IPTV is gearing up
Nov 1, 2006 12:00 PM, BY BRAD GILMER
Driving data from A to B faster requires a tech shift.
IPTV is one of the most talked about topics in our industry. It is changing workflows, lowering costs and providing new opportunities. Yet the only difference between traditional television and IPTV is the underlying delivery mechanism. So why is IPTV considered such a powerful technology?
It is important to realize that a lot more than the delivery mechanism is changing. (See “Why IPTV thrives.”)
Defining IPTV
Before reading any further, you should be aware that the IPTV terminology is evolving. Some people use the term IPTV to refer to video over IP. Others use IPTV to refer to delivery of content to the home, while reserving video over IP for professional applications.
While both of these terms correctly refer to IPTV, using the abbreviation VoIP to mean video over IP should be avoided at all costs. VoIP is used in the telecom industry to indicate voice over IP.
Is IPTV all hype?
Figure 1. TCP over IP frequently suffers from congestion collapse. If a link is congested, TCP will cut transmission rates by 50 percent until it finds a speed at which the transmission of packets is successful. In most algorithms, the time for TCP to reach full speed again can be orders of magnitude greater than the time it takes to throttle back. This is one of several reasons why TCP transfers may fail.
Click image to enlarge.
Some people in the industry believe that IPTV is a lot of hype and that it will never be successfully used for broadcast-quality video. I think they are wrong.
That said, if you try to send IPTV over a typical corporate network or over the Internet, you will fail. The cause of the failure will depend on what you are trying to do.
For example, if you are trying to FTP a large video file, the transfer will fail because FTP does not support the transfer of large files (files larger than 2GB), or because the traffic throttling mechanisms in FTP all but guarantee that a large transfer will fail in most situations. (See Figure 1.)
FTP exchanges files over any network that supports Transmission Control Protocol (TCP) over IP. TCP over IP frequently suffers from congestion collapse. If a link is congested, TCP will cut transmission rates by 50 percent until it finds a speed at which the transmission of packets is successful. In most algorithms, the time for TCP to reach full speed again can be much greater than the time it takes to throttle back. This is one of several reasons why TCP transfers may fail.
If you are trying to stream a live, high-bandwidth feed over the Internet, the characteristics of the network will likely result in numerous dropouts and perhaps in a complete failure of the link. But a video engineer experienced in IPTV knows not to use regular implementations of FTP for large video file transfers and that error correction will be required to transmit IPTV over the Internet.
Human error
Broadcasters have been using IP-based video transport for several years. Most of these broadcasters use specialized private networks, in many cases employing their own dark fiber-optic cables. IPTV has been used extensively to broadcast Olympic, football and baseball games.
Once the initial configuration is complete, IP-based contribution networks can operate for many days or weeks without a single error. The greatest source of errors in these networks comes from humans. People take equipment down for maintenance, expecting that end users will not notice the disruption as the network re-routes packets to their final destination. This may work for most IP-based traffic, but it definitely does not work for IPTV.
| Want to use this article? Click here for options! |  |
