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TECHNICAL SPECIFICATION
Digital cellular telecommunications system (Phase 2+) (GSM);
Universal Mobile Telecommunications System (UMTS);
LTE;
Global Text Telephony (GTT);
Stage 1
(3GPP TS 22.226 version 15.0.0 Release 15)
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3GPP TS 22.226 version 15.0.0 Release 15 1 ETSI TS 122 226 V15.0.0 (2018-07)
Reference
RTS/TSGS-0122226vf00
Keywords
GSM,LTE,UMTS
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3GPP TS 22.226 version 15.0.0 Release 15 2 ETSI TS 122 226 V15.0.0 (2018-07)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
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Foreword
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI
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3GPP TS 22.226 version 15.0.0 Release 15 3 ETSI TS 122 226 V15.0.0 (2018-07)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 4
Introduction . 4
1 Scope . 6
2 References . 6
3 Definitions and abbreviations . 7
3.1 Definitions . 7
3.2 Abbreviations . 7
4 High level Requirements . 7
5 General Requirements . 8
5.1 Text conversation host environments . 8
5.2 Text conversation management . 8
5.3 Registration of text conversation capabilities . 9
5.4 Session control . 9
5.5 Invoking text conversation . 9
5.6 Text conversation handling during calls . 9
5.7 Alerting . 10
5.8 Addressing . 10
5.9 Roaming . 10
6 Security and reliability . 10
7 Charging . 10
8 External Interfaces . 10
8.1 External interfaces in the terminal . 10
8.2 External interfaces to other networks . 11
9 Interworking . 11
10 Additional services . 11
10.1 Emergency services . 11
10.2 Relay services . 12
11 Network implementation considerations . 12
Annex A (informative): Background . 13
A.1 Total Conversation . 13
A.2 Interworking . 13
A.3 Additional services . 14
Annex B (informative): Initial requirements . 15
B.1 Transmission Performance . 15
B.2 Man Machine Interface (MMI) . 15
B.3 Compatibility . 16
B.4 Complexity of Implementation and Roll Out . 17
B.5 Referenced consumer requirements. 18
Annex C (informative): Change history . 19
History . 20
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3GPP TS 22.226 version 15.0.0 Release 15 4 ETSI TS 122 226 V15.0.0 (2018-07)
Foreword
rd
This Technical Specification has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
Introduction
Real time, character by character text conversation is a component that increases usability in a conversational session.
Global Text Telephony is a feature that adds the capability to use a text conversation component in a session. It is called
Global Text or GTT here.
Interworking with corresponding features in other networks is an important part of Global Text. Specifically, the
different kinds of PSTN text telephone systems supported by the international text telephone modem standard ITU-T
V.18 are included in the modes for interworking.
One important reason to offer the Global Text feature is to enable emergency service access to people who are
depending on a written dialogue.
A more elaborated background is found in Annex A, and requirements in Annex B.
Figure 1 gives an overview of the user environment for Global Text.
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3GPP TS 22.226 version 15.0.0 Release 15 5 ETSI TS 122 226 V15.0.0 (2018-07)
Fixed multimedia user
Fixed textphone user
Fixed Network
IP textphone or multimedia user
Cellular Network
IP
Mobile,
network
text capable
terminals
GTTFE
Cellular Network
Figure 1. Global Text service environment
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3GPP TS 22.226 version 15.0.0 Release 15 6 ETSI TS 122 226 V15.0.0 (2018-07)
1 Scope
This Technical Specification defines the stage one description of the Global Text Telephone Feature, GTT. Stage one is
the set of requirements which shall be supported for the provision of the real-time text conversation feature, seen primarily
from the subscriber’s and service providers’ points of view.
This TS includes information applicable to network operators, service providers, terminal and network manufacturers.
This TS contains the core requirements for the Global Text Telephony feature, which are sufficient to provide a complete
feature to incorporate in conversational services.
This TS defines the requirements for GTT to be understood as a framework to enable real-time transmission of text, for
the purpose of a text based or text supported conversation between users. Text may be transported alone or in
combination with other media in the session, especially video and voice.
Thus the GTT enables text conversation to be included in any mobile conversational service.
Interworking with existing text telephony in PSTN as well as emerging forms of standardised text conversation in all
networks is within the scope of this document. Interoperation with Multimedia Messaging Services is also within scope
of this feature.
Note: The Global Text Telephony feature may be enhanced due to e.g. operator's or regulator's requirements,
however such additional functionality shall not compromise conformance to the core requirements
documented in this TS.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TS 22.101: "Service Principles".
[2] ETSI ETR 333; Text Telephony; User requirements and Recommendations
[3] ITU-T H.248 Annex F Facsimile, Text conversation and call discrimination packages (2000)
[4] ITU-T Recommendation T.140 (1998) – Text conversation protocol for multimedia application.
With amendment 1 (2000).
[5] ITU-T Recommendation F.700 (2000) – Framework recommendation for audiovisual/multimedia
services.
[6] ITU-T Recommendation V.18 (2000) – Operational and interworking requirements for DCE:s
operating in the text telephone mode.
[7] 3GPP TS 22.140: "Multimedia Messaging Service; Stage 1"
[8] 3GPP TS 23.140: "Multimedia Messaging Service; Functional description; Stage 2"
[9] IETF RFC 2793. (2000) RTP Payload for text conversation.
[10] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
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3 Definitions and abbreviations
3.1 Definitions
Total Conversation: A service offering standardised simultaneous text, video and voice conversation or a subset
thereof.
Host environment : The session environment where the text component is added. E.g. Circuit switched voice, IP
Multimedia etc.
Text Conversation: A real time conversation in text with transmission character by character as entered.
Further definitions are listed in 3GPP TR 21.905 [10].
3.2 Abbreviations
For the purposes of this document the following abbreviations apply:
EDT European Deaf Telephone
GTT Global Text Telephony; The feature that adds real time text conversation to any 3GPP
conversational environment
GTTFE Global Text Telephony Feature Environment – The network components and functions forming
GTT
TTY Here used as the term for the text telephone type dominating in USA.
DTMF Here used as a term for the text telephone type used in Holland, using DTMF tones.
VCO Voice Carry Over: Alternating (or parallel) sending of Speech and receiving Text
HCO Hear Carry Over: Alternating (or parallel) receiving Speech and transmission of Text
FCC Federal Communications Commission (of United States of America)
PER Printable character Error Rate
MMI Man Machine Interface
SIM Subscriber Identification Module
ITU International Telecom Standardisation Union
GSM Global System for Mobile communication
3GPP Third Generation Partnership Project
CS Circuit Switched
IP Internet Protocols
Further abbreviations are listed in TR 21.905 [10].
4 High level Requirements
The following list gives the high level requirements of the GTT. These are requirements which are independent of the
user’s perception of the feature:-
- Service definition
Global Text shall provide a real time conversational text feature. A general definition is found in
Recommendation ITU-T F.700[5].
- Global Text Telephony host environments
A standardised method for Global Text Telephony shall at least be specified for each host environment in the
mobile networks that can carry voice.
- Standards compliant and forward compatible text conversation
Global Text Telephone mechanisms shall provide the capability to support current and evolving text telephony
and text conversation features by re-using existing standards as far as possible and proposing extensions (as
necessary) to existing standards (i.e. the global text telephony feature shall support the evolution of Total
Conversation technologies in all networks).
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- Consistent text conversation
Regardless of the selected host environment, the far end terminal, the interworking facilities involved, GTT shall
be capable of providing a consistent way of handling the conversation.
- Global Text Telephone access
Within the capabilities of networks and terminals, the user shall be provided consistent access to the GTT
regardless of the access point.
For example: the user shall be capable of accessing the text conversation features through a number of different
access points, including networks based on 3GPP specifications, access through dedicated multimedia terminals,
and access through combinations of mobile phones combined with text user interface devices.
- Interoperability
Global Text Telephony shall support interoperability with existing and emerging text telephone systems and text
conversation features.
Global Text Telephony shall support a minimum set of environments where text conversation is supported to
ensure full interoperability between different terminals and networks.
- Emergency calls
The implementation of Global Text Telephony shall enable a user to make emergency calls to, and receive calls
from, an emergency call centre via a text telephony device used in conjunction with GTT enabled user
equipment.
5 General Requirements
Network operators have many differing requirements, and GTT shall be supported in the network in a manner which
allows network operators to consider different configurations depending on their network and commercial requirements.
Thus, an identified set of functionalities and protocols shall be standardised to ensure interoperability across networks
and terminals to support GTT.
The following general requirements shall be supported.
5.1 Text conversation host environments
The protocol environments for text conversation shall be the same as the ones used for other multimedia conversation
calls and voice calls. The selected environment for a session is called the host environment.
Supported host environments are:
- Packet switched multimedia
- Circuit switched multimedia.
- The text conversation carried by an data transmission procedure, possible to combine with a voice session.
- Circuit switched voice telephony, with the text conversation carried in-band in the voice channel.
5.2 Text conversation management
It shall be possible to allow GTT use without GTT specific subscription.
Note: There is no requirement for GTT feature specific subscription, but for "normal GTT calls" a subscription
for telephony is required. For "emergency GTT call" no subscription of any kind is required.
Session start up delay and loss of initial characters should be minimised as far as practicably possible.
The text transport method should remain transparent to the network, unless specific functionality is required to provide
a satisfactory quality of service.
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5.3 Registration of text conversation capabilities
The availability of text conversation capabilities in the user terminal may need to be communicated to the network at
call establishment in order to access the GTT service. However, a user is expected to be able to access the GTT service
without explicit GTT registration with the operator.
5.4 Session control
The session control (call control ) functions shall use the same procedures as the selected host environment.
Additional operations needed to invoke the text component may be automated by the text conversation user interface.
It shall be possible to establish text-only calls as well as calls with other media components.
5.5 Invoking text conversation
Calls with terminals where text conversation is used shall bemonitored for requests to start the text feature.
When either party in a call begins usage of the text feature, an effort shall be made to establish text conversation. It shall
be possible to start text conversation during a call already established in voice or video mode by adding the text
component.
The mode selected for text conversation ( IP Multimedia, CS Multimedia, Voice path etc. ) shall be determined
according to a prioritised procedure.
Modes allowing simultaneous voice and text shall by default have higher priority, while the user shall be given
opportunities to prioritise text-only modes. The default order shall be: IP Multimedia, CS Multimedia, data path text
plus voice, voice path text.
The user shall be given call progress information and text invocation progress information in text or other non-audible
media.
5.6 Text conversation handling during calls
Text transmission shall be done character by character as entered, or in small groups transmitted so, that no character is
delayed before transmission more than 0.5 seconds. (as stated in ITU-T T.140 [4])
The text transmission shall allow a rate of at least 10 characters per second so that human typing speed as well as
speech to text methods of generating conversation text can be supported.
The end-to-end delay of characters shall be less than two seconds, measured between two mobile users, or between one
mobile user and any interworking fixed network user, assuming that the fixed network does not contribute with more
than one second to this figure.
The character corruption rate should be less than 1% in conditions where users experience the voice transmission
quality to be low but useful.
The transmission of the text conversation shall be made according to the character set and operations defined in ITU-T
T.140. [4]. This requirement enables smooth interworking with minimal loss of functionality between different text
conversation environments. The allowed limitations in character set support specified in ITU-T T.140 shall be obeyed,
so that two terminals always have a minimum common character set available for conversation.
Figure 2 gives an example of a possible layout of a real time text conversation according to ITU-T T.140.
ANNE EVE
Hi, this is Anne. Oh, hello Anne, I am glad you are calling!
It was long since we met!
Yes, have you heard that I will come to
Paris in November? No, that was new to me. What brings you
here?
Figure 2: A possible way to display a conversation with one window each
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Display of the conversation shall be done according to the principles specified in T.140, unless the display is provided
through interworking with a legacy mode text telephone, when the limitations of that device may govern.
NOTE: It shall be noted that support for any written language is possible with T.140, and that many languages require
other writing directions than left-to-right.
5.7 Alerting
Since many GTT users are deaf or hard-of-hearing, the terminals used for GTT shall provide an interface that can be
used to activate alternative alerting modes e.g. flash or vibration.
5.8 Addressing
GTT shall support the addressing formats of the host environments. to identify the different kinds of endpoints of the call
used in the different host environments (see section 9, interworking.)
5.9 Roaming
Access to the GTT service while roaming is desirable.
Note: Operators may consider using a Virtual Home Environment toolkit to provide GTT services to roaming
subscribers. It can be expected that the subscriber will need to specifically subscribe to this service and no
access to the GTT service will be possible if the visited network does not support the appropriate VHE
toolkit. It should also be noted that emergency calls bypass most VHE toolkits, therefore emergency calls
will require GTT support in the local network.
6 Security and reliability
The user shall be able to use and access GTT in a secure manner. Within the limitations enforced by the host
environments, the following apply.
- It shall be possible for the contents of GTT sessions to be read only by the intended recipient(s).
- The “Security Threats and Requirements” specified in 22.133 [3] shall not be compromised.
7 Charging
It is foreseen that users will not be expected to pay a premium for access to the GTT service. Hence the requirement to
capture detailed information relating to the use of GTT is seen as optional.
Various charging mechanisms may be supported in addition to what is defined for the host environment, the following
charging characteristics may be considered:-- Text was used in the call.- The duration for which text was used in a call.
8 External Interfaces
8.1 External interfaces in the terminal
It shall be possible to control and operate GTT from external digital devices, e.g, portable computers. For this purpose
interfaces shall be standardised between the terminal and such external digital devices.
It shall be possible to control and operate GTT from external analogue text telephones. For this purpose, interfaces shall
be standardised between the mobile terminal and such external analogue text telephones.
External interfaces specified for controlling and operating GTT between the terminal and an external device should
make it possible to use the external device for both Multimedia Messaging and GTT.
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8.2 External interfaces to other networks
No new network interfaces shall be specified for GTT, only the necessary elements to accomplish text interworking.
These are specified in ITU-T H.248 Annex F, in the Text Conversation and Text Telephone packages [3].
The networks for specified interworking include:
- PSTN for interworking with PSTN text telephones.
- IP networks for interworking with IP conversational multimedia terminals
...