Inverse multiplexing is a term that describes a scalable wide area access solution that is truly the opposite of traditional multiplexing. With traditional multiplexing, multiple data streams are combined and transmitted together over a single high-speed circuit. Inverse multiplexing, on the other hand, uses multiple circuits that act as a single logical channel to transmit a high-speed data stream. Because the term "inverse multiplexing" is a bit unwieldy, the shorter terms
"inverse muxing" and "imuxing" (pronounced eye-muxing) are frequently used. A number of factors have come together to make inverse multiplexing a major technology in contemporary internetworking environments. This booklet
examines those issues, discusses the advantages of several inverse muxing solutions and explains the key place of inverse muxing in the delivery of high-speed broadband services.
The Connectivity Revolution Only twenty years ago, simply placing computers on desktops was a revolutionary element in the day-to- day operation of businesses. Now, with desktop computing a well-established norm, the new, on going revolution is in the way computers are interconnected. Computer users are continually being offered, and
then demanding access to ever-more-powerful applications and services, regardless of the source's geographical
location. The challenge for network designers and implementers is how to successfully meet the rapidly growing connectivity requirements of their sophisticated user base.
The emergence of the local area network (LAN) as the core architecture in the corporate enterprise has had a dramatic impact on the networking industry. One of the chief characteristics of Local Area Networking is the relatively low cost of bandwidth, with many LANs today operating at 10 and 100 Mbps Ethernet speeds. Newer Ethernet technologies have increased the choice of operating speeds by orders of magnitude to one Gigabit per second, with 10 Gbps moving toward industry standardization. With higher LAN speeds readily available, increasingly sophisticated, bandwidth-intensive applications have become common. There has always been an asymmetrical relationship between LAN and WAN bandwidth. Many organizations use 56/64 Kbps services for wide-area connectivity. Larger organizations might employ T1 WAN services, which still require LAN traffic to be significantly throttled down (to 1.544 Mbps). While T1 rates represent a significant amount of bandwidth, some organizations
may need even more. For organizations needing native LAN speeds over their WAN links, the primary alternative
has been relatively expensive T3 (45 Mbps) circuits. Similar LAN/WAN asymmetry exists in Europe, where the E1 (2.048 Mbps) and E3 (34 Mbps) services are frequently unavailable or cost-prohibitive. For organizations with high-speed ATM LAN or backbone networks, the discrepancy between local and wide-area bandwidth can be even greater.
Network service providers are taking steps to meet the needs of their end customers to alleviate the WAN
bottleneck. High speed Frame Relay and wide-area ATM services can deliver WAN bandwidth more closely
matched to LAN speeds. As we shall see, there are also solutions that allow companies to extend their LANs over the wide-area at speeds between T1 and T3 (or the European E1 and E3).