2 cissp ® Official Study Guide Eighth Edition

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These are some of the hardware devices in a network: 
Repeaters, Concentrators, and Amplifiers
Repeaters
,
concentrators
, and
amplifi ers
are 
used to strengthen the communication signal over a cable segment as well as connect net-
work segments that use the same protocol. These devices can be used to extend the maxi-
mum length of a specifi c cable type by deploying one or more repeaters along a lengthy 
cable run. Repeaters, concentrators, and amplifi ers operate at OSI layer 1. Systems on either 
side of a repeater, concentrator, or amplifi er are part of the same collision domain and 
broadcast domain. 
Hubs
Hubs
were used to connect multiple systems and connect network segments that use 
the same protocol. A hub is a multiport repeater. Hubs operate at OSI layer 1. Systems on 
either side of a hub are part of the same collision and broadcast domains. This ensures that 
the traffi c will reach its intended host, but at the cost that all members of the same collision 
domain and broadcast domain will receive the communication as well. Most organizations 
have a no-hub security policy to limit or reduce the risk of sniffi ng attacks since they are an 
outmoded technology and switches are preferred. 
Modems
A traditional landline
modem
(modulator-demodulator) is a communications 
device that covers or modulates between an analog carrier signal and digital information in 
order to support computer communications of public switched telephone network (PSTN) 
lines. From about 1960 until the mid-1990s, modems were a common means of WAN 
communications. Modems have generally been replaced by digital broadband technologies 
including ISDN, cable modems, DSL modems, 802.11 wireless, and various forms of wire-
less modems. 
The term
modem 
is used incorrectly on any device that does not actually 
perform modulation. Most modern devices labeled as modems (cable, 
DSL, ISDN, wireless, etc.) are routers, not modems.