Cabletron Systems HSIM-W6 manual Hdsl, Bridging and Routing

Chapter 2: About the HSIM-W6

HDSL

High-bit rate Digital Subscriber Line (HDSL) technology uses existing copper twisted pair cables designed for conventional analog voice transmission from a telephone carrier servicing area as a low-cost alternative to the quality and speed of fiber optic cables, and provides high-speed full-duplex digital transmission links of up to 1.544 Mbps. The WPIM-HDSL is easy to install in your network over existing telephone lines, and it is a portable investment if a business, or individual user plans to relocate.

HDSL is a direct connection technology that allows connections to be made for distances of up to 12,000 feet over 24 American Wire Gauge (AWG) unconditioned Twisted Pair wire. To obtain the Full T1 line Rate of 1.544 Mbps, two wire pairs are necessary (four wires). If one pair of wires is used (two wires), then data rates of 772 Kbps are supported, which is equivalent to one-half of a T1 line.

Bridging and Routing

Bridging — Bridging connects two or more separate networks together. The bridge examines a portion of each network frame called the header. This header contains control information for the frame. The bridge compares the destination address of the frame to a table of source addresses (bridges dynamically learn the physical location of devices by logging the source addresses of each frame and the bridge port the frame was received on in the source address table). In transparent bridging, the decision to forward the frame is based on this comparison. If the address indicates that the sending station and the destination station are on the same side of the bridge, the frame is not forwarded across the bridge. If the addresses do not indicate that, the bridge forwards the broadcast frame across the bridge to the other network(s).

Bridging allows frames to be sent to all destinations regardless of the network protocols used. It also allows protocols that cannot be routed (such as NETBIOS) to be forwarded, and optimizes internetwork capacity by localizing traffic on LAN segments. A bridge extends the physical reach of networks beyond the limits of each LAN segment. Filters can be used to increase network security in bridged networks, and restrict message forwarding by using user-built address tables (non-transparent bridging).

16 HSIM-W6 User’s Guide