90 Chapter 3: Switched/Campus LAN Solutions
Wireless networks use four methods of transmitting infrared signals:
·
Line-of-sight networks--If the transmitter and receiver have a clear line of sight between
them, transmission and reception can occur.
·
Scatter infrared networks--The signals bounce off walls and ceilings and hit the
receiver.
·
Reflective networks--Optical transceivers transmit to receivers at a common location,
which redirects signals to its ultimate destination.
·
Broadband--Can handle high-quality multimedia and match cable networks.
Point-to-Point Transmission
Point-to-point technology is a bit different from the other wireless technologies in that it
transfers data directly from one computer to another.
Point-to-point communicates directly from PC to PC through walls and ceilings. Point-to-point
also supports data rates from 1.2 to 38.4 Kbps up to 200 feet indoors and up to a third of a
mile outdoors.
Other Wireless Technologies
Laser technology is similar to infrared technology. Like infrared technology, laser technology
requires a direct line of sight, and any object in the path of the laser beam blocks the
transmission.
Narrow-band (single-frequency) radio does not require line of sight. The broadcast range is
5000 square feet. The signal's high-frequency components don't allow it to pass through steel
or load-bearing walls.
Spread-spectrum radio broadcasts signals over a range of frequencies. The available
frequencies are divided into channels, or hops. The spread-spectrum adapters tune to a hop for
a predetermined interval and then switch to another hop for a predetermined interval.
Transmitter and receiver must be synchronized with regard to the hopping sequence.
A wireless bridge can connect networks up to 3 miles apart. Long range can cover 25 miles
using Ethernet and Token Ring topology. The cost can overcome or outweigh the need for
leased line or T1, although T1 can provide a much faster transfer rate of 1.544 Mbps.
LAN Switches
A LAN switch typically consists of many ports that connect LAN segments, such as Ethernet
and Token Ring, and a high-speed port, such as 100 Mbps Ethernet, FDDI, or 155 Mbps ATM.
The high-speed port, in turn, connects the LAN switch to other devices in the network.
87200333.book Page 90 Wednesday, August 22, 2001 2:18 PM