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Recommendation Q.500
DIGITAL LOCAL, COMBINED, TRANSIT AND INTERNATIONAL EXCHANGES
INTRODUCTION AND FIELD OF APPLICA TION
1 Introduction
This series of Recommendations Q.500-554 applies to digital local,
combined1, transit and international exchanges for telephony in Integrated
Digital Networks (IDNs) and mixed analogue/digital networks, and also to local,
combined, transit and international exchanges in an Integrated Services Digital
Network (ISDN).
The series of Recommendations comprises:
Q.500 Introduction and field of application
Q.511 Exchange interfaces towards other exchanges
Q.512 Exchange interfaces for subscriber access
Q.513 Exchange interfaces for operations, administration and maintenance
Q.521 Exchange functions
Q.522 Digital exchange connections, signalling and ancillary functions
Q.541 Design objectives - General
Q.542 Design objectives - Operations and Maintenance
Q.543 Performance design objectives
Q.544 Exchange measurements
Q.551 Transmission characteristics of digital exchanges
Q.552 Transmission characteristics at 2-wire analogue interfaces
Q.553 Transmission characteristics at 4-wire analogue interfaces
Q.554 Transmission characteristics at digital interfaces.
Considerations have been primarily on exchanges utilizing, at least in
part, time division switching techniques. However, these Recommendations are
implementation independent, and other system implementations using alternative
techniques (e.g., space division switching) may be possible, which would meet the
requirements of these Recommendations.
2 Field of application
These Recommendations are intended to be applied as indicated below.
2.1 Application and evolution to the ISDN
The selection of features, functions and interfaces to be provided in a
digital local, combined, transit or international exchange in a particular
network application will be determined by the administration concerned. Reference
to a function in these Recommendations, including their diagrams, does not imply
that it will necessarily be provided in every exchange type or configuration.
Similarly, it is possible that some functions may be provided which are not
mentioned.
1 A "combined" digital exchange is one which includes both local exchange and transit
exchange functions (see definition 1005 in Recommendation Q.9).
Fascicle VI. 5 - Rec. Q.500 PAGE1
2.2 Relationship of design performance requirements to operational performance
requirements
Performance requirements as defined in this series of Recommendations
should be considered as design objectives for systems under the conditions stated
in the Recommendations. These conditions are defined by such parameters as
average circuit occupancy, busy hour call attempts, etc. They should be
distinguished from the operational performance requirements which administrations
establish for exchanges operating in their particular environment.
Further clarification of this point can be obtained in Recommendation
G.102.
3 The Q.500-Series of Recommendations
3.1 Exchange interfaces (Recommendations Q.511, Q.512 and Q.513)
The interface functions defined are those necessary for interworking with
digital and analogue transmission systems on both circuits to other exchanges and
on subscriber lines, and with telecommunications management networks.
3.1.1 Characteristics of exchange interfaces towards other exchanges
(Recommendation Q.511)
This Recommendation describes the exchange interfaces used to provide
transmission facilities towards other exchanges. It applies to digital local,
combined, transit and international exchanges for telephony in integrated digital
networks (IDN) and mixed (analogue/digital) networks, and also to local,
combined, transit and international exchanges in an integrated services digital
network (ISDN).
3.1.2 Characteristics of exchange interfaces for subscriber access
(Recommendation Q.512)
The Recommendation describes the subscriber side interface
characteristics. It applies to digital local and combined exchanges for telephony
in Integrated Digital Networks (IDN) and mixed (analogue/digital) networks, and
also to local and combined exchanges in an integrated digital network (ISDN).
3.1.3 Exchange interfaces for operations, administration and maintenance
(Recommendation Q.513)
The interfaces defined are those necessary for transmission of messages
associated with operations, administration and maintenance of the exchange.
These interfaces include OAM interfaces between the exchange and the
following: OAM systems, mediation devices, user workstations, and other network
elements.
3.1.4 Interfaces to non-voice handling facilities
The need for the Recommendation of interfaces between digital transit,
local and combined exchanges and non-voice handling facilities remains for
further study. (An example of such a non-voice facility is a packet switched data
node.) Attention is drawn to Recommendation X.300 which describes the general
principles for interworking between public data networks and also to the
I.400/I.500-Series Recommendations for interworking between ISDN and other
dedicated networks.
3.2 Exchange functions (Recommendation Q.521)
This Recommendation covers the definition of the principal exchange
functions to support services and includes a description of an exchange
functional model.
PAGE2 Fascicle VI. 5 - Rec. Q.500
3.3 Exchange connections, signalling and ancillary functions (Recommendation
Q.522)
This Recommendation covers the following functions:
a) Connections through an exchange
This section includes the switch block(s), the characteristics
associated with connections through exchanges and a set of diagrams
showing typical types of connection.
A connection through an exchange may include one or more stages of time
and/or space division switching, providing a path for transmission
through the exchange.
b) Signalling
Signalling includes reception of call-related and other information,
interaction with the call control function and transfer of information
to subscribers and network(s) as required.
Signalling may involve common channel and/or channel associated
signalling.
c) Control and call handling
Control and call handling includes initiation, supervision and
termination of most actions in the exchange.
Commands are initiated and information passed/received to/from the
other functions within the exchange.
Control functions may be contained in one block or distributed
throughout the exchange.
d) Ancillaries
Examples of such functions are:
- recorded announcements;
- tone generation;
- conferencing facilities.
Their location is dependent on the function itself and the exchange
configuration.
3.4 Exchange design objectives (Recommendations Q.541, Q.542, Q.543 and Q.544)
3.4.1 General design objectives (Recommendation Q.541)
This includes the general design objective principles, availability and
hardware design objectives as well as the design objectives associated with the
operation of an exchange in an Integrated Digital Network. The latter encompasses
timing and synchronization design objectives.
Timing comprises the generation and distribution of timing signals and
includes timing of outgoing signals. It enables those parts of the exchange which
form the switched path of a connection to operate synchronously. Synchronization
will depend on the national synchronization plan and exchange timing
arrangements.
Exchanges will usually extract synchronizing information from one or more
incoming bit streams or a separate synchronization network and use this to adjust
the timing signals generated in the distribution within the exchange.
3.4.2 Operations and maintenance design objectives (Recommendation Q.542)
This covers the operations and maintenance design objectives including
network management controls, alarm handling and subscriber line maintenance and
testing.
3.4.3 Performance design objectives (Recommendation Q.543)
Exchange performance design objectives are defined for guiding system
design and for comparing the capabilities of different systems. (Recommendations
relating to provisioning and operational performance of exchanges in the network
are covered in the E.500-E.543 Series.)
3.4.4 Exchange measurements (Recommendation Q.544)
Measurements that may be used for planning, operation, maintenance and
network management of exchanges and their associated networks are described. The
measurement data consists primarily of event counts and traffic intensity levels
experienced by the various traffic handling elements of the exchange.
3.5 Transmission characteristics (Recommendations Q.551 to Q.554)
3.5.1 Transmission characteristics of digital exchanges (Recommendation Q.551)
This includes the general definitions associated with Recommendations
Q.551 to Q.554, and transmission parameters from a total exchange perspective
such as absolute group delay and the transfer function for jitter and wander.
These Recommendations define, for any connection which may be set up by a local,
combined, transit or international exchange, the necessary levels of transmission
Fascicle VI. 5 - Rec. Q.500 PAGE1
performance to conform with overall objectives for the complete user-to-user
connections in which the exchange may be involved.
3.5.2 Transmission characteristics at 2-wire interfaces (Recommendation Q.552),
4-wire interfaces (Recommendation Q.553) and digital interfaces
(Recommendation Q.554)
These cover the detailed transmission characteristics of the various types
of interface that may be provided on a digital exchange.
PAGE2 Fascicle VI. 5 - Rec. Q.500