Nortel BayStack 660, Use Manual

Page: 29 / 163

Introduction
203939-B
1-7
The physical layer is a 2.4 GHz spread spectrum, direct sequence radio that
replaces the Ethernet cable normally required between LAN workstations.
Figure 1-4 illustrates the frequency spectrum for this radio technology.
Figure 1-4. Radio Frequency Bands
A low-power radio operates within the 2.4000 to 2.4835 GHz band of the
unlicensed Industrial, Scientific, and Medical bands (ISM). It is divided into 78,
one MHz channels. The direct sequence scheme causes the radio to broadcast on
eleven channels simultaneously, each separated by a single channel. Interference
on any one channel can be tolerated as all eleven channels utilized carry the exact
same data.
Using Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA), each
string of data is sent with an additional signaling information designed to maintain
transmission efficiency. Every packet includes three signaling packets:
• Request to send (RTS)
RTS reserves the area around the sender.
• Clear to send (CTS)
Telecommunications
Super
High
5.850 GHz
Broadband
802.11
Cellular
5.725 GHz
2.4835 GHz
2.400 GHz
928 MHz
902 MHz
Television
Ultra
High
FM Broadcast
(88 to 108 MHz)
AM Broadcast
(560-1605 KHz)
Very
High
Short Wave Radio
High
Medium
Low
Audio Frequencies
Very
Low
8698EB
book.fm Page 7 Wednesday, September 22, 1999 1:41 PM