If your business has two locations, each with its own local area network, and you want to connect them together, how do you do it? The first idea that comes to mind is a dedicated line running from point to point. You order a T1 or T3 line and you enjoy continuous and exclusive use of it for the duration of the lease. That's great when you are basically looking for a piece of wire to connect two far flung networks that are busy all the time.
But what if your business locations are on opposite sides of the country and they only need to exchange sales and inventory data once a day. Or what if you have multiple locations? If you don't have a need to load up a T1 line or a bunch of them 24/7, there is another option that is a very mature technology but may be much more affordable. It's called frame relay.
Frame relay is a digital transmission service that is something of a cross between the public switched telephone service and a point to point dedicated line. With frame relay you don't have a length of wire "nailed up" between your locations. Instead, you have what's called a PVC or permanent virtual circuit within the frame relay network. When you order service, the frame routers are set up to know your location and all the of locations you are going to communicate with. Those are your permanent virtual circuits. Anytime you are using one of the circuits, it's just like having a direct line between locations. However, when you are not sending data, the actual physical network lines are busy transferring other customer's data.
The advantage of this arrangement is that you don't have to bear the whole cost of maintaining an extensive private network that you're not using all the time. The frame relay provider maintains the network and you pay only for your usage of it. Unlike the Internet, frame relay networks offer you a CIR or committed information rate. That's the speed of reliable transmission that you are guaranteed. In most cases, you will be allowed to "burst" above that rate for short periods of time, but the extra packets you send may or may not be guaranteed to get where they are destined. Frame relay networks are set up to be able to reduce congestion by dropping packets in excess of what you are guaranteed on the network.
Access to a frame relay network is done through an interface circuit known as a FRAD or Frame Relay Access Device. Sometimes it's called a Frame Relay Assembler/Disassembler. Most often, it's an option card in a router. Frame Relay network access can be as slow as a dedicated 64 Kbps ISDN line or a standard T1 at 1.5 Mbps or T3 at 45 Mbps. The shared network itself most likely runs at optical carrier speeds.
If you need to share data between business locations but wince at the cost of full time dedicated trunk lines, consider frame relay as a viable cost saving alternative.
John Shepler has been a published writer for over 30 years. With a background in electronics engineering technology, he has worked in a variety of industries including radio broadcast, aerospace and manufacturing. Involved in telecommunications since 1998, he combines his interests in writing and technology with T1Rex.com and T1 Rex's Business Telecom Explainer.
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