Broadcasting

November 16, 2006
Ensuring IPTV QoS: The picture must be clear

D. Wilson

NEW DELHI -- It has been said that the spending by the IT industry on R&D alone is equal to, or greater than, the entire size of the broadcast industry. This tremendous amount of investment has led to great advances in computer technology and office productivity over the years. This can be seen in faster desktop computers, more capable software applications, new and innovative services online, and interactive games that are a world away from Pong and Asteroids.

The broadcast industry has not been untouched by these improvements. Today, we can see general computing and IT technologies reaching almost every aspect of the broadcast business – from the journalist and camera crews working on primary content, to the creation and editing of that content, to, finally, the management, control, and transmission of that content to viewers. Similarly, network technologies have rapidly advanced to the point where ISPs are offering 10, 25, or even 100Mbps Internet service to the home. At the same time, off-the-shelf computers are sporting gigabit processors with gigabyte storage capacity.

Soon, the day will come when proprietary “broadcast interfaces” such as SDI and AES are rendered expensive and archaic relics of the past. In their place will be the IT-centric interfaces and protocols which still must somehow be retrofitted to accommodate the demanding and unique real-time requirements of professional television.

Handling video more efficiently

Building an IP network that supports video is a challenging job. Video is special because of the size of video files and its immediacy. Sending video on a data network puts a tremendous strain on the network so engineers have to find ways to transmit data in a more efficient way.

When video is transmitted over an IP network to multiple users, it usually uses a technique known as multicasting. In multicasting, instead of the video server handling sending a separate video stream to each TV viewer (known as unicasting), the video stream is sent out to a router, which duplicates the data, splits it and sends it off to other routers at different parts of the network. The other routers, in turn, receive the data, duplicate it and then send them off. In this way, the data is distributed in a tree-like structure that puts minimal strain on the network.

However, while this is very efficient, there are technical issues with the scalability of this structure. In addition, real-time video is usually sent using a different protocol from other data. Most data on an IP network is sent using TCP (Transmission Control Protocol). This is a way of sending packets of data so that if any packets get lost, the source is informed, and the missing packets are resent. This ensures that all files sent over are complete. However, TCP is not used to transmit real-time video. This is because the process of feedback takes too long. Instead, video is usually transmitted using a protocol called UDP (User Datagram Protocol). UDP is a very simple protocol that does not require any acknowledgement of success or failure of the transmission. It does not send feedback or call for retransmission if packets are lost.

As such, UDP is inherently unreliable. If a packet of data goes missing, the source will never know and the recipient will never be able to retrieve dropped packets. To make things worse, while UDP is supposed to be transmitted in an agreed upon fashion, not all UDP transmissions follow this standard. This further complicates the whole transmission process. The design of the IP network then is a wildcard that can have tremendous influence on the signal quality of the transmission, and hence the quality of the picture.

Keeping an eye on things

Given that video delivery over IP is going full speed ahead despite these limitations, companies need a way to monitor their networks to ensure that they are able to deliver a high quality of service to their customers.

Traditionally, operators are employed to eyeball a bank of monitors to look for problems with the video transmission. In a digital world, however, this is no longer viable. The explosion of channels means that it is not humanly possible to monitor hundreds of channels, which might include programs with options for soundtracks and subtitles in different languages. How can an operator know if the soundtrack and subtitles on any one channel are the right ones?

In addition, given the complexity of today's networks, determining what causes a problem is a big challenge as well. The source of the problem could lie in any number of places, from the multicast router, to the way the video was compressed, or at the head-end receiving the satellite feed.

Given all the potential problems associated with service delivery when using an IP network, it is critical that companies relying on IP have automated and cost-effective solutions that help them to monitor their network so they can deliver on their service level agreements.

Ideally, such a system would monitor service and signal integrity throughout the entire chain of transmission across all media. The monitoring systems should be able to do a check and compare at each stage of the delivery chain. This system should also be able look for problems on the transmission chain that are occurring now as well as to spot problems that are likely to come up.

Such a system should be able to check that the right subtitles and languages are being delivered on the right channel. That system should also be able to check the signal integrity to ensure that the data is being transmitted without problems. This means the ability to interface in a multi-vendor environment. Such a system needs to be able to monitor all of the equipment regardless of geography. It should not matter whether the equipment being checked is in the next room or the next city. And ideally, this system should also be able to plug into other information systems such as the billing platform or customer information database so that customer support issues can be dealt with quickly.

On an IP network, a problem with the TV transmission isn't a question of the wrong frequency being used. IP networks are very efficient at transmitting data in general, but transmitting a television program, which is larger and requires immediate delivery, is more challenging.

Quality of service (QoS) is a business issue when transmitting video over the IP network. When even channel surfing becomes a problem, companies need to pay close attention to the customer experience that results from a move to IP. To ensure service and signal integrity, preventive monitoring across the entire transmission chain is not optional. The volume, complexity and rapidity of data flow requires automated, integrated solutions. In the era of digital video over IP networks, "golden eyes" alone are not enough.

(The author is president, Pixelmetrix Corp., Singapore)