siness oriented applications running on their private Web servers. LAN-to-LAN Connectivity xDSL technologies have the potential to prove far more effective in low cost, high throughput, LAN to LAN connectivity than ISDN or traditional leased lines. Frame Relay Access Since xDSL operates at the physical layer, it could emerge as the most cost effective method of carrying frame relay traffic from the service subscribers to the frame relay network. ATM Network Access As with frame relay the xDSL technologies can also be used to carry ATM cells to an ATM access device, where they are statistically multiplexed over an ATM backbone. XDSL Types Digital Subscriber Line, or DSL, is fundamentally another name for an ISDN-BRI channel operating at the Basic Rate Interface with two 64 kbps switched channels and one 16 kbps packet switching and signaling channel. This circuit can carry both voice and data in both directions at the same time. xDSL refers to those various arrangements in which advanced modulating techniques are imposed onto the local channel in order to derive higher throughput in one or both directions. The various types of xDSL are described in the following paragraphs. HDSL High-bit-rate Digital Subscriber Line (HDSL) derives its name from the high bandwidth that is transmitted in both directions over two copper loops. HDSL has proven to be a reliable and cost effective means for providing repeater-less T1 and E1 services over two twisted pair loops. This proven technology has already resulted in the deployment of over 300,000 HDSL equipped circuits throughout the local access infrastructure. HDSL transceivers can reliably transmit a 2.048 Mbps data signal over two non-loaded, 24 gauge (0.5mm), unconditioned twisted wire pair loops at a distance of up to 13 kft (4.2 km) without the need for repeaters. Eliminating the need for repeater equipment and removal of bridged taps significantly simplifies the labor and engineering effort to ...
