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Question 15/16 – Voice gateway signal processing functions and circuit multiplication equipment / systems
(Continuation of Questions 15/16 and 17/16)


This Question deals with the specification of voice gateway equipment. Circuit switched systems and equipment have traditionally transported voice and voiceband traffic in international networks.

Digital Circuit Multiplication Equipment (DCME), a type of voice gateway interconnecting different general switched telephone networks (GSTN) with circuit multiplication capabilities has been utilized worldwide to optimize transmission bandwidth capacity. ITU has developed the G.76x series of Recommendations for DCME and systems.

With the increased popularity of packet-based networks using Internet Protocol (IP) and ATM, more and more speech traffic is expected to be carried over these transport networks. Therefore, it will also be observed a significant amount of voice and voiceband data traffic going through equipment interconnecting the GSTN and packet networks and equipment interconnecting different packet networks. For this reason, there is a need to ensure a high quality of service for voice and voiceband data carried in part or wholly via IP or ATM networks, and Recommendation G.799.1 was developed. Recommendation G.769 was developed and Recommendation I.733 is currently being developed for Voice Gateways interconnecting GSTN and packet-based networks with channel multiplexed capabilities.

One of the purposes of this Question is to apply the following aspects in a new generation of compression equipment reflecting the experiences gained from previous generations of equipment:

  • Enhancement of signal compression and channel multiplexing techniques to accommodate new types of signals and services
  • Enhancement of system controls to maintain end-to-end signal qualities as high as possible

Recommendations for protocols exist or are being developed for converting and transporting GSTN originated voice and voiceband data over packet and cell-based networks. The interworking of these is covered by other Recommendations. It is another purpose of this Question to encompass these Recommendations under various equipment specifications and to include performance requirements and tests that will help ensure that the correct and appropriate functionality is present in this equipment. It is not intended to define new protocols, but eventually new requirements for these protocols.

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:

  • Improvement of Voice Gateway speech performance with improved compression algorithms (e.g. support for wideband speech)
  • Extension of the capabilities of voiceband signal compression to account for new network services
  • Ensuring proper end-to-end operation of speech and voiceband signals through compression equipment
  • Accommodation of CME to new network transport technologies (e.g. multi-protocol label switching, MPLS)
  • Impact of speech processing issues related to voice gateway equipment on overall network performance
  • Specification and recommendation of functionality, interfaces, performance requirements and functional tests to provide good network performance for transport network equipment for interconnecting various type of networks
  • Identify protocols and Internet interworking functions needed to be supported
  • Support of functionality needed to ensure minimal end-to-end delay
  • Effects of placing voice gateway equipment in tandem and methods of minimizing the impact of these effects
  • Impact of evolving terminal equipment (such as text telephones, modems, facsimile, wireless and multimedia terminals) and optimization of voice gateway functionality for ATM and IP networks transport voice and voiceband data traffic
  • To 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:

  • Revision of existing DCME Recommendations G.763, G.767, G.768 to implement tandem avoidance mechanisms
  • Development and enhancement of new Recommendation I.733
  • Enhancement of Recommendation G.769/Y.1242 to support IP trunk interfaces, transport of different kind of signals including text telephony signals, signalling transport and larger number of channels in a single IP connection
  • Enhancement of G.799.1/Y.1451.1 to include support of ATM networks for GSTN interface
  • Develop new Recommendation on IP-to-IP Gateway that may be used for the bulk interconnection of voice and voiceband data traffic of two network operators
  • Maintain ITU-T Recommendations G.763, G.764, G.765, G.766, G.767, G.768, G.769/Y.1242, and G.799.1/Y.1451.1

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




  • G.72x series speech coding Recommendations, P.840, P.862 sub-series, Q.50, Q.50.1, Q.50.2, Q.55, Q.56, Q.115 sub-series
  • G.161, G.168, H.248 sub-series, T.30, T.38, V.150 sub-series


  • 14, 16, 18/16 on voiceband signal compression protocols and network signal processing
  • 1, 22/16, on multimedia systems, terminals, gateway control, protocols and architectures
  • 7, 8, 9, 10/16 on speech processing
  • 26/16 on Accessibility

Study Groups:

  • ITU-T SG 2 for guidance on Telecommunications Management Network (TMN)
  • ITU-T SG 11 on signalling interfaces and protocols
  • ITU-T SG 12 on speech performance, QoS and QoE
  • ITU-T SG 13 on network implications
  • ITU-T SG 15 on synchronization and management of transport systems and equipment
  • ITU-R SGs 4 and 5 on IMT and on voice on mixed terrestrial/satellite networks

Other Bodies:

  • IP/MPLS Forum on ATM, MPLS and frame relay transport
  • IETF working groups AVT, IPPM, IPTEL, MMUSIC, ROHC, SIGTRAN, SIP, SIPPING and SPIRITS on IP transport, MPLS on routing, FAX on internet fax application, RMONMIB and SNMPCONF on operation and management, MSEC and IPSEC on security and IPPM on IP performance metrics
  • ETSI TISPAN, 3GPP, 3GPP2 on mobile network architectures


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Updated : 2008-12-05