Over the last 20 years I've used the whole gamut of wireline STLs, including those from Graham-Patten, QEI, Intraplex and now the APT Oslo from WorldCast Systems. We use the Oslo for the main STL system for all of Clear Channel's FM stations here in New York City — and my hunch is that Oslo is well on its way to becoming one of those classic pieces of equipment that engineers will talk about for years to come. Oslo is a frame-based system (3RU) that accepts plug-in modules performing various functions. An entire system is made up of two frames.

Putting the system together

As with any piece of equipment with a tremendous amount of capability, configuration of the Oslo involves many choices. First, the user decides the number of audio channels to be transported along with the type (if any) of audio encoding (including the audio bandwidth and word length). These are the factors that determine the number of bits that need to be assigned to the payload audio. The user may also decide to add auxiliary data services, which will use part of the overall available bandwidth. By using two of the T1 transport modules, up to four T1 circuits can be configured, allowing for up to 96 timeslots (6.4Mb/s of available bandwidth). Here in New York we use the Ethernet transport module, and we use about 11.5Mb/s of data over a 100baseT connection.

Another configuration option for Oslo is to use one T1 interface card (connects up to two T1s) in addition to an IP/MUX card (Ethernet transport). This allows the capability to drop and insert timeslots from T1 to Ethernet and vice versa.

Once the system requirements are determined, the factory will put the system together, configure and test it prior to shipping.

The bench test

When the units arrived, I connected them via an Ethernet crossover and finished the final configuration myself. We hadn't decided on the IP addresses when the unit was tested by the factory. I used this opportunity to learn how to use the NMS GUI as well. I set up a hub so the computer was on the same network as both the MCU cards (these are used to communicate with and configure the system).

Once the GUI was running, I viewed a page called the tree, which shows only the computer. From there I added icons to the tree view to correspond to each individual frame. Double-clicking on the frame icon opens all the unit-specific configuration tabs.

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