Cabletron Systems CyberSWITCH CSX400, Руководство пользователя

Страница: 30 / 275

About the CSX400
16 CSX400 and CSX400-DC User’s Guide
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).