Multicasting gets musical

Communications News, Feb, 1998 by Paul Sartain

Reaching more than 30 million households worldwide, The Box, a subsidiary of the box Worldwide, Inc., is an interactive, 24-hour, all music channel. Controlling how the latest and hottest videos get to our local channels is business-critical.

Our broadcast system worked well, but we wanted to smooth out how our videos got to the viewer selection libraries. Because the music industry changes so rapidly and new video clips are released constantly, we needed a way to efficiently and reliably send clips daily to local servers.

In the U.S., our music television service depends on an electronic distribution network to keep more than 100 nationwide Windows NT servers stocked with community-specific videos.

Viewers choose videos from a constantly updated menu of up to 300 videos displayed on their TV or on our Web site, and then dial a 1-900 number to order their selections. The cost of the video appears on the viewer's telephone bill.

Customers select videos by using a touch-tone telephone and accessing a video server unit stationed at a local cable or broadcast company. Videos are stored there as digital MPEG files and housed in a library.

When an order comes in, the server finds the video in the library and puts it in the broadcast queue behind other viewers' requests. We use proprietary computer systems utilizing MPEG2 decoders to transform these digital files into high-quality music videos that are then broadcast to everyone in the viewing area.

We had already made a first step towards simplifying video distribution by upgrading to a digital distribution system in our U.S. markets. This system transfers new videos as MPEG computer files over a two-way, interactive very small aperture terminal (VSAT) satellite network.

We originally used a simple file broadcast solution from Hughes Network Systems over our VSAT network, but found it slow and difficult to administer. The file broadcast's method of guaranteeing reliable file delivery resulted in very long transfer times for large MPEG video files.

We found multicast file transfer a compelling alternative to file broadcast. Multicasting allows a server to send a single stream of traffic to some but not all recipients in any given group, with the network replicating the traffic stream to the receivers.

Using IP multicast, our transmissions are now fast, reliable, and simple.

We chose Starburst multicast cast software from Concord, Mass-based Star-burst Communications as our IP multicast solution. The software, based on Starburst's multicast file transfer protocol (MFTP), guarantees 100% reliability of one-to-many file deliveries. Its reliability and speed stem from a negative acknowledgment (NAK)-based scheme for guaranteeing delivery.

We use the software to multicast 8-10 GB of MPEG music video files each week to more than 100 nationwide servers controlling local play lists. Starburst Multicast operates over our VSAT satellite network. We slashed our transmission time by more than 50% by removing the T1 link and increasing transfer reliability.

The NAK-based method for receivers to request re-transmission conserves network resources and speeds file distribution. The software only re-sends lost or bad frames, and re-transmission requests are batched into smaller NAK packets, further reducing the number of re-transmissions complete a transfer.