07.10.2006 10:58 AM
With the right FEC, IPTV can go a long way

Think packet loss is a bad thing? Think again, according to Digital Fountain President and CEO Charlie Oppenheimer.

A little bit of packet loss might indicate your IPTV network is sized just right, and with the right forward error correction, no one will be the wiser, he says. Digital Fountain has racked up a number of impressive industry wins for its core forward error correction technology (DF Raptor) in a wide range of fields, including mobile multimedia, automotive, government and defense. Now, with the addition of the DF ToughStream Engine for streaming applications, the technology is ready to make its mark on the IPTV landscape, and Oppenheimer explains exactly why.

IPTV Update: Could you pleasediscuss your company’s role in the IPTV space and the benefit your flavor of forward error correction delivers?

Charlie Oppenheimer: For IPTV, the benefit Digital Fountain’s technology enables is “television quality” over ordinary IP networks. Digital Fountain’s ToughStream Engine provides application and equipment vendors with the easiest way to incorporate FEC technology into streaming applications. ToughStream “makes streams tough” protecting video and audio streams from common impairments including packet loss, latency and jitter, and lost packets typical of IP networks, allowing reliable and efficient delivery to the end-user without interruptions.

Our technology makes sure the data is received in its entirety, while minimizing the resources that are used in terms of networks and hardware. The DF ToughStream Engine is the easiest means to make IPTV truly entertainment or television grade. As a small software engine (library) that incorporates our forward error correction technology, DF Raptor FEC, the DF ToughStream Engine is built directly into servers and set-top boxes. The DF ToughStream Engine itself provides extensive packet loss protection using minimal bandwidth.

IPTVU: Why is your method the easiest way to get the television quality experience via IPTV?

CO: IP networks, such as the Internet or IPTV networks, have the characteristic that by design, data reliability is “best effort” — meaning that the network will “do its best” to get the data delivered from the source to the destination, but there is actually no guarantee that all the data will be delivered. People ordinarily think of packet loss — packets that do not get from source to destination — as being a bad thing. Digital Fountain is helping people understand that packet loss in modest quantities can actually be a good thing.

The reason why IP networks are “best effort” is the same reason why they are economically sound and why the world is standardizing on IP. In an IP network, all of the nodes share the same network resources and all data is co-mingled. If the IP network becomes congested, routers (which interconnect the networks together) will “drop,” or not forward, certain packets, which means these packets will be considered “lost.”

Generally, if there is packet loss in an otherwise sound network, it just means that there are momentary periods of congestion. Packet loss is good because it indicates that the IP network is appropriately sized. If there were never any packet loss, it would be similar to designing an interstate highway system big enough for every car in America to be on the road at the same time, with no traffic jams. It just does not make any sense — economically it would be a flawed idea.

With slight packet loss, the network is sized appropriately, as there is a little bit of congestion periodically.

Regardless of packet loss, the DF ToughStream Engine ensures that all of the data is still arriving at the destination so that the set-top box has a perfect playout. In essence, our technology enables quality entertainment while allowing for a little forgiveness of network congestion.

IPTVU: So what makes your FEC unique? And how does it accomplish it?

CO:In forward error correction there are two broad families — error coding and erasure coding. Digital Fountain’s FEC technology is an erasure code.
Error coding is in every digital communications system in the world today. Incorporated into the physical layer of a network or a wireless digital transmission device, error codes correct bits that are somehow corrupted or ambiguous in transmission. Erasure coding is a complement to error coding. It is not used in place of error codes, but rather in addition to error codes. Erasure codes recover data that is lost in transmission, ensuring the data received is valid.

Digital Fountain’s DF Raptor FEC technology and ToughStream Engine are unique in multiple ways: The first is that every other forward error correction code has a property known as a rate. A rate is a ratio that defines, in a fixed fashion, the amount of correction that can be done. For example, a three-quarter code — a ratio of three to four — is the amount of total information that can be generated in relation to the original. Digital Fountain’s DF Raptor technology has the property of no rate — there is no fixed ratio between the original information and the total amount of information that can generated. It is completely dynamic.

And so, the DF Raptor FEC technology is able to accommodate a great range of conditions, from minor packet loss to significant packet loss. In Digital Fountain’s various deployments, we deal with those who may lose only one packet out of 1 million, to those who might have as high as 90 percent packet loss, say on a battlefield. This technology allows you to accommodate that range with a single algorithm.

Additionally, our technology is exceptionally computationally efficient — there is no need for much processing horsepower to accomplish this. For example, if you took a Reed-Solomon error code, or similar forward error correction algorithm, and look at the computational requirements, it will increase with the square of the amount of data over which you are performing the algorithm. However, with the DF Raptor FEC technology, computational requirements scale linearly with the amount of data, and have lower overhead, which is the amount of bandwidth used incremental to the original source data rate.

IPTVU:You said your algorithm requires code on the server and the set-top box in an IPTV environment. What partners are you working with in the IPTV space?

CO: We work with a number of companies in the IPTV market. In particular, our technology is commercially deployed in Japan by NTT through our partner Sumitomo Electric Networks.

IPTVU: Could you put the significance of this FEC technology into perspective in the IPTV environment?

CO: NTT conducted a study a few years ago to determine whether to deploy Digital Fountain’s technology in their production service. The question NTT asked was, “Is Digital Fountain’s technology important and required?” NTT placed the Sumitomo Electric set-top box with the built-in DF Raptor FEC technology in 300 subscribers’ homes and delivered various different video streams. NTT asked Sumitomo to modify the equipment so that it would randomly turn the DF Raptor FEC on and off when the consumers were watching.

Three statistics were measured:

  • whether DF Raptor was on or off;
  • how much packet loss there was during that viewing; and
  • how long the consumers actually watched.

NTT found that when packet loss was even one-tenth of 1 percent or less, viewing times doubled when the DF Raptor FEC was turned on. That ended the question on whether they were going to deploy the technology. DF Raptor was the ingredient that caused people to watch twice as much.
Digital Fountain’s ToughStream Engine is particularly important to IPTV providers because of two things I hear operators say regularly. One, if you ask operators how much packet loss there is, the number one answer is “We don’t have any.” Operators instinctively believe that if their network has packet loss, they would think this is the same as saying it is flawed. But as I said earlier, a little bit of packet loss suggests that the network was actually designed appropriately. So, in this sense, ToughStream enables operators to create economically sound networks.

Second, some operators suggest that consumers are growing accustomed to occasional errors and glitches on their screen. They say that because consumers are familiar with the Internet, minor packet loss will not matter because content delivery for IPTV will be much better than the Internet. Well, the NTT trial proves that consumers are sensitive to quality and higher quality drives usage. So, by protecting against errors and glitches, ToughStream can increase viewership.

Because IPTV is in the initial stages of commercial deployment, the importance of quality delivery and how much packet loss a network has are relatively new issues to be addressed in the industry.
What Digital Fountain is doing in the U.S. and around the world, similar to the NTT trial, is offering an evaluation system that allows operators to test ToughStream with their existing servers and set-top boxes.

Our trials show that, without the DF ToughStream Engine on, one-tenth of 1 percent packet loss every four or five seconds will produce a trace of blocking on the screen. As we move up to half of 1 percent, glitches become so frequent and so constant that it is not worth watching.

When the DF ToughStream Engine is turned on, it corrects the glitches and drop outs, allowing for perfect delivery of content. With the amount of packet loss increasing — 1 percent, 5 percent, 10 percent and up to 15 percent — the picture is still perfect. The DF ToughStream Engine can protect against any amount of packet loss.

IPTVU: How does this work?

CO: With Digital Fountain’s DF Raptor FEC technology included, the DF ToughStream Engine is embedded into both the server and the set-top box application and sits between the video application and the network.

In terms of required resources, it is particularly small — roughly 100kB of code. With CPU resources, it uses a minimal amount of processing. The DF ToughStream Engine presents the developer with a socket interface, the most familiar application-programming interface to software developers doing network software. Moving the data from the source to the destination is done transparently. The DF ToughStream Engine parameters are scalable and can be set to protect against specific amounts of packet loss, making it simple to incorporate this kind of protection into an IPTV deployment.

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