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Remote Site Access and Connectivity via Wireline
The minute I leave a transmitter site I have a concern about remaining in contact with all the equipment that is running there. Having remote access to the site is very important for my peace of mind. There's nothing worse (in our line of work) than having something bad happen at the transmitter site, and not being able to see exactly what it is. The ability to take action remotely is clearly just as important.
The business continues to evolve: I used to have one transmitter site to worry about. Now it's a half-dozen. We all know that studios used to be occupied all the time -- and that's no longer the case. For that reason, having remote access to the studio site has become important as well. As the number of sites a typical Broadcast Engineer has to deal with increases, it's plain to see that remote access has become an absolute necessity. That's our topic this time around -- specifically, via "wireline". (Next month we'll talk about wireless access to a site.)
When I say "wireline" access I mean more than just the ability to call up a site on the phone. For many years that was good enough -- but it just isn't any more. Sure, it's great to able to talk on the phone -- and dial-up access can provide for a great backup for more complicated systems. ("More complicated" means they need to be booted occasionally.) Dial-up only access is very, very limiting though.
The nature of remote sites sometimes precludes them from easy wireline access, but for purposes of this article we need to assume that some sort of connectivity to the local telephone (or cable TV) company exists.
If you know you can get a T1 from your local telco than more likely than not you are already using one for an STL. The question then becomes one of capacity. What data rate do you need up to the site? Are there any spare timeslots available on the current link, and if so, can they accommodate the data rated needed?
The most common T1 STL in use is probably the Harris/Intraplex STL HD. This system was designed to accommodate IP transport for HD radio. At bare minimum, the transport for HD uses two timeslots (128kb/s) and as such won't accommodate any other uses for data at the far end. On the other hand, if you find yourself with an Intraplex system, with spare timeslot capacity, you might want to consider a LAN extension by way of a pair of Harris DS64NC cards and a pair of MA427 interface cards. Each available timeslot adds 64kb/s to the total available across the link.
A pair of DS64NC cards makes up a LAN bridge, which is a simple means of making a Layer-2 (Ethernet) connection between two isolated locations. The network number will be the same on both sides of the bridge. Another advantage of the LAN bridge (aside from ease of setup) is that a certain amount of traffic regulation is afforded to your system; the bridge only passes frames from location to location if they truly need to pass.
Another option is the Moseley SL9003T1. This device also allows the user to make use of part of the T1 bandwidth for the transmission of data via IP. Each end has an Ethernet interface and the system acts as a LAN bridge. There is, of course, a tradeoff between how much data you can use for audio transport and how much you can use for data transport, since the sum total is limited. As an example, with the SL9003T1 you can go up to 512kb/s while passing an uncompressed audio pair at a 32kHz sample rate.
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