the longer round trips typical of wireless nets. "Longer round-trip times mean that ackn owledgements [of] a problem with a compressed or real header can take quite some time, greatly affecting voice quality," said Stamm. In addition, the high overhead of IP packet headers makes a severe hit on the spectral efficiency of any given wireless link, he said.

"For IPv4, if you carry voice-over-IP to a mobile handset, you're spending 66 percent of the bandwidth on the header alone," he said. "For IPv6, it'll be even more, up to 75 percent."

Assuming the use of Internet Protocol version 6, a typical voice-over-IP packet "might have 20 bytes in the payload and 60 bytes in the header," but the header can be "reduced to 1 byte, or 5 percent of the total packet size" by using the robust header compression (ROHC) algorithm, said Stamm. This gives a 300 percent improvement in spectral efficiency if the IPv6 header is removed, he said.

While header compression goes a long way toward freeing up extremely valuable wireless bandwidth, for which carriers have paid heavily, smaller packets also impro ve upon the real-time response of the network, and hence its interactive capabilities.

"Smaller packets take less time to complete," said Stamm, "thereby allowing another stream of packets to get in and out."

An alternate solution to the problem of header overhead is to use larger packets, thereby making the header overhead a smaller percentage of the entire packet. "But when you do that, you lose the interactivity, since the incoming packet must complete its cycle before the outgoing packet can begin its own cycle," he said. "For voice, that's extremely noticeable."

The other advantage of smaller packets is that they're less susceptible to bit errors. "If the payload is corrupted in a voice packet, it's no big deal," said Stamm, "But if the header is corrupted, you lose the packet and you get into acknowledgements and retries, and you start to lose pieces of words."

The ROHC compression scheme is part of the UMTS Release 4 and 5 specifications, in which header compression is a fundamental component of the interactive multimedia subsystem. There, ROHC is specified for the transport of multimedia IP for interactive applications. "In the United States, we expect cdma2000 to adopt the same set of standards for robust header compression," said Stamm.

However, for any company thinking of designing it into their devices, RFC 3095 is a 168-page read. "That's where we come in," said Stamm. As the only commercially available implementation of RFC 3095, the EffnetEdge Suite is designed to unburden the designer from the risks and time delays inherent in a ground-up approach. To date, Nokia, Ericsson and Siemens are the only other companies actively developing solutions — but those are for in-house applications.

The Effnet suite includes products for RFC 2507 (IP header compression) and 2508 (compressed Real-Time Protocol) as well as RFC 3095. Fully standards compliant but with proprietary performance enhancements, the suite was designed by Michael Degermark, an Effnet employee who is also co -chair of the ROHC Working Group within the IETF. Degermark is also leading interoperability testing with Nokia, Ericsson and Siemens. "This guarantees that the implementation is robust, interoperable and kept up to date as new profiles are added by the IETF," said Stamm.

To facilitate integration, the suite's C-based reference implementations are platform independent and can migrate into various OS kernels. "We'll even offer to do the porting as a service if necessary," said Stamm. The memory footprint is approximately 200 kbytes and the suite works for both IPv4 and IPv6, "a must for the mobile world," he said.

The suite comes with a test and validation environment, with hundreds of test cases. It also provides a test-case generation language to create new packet streams and exercise features that designers might put into Effnet's code.

"We're also planning production implementations that are optimized for specific targets," said Stamm. "The first will be for the ARM core, which is in almost e very handset on the planet right now."

Available this quarter, the EffnetEdge can be licensed for $50,000 to $1 million, depending on the usage model. Both fixed-fee and royalty-bearing licenses are available.