Boca Bocamodem M144EW, User Manual, Page: 76 / 84

76
14.4Kbps BOCAMODEM
G
guard tone . Guard tones are used in the United Kingdom and other
countries. This requires that the modem transmit an 1800-Hz tone
after it sends an answer tone. The guard tone is controlled by the &G
command. Guard tones are not used in the U.S.A.
H
half-duplex . Signal flow in both directions, but only one way at a
time with each modem alternating between send and receive.
Hayes-compatible
. Hayes Microcomputer Products, Inc. developed
the AT command set which has become a de facto industry standard.
Hayes commands are always initiated with an AT (attention code)
prefix.
hook flash . The dial modifier “!” causes the modem to go on-hook
(hang-up) for one-half second. Also controlled by the ATH command.
L
LAPM . Link Access Protocol Modem. A V.42 ARQ type of error
correction protocol which is controlled by S-Register 46, where LAPM
may be activated with or without V.42bis data compression.
leased line . Also referred to as a private line. A leased line is obtained
from a communications company (carrier) to provide a transmission
medium between two points. The line consists of a permanent
dedicated circuit between two points, or to set of previously arranged
points. The cost of the line is usually based on the distance between
locations. This is in contrast to switched or dial-up lines, which can be
connected to any point on the network.
line modulation . The means by which a carrier is varied to represent
a signal carrying information. In a modem, the user’s digital data is
used to modulate the modem’s transmitter’s carrier or carrier to allow
the digital signal to be carried over analog facilities.