X Series Recommendations
drawn up 51 by the ITU-TS to establish interfaces for Terminal
Equipment (DTE) and Data Circuit Terminating Equipment (DCE) and
public data networks (PDN). The series includes:
X.1 International
user classes of service.
X.2 International
data transmission services and optional facilities.
X.3 Packet Assembly/Disassembly
(pad).
X.4 International
Alphabet No.5 for character oriented data.
X.20 Asynchronous
communications interface definitions for use over the PSTN.
X.20 bis V-series
compatible modem, asynchronous communications interface definitions
for use over the PSTN.
X.21 Synchronous communications
interface definitions for use over the PSTN.
X.21bis V-series compatible
modem, synchronous communications interface definitions for use
over the PSTN.
X.25 Interface between
DTE and DCE for terminals using packets over public data networks.
X.28 DTE/DCE interface
for asynchronous DTE accessing a pad.
X.29 Definition of
handshake protocol for use between pads and between the pad and
DTE.
X.30 Support of X.20
bis, X.21 and X.21 bis DTEs by ISDN.
X.31 Support of packet
mode DTEs by ISDN.
X.32 Interface between
DTE and DCE for terminals operating in packet mode accessing public
data networks via PSTN, ISDN or circuit switched PDN.
X.50 Fundamental parameters
of multiplexing scheme for the international interface between
synchronous data networks.
X.50bis Fundamental
parameters of 48Kbit/s transmission for the international interface
between synchronous data networks.
X.51 Fundamental parameters
of multiplexing scheme for the international interface between
synchronous data networks using 10-bit envelope structure.
X.51bis Fundamental
parameters of a 481Kbit/s transmission scheme for the international
interface between synchronous data networks using a 10-bit envelope
structure.
X.58 Fundamental parameters
of multiplexing scheme for the international interface between
synchronous data networks using a 10-bit envelope structure.
X.60 Common channel
signaling for circuit switched data applications.
X.61 Signaling system
no.7 - data user part.
X.70 Terminal and
transit control signaling for asynchronous services on international
circuits between anisochronous data networks.
X.71 Decentralized
terminal and transit control signaling on international circuits
between synchronous data networks.
X.75 Packet switched
signaling between public networks providing data transmission
services.
X.80 Interworking
of inter-exchange signals for circuit switched data services.
X.92 Hypothetical
reference connections for synchronous PDNs.
X.96 Call progress
signals in PDNs.
X.110 international
routing principles and routing plan for PDNs.
X.121 International
numbering plan for PDNs.
X.130 Call set-up
and clear-down times for international connection to synchronous
PDNs.
X.132 Grade of service
over international connections to PDNs.
X.400 A message handling
system standard that permits the electronic exchange of text as
well as other electronic data like graphics and fax. The X.400
standard is an overview which is broken down under these numbers:
X.402 Overall Architecture.
X.403 Conformance
Testing.
X.407 Abstract service
definition conventions.
X.408 Encoded information
type conversion rules.
X.411 Message transfer
system.
X.413 Message store.
X.419 Protocol specifications.
X.420 Interpersonal
messaging system.
X.500 A directory
standard that lets applications like e-mail access information
which can either be central or distributed. The benefit of a directory
is the ability to minimize the impact on the user of changes to
a network. The standard is broken down under subsequent numbers:
X.501 Models.
X.509 Authentication
framework.
X.511 Abstract service
definition.
X.518 Procedures for
distributed operation.
X.519 Protocol specifications.
X.520 Selected attribute
types.
X.521Selected object
types.
Xapia (X.400 Application Programming Interface
Association) Body standardizing the interface
to X.400 e-mail services. Other APIS, like VIM and MAPI, are likely
to comply with Xapia when it is finalized.
X/Open A body comprising
of computer vendors, responsible for researching, defining and
publicizing open systems.
X.Windows A networked
GU I based on a client/server architecture, it displays information
from multiple networked hosts on a single workstation. Available
on PCs as X.terminal emulation and emulation on LAN servers.
