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Question 14/16 – Voiceband modems and facsimile terminals and protocols: specification, performance evaluation and interworking with NGN
(Continuation of Questions 11/16 and 14/16)


This Question brings together all the aspects of voice band dial up access and facsimile transmission.

Dial up access over the GSTN is a ubiquitous method of providing connectivity for many applications including Internet access, facsimile transmission, point-of-sale terminals, text telephony, security systems, etc. With the changing paradigm in network access voice band access has evolved to be included in IP and next generation networks.

With the emergence of packet based networks and specifically voice over packet, the GSTN has expanded to include the advantages of these network types. The need to ensure the best performance transmission of voiceband modems and facsimile over both circuit and packet switched networks is a necessary requirement. Packet based networks that are designed for voice require methods and procedures to allow end-point modems to interoperate with the same performance as expected from circuit switched networks. In this spirit, the Question has developed Recommendations V.150.1, V.151, V.152, T.37 and T.38, all of which support different aspects of the transport of either voiceband modem signals or facsimile over IP networks.

Although digital networks are rapidly being deployed around the world, analogue access will remain the only choice in many locations. Users in these locations will continue to have the need to access and exchange electronic information. Therefore, the continued study of modem technology is required to supply these users with the best standardized tools to meet their needs.

In summary this Question is responsible for all aspects of voice band modem and facsimile terminal standardization. This includes the functionality and performance of the terminals and the transport of the signals they generate across different network types.

The Question will attempt to work electronically where possible and to make full use of e-mail and conferencing facilities in an attempt to reduce its carbon footprint.

Study items

Study items to be considered include, but are not limited to:

  • Optimised techniques to support the transmission of voice band modem and facsimile signals over packet switched networks (IP ones in particular), using media gateways
  • Modulation techniques for high-speed voiceband modems and facsimile connected to either an analogue local loop or directly to a circuit-switched digital network. Also to be considered are methods and procedures for initial training, retraining, rate re-negotiation, optimised modulation and data transmission performance, fallback to other modulation modes, etc
  • Compatibility and interaction with network equipment, such as CME, VED and echo control devices
  • Interworking issues arising from the use of modems on various multimedia platforms
  • Means for evaluating voiceband modem and facsimile terminal performance, including the specification of network models and test procedures
  • DTE-DCE interchange circuits including functional and electrical characteristics
  • Protocols to be used by the DTE to transfer information over the DTE-DCE interface for the purposes of configuration and control of the local DCE by the DTE and reliable interworking between DTEs on the GSTN
  • DCE to DCE protocols for half-duplex operation, statistical multiplexing, secure access and privacy of data, compression of synchronous data, improved data compression algorithms and management of remote DCEs
  • Terminal adapters (TAs) for devices having V-series interfaces for use on ISDN bearer services. This includes their use on multi-use bearer and other bearer services
  • Definition of new or amended capabilities and their implementation for Group 3 and/or Group 4 terminals:
    • Definition of service and new usage of facsimile
    • Support for new image compression and colour schemes for facsimile
  • Develop new and updated test images and documents
  • Inter-working between facsimile terminals connected to different networks types
  • The study of methods and procedures for the enhancement of real-time facsimile transmission over NGN including:
    • Revisions to transport layer and call control protocols, operation over mobile packet networks, Gateway and IAF functionality and secure transmission
    • Study of hybrid GSTN/IP tandem networks upon facsimile transmission
  • The study of methods and procedures for the enhancement of store and forward facsimile transmission using Internet mail capabilities
  • Consideration of the effect on the facsimile quality of service of the changes being made to those networks that support facsimile communication. Examples include the following list of items:
    • Terminal-network interaction
    • Improvement of performance on networks with different quality of service
    • Maintenance of related Recommendations: F.162, F.163, F.170, F.171, F.182bis, F.185, F.190, T.4, T.5, T.6, T.22, T.23, T.24, T.30, T.31, T.32, T.33, T.35, T.36, T.37, T.38, T.39, T.42, T.43, T.44, T.45, T.503, T.563,V.8, V.8bis, V.17, V.21, V.22, V.22 bis, V.24, V.27, V.27 bis, V.27 ter, V.29, V.32, V.32 bis, V.34, V.42, V.42 bis, V.43, V.44, V.56 bis, V.56 ter, V.59, V.61, V.70, V.75, V.76, V.80, V.90, V.91, V.92, V.110, V.120, V.130, V.150.0, V.150.1, V.250, V.251, V.252, and V.253
  • Consider any additions to Recommendations that may help to measure and reduce the impact of climate change. Examples include reduced power consumption of hardware and hardware tools, and reduced complexity of algorithms


Tasks include, but are not limited to:

  • Development of enhancements to Recommendation V.150.x (2005) series
  • Develop new Recommendation for the transport of facsimile and modem signals between two IP networks that use different transport methods
  • Coordinate the application and integration of V.150.1, V.151 and V.152 with other relevant Recommendations
  • Development of new DTE-DCE interface-related Recommendations as well as the revision of existing ones, new control Recommendations as well as the update of Recommendations V.25X-series and V.80
  • Development of new and improved data compression techniques
  • Extension of Group 3 and Group 4 facsimile capabilities
  • Revision of T.44, T.43, T.4 and T.30 on display oriented colour space
  • Enhancement of T.38 on gateway functionality and security aspects

An up-to-date status of work under this Question is found in the SG 16 work programme (




  • E.451 through E.459, E.460, F.162, F.163, F.170, F.182 bis, F.185, G.711, G.799.1, G.769, H.225, H.323, H.245, H.248, I.366.2, I.741, T.6, T.22, T.23, T.24, T.31, T.32, T.33, T.35, T.36, T.39, T.66, T.400 series,T.8x series, T.800 series, X.3, X.38 and X.39


  • 1, 2 and 3/16 on gateway access to IP networks
  • 15, 16 and 18/16 on network signal processing

Study Groups:

  • ITU-T SG 2 on services
  • ITU-T SG 11 on network signalling systems
  • ITU-T SG 12 on speech performance, QoS and QoE
  • ITU-T SG 13 on ISDN, voiceband and text telephone modems over AAL2
  • ITU-T SG 15 on access network issues
  • ITU-T SG 17 on DTE-DCE interface issues

Other Bodies:

  • ISO/IEC JTC 1/SC 6 on DTE-DCE interface issues HDLC and data compression
  • Other organizations using "AT" commands, e.g. ETSI, 3GPP, 3GPP2, TIA
  • ISO/IEC, IETF, ETSI, TIA, CIE, ICC for facsimile and audio conferencing


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Updated : 2008-12-05