V.21 Standard for modem communications at 300 bps. Modems made in
the US or Canada follow the Bell 103 standard. However, the
modem can be set to answer V.21 calls from overseas.
V.22 Standard for modem communications at 1200 bps, compatible
with the Bell 212A standard observed in the US and Canada.
V.22 bis Standard for modem communications at 2400 bps. The standard
includes an automatic link negotiation fallback to 1200 bps
and compatibility with Bell 212A/V.22 modems.
V.23 Standard for modem communications at 1200 bps with a 75 bps
back channel.
V.24 Standards layed down by the CCITT for interfacing a digital
device to a PTT-supplied modem. V.24 is also used as an
interface standard for connecting a peripheral device, such
as a visual display unit or a printer, to a computer.
V.25 Standard for modem communications that specifies an answer
tone different from the Bell answer tone used in the US and
Cananda.
V.32 Standard for modem communications at 9600 bps and 4800 bps.
V.32 modems fall back at 4800 bps when line quality is
impaired, and fall forward again to 9600 bps when line
quality improves.
V.32 bis Standard that extends the V.32 connection range: 4800,7200,
9600, 12K and 14.4K bps. V.32 bis modems fall back to the
next lower speed when line quality is impaired, and fall back
further as necessary. They fall forward to the next higher
speed when line quality improves.
V.34 28.800 CCITT standard
V.34+ 31.200 & 33.600, currently only supported by US Robotics
(V.EveryThing modems) under consideration by CCITT.
V.35 See V.24.
V.42 Standard for modem communications that defines a two-stage
process of detection and negotiation for LAPM error control.
V.42 also supports the MNP error control protocol.
V.42 bis An extention of V.42 that defines a specific data compression
scheme for use with V.42 and MNP error control.
X.3 It describes the functions of an X.25 PAD and the parameters
used to control its operation.
X.21 Interface between DTE and DCE for synchronous operation on
on public data networks.
X.25 Interface between DTE and DCE for terminals operating in
packet mode on public data networks.
X.28 It defines the interactions between a terminal and an X.25
PAD.
X.29 It defines the interactions between a host and its associated
PAD.
X.75 ISDN, EuroStandard, 64000.
X.400 Message handling systems : System model and service elements.
X.401 Message handling systems : Basic service elements and
optional user facilities.
X.408 Message handling systems : Encoded information type
convertion rules.
X.409 Message handling systems : Presentation transfer syntax and
notation.
X.410 Message handling systems : Remote operations and reliable
transfer server.
X.411 Message handling systems : Message transfer layer.
X.420 Message handling systems : Interpersonal messaging user agent
layer.
X.430 Message handling systems : Access protocol for teletex
terminals.
X.500 The directory (OSI Directory Services).
