IP videotelephony service
TAGS: F.724ip videotelephony service

IP videotelephony service

The IP videotelephony service provides real-time end-to-end bidirectional communications between two subscribers in different locations on the IP network by means of voice, video, real-time text and other forms of multimedia data and/or control facility.

The way to place a call on IP videotelephony services is the same as that for conventional telephony services in the sense that the subscriber dials a number, or enters another type of identifier, to initiate a call. In addition to videotelephony calls, the subscriber can also use the videotelephony services in other applications.

A subscriber of IP videotelephony services can be located in any place covered by IP networks, e.g., office buildings, meeting rooms, hotels, residences, telephone booths on the street or even on board a transport vehicle.

There are two types of IP videotelephony calls:

  • Point-to-point calls;
  • Multiparty calls (utilizing devices for audio, video and text mixing, e.g., the Multipoint Control Unit (MCU)).

There are two major types of IP videotelephony terminals:

  • Videotelephony sets;
  • Softphones running on computers.

Other types of videotelephony terminals, such as PSTN videophones, ISDN videophones or even conventional phones and mobile phones, can communicate with the IP videophones. These terminals may have limited capabilities regarding sending or receiving various types of information in videotelephony calls, but they can at least intercommunicate with IP videophones in a voice-only mode.

Functional model and service profile

Functional model

Functional model of IP videotelephony services

The functional model of IP videotelephony services is shown in Figure 1. IP videotelephony terminals exchange voice, video, real-time text and multimedia data in a point-to-point or multipoint way over IP networks. They can also intercommunicate with other videotelephony or conventional telephony terminals via interworking units. The call control unit processes call signalling and controls sessions, and the Authentication, Authorization and Accounting (AAA) unit performs the function of the user, authentication, authorization and accounting.

Service model

Service model: the functional view

There are two models for IP videotelephony services from the functional view. Other models may exist or can be developed. However, they are a subject beyond the scope of this Recommendation and are thus for further study.

Basic videotelephony services

They refer to those IP videotelephony services that support the mandatory basic features. Only the voice, video and real-time text of conversational parties are transmitted between them.

Enhanced videotelephony services

They refer to those IP videotelephony services that support the enhanced optional features (i.e., other forms of multimedia data and/or remote control function). In addition to voice, video and real-time text, multimedia data like still pictures, pre-recorded audio/video clips, text messages, and collaboration-related data such as white-boarding information can be transmitted between videophones. Other optional features should include the convening of a conference and control of a conference, support for far-end camera control and other remote control.

Service model: the usage view

From the view of use environment, there are two types of IP videotelephony services.

Residential videotelephony services

For residential videotelephony service users, the following applications should be supported:

  • Face-to-face conversation with audio, video, and real-time text;
  • Face-to-face conversation with simultaneous transfer of pictographic data such as picture, pre-recorded video clips and files of other kinds;
  • Remote video surveillance for home security inspection and unmanned babysitting for kids, etc;
  • Emergency calls in audio, video and text.
Business videotelephony services

For business service users, the following applications should be supported:

  • Face-to-face conversation with audio, video, and real-time text;
  • Face-to-face conversation with simultaneous transfer of pictographical data such as images, documents and files of other kinds;
  • Remote video surveillance;
  • Remote consultation;
  • Remote diagnosis in telemedicine;
  • Participation in videoconferencing;
  • Emergency calls in audio, video and text.

 Service profiles

While all videotelephony services have the common capability for transmission of audio, video and real-time text, they can be divided into different types of profiles according to the quality level of audio and video, and other multimedia data exchanged.

An IP videotelephony service may be offered with two levels of audio quality, three levels of video quality, one level of real-time text, five types of exchanged data and two types of control facility. The basic audio quality is level A0, equivalent to 3.4 kHz PCM telephony; the enhanced audio quality is level A1, equivalent to 7 kHz or 14 kHz wideband audio. The three levels of video are level V1 for QCIF video, level V2 for CIF video and level V3 for SDTV video. The level of real-time text is T2, good conversational text. The five types of exchanged multimedia data are still pictures, video clips, text messages, file transfer and joint editing. The two types of control facility are remote control and conference conductor.

Taking into account the factors mentioned above, the following profiles of videotelephony service are defined. The service profile descriptions are not intended to impose a particular and detailed way of offering the services, but to illustrate the approach to the profile definition.

  • Profile a: Basic videotelephony service: basic audio, QCIF or CIF video, real-time text, optional multimedia data or control facility;
  • Profile b: Enhanced Basic videotelephony service: wideband audio, CIF video, real-time text, optional multimedia data or control facility;
  • Profile c: Enhanced videotelephony service: wideband audio, CIF or SDTV video, real-time text, multimedia data and/or control facility.

These profiles ensure at least a minimum level of communication. Conformance to a profile ensures intercommunication with other terminals of the same profile. A terminal or a service function unit may conform to one or several profile(s), and may have capabilities beyond those embodied in the profile(s).

Service scenarios

This clause describes typical service scenarios to illustrate the videotelephony service and to derive its technical requirements.

  1. Business videotelephony service scenarios

    1. Business call
    2. Business trip
    3. Customer service
    4. Call between a deaf and blind person and a service centre
  2. Residential videotelephony service scenarios

    1. Family call
    2. Monitoring

IP videotelephony service requirements

User requirements

Basic requirements:

  • Ability to exchange real-time video, audio and real-time text;
  • Ability to select audiovisual mode or voice-only mode;
  • Ability to make videotelephony calls at any place covered by IP networks;
  • Ability to make videotelephony calls in handset mode and handsfree mode;
  • Ability to make videotelephony calls by people with hearing or speech disabilities.

Enhanced requirements:

  • Ability to exchange multimedia data including still images, live and pre-recorded video clips, and collaboration data such as whiteboard;
  • Ability to implement remote control;
  • Ability to join and conduct a videoconference.
 Application requirements

Basic requirements:

  • Voice and video switching processing;
  • Allow for various access means, such as xDSL, Ethernet, WLAN, GSM and 3G etc., and videotelephony service provider should support at least one of them;
  • Support for interworking between different videotelephony systems or networks through gateways;
  • Support for subscriber management and numbering. Use of E.164 numbering plan is mandatory;
  • Support for PSTN-like dialling modes. A keypad should be implemented on the videophone;
  • Support for audio arrangement of handset function and handsfree function;
  • Support for entry and display of real-time text. The specific method for text entry (e.g., keypad, integral or detachable keyboard, touch screen, verbal recognition) is beyond the scope of this Recommendation. The specific method for text display (e.g., video screen, Braille, verbal) is beyond the scope of this Recommendation.

Enhanced requirements:

  • Support for dynamic creation and termination of video streams;
  • Support for fallback from audiovisual mode to voice-only mode;
  • Support for upgrading from voice-only mode to audiovisual mode;
  • Support for real-time multimedia data exchanging, such as still pictures, live and prerecorded video clips, text messages, and collaboration data;
  • Support for other types of dialling modes, such as use of aliases.
 Security requirements

The security of IP videotelephony calls should be guaranteed. There are three levels of security:

  • Subscriber authentication and authorization;
  • Call security;
  • Security of media streams.
 Authentication and accounting requirements

The subscriber authentication of IP videotelephony services is used to ensure that only legal subscribers can have access to IP videotelephony services and accurate accounting should be implemented for the IP videotelephony calls made by subscribers.

Interworking and intercommunication requirements

Three types of interworking or intercommunication are related to IP videotelephony service:

  • Interworking and intercommunication between terminals with different capability sets;
  • Interworking and intercommunication between terminals in different networks (PSTN, ISDN, 3G etc.);
  • Interworking and intercommunication between different IP videotelephony systems. Transcoding or bit-rate conversion in the interworking unit may be needed so that each terminal receives and transmits the signals it is able to handle.
Terminals with different capabilities

Terminals may have different characteristics and capabilities, thus conforming to different profiles that the videotelephony service provider may offer. When they intercommunicate with each other, a common mode of the profiles will be used. This will adapt the service quality and functionalities to those of the terminal with the lowest quality level for each media component; however, communication is always possible because all terminals conform to the common basic profile.

 Terminals in different networks

IP videotelephony service needs to intercommunicate and interwork with the videotelephony service in other (non-IP) networks. In addition, the interworking between IP videotelephony calls and conventional telephony calls should be guaranteed.

  • Intercommunication and interworking between IP videotelephony terminal and PSTN/ISDN/3G, etc. videotelephony terminal;
  • Intercommunication and interworking between IP videotelephony terminal and PSTN/ISDN/mobile phone.

The requirements of this type of intercommunication include:

  • Audio transcoding or bit-rate conversion;
  • Video transcoding or bit-rate conversion;
  • Real-time text transcoding;
  • Data transcoding or bit-rate conversion;
  • Call control signalling conversion.

 Different IP videotelephony systems

There may be many IP videotelephony systems, such as H.323-based and SIP-based videotelephony systems. Intercommunication is needed if the terminals are located in different service systems. The requirements of this type of intercommunication include:

  • Audio/video/text/data transcoding or bit-rate conversion;
  • Authentication between different systems;
  • Accounting between different systems;
  • Call control signalling conversion;
  • Subscriber resource sharing and security.
 QoS requirements

The QoS of IP videotelephony calls should be guaranteed. Since the major media elements of videotelephony calls are voice, video and text, it is necessary to guarantee clear voice, clear headand-shoulder image, continuous and smooth video of certain motion levels and text with good performance. In enhanced videotelephony services, the quality of multimedia data should also be guaranteed.

To guarantee the QoS of IP videotelephony services, IP networks should provide QoS guarantee to support the bidirectional real-time service.

 Audio quality

IP videotelephony should support basic audio (3.4 kHz) and wideband audio (7 kHz or 14 kHz).

IP videotelephony should be capable of performing acoustic echo-cancellation.

IP videotelephony should have error resilience mechanisms to recover from packet loss.

For a videotelephone with the audio arrangement of handset or handsfree function, the sensitivity and loudness rating should be guaranteed.

 Video quality

IP videotelephony should be able to provide a smooth video depending on the application.

IP videotelephony should be able to provide reliable video colours.

IP videotelephony should have error resilience mechanisms to recover from packet loss.

Text quality

IP videotelephony should support good text quality for real-time conversation. The presentation should be smooth, covering any jerkiness caused by transmission in blocks. The delay between each character entry and its display should be low so that the experience of a direct conversation is maintained. The reliability should be good, so that transmission errors are much rarer than typing errors, and indicated to the users.

 Lip synchronization

IP videotelephony should be capable of performing lip-synchronization so that there is no humanly perceptible asynchronism between audio and video.

 Overall delay

The overall delay comprises two parts: network transmission delay and delay due to processing on IP videophone terminals. The latter is caused by the codec on terminals to perform encoding and decoding.

The overall delay for IP videotelephony should be within specified limits since any delay greater than this threshold will cause an unacceptable degradation in QoS.

 Network transmission quality

In order to provide videotelephony services over an IP network, the IP network should be able to provide end-to-end QoS guarantee. The required QoS has different aspects such as low delays, low jitters, and low packet loss. The required network transmission quality for the IP videotelephony service should be defined according to ITU-T Rec. Y.1541.

 

Sanmati
Author

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