Last month, we talked about Ethernet and IP and the advantages of a layered network stack. Let’s look at an application that uses these layers — the streaming of JPEG 2000 over IP.
JPEG 2000 (J2K) is one of a number of compression formats that are used by professional media companies every day all over the world. The purpose of this article is not to go into detail about how J2K works — there are many excellent tutorials and books on this subject — but, there still are a few things you should know.
First, J2K is generally used when high quality is required, such as for backhaul of national sporting events or for transfer of content between production facilities. Second, it can be configured to provide lossless compression, meaning that it is possible to prove that the video, after a compression/de-compression cycle, is mathematically identical in every way to the video prior to compression (lossless compression). Finally, the J2K specification does not cover audio; it only tells you how to compress video images.
In the 1950s, AT&T (note the capital letters — we are talking about the old telephone company) built a nation-wide, terrestrial, video network for the big three networks. This was an RF-based analog system that remained in place for many years. In the 1960s, AT&T launched communications satellites, and AT&T and other satellite operators added video capability to these platforms over time. As a result, in the 1980s, satellite became the dominant long-haul technology. During the dot-com boom, tens of thousands of miles of fiber optic cable were installed all over the country. The boom was followed by a bust, but the fiber was already in the ground. Thanks to this, megabit and now gigabit networking has become available on long-haul networks — at surprisingly reasonable prices in some cases.
If you remember from last month’s article, we said that one of the keys to networking is layering and encapsulation. Packetized networks use packets composed of a header and a payload section. The header contains information that is used to perform functions associated with that layer of the network functionality, and the payload section contains the information we want to transport across the network. Each layer performs a specific function. Let’s look at a specific example — the transport of J2K with audio over IP — to see how a layered approach is applied in a working scenario.
Figure 1 shows the protocol stack used in this case. We start with live professional video and audio — perhaps the output of a sports production truck. The video out of the truck is compressed using J2K, resulting in something called a JPEG 2000 Elementary Stream (ES). The audio at the side of the truck is already an AES stream.