 of 1MHz to 600MHz. ISO/IEC11801:2002 Category 7/Class F is a cable standard for Ultra Fast Ethernet and other interconnect technologies that can be made backward compatible with traditional Cat 5 and Cat 6 Ethernet cable. Cat 7, which is based on four twisted copper pairs, features even more stringent specifica- tions for crosstalk and system noise than Cat 6. To achieve this, shielding has been added for individual wire pairs and the cable as a whole. The predominant cable categories in use today are Cat 3 (due to widespread deploy- ment in support of 10Mbps Ethernet-although it is no longer being deployed) and Cat 5e. Cat 4 and Cat 5 are largely defunct. Applications of Twisted-Pair The primary applications of twisted-pair are in premises distribution systems, tele- phony, private branch exchanges (PBXs) between telephone sets and switching cabinets, LANs, and local loops, including both analog telephone lines and broad- band DSL. Analog and Digital Twisted-Pair Twisted-pair is used in traditional analog subscriber lines, also known as the tele- phony channel or 4KHz channel. Digital twisted-pair takes the form of Integrated Services Digital Network (ISDN) and the new-generation family of DSL standards, collectively referred to as xDSL (see Chapter 12). Narrowband ISDN (N-ISDN) was introduced in 1983 as a network architecture and set of standards for an all-digital network. It was intended to provide end-to- end digital service using public telephone networks worldwide and to provide high-quality, error-free transmission. N-ISDN entails two different specifications: Basic Rate Interface (BRI)-Also referred to as Basic Rate Access (BRA), BRI includes two B-channels and one D-channel (often called 2B+D). The B-channels are the bearer channels, which, for example, carry voice, data, or fax transmissions. The D-channel is the delta channel, where signaling takes place. Because signaling doesn't occur over long periods of time, where allowed by the service provider, the D-channel can also be used to carry low-speed