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Extended Reach: Remote Network Connectivity
Trends in Technology, July 2010
How to establish remote connectivity for a bigger network footprint.
In at least a few of my previous articles I've written about the obvious advantages of having network connectivity at a transmitter site. This time around I'll cover several ways to establish that remote connectivity, how to safely use the public Internet for WAN functionality, and some of the other less obvious considerations you can do once that connectivity is established.
Over the last 10 years the number of ways to establish network connectivity has certainly increased -- mainly in terms of wireless connectivity. Before going there, though, let's review the ways of doing it by wire. With respect to the wireless connectivity I mentioned, many telcos have increased their data capacity to remote mountain tops and other tower farms. Generally speaking, it's much easier to get a T1 to these locations than it used to be. There are a number of ways to take advantage of this. The one most familiar to broadcast engineers is the use of a Harris/Intraplex system with the TDM interface. The CM5 (common module) in this frame has a built-in CSU and interfaces directly with a T1. In the configuration of this unit, a certain number of timeslots are assigned for a set of DS-64NCs (LAN bridge) cards. By way of the LAN bridge, packets that need to get to the far end are allowed through, and those that do not are not. This allows you to effectively extend the network that resides at your HQ (or wherever that one end of the system lives) in a very convenient fashion -- Ethernet on both sides of the bridge.
If in your case you find that you can afford an entire T1 just for data purposes, then you will find yourself more in the realm of the IT department (which could very well be you anyway, right?). In this case, you would acquire a set of routers that have T1 interfaces along with at least one Ethernet interface. (You may already have a router in-house that has this capability, or at least an empty slot into which a WAN interface can be installed that has a built-in CSU so it connects directly to a T1. You'll still need a router for the far end though.) With the entire T1 in use for your network connectivity, you'll have a 1.536Mb/s connection -- not too shabby. The neat thing now is the capability of allocating timeslots to different networks. It's beyond the scope of this article to describe how it's done, but a router that has multi-link capability (and at least two Ethernet ports) will allow you to do this. Here's the advantage: You could configure the router in such a way that one network allows for nothing but traffic for HD Radio. In this configuration you would allocate just enough timeslots for this -- and the remaining timeslots would then be used for the remote LAN purposes. Now if you (for example) download a PDF manual, you won't need to worry about causing dropouts in your HD Radio stream.
No T1? No problem
It's certainly possible that your remote site doesn't have T1 accessibility from your local telco, and in that event, you'll need to look at how to make the connection wirelessly. Probably the most well-known equipment for doing this is the Moseley LanLink. Like the Intraplex DS64NC cards, the LanLink functions as a network bridge -- and its interface is Ethernet on both ends. The LanLink provides up to a 1Mb/s data rate. Perhaps the most convenient aspect of the LanLink is that it operates in the 900MHz ISM band, so by way of a set of duplexers, you can use the 950MHz antennas already in place.
I should also mention that you could roll your own 900MHz ISM-band system. A few minutes of research on the Internet will reveal a number of companies that make transceivers for that band with Ethernet interfaces. Duplexers can be used with an established 950MHz link, or you could simply find some directional antennas for that band and make a new link.
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