When network radio first came in to existence, the only means of real-time distribution of audio was the telephone company of course. Obviously there was also the transcription disk; then came tape, then analog satellite, then CDs, then digital satellite, ISDN, and finally the various methods based on IP. Interestingly enough, we've kind of come full-circle, because IP is almost wholly done on the wire, just like the old days.

While you can still use satellite distribution of course, and ISDN still exists for the most part, the ubiquitous nature of Ethernet and the Internet make IP distribution worth considering.

Case #1

The first example is that of the Classical Network from WWFM at Mercer County Community College, in Trenton, NJ. In addition to its carriage on WWFM, the Classical Network is distributed to three other full-service FM stations in New Jersey and Pennsylvania: WWNJ Toms River, NJ; WWCJ Cape May, NJ; and WWPJ, Pen Argyl, PA. The Classical Network is also heard via WKCR-HD2 in New York City, as well as WKVP-HD2 in Philadelphia. Mercer also originates a jazz network known as JazzOn2; this network is carried on the HD2 facilities of WWFM, WWPJ and WWCJ.

To distribute the two network feeds, Mercer chose the APT Horizon from Worldcast Systems. This single rack unit is a full-duplex, two channel stereo codec designed to enable real-time transport of broadcast quality audio over IP networks, using linear audio or Enhanced Apt-x coding. A 10Base-T/100Base-TX RJ-45 interface is used for both audio transport and remote control/supervision. Network quality of service is provided using DiffServ (though keep in mind that QoS must be supported end-to-end on the network to truly take advantage of this feature). Some other nice features of the Horizon are its available audio bandwidth: 10Hz up to 24kHz (obviously dependent upon the algorithm chosen); four optically coupled GPIO inputs, and seven relay-closure outputs; event alarm and logging; and support for SIP and SDP, which means you can communicate with other manufacturers' codecs as long as they're N/ACIP compliant.

The WWFM studios have access to the public Internet through two separate ISPs: Comcast and Verizon. Software from Radware is used to ensure the streams continue make it to the public Internet, even in the event of a failure of either of those two connections.

WWCJ and WWPJ each have their own unicast stream served by the Horizon used for JazzOn2. The Horizon used to encode the Classical Network is working a little harder: It serves up unicast streams for WWPJ, WWCJ, WWNJ, the New York City stream, Blue Ridge Cable in the Eastern Pennsylvania region, translator K216FW in Steamboat Springs, CO, as well as the Philadelphia stream.

Worldcast Systems APT Astral

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At the far ends, Mercer uses the APT Astral from Worldcast Systems. This 1RU device comes standard with the ability to provide audio bandwidth of 22.5kHz, using algorithms such as linear PCM (16- and 24-bit resolution) as well as Enhanced Apt-x (also 16 or 24-bit resolution). It also supports MPEG Layer 2, Layer3, G.711 and G.722, and it's N/ACIP compliant. In addition to a serial data path, which could be used for RBDS or PSD (for HD radio), it has eight GPIO inputs and outputs. User configuration of the Astral allows for management of network conditions such as packet size, buffers and QoS.

Worldcast Systems APT Horizon

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Mercer has plans to install APT Horizon Nextgen codecs at both the New York and Philadelphia affiliates to the Classical Network. This will allow for the implementation of Surestream, a feature from APT that makes use of two independent (unicast) streams, each carrying the same data, received by two different physical-layer connections on the receive side.

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