Inside the Radio Network
Backhaul, contribution and ingest
A network head end can house an amazing array of telecommunications. Some of the studios are located at the same location as the head end. For those, direct wiring via the router is the connection method. But for studios not on site or for remotes, there are various ways to connect. Common backhaul methods used to get programming to the head end include ISDN and T-1. For studios that require 24/7 connectivity, the point-to-point T-1 has been the method of choice. We can get high-quality audio across a T-1 and it has bidirectional paths for monitoring feeds and return cues (IFB). To send automation cues to the head end, we'll typically use serial or IP connectivity on the T-1 to send next event closures from a remote studio to the head end. These are to signal a commercial break or station identification. We use ISDN codecs to back up the T-1s in the event of a failure.
For short-form content or remotes like sporting events, ISDN works well. T-1 circuits tend to be impractical in these examples. While Internet codecs have become popular and work well, they introduce latency, which is terrible for live events, and shared Internet connections tend to be unreliable, even if they are broadband. In our experience, they are okay to file a news story, but not very good to go live with.
Lately, we're seeing an increase in the use of IP codecs over a PTP Ethernet link or MPLS. A few manufacturers make hybrid units that will connect to an IP link and use ISDN as a backup using an auto-failover feature. The quality on an MPLS or PTP Ethernet line is superior to a shared Internet connection in that the bandwidth is dedicated and the quality of service on the line is guaranteed by the provider. Latency is typically lower on these lines because of the higher quality of service. Audio quality over MPLS can be adjusted to various algorithms and compression schemes - it all depends on how much you want to spend for the bandwidth.
Another backhaul method is satellite, where some program producers with small networks of their own will deliver their program to us via satellite and we'll rebroadcast that. We downlink their signal, decode it, run it into our router as a source and then re-uplink it as necessary.
It is desirable to have the programs delivered to the network head end without any audio compression. While not always possible, we strive to keep all audio backhauls in linear PCM formats as much as possible to minimize transcoding effects downstream.
- continued on page 3
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