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.nr LL 40.5P
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.nr HM 3P
.nr FM 6P
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.rs
\v | 5i'
.sp 1P
.ce 1000
\v'3P'
SECTION\ 5
.ce 0
.sp 1P
.ce 1000
\fBDATA\ TRANSMISSION\ SERVICES\fR 
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ F.600\fR 
.RT
.sp 2P
.ce 1000
\fBSERVICE\ AND\ OPERATIONAL\ PRINCIPLES\ FOR\ PUBLIC\fR 
.EF '%	Fascicle\ II.5\ \(em\ Rec.\ F.600''
.OF '''Fascicle\ II.5\ \(em\ Rec.\ F.600	%'
.ce 0
.sp 1P
.ce 1000
\fBDATA\ TRANSMISSION\ SERVICES\fR 
.ce 0
.sp 1P
.LP
\fB1\fR 	\fBIntroduction\fR 
.sp 1P
.RT
.sp 1P
.LP
1.1
	\fIScope\fR 
.sp 9p
.RT
.PP
These provisions fix the rules to be followed for International
Public Data Transmission Services.
.RT
.sp 1P
.LP
1.2
	\fIDefinition\fR 
.sp 9p
.RT
.PP
The definition of <<public data transmission service>> is a data
transmission service established and operated by administration and provided
by means of a public network. Circuit switched, packet switched, and leased
circuit data transmission services are specified.
.PP
\fINote\ 1\fR \ \(em\ A public data transmission service may be subdivided 
into derived services. 
.PP
\fINote\ 2\fR \ \(em\ A public data transmission service or a derived service
consists of service elements forming a basic service and of other service
elements which are called optional user facilities.
.PP
\fINote\ 3\fR \ \(em\ There is an implicit definition of data transmission
services in Recommendations X.1 and X.2.
.RT
.PP
1.3
Issues of an essentially technical nature concerning
International Public Data Transmission Services are dealt with in other
CCITT Recommendations.
.sp 9p
.RT
.PP
1.4
Issues of an essentially technical nature concerning compatibility of terminals 
and connected equipment are dealt with in Recommendations\ A.20 
and\ A.21.
.sp 2P
.LP
\fB2\fR 	\fBTerms\fR 
.sp 1P
.RT
.sp 1P
.LP
2.1
	\fBdata transmission relations\fR 
.sp 9p
.RT
.PP
A data transmission relation between two terminal countries exists when 
there is between them an exchange of data traffic (and normally a 
settlement of accounts).
.RT
.sp 1P
.LP
2.2
	\fBprimary route\fR 
.sp 9p
.RT
.PP
The route normally used in a given relation.
.bp
.RT
.sp 1P
.LP
2.3
	\fBalternative route\fR 
.sp 9p
.RT
.PP
The route normally used when the primary route is not available
for any reason.
.RT
.sp 1P
.LP
2.4
	\fBdata service calls\fR 
.sp 9p
.RT
.PP
Those data calls that relate to the operation of the international telecommunications 
services. 
.RT
.sp 1P
.LP
2.5
	\fIOther terms\fR 
.sp 9p
.RT
.PP
These are given in the appropriate CCITT Recommendations and
publications.
.RT
.sp 2P
.LP
\fB3\fR 	\fBAccess to the service\fR 
.sp 1P
.RT
.sp 1P
.LP
3.1
	\fITypes of access\fR 
.sp 9p
.RT
.PP
Two types of terminal can access the public data transmission
service.
.RT
.PP
3.1.1
Terminals defined by ISO operating at OSI levels\ 1 to\ 3
(Recommendation\ A.20).
.sp 9p
.RT
.PP
3.1.2
Other terminals (e.g., teletex terminals as defined by Study
Group\ VIII) providing telematic services (Recommendation\ A.21) or other
new as yet undefined CCITT services operating at OSI levels\ 1 to\ 7.
.PP
3.1.3
Access may be either packet mode (Recommendations X.25 or\ X.32) or start\(hystop 
mode (Recommendation\ X.28) terminals. Details of services offered 
are contained in Table\ 1/X.1, parts\ (c) and (d).
.sp 2P
.LP
\fB4\fR 	\fBInternational data circuits/routes\fR 
.sp 1P
.RT
.PP
4.1
An international route established and operated between
Administrations for the specific purpose of providing public data transmission 
services. Circuit switched and/or packet switched data transmission techniques 
are feasible. 
.sp 9p
.RT
.PP
4.2
For each data transmission relation the Administrations concerned shall 
by mutual agreement decide upon the necessity and possibility of 
alternative data routes. In this respect Administrations should conform with
the principles in the appropriate CCITT Recommendations.
.PP
4.3
The networks of the Administrations operating data services shall, as far 
as possible be directly connected using appropriate conversion 
facilities as necessary. If international transmit points are used, they 
should be restricted in principle to the definitions given in CCITT 
Recommendation\ X.92 and others.
.PP
4.4
In the event of interruption to the data transmission service
every effort must be made to restore the service with minimum delay.
.sp 2P
.LP
\fB5\fR 	\fBDuration of service\fR 
.sp 1P
.RT
.PP
5.1
International data transmission services are in principle
continuously available.
.sp 9p
.RT
.PP
5.2
Services that are not available continuously are required to
extend beyond the normal closing hours until calls in progress are terminated.
.PP
5.3
Each Administration shall designate universal time in all
telecommunication activities. Recommendation\ B.11 refers.
.sp 2P
.LP
\fB6\fR 	\fBType of call\fR 
.sp 1P
.RT
.PP
6.1
Data calls may originate on one data network (e.g. packet) and terminate 
on the same type of network. In addition it is possible that data 
calls may originate on one network e.g. telephone and terminate on another
network e.g. packet. Possible routines may include:
.sp 9p
.RT
.LP
	\(em
	Telephone to/from packet;
.LP
	\(em
	Packet to/from telex (Recommendation F.73);
.bp
.LP
	\(em
	Circuit to/from packet;
.LP
	\(em
	Telephone to/from telex.
.PP
Implementation to be subject to bilateral agreement between
Administrations.
.sp 2P
.LP
6.2
	\fIService calls\fR 
.sp 1P
.RT
.PP
6.2.1
In principle the use of data transmission services for service calls between 
Administrations concerned with the international data services 
should be excluded from international accounts.
.sp 9p
.RT
.PP
6.2.2
Data service calls may only be originated as authorized by the
respective Administrations.
.PP
6.2.3
Data service calls should as far as possible be made outside the busiest 
hours. 
.PP
6.2.4
The identification of service calls is for futher study.
.sp 2P
.LP
\fB7\fR 	\fBModes of operation\fR 
.sp 1P
.RT
.sp 1P
.LP
7.1
	\fIGeneral provisions\fR 
.sp 9p
.RT
.PP
7.1.1
The data transmission service should be operated in the
automatic mode. It is noted that semi\(hyautomatic or manual operation may be
necessary.
.sp 9p
.RT
.PP
7.1.2
Administrations shall reach mutual agreement on the most
appropriate method of operation to be applied in the case of the data
transmission service concerned.
.sp 2P
.LP
7.2
	\fIAutomatic operation\fR 
.sp 1P
.RT
.PP
7.2.1
In principle the data network of each Administration should be interconnected 
on an automatic basis permitting all subscribers to reach one 
another either directly or by automatic means.
.sp 9p
.RT
.PP
7.2.2
To establish an international data call by automatic means the
subscriber shall normally follow the appropriate CCITT Recommendation
(e.g.\ X.121).
.PP
7.2.3
The duration of normal calls in the automatic service should not   be limited.
.sp 2P
.LP
7.3
	\fISemi\(hyautomatic and manual operation\fR 
.sp 1P
.RT
.PP
7.3.1
Semi\(hyautomatic and manual operation may be offered on an
exceptional basis, subject to bilateral agreement.
.sp 9p
.RT
.sp 2P
.LP
\fB8\fR 	\fBDirectories \(em compilation and supply\fR 
.sp 1P
.RT
.PP
\fINote\fR \ \(em\ This is for further study in conjunction with
Question\ 14/I.
.RT
.PP
8.1
As far as possible each Administration shall make available a directory 
of its dedicated data subscribers which is updated at least once a 
year. Customers may elect to be excluded from the directory.
.sp 9p
.RT
.PP
8.2
Printed directories for international use should not be larger
than 216\ \(mu\ 297mm (A4).
.PP
8.3
The directories for international use shall be set up in Roman
letters. The call number published shall be that which the calling subscriber 
has to transmit in order to obtain the called subscriber after he has followed 
the procedure prescribed in his own country to gain access to the destination 
country. 
.PP
8.4
When directories are written in a language other than a language used in 
that country, they shall be accompanied by an explanatory note to 
facilitate the use of such directories. This note shall be drawn up in 
whatever official language of the Union has been agreed upon by the Administration 
concerned.
.PP
8.5
Each Administration will supply to the Administration with which data service 
exists, a number of copies of its subscribers directories. The 
number of such copies shall be fixed in advance by mutual agreement and 
shall be regarded as applying until a request to change it is received. 
.bp
.sp 2P
.LP
\fB9\fR 	\fBCall progress signals on public data networks\fR 
.sp 1P
.RT
.PP
These are defined in Recommendation X.96. (The interpretation of
these codes needs further consideration.)
.RT
.sp 2P
.LP
\fB10\fR 	\fBQuality of service\fR 
.sp 1P
.RT
.PP
The quality of service criteria for the various public data
transmission services are to be defined separately in the F.600 series
recommendations taking due account of existing CCITT Recommendations. The
following are examples of service criteria which need to be covered in
individual Recommendations:
.RT
.LP
	\(em
	service availability;
.LP
	\(em
	percentage of effective calls;
.LP
	\(em
	data throughput;
.LP
	\(em
	bit error rate;
.LP
	\(em
	transmission delay;
.LP
	\(em
	blocking aspects.
.sp 2P
.LP
\fB11\fR 	\fBProvision of customer support\fR 
.sp 1P
.RT
.PP
Administrations should provide customers with the following
information:
.RT
.LP
	\(em
	access and log\(hyon procedures;
.LP
	\(em
	explanation of call progress and error messages;
.LP
	\(em
	fault reporting arrangements;
.LP
	\(em
	disputed calls arrangements;
.LP
	\(em
	directory facilities.
\v'1P'
.sp 2P
.LP
\fBRecommendation\ F.601\fR 
.RT
.sp 2P
.ce 1000
\fBSERVICE\ AND\ OPERATIONAL\ PRINCIPLES\ FOR\fR 
.EF '%	Fascicle\ II.5\ \(em\ Rec.\ F.601''
.OF '''Fascicle\ II.5\ \(em\ Rec.\ F.601	%'
.ce 0
.sp 1P
.ce 1000
\fBPACKET\(hySWITCHED\ PUBLIC\ DATA\ NETWORKS\fR 
.ce 0
.sp 1P
.LP
	The\ CCITT\fR 
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that Recommendation X.1 specifies the user classes of
service applicable to networks offering packet\(hyswitched services;
.PP
(b)
that Recommendation X.2 specifies the virtual call
service as an essential service to be provided by all networks offering
packet\(hyswitched services.
.PP
(c)
that Recommendation X.25 specifies the DTE/DCE
interface for packet mode terminals in networks providing packet\(hyswitched
services.
.PP
(d)
that Recommendation X.75 specifies signalling
procedures between packet\(hyswitched networks.
.PP
(e)
that Recommendation X.92 specifies hypothetical
reference connections packet\(hyswitched services;
.PP
(f
)
that Recommendation X.96 specifies the call
progress signals in public data networks;
.PP
(g)
that Recommendation X.110 specifies the routing plan
to be applied in the international portion of networks providing
packet\(hyswitched services;
.PP
(h)
that Recommendation X.121 specifies the international
numbering plan for public data networks;
.bp
.PP
(i)
that Recommendation X.134 specifies boundaries and
packet level reference events;
.PP
(j
)
that Recommendation X.135 specifies the delay
aspects of the grade of service in networks providing packet\(hyswitched
services;
.PP
(k)
that Recommendation X.136 specifies the blocking
aspects of the grade of service of networks providing packet\(hyswitched
services;
.PP
(l)
that Recommendation X.137 specifies availability
performance values for public data networks;
.PP
(m)
that Recommendation X.140 specifies the
user\(hyoriented quality of service parameters applicable to all services;
.PP
(n)
that Recommendation X.213 specifies the OSI network
layer service;
.PP
(o)
that Recommendation F.600 specifies the general service and operational 
principles for public data transmission services. 
.sp 1P
.LP
\fIunanimously declares\fR 
.sp 9p
.RT
.PP
That the provisions specified in this Recommendation fix the rules to be 
followed for international data transmission services via packet\(hyswitched 
public data networks, PSPDN. The Recommendation covers service definitions, 
quality of service and provision of customer support aspects.
.sp 2P
.LP
\fB1\fR 	\fBIntroduction\fR 
.sp 1P
.RT
.sp 1P
.LP
1.1
	\fIDefinition\fR 
.sp 9p
.RT
.PP
1.1.1
The definition of packet\(hyswitched public data network (PSPDN) is found 
in Recommendation\ X.1. 
.sp 9p
.RT
.PP
1.1.2
Issues of an essentially technical nature concerning compatibility of terminals 
and connected equipment are dealt with in Recommendations\ A.20 
and\ A.21.
.sp 1P
.LP
1.2
	\fIClass of service (Recommendation X.2)\fR 
.sp 9p
.RT
.PP
The definition of PSPDNs is found in Table 1/X.2.
.RT
.sp 1P
.LP
1.3
	\fITypes of traffic\fR 
.sp 9p
.RT
.PP
The packet\(hyswitched data transmission service accepts different
types of traffic originated by the users either Permanent Virtual Circuits
(PVC) or Virtual Calls (VC). The following table lists the most frequent 
of these types. Also indicated is a technical solution which could provide 
a 
definition of the corresponding type of traffic.
.PP
The following list is not exhaustive, but indicative only. New
services may spawn different classifications, and possibly create the need 
to define new facilities in Recommendations\ X.25 and\ X.75. 
.RT
.LP
	\fITraffic types\fR 	\fIPossible technical solution\fR 
.LP
	Short transactions
	Fast select with restriction process
.LP
	Interactive (average duration
	No specific technical frame
.LP
	and volume) transactions
.LP
	Batch mode transactions
	No specific technical frame
.LP
	Also possible on other services
.PP
The need to associate specific, or a group of specific, quality of service 
parameters to each of the perceived or identified traffic types is for 
further study. 
.sp 2P
.LP
\fB2\fR 	\fBTerms\fR 
.sp 1P
.RT
.sp 1P
.LP
2.1
	\fBdata transmission relations\fR 
.sp 9p
.RT
.PP
A data transmission relation between two terminal countries exists when 
there is between them an exchange of data traffic (and normally a 
settlement of accounts).
.bp
.RT
.sp 1P
.LP
2.2
	\fBdata service calls\fR 
.sp 9p
.RT
.PP
Those data calls that relate to the operation of the international services 
via PSPDNs. 
.RT
.sp 1P
.LP
2.3
	\fIOther terms\fR 
.sp 9p
.RT
.PP
These are given in the appropriate CCITT Recommendations in
particular Annex\ A of Recommendation\ X.110.
.RT
.sp 2P
.LP
\fB3\fR 	\fBAccess to the service\fR 
.sp 1P
.RT
.PP
Access can be either in a packet mode (Recommendations X.25 or
X.32) or in a start\(hystop mode (Recommendation\ X.28). Details of services
offered are contained in Table\ 1/X.1, parts\ (c) and (d).
.RT
.sp 2P
.LP
3.1
	\fIPacket mode access\fR 
.sp 1P
.RT
.sp 1P
.LP
3.1.1
	\fIAccess via X.25 DTEs\fR 
.sp 9p
.RT
.PP
The access to a packet\(hyswitched public data network by means of
equipment capable of handling X.25 is automatic. In general, there is no 
human intervention required. 
.RT
.sp 1P
.LP
3.1.2
	\fIAccess via X.32 DTEs\fR 
.sp 9p
.RT
.PP
The access to a packet\(hyswitched public data network by means of
equipment capable of handling and interfacing to the network using
Recommendation\ X.32 in general does need manual intervention. Where manual
intervention is required the operational procedures should be standardized
(according to Recommendation\ A.20), user friendly, and automatable.
.RT
.sp 1P
.LP
3.2
	\fIStart\(hystop mode access\fR 
.sp 9p
.RT
.PP
The access to a packet\(hyswitched public data network by means of
equipment capable of handling and interfacing to the network via Packet
Assembler/Disassembler equipment is referred to in Recommendations\ X.3, X.28
and X.29.
This access method in general requires manual intervention. Where manual
intervention is required the operational procedures should be standardized
(according to Recommendation\ A.20) and user\(hyfriendly. For further
study.
.RT
.sp 1P
.LP
3.3
	\fIAccess methods\fR 
.sp 9p
.RT
.PP
Log\(hyon procedures should be user\(hyfriendly and provide security
of access. The access methods as specified in \(sc\(sc 3.1.2 and 3.2 require
manual intervention and hence standardized log\(hyon procedures are desirable. 
The international log\(hyon procedure standardization is for further study. 
.RT
.sp 2P
.LP
\fB4\fR 	\fBInternational data route\fR 
.sp 1P
.RT
.PP
4.1
An international data route is established and operated between Administrations 
for the specific purpose of providing an international 
packet\(hyswitched public data service.
.sp 9p
.RT
.PP
4.2
The networks of the Administrations operating PSPDNs should be
directly connected when justified. If international transit points are used,
they should be restricted to the definitions given in Recommendation\ X.92.
.PP
4.3
For each PSPDN relation, the Administrations concerned should
provide alternative data routes where practical, in accordance with
Recommendation\ X.110.
.PP
4.4
In the event of interruption to the international data route every effort 
must be made to restore the service with minimum delay, taking into 
account Recommendation\ X.137.
.sp 2P
.LP
\fB5\fR 	\fBDuration of service\fR 
.sp 1P
.RT
.PP
International PSPDNs are in principle continuously
available.
.bp
.RT
.sp 2P
.LP
\fB6\fR 	\fBType of call\fR 
.sp 1P
.RT
.PP
Types of call correspond to calls based on PVCs or on VCs. Calls
based on VCs may be service calls or subscriber calls, the latter being
included in international accounting.
.RT
.sp 1P
.LP
6.1
	\fIService calls\fR 
.sp 9p
.RT
.PP
Service calls should be kept to a minimum and not hamper subscriber calls.
.RT
.sp 2P
.LP
\fB7\fR 	\fBModes of operation\fR 
.sp 1P
.RT
.sp 1P
.LP
7.1
	\fIGeneral provisions\fR 
.sp 9p
.RT
.PP
Administrations should provide PSPDN services in accordance with
Recommendations\ X.25, X.28 and, if possible, Recommendation\ X.32
protocols.
.RT
.sp 1P
.LP
7.2
	\fIAutomatic operation\fR 
.sp 9p
.RT
.PP
All call operations in the network are automatic (see
Recommendations\ X.25, X.28, X.29, X.75,\ etc.). Call operations may be manual
or automatic when initiated by the user from his DTE.
.RT
.sp 1P
.LP
7.3
	\fISemi\(hyautomatic and manual operation\fR 
.sp 9p
.RT
.PP
Semi\(hyautomatic and manual operation are not available.
.RT
.sp 2P
.LP
\fB8\fR 	\fBDirectories\fR \fB\(em compilation and supply\fR 
.sp 1P
.RT
.PP
See Recommendation F.600, \(sc\ 8.
.RT
.sp 2P
.LP
\fB9\fR 	\fBCall progress signals on PDNs\fR 
.sp 1P
.RT
.PP
Call progress signals are defined in Recommendation\ X.96. The
interpretation of these codes shall be user friendly and details are for
further study.
.RT
.sp 2P
.LP
\fB10\fR 	\fBQuality of service\fR 
.sp 1P
.RT
.PP
The quality of service criteria for the PSPDNs to be defined under the 
following headings taking due account of existing CCITT 
Recommendations.
.RT
.sp 1P
.LP
10.1
	\fIService availability\fR 
.sp 9p
.RT
.PP
Service availability is the ratio of aggregate time during which
satisfactory or tolerable service is or could be provided to the total
observation period, Recommendation\ X.137 refers. This is for futher
study.
.RT
.sp 1P
.LP
10.2
	\fIPercentage of effective calls\fR 
.sp 9p
.RT
.PP
Technical aspects are examined in Recommendation X.136. For
further study.
.RT
.sp 1P
.LP
10.3
	\fIData throughput\fR 
.sp 9p
.RT
.PP
Technical aspects are examined in Recommendation X.135. For
further study.
.RT
.sp 1P
.LP
10.4
	\fIBit error rate\fR 
.sp 9p
.RT
.PP
A bit error rate (BER) of at least 1 in 10\u6\d is required. (For
further study with particular respect to the effect of access networks.)
.RT
.sp 1P
.LP
10.5
	\fITransmission delay\fR 
.sp 9p
.RT
.PP
This should be expressed in milliseconds. See Recommendation\ X.135. For 
further study. 
.bp
.RT
.sp 1P
.LP
10.6
	\fIBlocking aspects\fR 
.sp 9p
.RT
.PP
Recommendation X.136 sets forth values of unavailability of the
packet\(hyswitched service due to network congestion.
.PP
The end to end user service blocking aspects with particular respect to 
the network used is for further study. 
.RT
.sp 2P
.LP
\fB11\fR 	\fBProvisions of customer support\fR 
.sp 1P
.RT
.sp 1P
.LP
11.1
	\fIProcedures for updating customer information\fR 
.sp 9p
.RT
.PP
The provision of service information should be available to the
user on request. This is for further study.
.RT
.sp 1P
.LP
11.2
	\fIProcedures for updating inter\(hyadministration information\fR 
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
11.3
	\fIProcedures for handling customer international difficulties\fR 
.sp 9p
.RT
.PP
Administrations should provide customer support facilities, which may include 
a \*QHelp Desk\*U, to provide: 
.RT
.LP
	\(em
	accurate information from the operator at the time of
problem;
.LP
	\(em
	explanation of corrective action subsequent to failure;
.LP
	\(em
	further assistance in the event of unresolved problems.
.PP
For further study.
.LP
.rs
.sp 28P
.ad r
\fBBLANC\fR 
.ad b
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 6
.ce 0
.sp 1P
.ce 1000
\fBTELECONFERENCE\ SERVICE\fR 
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ F.710\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTELECONFERENCE\ SERVICE\fR 
.EF '%	Fascicle\ II.5\ \(em\ Rec.\ F.710''
.OF '''Fascicle\ II.5\ \(em\ Rec.\ F.710	%'
.ce 0
.sp 1P
.LP
\fB1\fR 	\fBIntroduction\fR 
.sp 1P
.RT
.sp 1P
.LP
1.1
	\fIScope\fR 
.sp 9p
.RT
.PP
1.1.1
This Recommendation fixes the general rules to be followed in the international 
Teleconference Service (TCS), preferably to be provided on digital network. 
.sp 9p
.RT
.PP
1.1.2
Teleconference (TC) is an international telecommunication service, offered 
by Administrations, enabling conference conducted in real time between 
users placed in different locations, connected by terminals and 
telecommunication networks.
.PP
1.1.3
The TCS can be a multimedia service, i.e., several media could use the 
same transmission channel. 
.PP
1.1.4
This Recommendation is a general Recommendation for
teleconferencing services. Annex\ A is a table of present and future
Recommendations on audiovisual services. AVxxx numbers are references for
classification in this table and not actual Recommendations' numbers. This
classification will be updated as the work progresses.
.PP
The services are described in Recommendations AV 100\(hyseries. The infrastructural 
needs are described in Recommendations\ AV\ 200\(hyseries. The 
facilities are described in Recommendations\ AV\ 300\(hyseries.
.PP
1.1.5
Computer conferencing and MHS do not constitute part of
real\(hytime teleconference service. However, the facilities of computer
conferencing an MHS may additionally be used in a teleconference.
.sp 9p
.RT
.PP
These services are not covered by this Recommendation.
.sp 2P
.LP
1.2
	\fIService definitions\fR 
.sp 1P
.RT
.sp 1P
.LP
1.2.1
	\fIGeneral\fR 
.sp 9p
.RT
.sp 1P
.LP
1.2.1.1\ \ The \fBteleconference service\fR provides the necessary arrangements 
for a real\(hytime conferencing among single individuals or groups of individuals 
at two or more locations, by means of telecommunication networks. 
.sp 9p
.RT
.PP
The concept of conferencing implies that the exchange of speech
signals is always provided for as a basic facility. The use of supplementary
facilities, for the exchange of signals other than speech, is to be determined 
by the conference participants. 
.bp
.PP
For the interconnection of terminal equipment at three or more
locations, a specific interconnection facility is required, namely the
Multipoint Control Unit (MCU), to which all locations are connected
individually.
.PP
The MCU provides proper distribution of the various signals among the connected 
locations and takes part in maintaining the proper procedures among the 
connected terminals. 
.RT
.sp 1P
.LP
1.2.1.2\ \ TCS is a real\(hytime service which can be divided according to
the following categories:
.sp 9p
.RT
.LP
	a)
	\fBaudiographic conference service\fR 
.FS
A Telephone
Multipoint conference may be considered as a simple form of Audiographic
conference. Other forms of Audiographic conference may imply loudspeaking
terminals working in full duplex or half duplex mode, providing a considerably 
better sound quality than normal telephone (they may even contain wideband 
speech coding). Supporting signalling like request for floor, grant request 
for floor and speaker identification may also be present. 
.FE
.LP
	A type of TCS in which audiosignals are exchanged together
with non\(hyvoice information (data, text, graphic,\ etc.),
except video and signalling.
.LP
	The transmission of documents during a Teleconference will
be supported by the use of the Recommendations such as in
the T.400, T.500, T.600 series and the telewriting
Recommendations.
.LP
	Interworking and intercommunication between different types
of audiographic conference is for further study.
.LP
	b)
	\fBvideo conference service\fR 
.LP
	A type of TCS in which both voice and moving picture video
information can be exchanged together with optional
non\(hymoving visual information, telematic information and
signalling (speaker identification, floor
request,\ etc.).
.sp 1P
.LP
1.2.1.3\ \ The terms used in this Recommendation have the meaning given in
Annex\ B.
.sp 9p
.RT
.sp 1P
.LP
1.2.2
	\fIBasic requirements\fR 
.sp 9p
.RT
.PP
The basic requirements of TCS are as follows:
.RT
.LP
	a)
	It is intended that the service should require no changes to
the Recommendations for existing services or networks.
.LP
	b)
	With respect to the interworking/intercommunication of
teleconference terminals, a basic level of capabilities is defined; this
basic level corresponds to the default conditions.
.LP
	High levels of intercommunication capabilities have to be
negotiated via the teleconference protocol.
.LP
	c)
	It should be possible to extend TCS to any number of
Administrations.
.LP
	d)
	It is for each Administration to decide on the network(s)
on which TCS will be provided.
.LP
	e)
	It is essential at least to provide the intercommunication
on Audio basis (Recommendation\ G.711).
.LP
	f
)
	TCS indicated in \(sc\ 1.2.1.2 as a) and b) in particular
will provide the following basic functions:
.LP
	f1)
	Conference management functions:
.LP
	\(em
	call set\(hyup, call establishment and call
clearing at network level;
.LP
	\(em
	handling of multipoint functions;
.LP
	\(em
	switching of proper channels to the various
terminal and equipments during the call control
phases of TCS (\(sc\ 3.2).
.bp
.LP
	f2)
	Terminal management functions:
.LP
	\(em
	handling and management of terminal functions
like audio and video;
.LP
	\(em
	handling and management of all telematic
terminal\(hyfunctions that can be used during the
service, depending on the type of Teleconference
service, e.g. communication function for:
.LP
	\(em
	using a telewriter
.LP
	\(em
	using a marker
.LP
	\(em
	using a facsimile
.LP
	\(em
	using a still picture
.LP
	\(em
	using a teletex
.LP
	\(em
	conference set\(hyup and clearing
.LP
	\(em
	identification of speaker
.LP
	\(em
	floor request, grant floor request
signalling
.LP
	\(em
	control of speakers microphone
.LP
	\(em
	line breakdown signalling
.LP
	\(em
	etc.
.LP
	f3)
	Coordination and conference management and
Terminal protocols in order to make available, during
the various TCS phases, the service required (audio
is presumed to be always available), e.g.:
.LP
	\(em
	Telewriting
.LP
	\(em
	Facsimile
.LP
	\(em
	Teletex
.LP
	\(em
	Still picture
.LP
	All the above functions have to be accomplished in
such a way that can be easily controlled by an actual
participant in the conference, without special
training
.FS
Personnel by Administrations should not
be required.
.FE
.
.LP
	f4)
	Local conductor functions:
.LP
	\(em
	chairing the local meeting
.LP
	\(em
	enabling/disabling local functions.
.sp 2P
.LP
1.2.3
	\fIFunctional options\fR 
.sp 1P
.RT
.sp 1P
.LP
1.2.3.1\ \ Functional options like encryption may be provided in the
terminal or by the network. The use may be made only by bilateral or
multilateral agreement.
.sp 9p
.RT
.sp 2P
.LP
1.2.4
	\fIStandardized options\fR 
.sp 1P
.RT
.sp 1P
.LP
1.2.4.1\ \ It shall be possible for more sophisticated terminals to
provide particular facilities different from the basic ones (e.g.\ editing,
autocall, set\(hyup,\ etc.).
.sp 9p
.RT
.PP
These optional facilities should be normalized. Some optional
facilities have to be provided by network (supplementary services), e.g.\ 
Closed User Group (CUG). In general the supplementary services are the 
same as for 
telephony.
.sp 1P
.LP
1.2.4.2\ \ Since in the near future TCS will be increased by special
services such as those given in the list of examples below, Administrations
should give attention to their early introduction:
.sp 9p
.RT
.LP
	\(em
	Abbreviated Address Calling.
.LP
	\(em
	Multiaddress Calling.
.LP
	\(em
	Indication of Charge.
.sp 1P
.LP
1.2.4.3\ \ They may also be provided from TCS terminal instead of, or as
well as, from the network.
.bp
.sp 9p
.RT
.LP
1.2.4.4\ \ By means of a negotiation procedure between terminals and, in
multipoint connections, the MCU, terminals are aware of the facilities 
of the other terminal(s). 
.PP
\fINote\ 1\fR \ \(em\ Administrations are encouraged to ensure that
standardized and nationally defined options are used in such a way as to
minimize the need for the introduction of private use option.
.PP
\fINote 2\fR \ \(em\ There is a need for further study as the service
develops.
.RT
.sp 2P
.LP
1.2.5
	\fIPrivate use options\fR 
.sp 1P
.RT
.sp 1P
.LP
1.2.5.1\ \ These optional requirements should not be CCITT defined.
.sp 9p
.RT
.sp 2P
.LP
1.3
	\fIDefinition of terms used in TCS\fR 
.sp 1P
.RT
.PP
1.3.1
The terms listed in Annex B have the definitions given there
when used in these provisions.
.sp 9p
.RT
.sp 2P
.LP
\fB2\fR 	\fBNetwork requirements\fR 
.sp 1P
.RT
.PP
2.1\fR 
Ultimately the TCS is intended for ISDN. As long as ISDN is not universally 
available, it is the responsibility of Administrations to decide on which 
network(s) national TCS is to be provided. 
.sp 9p
.RT
.PP
2.2
TCS can be accessed via:
.LP
	a)
	Multiple of 64 kbit/s switched, semi\(hypermanent and permanent
connections in an ISDN.
.LP
	b)
	Multiple of 64 kbit/s switched, semi\(hypermanent and permanent
connections in a CSPDN.
.LP
	c)
	Multiple of 64 kbit/s connections in any other network if
available.
.LP
	d)
	Switched semi\(hypermanent and permanent connections at bit
rates being multiples of 64\ kbit/s.
.LP
	e)
	PSTN from some Administrations.
.PP
\fINote\fR \ \(em\ The Packet Switched Public Data Network (PSPDN) and 
the Public Switched Telephone Network (PSTN) could be used in some cases 
to carry certain telematic services used in teleconferencing. The PSPDN 
is not capable of carrying audio and moving video. The use of different 
networks adopted for one terminal 
connection\ must however be considered as an unwanted temporary solution 
to serve as a bridge from the 
existing situation to ISDN.
.PP
2.3
Interworking between different types of networks should be
assured on international connections.
.sp 9p
.RT
.PP
2.4
The international connections shall use international digital
transmission facilities. Only by bilateral agreement the use of other means 
may be made where necessary. 
.PP
2.5
For interworking between networks of different types, the same
network(s) should be used for both traffic directions.
.PP
2.6
In the case of international interworking between TC terminals
connected to dissimilar networks, Recommendation\ X.300 shall be applied 
where appropriate. 
.PP
2.7
The network should not impose any limitation on optional and
private use applications.
.PP
2.8
If satellite connections are used, then more than two hops are to  be avoided.
.sp 2P
.LP
\fB3\fR 	\fBOperation of TCS\fR 
.sp 1P
.RT
.sp 1P
.LP
3.1
	\fIGeneral\fR 
.sp 9p
.RT
.PP
3.1.1
TCS in the international connections shall use any of the
following:
.sp 9p
.RT
.LP
	\(em
	reserved or semi\(hypermanent connections (e.g. manual set\(hyup);
.LP
	\(em
	on demand connections (automatic switching);
.LP
	\(em
	permanent connections (leased circuits).
.PP
See also Recommendations AV 111, 112, 113.
.bp
.PP
3.1.2
The communication ways should be:
.sp 9p
.RT
.LP
	\(em
	two ways alternate (TWA), (but always TWS for audio and
moving video, if applicable);
.LP
	\(em
	two ways simultaneous (TWS).
.PP
See also Recommendations AV 111, 112, 113.
.PP
3.1.3
Interworking and intercommunication will be assured
between:
.sp 9p
.RT
.LP
	a)
	different types of network;
.LP
	b)
	different terminals (e.g. with different transmission
rates);
.LP
	c)
	different kinds of service.
.PP
The extent and functionality for interworking are for further
study.
.PP
In Recommendations AV 111, 112, 113, 240, 241 and 242 the detailed
interworking possibilities are pointed out.
.RT
.sp 2P
.LP
3.2
	\fICall operations\fR 
.sp 1P
.RT
.PP
3.2.1
The operations for each call may be divided in the following
two phases:
.sp 9p
.RT
.LP
	\(em
	call control phase;
.LP
	\(em
	communication phase.
.sp 1P
.LP
3.2.1.1
	\fICall control phase\fR 
.sp 9p
.RT
.PP
It comprises:
.RT
.LP
	a)
	\fICall set\(hyup\fR 
.LP
	The network connections are established among the meeting
locations either directly or through a connection between
any meeting location and an MCU. Each meeting location and
MCU is normally connected to a single network, ultimately
this will be ISDN.
.LP
	For the time being, however, connections to multiple
networks may occur. They can be requested according to the
telematic services used during TCS (e.g.,\ PSTN for Audio
plus CSDN for Teletex transmission).
.LP
	 In this phase any supplementary services to be used should be requested. 
For example: 
.LP
	\(em
	closed User Group (CUG);
.LP
	\(em
	call Identification;
.LP
	\(em
	charge Advise;
.LP
	\(em
	reverse Charging.
.LP
	 The management of a teleconference is handled by the \*Qconference conductor\*U. 
The control functions to manage the conference may be operated by the \*Qconference 
conductor\*U, by the TCS operator, or by an automatic method 
offered through the MCU. The control functions offered to a teleconference 
may consist of any combination of the following, depending on the teleconference 
type, i.e., audio, audiographic or video. The control functions are the 
ability to: 
.LP
	\(em
	connect participants to a conference;
.LP
	\(em
	re\(hyconnect a dropped teleconference participant;
.LP
	\(em
	contact an operator for assistance;
.LP
	\(em
	disconnect selected conference participants;
.LP
	\(em
	identify participants on the teleconference or screen
participants before connection to the teleconference;
.LP
	\(em
	terminate the conference;
.LP
	\(em
	perform other control functions required by the supplementary
facilities if used.
.LP
	b)
	\fIIntercommunication set\(hyup\fR 
.LP
	Once the network connections have been established, the
communication among the respective meeting locations takes
place under the control of teleconferencing protocols (see
Question\ 23, COM\ VIII).
.LP
	c)
	\fICommunication termination\fR 
.LP
	A teleconference will terminate by one of the following
methods:
.LP
	1)
	The conference conductor determines the conference is
over and proceeds to terminate it.
.LP
	2)
	All of the conference participants hang up.
.LP
	3)
	The MCU disconnects the participants (e.g., expiration
of reservation time).
.bp
.LP
	Individual locations may disconnect without terminating the
conference.
.LP
	d)
	\fIClearing of connection\fR 
.LP
	The network clearing of connection is a matter of signalling
procedures in the relevant networks and/or of
Administrative procedures (e.g.,\ in case of leased
lines).
.sp 1P
.LP
3.2.1.2
	\fICommunication phase\fR 
.sp 9p
.RT
.LP
	a)
	At each meeting location the functions of \*QConference
conductor\*U and \*QLocal conductor\*U can at the wish of the
participants, be fulfilled (see Annex\ 2 for clarification
of the terms \*QConference conductor\*U and \*QLocal conductor\*U).
In this case the conference is termed \*Qconducted\*U. Only one
of the local conductors can have the additional \*Qrole\*U of
conference conductor.
.LP
	b)
	The main task of the conference conductor is to chair the
meeting in the classical sense. The \*Qbuttonpushing\*U for the
conductor must be kept to a minimum. Opening and closing of
channels (for telewriter, facsimile,\ etc.) is done
automatically. Only the microphones and/or the cameras of
participants may be controlled by the conference conductor
but like in normal meetings this should only be performed
in large or very formal meeting. If the microphones and the
cameras are not controlled by the conference conductor the
conference is termed \*Qnon\(hyconducted\*U.
.LP
	c)
	The initial mode in the set\(hyup phase and the fall back mode
after change configuration is non\(hyconducted.
.LP
	d)
	Also in this phase some supplementary services should be
provided (left for further study).
.sp 2P
.LP
3.3
	\fIBasic call identification\fR 
.sp 1P
.RT
.PP
3.3.1
In Audiographic conferences and Videoconferences protocols are involved 
in sending and receiving of all audio modes, messages, 
documents,\ etc.
.sp 9p
.RT
.PP
Exchange of addresses of transmitting and receiving terminals
and/or MCU(s) is for further study.
.sp 2P
.LP
3.4
	\fICommunication related security\fR 
.sp 1P
.RT
.PP
3.4.1
It is essential to have TCS users` confidence that their
teleconference will be secure. During both the call set\(hyup phase and the
communication phase, it will be the responsibility of the individual
administrations to \fIoffer\fR security mechanism based on bilateral or
multilateral agreements. There are two levels of security which need to be
addressed for teleconferencing:
.sp 9p
.RT
.LP
	\(em
	To safeguard privacy.
.LP
	\(em
	To prevent unauthorized network access.
.PP
Basic requirements for both levels are for further study.
.sp 2P
.LP
\fB4\fR 	\fBQuality of the service\fR 
.sp 1P
.RT
.sp 1P
.LP
4.1
	\fIGeneral\fR 
.sp 9p
.RT
.PP
4.1.1
The quality of the individual services should be the same as
that for the individual services (in general this is prescribed in the
appropriate Recommendations) comprised in the teleconference (e.g.\ Audio,
Facsimile, Teletex, Videotex, Moving Picture Video,\ etc.).
.sp 9p
.RT
.sp 2P
.LP
4.2
	\fIMaintenance\fR 
.sp 1P
.RT
.PP
4.2.1
Every Administration should provide for each TCS network a
maintenance centre for assisting the operators, if necessary.
.sp 9p
.RT
.sp 2P
.LP
4.3
	\fIDuration of service\fR 
.sp 1P
.RT
.PP
4.3.1
The international TCS, where it is possible, should be open
continuously for 24 h/day.
.bp
.sp 9p
.RT
.sp 2P
.LP
\fB5\fR 	\fBTerminal\fR 
.sp 1P
.RT
.sp 1P
.LP
5.1
	\fIGeneral\fR 
.sp 9p
.RT
.PP
5.1.1
The terminal station (see Figure 1/F.710) is composed by:
.sp 9p
.RT
.LP
	\(em
	TC Common Box (TCCB).
.LP
	\(em
	Associated equipments (AE).
.LP
.rs
.sp 37P
.ad r
\fBFigure 1/F.710, p. 
.sp 1P
.RT
.ad b
.RT
.PP
5.1.2
TCCB matches at one side (network side) the interface of the
network, while at the other (user side) the interface of each AE.
.sp 9p
.RT
.PP
5.1.3
AE are the application terminals.
.PP
5.1.4
The terminals will be described in Recommendations AV 310, 311,
312, 313 and 330.
.bp
.sp 2P
.LP
5.2
	\fIControl functions\fR 
.sp 1P
.RT
.PP
5.2.1
The control functions to provide are:
.sp 9p
.RT
.LP
	a)
	General control functions (on/off switch, call set\(hyup,
volume control, floor request, grant floor request,\ etc.). Some of these
functions are optional; this is a matter for further study.
.LP
	b)
	Control functions joined to AE.
.sp 1P
.LP
5.2.1.1\ \ The general control functions are joined to the handling of a
command console.
.sp 9p
.RT
.PP
There are two kinds of control functions to consider:
.LP
	\(em
	The control functions of a local conductor (to be
described).
.LP
	\(em
	The control functions of the conference conductor (to be
described).
.sp 1P
.LP
5.2.1.2\ \ The control functions joined to AE are those defined in the
corresponding CCITT Recommendations.
.sp 9p
.RT
.LP
5.2.1.3\ \ The necessity for the conductor to handle controls should be
kept to a minimum.
.sp 2P
.LP
5.3
	\fITCCB identification\fR 
.sp 1P
.RT
.PP
5.3.1
Each TCCB shall have a unique identification (\(sc\ 3.3.1).
.sp 9p
.RT
.PP
5.3.2
It is the responsibility of the conference conductor to verify
the identification of connected TCCBs during the control phase of the call.
.PP
For this purpose the identification of connected terminals could be visualized 
to the conference conductor. 
.sp 2P
.LP
\fB6\fR 	\fBMultipoint operation\fR 
.sp 1P
.RT
.PP
6.1
The international multipoint teleconference service is provided by means 
of one or more MCUs. Each MCU may serve one or more terminals and be interconnected 
with other MCUs. 
.sp 9p
.RT
.sp 1P
.LP
6.2
	\fIMultipoint audiographic teleconferencing\fR 
.sp 9p
.RT
.PP
The MCU provides the capability to interactively exchange
audiovisual information among many connected terminals and/or other MCUs.
.PP
It can be located in a network or it can be considered as a part of
terminal giving the possibility of multiple connections to the network.
.PP
Although particular attention must be paid to network topology in the case 
of satellite transmission, the basic functions of the MCU for a 
terrestrial or a satellite network are similar.
.PP
In order to provide the basic features in an international
audiographic conference service the tasks to be performed by an
MCU are:
.RT
.LP
	\(em
	network access and interface;
.LP
	\(em
	management of framing structure; multiplexing and
demultiplexing;
.LP
	\(em
	mixing of audio signals;
.LP
	\(em
	processing of the subchannels;
.LP
	\(em
	analysis of control messages;
.LP
	\(em
	routing of signals to audiographic teleconference terminals
and other MCUs;
.LP
	\(em
	handling of encrypted signals;
.LP
	\(em
	terminal interconnection;
.LP
	\(em
	office automation facility;
.LP
	\(em
	operator's console;
.LP
	\(em
	notification to the \*Qconference conductor\*U of a disconnected
participant;
.LP
	\(em
	reconnection of a disconnected participant to a conference;
.LP
	\(em
	providing announcements to the conference participants
whenever necessary.
.PP
A reservation system could be integrated into the MCU or it may be offered 
through a separate system connected to an MCU. 
.PP
Reservations for a teleconference will be provided through a
Reservation Centre.
.bp
.RT
.sp 1P
.LP
6.3
	\fIMultipoint videoconferencing\fR 
.sp 9p
.RT
.PP
The operating modes and consequently the switching decision
criterion depend on the conception of the multipoint videoconference service 
of each Administration. Any solution, automatic or manual, can be implemented 
without altering the basic philosophy of multipoint videoconferencing. 
In each solution, the MCU provides each output port with the mixed audio 
signals from all other ports. 
.PP
The minimum MCU working mode is as follows: the MCU, by comparing the incoming 
sound channels, selects the loudest speaker (called New Speaker or 
NS). A second channel is selected by the MCU being the previous loudest 
speaker (called Previous Speaker or PS). The NS is sent the PS channel 
and the other 
rooms are sent the NS channel. This mode is normally used when the
multiconference is established.
.PP
The minimum MCU mode is automatic and doesn't require any extra
facility. The basic functions of the MCU for terrestrial or satellite networks 
are identical. In order to provide the basic features in an international 
videoconference service, the MCU shall have the capability:
.RT
.LP
	\(em
	to synchronize the incoming streams to a single pilot clock;
.LP
	\(em
	to extract frame alignment in order to synchronize the
different streams to the frame clock;
.LP
	\(em
	to extract frame parity, multiframe and supermultiframe
alignment from the signalling channel in order to access the
codec\(hyto\(hycodec signalling channel in each incoming stream;
.LP
	\(em
	to process this signalling channel;
.LP
	\(em
	to process the sound channels in order to create an open
sound system, in the case of unencrypted service;
.LP
	\(em
	to decide image switching and dispatching according to a
selection criterion (automatic or on request);
.LP
	\(em
	to signal the decision of switching to the codecs in order to
prepare them and to avoid any degradation during and after
the switching;
.LP
	\(em
	to multiplex the selected video channels with the open sound
channel and the effective channel;
.LP
	\(em
	to distribute the reconstructed streams to the corresponding
access ports.
.PP
Procedures for multipoint operation (call set\(hyup, protocols, etc.) and 
a description of the MCU are given in Recommendations\ AV\ 231, 232, 233 
and 4xx (the matter should be extended for further study). 
.sp 2P
.LP
\fB7\fR 	\fBIntercommunication\fR 
.sp 1P
.RT
.PP
Intercommunication of various kinds of TCS and between TCSs and
other services (e.g.\ telephony or videophone) is described in
Recommendations\ AV\ 240, 241, 242 (the matter should be extended for further
study).
.RT
.sp 2P
.LP
\fB8\fR 	\fBReservation of international teleconference\fR 
.sp 1P
.RT
.sp 1P
.LP
8.1
	\fIAudiographic teleconference\fR 
.sp 9p
.RT
.PP
In order to ensure the performance of an audiographic
teleconference service for an appointed time, a reservation will be required 
at least for the MCU. Normally, reservation will be handled by the customer 
as the service will be an automatic one. Administrations may also provide 
a manual 
version of a reservation system. This process is normally left to each
Administration; however, general guidelines for an harmonized operation 
of the international audiographic teleconference service follow below. 
The reservation is made through the operator service. The following information 
must be given by the convenor: 
.RT
.LP
	\(em
	list of participating terminals;
.LP
	\(em
	starting time of the session;
.LP
	\(em
	closing time of the session;
.LP
	\(em
	symbolic name of the session;
.LP
	\(em
	symbolic names of the terminals.
.PP
It will be possible for a convenor to access the Reservation
Centre (RC) through an ordinary telephone connection to register a reservation 
for a conference. A data terminal can be used in an automatic system, 
alternatively, a reservation can be made by voice in a manually operating
system. The RC determines which MCUs and which connections are required 
for the meeting and subsequently reserves these facilities. Each terminal 
will be 
notified of the MCU it has to connect to.
.bp
.PP
During a conference session the chairman may be able to access the
reservation diary. In this way it will be possible during a conference 
to agree on a subsequent conference. 
.RT
.sp 1P
.LP
8.2
	\fIVideoconference\fR 
.sp 9p
.RT
.PP
Due to the higher bit rates used for videoconference, a reservation will 
be required not only for the MCU but also at least for the international 
links in multipoint as well as in point\(hyto\(hypoint conferences. Normally, 
the 
reservation of international videoconferences will be made manually.
Administrations may also provide an automatic version of a reservation 
system for national videoconference or for the national part of international 
videoconferences.
.PP
The process of manual reservation of international point\(hyto\(hypoint 
and multipoint videoconferences needs general guidelines to ensure a harmonized 
operation of the international videoconference service.
.PP
All reservation arrangements for international videoconferences are to 
be made by the National Reservation Office (NRO) of the participating 
Administrations. Negotiations are preferably carried out by telephone, but
agreed reservations must be confirmed before the call.
.PP
The information needed for a reservation of a videoconference is
similar to that needed for the reservation of an audiographic teleconference
(details for further study).
.PP
The participating Administration in an international
videoconference service must agree on the following items:
.RT
.LP
	\(em
	minimum notice time for reservation;
.LP
	\(em
	maximum notice time for reservation;
.LP
	\(em
	minimum reservation time (duration of the session);
.LP
	\(em
	acceptable increments for reservation;
.LP
	\(em
	procedure for establishing a reservation between the
NROs:
.LP
	a)
	occasional use of booking
.LP
	b)
	regular booking;
.LP
	\(em
	procedure of last minute extensions;
.LP
	\(em
	billing procedure.
.PP
(List not exhaustive, details for further study.)
.sp 2P
.LP
\fB9\fR 	\fBOperational and commercial aspects\fR 
.sp 1P
.RT
.PP
Matters of maintenance, tariff principles, etc. are for further
study.
.RT
.sp 2P
.LP
\fB10\fR 	\fBResults of questionnaire on TCS\fR 
.sp 1P
.RT
.PP
The results are reported in Contribution COM I\(hy98, 1985\(hy1988\ Study 
Period. (Responses to the questionnaire on Teleconference 
Service).
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation F.710)
.sp 9p
.RT
.ce 0
.ce 1000
\fBRecommendations list for audiovisual service\fR 
.sp 1P
.RT
.ce 0
.LP
A.1
	\fIService definition\fR 
.sp 1P
.RT
.LP
	AV\ 100
	General Recommendation for AV services
	SG I
.LP
	AV\ 110
	Teleconference services
	SG I
.LP
	AV\ 111
	Audiographic conference service
	SG I
.LP
	AV\ 112
	Videoconference service
	SG I
.LP
	AV\ 120
	Videophone service
	SG I
.LP
	AV\ 130
	. |  |  (Other AV services)
	SG I
.bp
.sp 2P
.LP
A.2
	\fIInfrastructure\fR 
.sp 1P
.RT
.LP
	AV\ 200
	General Recommendation for AV services Infrastructure
	SG XV/VIII
.LP
	AV\ 210
	Reference network configuration
	SG XV
.LP
	AV\ 220
	General Recommendation for Frame Structure
	SG XV/VIII
.LP
	AV\ 221
	Frame structure for a 64 kbit/s channel
.LP
in audiovisual teleservices
	SG XV/VIII
.LP
	AV\ 222
	Frame structure for 384\(hy2048 kbit/s channels
.LP
in audiovisual teleservices
	SG XV
.LP
	AV\ 223
	. |  |  (Frame structure for higher bit/rates
.LP
in audiovisual teleservices)
	SG XV
.LP
	AV\ 230
	General Recommendation for AV system controls
.LP
and indications
	SG XV/VIII
.LP
	AV\ 231
	Multipoint Control Unit for 64 kbit/s
	SG XV/VIII
.LP
	AV\ 232
	Multipoint Control Unit for 384\(hy2048 kbit/s
	SG XV
.LP
	AV\ 233
	. |  |  (Multipoint Control Unit for higher bit rates)
	SG XV
.LP
	AV\ 240
	Intercommunication principle
.LP
	AV\ 241
	Intercommunication between 64 kbit/s AV services
.LP
using the Frame Structure of Recommendation\ AV\ 220
	SG XV/VIII
.LP
	AV\ 242
	Intercommunication between 64 kbit/s AV services
.LP
to Recommendation\ AV\ 220 and 64\ kbit/s audio\(hyonly and
.LP
data\(hyonly terminals
	SG XV/VIII
.LP
	AV\ 243
	Interworking between higher bit rate AV
.LP
and data\(hyonly terminals
	SG XV/VIII
.sp 2P
.LP
A.3
	\fISystems and terminal equipment\fR 
.sp 1P
.RT
.LP
	AV\ 300
	General Recommendation for AV systems and terminals
.LP
	AV\ 301
	General Recommendation on AV terminal equipment
.LP
	AV\ 310
	Requirements for teleconferencing
.LP
	AV\ 311
	Audiographic system and terminal requirements
	SG XII/XV/VIII
.LP
	AV\ 312
	Videoconference system and terminal requirements
	SG XV
.LP
	AV\ 320
	Requirements for videophone service
.LP
	AV\ 321
	Audio
	SG XII/XV
.LP
	AV\ 323
	Video
	SG XV
.LP
	AV\ 330
	Facility coding
.sp 2P
.LP
A.4
	\fIProtocols\fR 
.sp 1P
.RT
.LP
	AV\ 400
	Protocol structure for Audiovisual services
	SG I/XVIII/XV/VIII
.LP
	AV\ 410
	Audio protocol for Audiovisual services
	SG XVIII
.LP
	AV\ 420
	Video protocol for Audiovisual services
	SG XV
.LP
	AV\ 430
	Graphics protocol for Audiovisual services
	SG VIII
.LP
	AV\ 431
	Graphics terminal protocol
	SG VIII
.LP
	AV\ 451
	Audiographic conference protocol
	SG VIII
.sp 2P
.LP
A.5
	\fIOther requirements\fR 
.sp 1P
.RT
.LP
.sp 3
.bp
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation F.710)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDefinition of terms used in TCS\fR 
.sp 1P
.RT
.ce 0
.LP
B.1
	\fBbasic requirement\fR 
.sp 1P
.RT
.PP
A service feature defined by CCITT as essential for the basic
operational mode, available in terminal or network on an international
basis.
.RT
.sp 1P
.LP
B.2
	\fBcommunication\fR 
.sp 9p
.RT
.PP
An exchange of information between two or more subscribers of a
telecommunication network by agreed conventions.
.RT
.sp 1P
.LP
B.3
	\fBconference\fR 
.sp 9p
.RT
.PP
A meeting of a number of people in more than one location for
discussion or consultation on subjects of common interest.
.RT
.sp 1P
.LP
B.4
	\fBconference conductor\fR 
.sp 9p
.RT
.PP
One who sets up, chairs and clears the conference. If necessary he coordinates 
and manages Network and Terminal functions such as giving the 
floor. All functions have to be accomplished in such a way that can be 
easily controlled by an actual participant in the conference, without special 
training (e.g.\ Administration's personnel should not be required). 
.RT
.sp 1P
.LP
B.5
	\fBmarker\fR 
.sp 9p
.RT
.PP
It is a conference tool used to draw attention to a particular
part of a displayed image.
.RT
.sp 1P
.LP
B.6
	\fBmeeting\fR 
.sp 9p
.RT
.PP
Coming together of a number of people at a certain time in a place to participate 
at a conference. 
.RT
.sp 1P
.LP
B.7
	\fBlocal conductor\fR 
.sp 9p
.RT
.PP
Who has the main function in TCS to direct locally the conference. A meeting 
conductor may be provided for each meeting location. Every 
meeting conductor is identified by a number.
.RT
.sp 1P
.LP
B.8
	\fBmeeting location\fR 
.sp 9p
.RT
.PP
A place in which a meeting is set up.
.RT
.sp 1P
.LP
B.9
	\fBmultipoint control unit (MCU)\fR 
.sp 9p
.RT
.PP
A device which enables more than two teleconference terminals to be interconnected. 
It can be located in a network or it can be considered as a part of terminal 
giving the possibility of multiple connections to the 
network.
.RT
.sp 1P
.LP
B.10
	\fBprivate use option\fR 
.sp 9p
.RT
.PP
A service feature not defined by CCITT as an addition to the basic requirements, 
that may optionally be used by subscribers in the international TCS, but 
requiring always a previous agreement between subscribers. 
.RT
.sp 1P
.LP
B.11
	\fBstandardized option\fR 
.sp 9p
.RT
.PP
A service feature defined by CCITT as an addition to the basic
requirements, that may optionally be used by subscribers in the international 
TCS. These options may be provided from the networks as well from the 
terminals.
.bp
.RT
.sp 1P
.LP
B.12
	\fBtelecommunications\fR 
.sp 9p
.RT
.PP
All the transmissions, emissions, receptions of signals, writings, images, 
sounds of every nature by wires, electricity, or other 
electromagnetical systems.
.RT
.sp 1P
.LP
B.13
	\fBtelewriting\fR 
.sp 9p
.RT
.PP
It is a text communication service which enables the transmission of graphic 
information to be displayed at the receiving side in accordance with the 
writing movements at the sending side. This display is normally effected 
on a real\(hytime basis; a delay in the transmission may be included. 
.RT
.sp 1P
.LP
B.14
	\fBreal\(hytime conferencing\fR 
.sp 9p
.RT
.PP
The concept of real\(hytime conferencing implies:
.RT
.LP
	1)
	The time required for the transmission of the various
signals between the connected terminals is short in comparison
to the human reaction times in conference situations.
.LP
	2)
	The conferees participate simultaneously to the
conference.
.sp 1P
.LP
B.15
	\fBconvenor\fR 
.sp 9p
.RT
.PP
A person who arranges and reserves the conference
facilities.
.RT
.sp 1P
.LP
B.16
	\fBconducted conference\fR 
.sp 9p
.RT
.PP
A conference where the conductor handles the (electronic) signals such 
as grant floor request (as a reaction on a floor request) and where the 
conductor opens and closes microphones of participants.
.RT
.sp 1P
.LP
B.17
	\fBnon\(hyconducted conference\fR 
.sp 9p
.RT
.PP
In this kind of conference no (electronic) conductor action is
taken. All microphones are open or automatically switched by means of a 
voice switch for acoustic stability reason. 
.RT
.sp 1P
.LP
B.18
	\fBreservation office\fR 
.sp 9p
.RT
.PP
A national administrative centre where reservations for
connections and if applicable MCU(s) and other equipment are made.
.RT
.sp 1P
.LP
B.19
	\fBmaintenance centre\fR 
.sp 9p
.RT
.PP
A national administrative centre where notification is taken from irregularities 
and from where action is taken for resolving these 
irregularities.
.RT
.sp 1P
.LP
B.20
	\fBfacsimile\fR 
.sp 9p
.RT
.PP
Reproduction of all forms of graphics, handwritten or printed
material, in the sense of a distant reproduction of the original within the
limits and characteristics specified by the relevant recommendation.
.RT
.sp 1P
.LP
B.21
	\fBintercommunication\fR 
.sp 9p
.RT
.PP
Intercommunication in the teleconference area implies to have the capability 
(this capability could be distributed between networks or terminals) to 
translate the presentation of information given for a service to information 
available to be presented in another service and, if necessary, interworking 
between networks.
.PP
This is valid between services used in the TC environment and between TC 
service and another service. 
.RT
.sp 1P
.LP
B.22
	\fBinterworking\fR 
.sp 9p
.RT
.PP
The relationship between systems, networks, terminals and their
components, primarily refers to signalling, protocols (lower levels) and 
other technical means for provisioning services. 
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ F.721\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBBASIC\ NARROW\ BAND\ VIDEOPHONE\ SERVICE\ IN\ THE\ ISDN\fR 
.FS
This
Recommendation may require further consideration, alignment and completion
in the next study period.
.FE
.EF '%	Fascicle\ II.5\ \(em\ Rec.\ F.721''
.OF '''Fascicle\ II.5\ \(em\ Rec.\ F.721	%'
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that considerable efforts have been undertaken
worldwide in order to develop videophone equipment based on rapid improvements 
in the quality of video codec algorithms; 
.PP
(b)
that videophones of some companies are already
available on the market;
.PP
(c)
that first trials of videophone have been performed
nationally as well as internationally;
.PP
(d)
that a number of countries intend to introduce the
videophone service as soon as possible;
.PP
(e)
that the ISDN will be an appropriate network for
providing the narrowband videophone service;
.PP
(f)
that ISDN trials are going on in a number of
countries,
.sp 1P
.LP
\fIrecognizes\fR 
.sp 9p
.RT
.PP
the need for a standardized international videophone service,
which will guarantee the compatibility of videophones on a worldwide basis
and it therefore,
.sp 1P
.LP
\fIrecommends\fR 
.sp 9p
.RT
.PP
that the narrowband videophone service, where implemented, respect the 
requirements stated in this Recommendation. 
.sp 2P
.LP
\fB1\fR 	\fBIntroduction\fR 
.sp 1P
.RT
.sp 1P
.LP
1.1
	\fIScope\fR 
.sp 9p
.RT
.PP
The narrowband videophone service is to be defined for networks
providing 64\ kbit/s channels. This Recommendation only deals with ISDN 
which is recognized as a strong candidate for providing this service. 
.RT
.sp 1P
.LP
1.2
	\fIBearer capabilities\fR 
.sp 9p
.RT
.PP
Videophone services requiring one or two 64 kbit/s channels are
under study. If two rates are eventually standardized, it will become necessary 
to provide for basic intercommunication at the audiovisual qualities of 
the 
lower rate. Such basic intercommunication should be provided in the
terminals.
.RT
.sp 2P
.LP
\fB2\fR 	\fBDescription of videophone service supported in the ISDN\fR 
.sp 1P
.RT
.sp 1P
.LP
2.1
	\fIDefinition\fR 
.sp 9p
.RT
.PP
The \fBvideophone service\fR is a symmetrical, bidirectional,
real\(hytime, audiovisual teleservice in which speech and moving pictures are
communicated; the picture information transmitted is sufficient for the
adequate representation of fluid movements of persons.
.RT
.sp 1P
.LP
2.2
	\fIService description\fR 
.sp 9p
.RT
.PP
The videophone service is likely to be used in much the same way as the 
telephone service for personal communication, the enhancement being in 
the visibility of the communication partners which implies a number of 
possible new applications. 
.bp
.RT
.PP
A redundancy and irrelevance reduction technique (codec) in the
terminal allows moving pictures to be displayed continuously in colour, 
even if transmission takes place at the comparatively low bit rate of the 
narrowband 
ISDN.
.PP
The speech quality of this new service must be at least as good as
that applicable to the telephone service in the 64\ kbit/s ISDN using a
bandwidth of 3.1\ kHz up to 7\ kHz.
.PP
The videophone service is a teleservice, i.e. a fully standardized
service as defined in Recommendations\ I.210 and I.240.
.PP
The basic videophone service is characterized by the continuous
transmission of moving pictures simultaneously with the speech of the persons 
involved in the call (generally two in the case of a point\(hyto\(hypoint 
connection) via one or two 64\ kbit/s channels. 
.PP
An optional enhancement available in some terminals provides for
transmission of images of documents or other objects alternate to face\(hyto\(hyface 
communication. Transfer of documents at higher resolution may be an optional 
feature. Further study is required.
.PP
Two different types of calls should be possible: point\(hyto\(hypoint calls 
(basic requirement) and multipoint calls. 
.PP
\fINote\fR \ \(em\ For multipoint calls a central facility is required for
mixing speech signals and switching and/or combining video signals. This
facility is to be defined in another Recommendation.
.PP
Videophone terminals must also be capable of supporting the telephone  service.
.PP
In some installations a videophone will be attached to a passive bus configuration 
(S\ interface) along with terminals for other services. 
.PP
\fINote\fR \ \(em\ Speech supported only by still picture transmission and/or
telewriting is \fInot\fR considered as part of the videophone service.
.RT
.sp 1P
.LP
2.3
	\fIApplications of the videophone service\fR 
.sp 9p
.RT
.PP
The examples given below are not exhaustive. Other enhanced
videophone applications may emerge.
.PP
\fIExamples\fR :
.RT
.LP
	a)
	\*QFace\(hyto\(hyface\*U dialogues involving at least
head\(hyand\(hyshoulder images.
.LP
	b)
	 Dialogues including interactive viewing of documents such as sketches, 
diagrams or charts. 
.LP
	c)
	Access of the user to a videoconference.
.LP
	d)
	Participation in videophone conferences.
.LP
	e)
	Audio\(hyvisual tele\(hyeducation.
.LP
	f
)
	Remote health \*Qvisiting\*U (limitations for further
study).
.LP
	g)
	Deaf\(hyand\(hydumb communication (limitations for further
study).
.sp 1P
.LP
2.4
	\fINecessary quality characteristics\fR 
.sp 9p
.RT
.LP
	\(em
	Synchronism of speech and lip movement (lip synchronism)
.LP
	 (No subjectively discernible difference in the delay of the speech and 
video signal.) 
.LP
	\(em
	Sound quality
.LP
	Speech quality as in the 64\(hykbit/s ISDN telephone service
based on a 3.1\ kHz or 7\ kHz bandwidth.
.LP
	\(em
	 Optimization of the picture quality is under study, including the need 
for adequate representation of fluid movements. 
.PP
The overall effect on quality by the delays introduced by video
codecs and transmission facilities needs to be taken into account in the
service. If satellite connections are used, then two or more hops are to be
avoided, because increased delays may impair user acceptability. Further 
study is needed for establishing criteria for \*Qacceptable\*U signal delays. 
.PP
For the convenience of the user visual user guidance between the
videophone system and the user should be preferably provided with the aid of
alphanumeric display.
.bp
.RT
.sp 2P
.LP
\fB3\fR 	\fBIntercommunication\fR 
.sp 1P
.RT
.LP
	\(em
	Intercommunication with the telephone service is
essential.
.LP
	\(em
	 Intercommunication with the videoconference service and other audio and 
visual services is necessary (but for further study). 
.LP
	\(em
	Intercommunication between videophone services based on
different bit rates is required.
.sp 1P
.LP
3.1
	\fIIntercommunication with telephony\fR 
.sp 9p
.RT
.PP
Considering the fact that at the beginning of the introduction of the videophone 
service the number of videophone subscribers compared to the 
number of telephone subscribers will be negligible, a fundamental requirement 
must be fulfilled in order to avoid that videophone subscribers could only 
communicate in a kind of a closed user group. It is \fIessential\fR that every
videophone subscriber is able to reach from his videophone terminal every
telephone subscriber. This condition must be met regardless of the technology 
(analogue, digital, ISDN) applied in the local exchange to which the other 
telephone subscriber is connected.
.PP
If in case of intercommunication a videophone connection cannot be
provided, a telephone call should be immediately initiated. If then no
connection results, an appropriate cause indication shall be given.
.PP
On the other hand, every telephone terminal must be able to reach
every videophone terminal. (The videophone terminal will be a multiservice
terminal, i.e.\ appropriate for videophone calls as well as for telephone
calls.)
.RT
.sp 1P
.LP
3.2
	\fIIntercommunication between different videophone services\fR 
.sp 9p
.RT
.PP
Basic intercommunication between videophone services based on
different bit rates will be provided at the audiovisual qualities of the 
lower bit order. 
.RT
.sp 1P
.LP
3.3
	\fIIntercommunication with other audiovisual and audiographic\fR 
\fIservices\fR 
.sp 9p
.RT
.PP
For further study.
.RT
.sp 2P
.LP
\fB4\fR 	\fBService operation\fR 
.sp 1P
.RT
.sp 1P
.LP
4.1
	\fICall set\(hyup\fR 
.sp 9p
.RT
.PP
Two possibilities are required:
.RT
.LP
	\(em
	Call set\(hyup starting directly as videophone service.
.LP
	\(em
	 Call set\(hyup by means of a service change, starting from the telephone 
service. 
.PP
Several service changes between telephony and videophony must be possible 
during a single call. 
.sp 1P
.LP
4.1.1
	\fIPoint\(hyto\(hypoint videophone call\fR 
.sp 9p
.RT
.PP
The call set\(hyup procedure from the user's point of view must be as simple 
as possible in order to achieve a good acceptability. 
.PP
Call set\(hyup procedure from the user's point of view:
.RT
.sp 1P
.LP
\fICase\ 1\fR \ \(em\ \fIVideophone service from the very beginning\fR 
.sp 9p
.RT
.LP
	e.g.:
	\(em
	going off\(hyhook
.LP
	\(em
	dialling tone
.LP
	\(em
	initialization of videocommunication
.LP
	\(em
	keying in the number of the called subscriber
.LP
	\(em
	videophone call
.bp
.sp 1P
.LP
\fICase\ 2\fR \ \(em\ \fITelephone service first\fR 
.sp 9p
.RT
.LP
	e.g.:
	\(em
	going off\(hyhook
.LP
	\(em
	dialling tone
.LP
	\(em
	keying in the number of the called subscriber
.LP
	\(em
	telephone call
.LP
	\(em
	initialization of videocommunication
.LP
	\(em
	videophone call
.PP
\fINote\fR \ \(em\ Interruption of the audio connection recognizable for 
the users should be avoided when changing between the telephone call and 
the 
videophone call.
.sp 1P
.LP
4.1.2
	\fIMultipoint videophone call\fR 
.sp 9p
.RT
.PP
The multipoint videophone call is in other terms the supplementary service 
\*QConference videophone call\*U. Conference facilities (three\(hyparty 
service, conference call) within the videophone service should be optionally
provided. Appropriate support (network or user premises equipment) is
necessary.
.PP
The procedure for operation of those conference calls is for further   study.
.RT
.sp 1P
.LP
4.2
	\fICall release\fR 
.sp 9p
.RT
.PP
In general, the release of a videophone call should be similar to the release 
of a telephone call; picture and sound are released 
simultaneously.
.RT
.sp 1P
.LP
4.3
	\fIChange of service\fR 
.sp 9p
.RT
.LP
	\(em
	 A service change will be controlled via the D\(hychannel; thus several 
service changes are possible during a call provided an end\(hyto\(hyend 
64\ kbit/s transparent channel is available.
.LP
	\(em
	Service change to and from videophony must be possible to
other services which need a single B\(hychannel or two B\(hychannels.
.PP
\fINote\fR \ \(em\ Details are for further study.
.sp 1P
.LP
4.4
	\fIAddressing of terminals\fR 
.sp 9p
.RT
.PP
Additional call set\(hyup functions such as terminal selection on a
passive bus, using multiple subscriber number may be offered. This is under
study.
.RT
.sp 2P
.LP
\fB5\fR 	\fBControls and indications\fR 
.sp 1P
.RT
.sp 1P
.LP
5.1
	\fIUser guidance\fR 
.sp 9p
.RT
.PP
User guidance plays a major role in the acceptance of the
videophone service by the subscriber. User guidance may take place in the 
form of a dialogue between the system and the user. 
.PP
Information concerning the status of the call will be displayed on the 
screens or on other displays of the calling and the called users. Some 
standardization of icons is required.
.PP
The audible call progress signals used in the videophone service
should comply to those of the telephone service.
.PP
User guidance may be based on the display of alphanumeric characters, e.g.\ 
on the screen, or by other visual means, and/or on audible announcements. 
.PP
It must be possible for the sending user (calling as well as called
user) to switch on and off the facility \*Qsuppressing the outgoing picture\*U.
.PP
In the case that one communication partner does not want to send his own 
picture to the other, a substitutional image or a suitable pictogram should 
be transmitted and displayed at the remote terminal. 
.PP
Call set\(hyup and user contact procedures may need harmonization with
those used for voice services. This point is for further study.
.bp
.RT
.sp 1P
.LP
5.2
	\fIAdditional items\fR 
.sp 9p
.RT
.LP
	\(em
	 The display of the called and calling subscribers' pictures on the screen 
should be possible, not necessarily simultaneously. 
.LP
	\(em
	The subscriber's own picture should be switchable on and off, as required.
.LP
	\(em
	Hands\(hyfree communication and loudspeaking should be
optionally possible.
.sp 2P
.LP
\fB6\fR 	\fBSupplementary services\fR 
.sp 1P
.RT
.LP
	\(em
	Same as for telephony (including conference call). Further
study required.
.LP
	\(em
	Other supplementary services, e.g. \*Qchange of service
including change of connection\*U have to be studied.
.sp 2P
.LP
\fBRecommendation\ F.730\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSERVICE\ ORIENTED\ REQUIREMENTS\ FOR\ TELEWRITING\ APPLICATIONS\fR 
.EF '%	Fascicle\ II.5\ \(em\ Rec.\ F.730''
.OF '''Fascicle\ II.5\ \(em\ Rec.\ F.730	%'
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that telewriting could offer graphic\(hyoriented
communication on real time or store\(hyand\(hyforward basis;
.PP
(b)
that telewriting could serve as an optional facility to the general public 
telephone service, which could be of interest to several categories of 
users (e.g. deaf people, architects, advertising 
agencies,\ etc.);
.PP
(c)
that telewriting could support applications like
educational communication services (\*Qelectronic blackboard\*U);
.PP
(d)
that telewriting could be a facility within a
teleconference service;
.PP
(e)
that telewriting could add a graphic\(hyoriented
facility to telematic services.
.sp 1P
.LP
\fIconcludes\fR 
.sp 9p
.RT
.PP
that telewriting can be applied as either a communication service or a 
communication technique within other services; 
.sp 1P
.LP
\fIrecommends\fR 
.sp 9p
.RT
.PP
that the service oriented aspects of telewriting applications be in accordance 
with this Recommendation. 
.sp 2P
.LP
\fB1\fR 	\fBGeneral\fR 
.sp 1P
.RT
.sp 1P
.LP
1.1
	\fIScope\fR 
.sp 9p
.RT
.PP
This Recommendation specifies the service\(hyoriented requirements for 
the application of telewriting in combination with telephony. 
.PP
Use of telewriting as an independent telecommunication service or in combination 
with other services than telephony is for further study. 
.PP
The technical characteristics of telewriting are specified in
Recommendation\ T.150.
.RT
.sp 1P
.LP
1.2
	\fIDefinition\fR 
.sp 9p
.RT
.PP
Telewriting enables the transmission of graphic information to be displayed 
at the receiving side in accordance with the writing movements at the sending 
side. This display is normally effected on a real time basis; a delay in 
the transmission may be included. 
.bp
.RT
.sp 2P
.LP
1.3
	\fIApplications\fR 
.sp 1P
.RT
.PP
1.3.1
Telewriting can support:
.sp 9p
.RT
.LP
	a)
	explanatory information exchange;
.LP
	b)
	teleconferencing;
.LP
	c)
	distant teaching or lecturing;
.LP
	d)
	telecommunication between speech\(hy and/or ear\(hyhandicapped
people.
.PP
1.3.2
Applications in combination with services other than the
telephone service and/or non\(hyreal time applications are for futher
study.
.sp 9p
.RT
.sp 2P
.LP
\fB2\fR 	\fBGeneral characteristics of telewriting\fR 
.sp 1P
.RT
.PP
2.1
The main characteristics of telewriting in this context are
real time display and interactive communication during one session, which
requires availability of a terminal at each side. Consequently, both sides 
of the connection will be able to contribute to the same image. 
.sp 9p
.RT
.PP
2.2
The presentation functionalities along with their attributes
are described in Recommendation\ T.150. They allow mainly for:
.LP
	\(em
	the generation, transfer and representation of curves of
arbitrary shapes; the effect of the movement of the writing
instrument at the sending side is retained during
reproduction;
.LP
	\(em
	marking single positions in a telewriting image by means of a
cursor;
.LP
	\(em
	erasure of all or part of a telewriting image.
.PP
2.3
The image input is provided by appropriate writing tools, such as a writing 
tablet and a writing pencil. 
.sp 9p
.RT
.PP
2.4
At the originators' terminal, the input information is made
visible either by a display unit or on the writing tablet itself.
.PP
2.5
The reproduction at the recipients' terminal will take place on a screen, 
on paper or on any other means, normally resulting in a real time copy. 
The writing speed at the transmitting and receiving end should generally 
be the same. 
.PP
2.6
In principle, any type of network can be used as a carrier for
telewriting signals.
.sp 2P
.LP
\fB3\fR 	\fBTelewriting in combination with telephony\fR 
.sp 1P
.RT
.PP
3.1
The general characteristics are as mentioned in \(sc\ 2.1.
.sp 9p
.RT
.PP
3.2
The subset of presentation functionalities available are the
default capabilities of the basic terminal as defined in
Recommendation\ T.150.
.PP
3.3
The following terminal operating modes are defined:
.LP
	a)
	speech plus telewriting: speech signals and telewriting
signals can be sent simultaneously;
.LP
	b)
	telewriting only: in this mode sending of speech signals is
blocked, reception of speech signals is still
possible.
.PP
3.4
The public switched telephone network is used for carrying the telewriting 
information. In practice, a 300\ bps sub\(hychannel derived from the 
available speech channel bandwidth is used.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ Use of the ISDN for carrying telewriting information 
is for futher study. 
.PP
3.5
The quality of service depends on the characteristics of the
telephone network and of the telewriting equipment.
.sp 9p
.RT
.PP
In case of simultaneous transmission of speech and telewriting
signals, mutual interference should be relatively small. Faults caused by
speech interference on the telewriting band are not tolerable. The influence 
of the telewriting signals on the quality of the speech conversation must 
be 
limited.
.LP
.bp