what is a dial back modem

Hi! Thanks for the question.

I found the following descriptions for a dial-back modem.

Dial-back Modem - "A special modem placed on a central computer. When
a user attempts to log in, the dial-back modem breaks the connection
and calls back a predefined phone number. Its use minimizes the threat
of outsiders gaining access to the central computer."

MIS Glossary
http://www.mhhe.com/business/mis/post/mis2e/student_resources/glossary.html


"Dial-Back Modem Primitive form of authentication in which the network
calls a user back using previously provided contact information in
order to authenticate the user's identity."
http://cybersummit.org/djones/512_633articles/glossary/dmain.htm


"A dial-back modem stores a list of valid login names and phone
numbers. You dial the modem, go through an authentication procedure,
and hang up. The modem consults its list of phone numbers and users,
and calls you back. A cracker who discovers your modem through random
dialing can't connect to your computer unless he's calling from one of
the listed numbers."

"Dial-back modems can be tricked by clever crackers who use special
equipment to generate the proper tones to trick your modem into
thinking the calling modem has hung up when it hasn't. If your
dial-back modem then looks up the "secure" number of the good guy's
phone and calls back on the same line, the bad guy's modem picks up
the call and gets in anyway. The best defense against this attack is
to use one line for incoming connection requests and a second line for
the dial-back. Some telcos even provide a one-way line for call-back,
so they can't be tricked by the method described here."

"Dial-back modems work well for organizations with relatively immobile
users. They are also useful if you offer modem-based Internet access
to users via the SLIP or PPP protocols. However, they don't work well
for peripatetic users who need remote access to your system--S/Key is
a better solution in that case."

"Security Technologies"
http://docs.rinet.ru/UNIXi/ch13.htm 


A picture and a description of some of the capabilities of the
dial-back modem can be seen on our next link. Here is a description:

"The Security Gateway is a firewall for dial-up phone access. It
provides a barrier against unauthorized access to any RS-232 device.
It can be used in a dial-back mode with up to 240 numbers and
passwords. These passwords are stored in battery backed memory and are
secure against tampering by jumpers. The number of tries can be
controlled so protection against ?dictionary hacking? is exceptionally
good."

"When the Monitor Mode is enabled, the Security Gateway will generate
reports of attempts both successful and unsuccessful. Ths will alert
the system operator of attemped access by unauthorized users."

"The Security Gate can also be used without the dial-back feature to
secure host ports from unauthorized access by in house communications
lines or a terminal server confirguration port."

"Dial Back Modem Security Gateway"
http://www.bomara.com/WTI/sg232.htm


Search terms used:  
"dial-back modem" "dialback modem" glossary basic overview

I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
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Easterangel-ga                              
Google Answers Researcher

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Clarification of Answer by easterangel-ga on 15 Apr 2004 00:09 PDT

Here is another description on how a dialback modem works.

"A dial-back modem will answer an incoming call and listen for a code
number only.  The code number will tell the modem to hang up and call
a specific number from a pre-stored directory.  If anything but a
pre-designated code number is received, the modem disconnects.  Use of
the dial-back method virtually insures that only personnel at a
pre-stored telephone number can gain access to the substation. 
However, there is one disadvantage in that the dial-back modem limits
the mobility of the person requiring access."

"Draft Proposal for C37.1 Standard, Section on ACCESS SECURITY"
http://216.239.53.104/search?q=cache:g458YC7MgQgJ:grouper.ieee.org/groups/sub/wgc3/c37sections/clause9/Draft%2520Proposal%2520for%2520C37-access-security-rev%25201.doc+%22dial-back+modem%22+introduction&hl=en&ie=UTF-8


"In a typical dial-back modem sequence, a user calls the dial-back modem and
enters a password.  The modem hangs up on the user and performs a
table lookup for the password provided.  If the password is found, the
modem places a return call to the user (at a previously specified
number) to initiate the session.  The return call itself also helps to
protect against the use of lost or compromised accounts.  This is,
however, not always the case. Malicious hackers can use such advanced
functions as call forwarding to reroute calls."

"SECURITY ISSUES FOR TELECOMMUTING"
http://csrc.nist.gov/publications/nistbul/itl97-01.txt

Thanks! :)

this was exactly what i was looking for