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Question 11/15 - Signal structures, interfaces and interworking for transport networks

(Continuation of Question 11/15)

Background and justification

During the previous Study Period, a great part of the activity of the Question has been dedicated to the definition of the Network Node Interface (NNI) for the Optical Transport Network (OTN). This work led to the development of the first version of Recommendation G.709.

Moreover, new functionalities necessary to allow for the transport of data (ATM, IP) over previously defined technologies (such as SDH) have also been specified.

In view of the importance of IP-type traffic in the transport network, there is no doubt that work will have to be further progressed in these two areas.

The area of responsibility under this Question includes:

  • Transport signal structure
  • Client signals adaptation into transport signal
  • Interfaces characteristics for the transport and supervision of client signals

Responsibilities under this Question include the following draft or published Recommendations:

  • G.702 (11/88)

- Digital hierarchy bit rates

  • G.703 (10/98)

- Physical/electrical characteristics of hierarchical digital interfaces

  • G.704 (10/98)

- Synchronous frame structures used at 1544, 6312, 2048, 8488 and 44 736 kbit/s hierarchical levels

  • G.706 (04/91)

- Frame alignment and Cyclic Redundancy Check (CRC) procedures relating to basic frame structures defined in Recommendation G.704

  • G.707 (03/96)

- Network Node Interface for the Synchronous Digital Hierarchy (SDH)

  • G.708 (06/99)

- Sub STM-0 Network Node Interface for the Synchronous Digital Hierarchy (SDH)

  • Draft G.709

- Network Node Interface for the Optical Transport Network (OTN)

  • G.712 (11/96)

- Transmission performance characteristics of Pulse Code Modulation channels

  • G.775 (10/98)

- Loss of Signal (LOS), Alarm Indication Signal (AIS) and Remote Defect Indication (RDI) detection and clearance criteria for PDH signals

  • G.780 (06/99)

- Vocabulary of terms for Synchronous Digital Hierarchy (SDH) networks and equipment

  • G.796 (09/92)

- Characteristics of a 64 kbit/s cross-connect equipment with 2048 kbit/s access ports

  • G.797 (03/96)

- Characteristics of a flexible multiplexer in a Plesiochronous Digital Hierarchy environment

  • G.804 (02/98)

- ATM cell mapping into plesiochronous digital hierarchy (PDH)

  • G.832 (10/98)

- Transport of SDH elements on PDH networks: Frame and multiplexing structures

  • G.861 (08/96)

- Principles and guidelines for the integration of satellite and radio systems in Synchronous Digital Hierarchy (SDH) transport networks

  • Q.55x

- Hardware aspects of digital exchanges


  • What enhancements should be made to the existing Recommendations or what new Recommendations should be developed, to reflect additional transport network applications and interworking scenarios?
  • What should be specified for the definition of new transport network, while insuring transverse compatibility and interworking with previously defined ones?
  • What enhancements should be made to existing Recommendations or what new Recommendations should be developed for networks optimized for transport of packet data?

Study items

  • Complete/enhance the definition of the OTN Network Node Interface as regards its structure, the various embedded overhead functionalities and the client signals (SDH, ATM, IP, Ethernet …) mappings
  • Specifications of the features necessary to implement an Automatically Switched Optical Network (ASON)
  • In the context of the evolution of the OTN, take into account a more extensive use of (all) optical technology
  • Outstanding study items identified in previously developed Recommendations
  • Specify additional Section Overhead (SOH) and Path Overhead (POH) capabilities of the SDH for new network applications or maintenance related aspects
  • If appropriate, modify existing PDH related Recommendations
  • Transverse compatibility of transport equipment in a multi-vendor, multi-operator environment
  • When applicable, backwards compatibility between new and previously specified functionalities

Specific tasks

  • Revisions to Recommendation G.703 by 2002
  • Revisions to Recommendation G.707 by 2003
  • Approval of G.709 by 02/01 and further revisions during the Study Period
  • Revisions to other Recommendations as required.
  • Development of other relevant new Recommendations


  • Other Questions of SG 15 addressing transport equipment and optical networks aspects
  • ITU-T SG 4 on TMN and network maintenance.
  • ITU-T SG 5 on overvoltage protection and EMC
  • ITU-T SG 7 on IP related aspects
  • ITU-T SG 13 on transport network architectures and network performance objectives
  • ITU-R SG 4 on satellite systems
  • ITU-R SG 9 on radio-relay systems
  • IETF - pppext Working Group on IP transport
  • IEEE on Ethernet transport
  • ATM Forum on ATM transport
  • ATIS Sub-Committee T1X1.5
  • ETSI
  • Other fora and standardization bodies, as appropriate


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