New Technologies for Distributing Public Radio Programming Over Satellite

The functional design of the ContentDepot^® is the result of many years of ongoing system consultation both with station and producer advisors as well as with independent system contractors. At the direction of the DI Committee, NPR Distribution developed the following operational requirements for the new system:

Consolidate ancillary data (metadata) to support new services such as HD Radio
Accomplish transition with minimal disruption to current station operations
Be able to adapt over time to new demands and technologies without a complete system rebuild
Use cost effective, supportable, and off-the-shelf equipment, so that the barrier of entry for new users of the system is lower than with today's system
Be capable of interfacing to a variety of distribution platforms, not just satellite
Provide data to producers about who's using their programs

After evaluating available technical solutions, the IP-based ContentDepot solution was selected because of its ability to meet these requirements and position the public radio distribution system for the future. IP protocols supported by the DVB-S (Digital Video Broadcasting - Satellite) standard are established and stable and already provide an industry-accepted method for transporting audio and data over short and long distances. Industry experts believe that IP transmission will continue to migrate to other applications and platforms throughout the broadcast industry.

Is the IP Streaming solution "cutting edge"?
IP over satellite is a well-established technology that has been subject to rigorous specifications on live audio delivery. Numerous systems use IP technology to deliver audio through local networks. The ContentDepot will use IP streams in a unique, integrated delivery solution.

Is IP the only solution?
No, there is more than one technical solution-each with its own benefits and disadvantages. Based on the criteria put forth, an IP based solution for both files and streams was the best fit.

What other solutions did we evaluate for live streams?
NPR Distribution evaluated several available technology solutions available for satellite distribution of live streams. We reviewed the traditional single-channel-per-carrier (SCPC) currently used by the PRSS, as well as multiple-channel-per-carrier (MCPC) systems, and the use of DVB MPEG audio streams.

In industry usage as well as proof of concept testing, DVB-S is an accepted international standard for digital satellite transmissions. When the performance and overall requirements for the ContentDepot were evaluated, IP was the best fit. The combination of IP using DVB-S transmission protocols offers us the benefits of two strong technologies and will position the PRSS for future growth and technology innovations.

Are there disadvantages of IP over satellite for live streams?
The only identified disadvantage is a slight increase in latency (delay). In today's satellite system, the end-to-end satellite transmission latency is 290ms behind "real time". This latency is a function of physics (speed of light) and the minor delays caused by encoding an MPEG file to send to the satellite and the decoding that occurs at a station downlink. Using the IP-based technology in the ContentDepot will increase this latency by an additional 400ms compared to today's system. The total latency for satellite transmission for the ContentDepot would be 700ms-well within the one-second specification that was established for today's system.

Will the additional latency in the system require compensation?
Stations and producers will ultimately determine whether the additional latency requires compensation. Much of the feedback from our users suggests that the additional 400 ms of latency in the ContentDepot falls within the operating norms for today's system and the specifications for the ContentDepot, and should not require correction by stations.

What was done to ensure the live streaming solution is reliable and robust?
NPR Distribution took a three-fold approach to ensure the quality of the IP over satellite streaming solution.

A pilot deployment of streaming decoders at stations validated performance of the units
NPR Distribution used data from those test sites to work with IDC and other satellite transmission experts to optimize downlink performance at sites not performing as expected
At the encouragement of the DI Committee, NPR Distribution conducted a rigorous technical review of the decoder performance.

How does audio sound when distributed through an IP-based system?
The audio encoding standard for the ContentDepot is MPEG1, Layer 2, exactly the same as today's system. The IP over satellite using DVB-S technology is simply a different transport mechanism. It does not alter the quality of the sound being delivered. Therefore, the audio quality is identical to today's system.