estination. Once received, the I-MUX reconstructs the frame and presents it to the codec (or other high-bandwidth device). Depending on the configuration, I-muxes can perform additional tasks. Some are switches (hubs) that patch incoming channels to outgoing channels. Others receive ISDN PRI signals and convert them to T-1 or E-1/CEPT. An I-MUX may, among other things, convert protocols, perform overflow routing, and provide private line back-up service. When I-muxes were first introduced, they could not interoperate-identical devices had to be installed on both ends. This presented another obstacle for inter-company videoconferencing. To address the problem, a consortium, which included almost 40 vendors, developed the BOnDInG standard; the first draft was approved on August 17, 1992. BOnDInG stands for Bandwidth On Demand Interoperability Group. The BOnDInG specification describes how I-muxes can dial up channels across a network and combine them to create a single higher-speed connection. BOnDInG is discussed in more depth in Chapter 13. FOLLOW THE MEGABIT ROAD Today, organizations can get as much bandwidth as they need. Internet Protocol (IP) networks offer all-in-one support for voice, data, image, and motion video and have, therefore, become the norm. At the bottom of the network, however, are more choices than ever before. Cable Circuit-switched Networks modems and DSL modems have become the standard for connecting homes and even backup connections for small businesses. However, the real news is that wireless is displacing wired access. At offices, DS-1, DS-3, and a technology known as Synchronous Optical NETwork, or SONET have become the common physical network connections. Above the physical layer (but below the networking functions of the upper layer transport protocols) lies another technology known as asynchronous transfer mode (ATM). Above the ATM layer are two basic services: those that are designed for variable bit-rate (data-oriented) transmission and those that are aimed at constant bit-rate (str