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Home : ITU-T Home : Study Groups : Study Group 15
Question 11/15 – Signal structures, interfaces and interworking for transport networks
(Continuation of Part of Question 11/15 studied in 2005-2008)


During the previous Study Period, a great part of the activity of the Question was dedicated to the definition of the Network Node Interface (NNI) for the Optical Transport Network (OTN). This work focused on the best means of transporting packet technology based client signals in an OTN hierarchy. The work required close interaction with the IETF and the IEEE. Developing new high speed packet interfaces requires continuing work in this area.

Specifications on new functionalities (LCAS, Virtual concatenation, GFP), that allow for an optimization of the transport of packet data (ATM, IP, Ethernet, T-MPLS) over constant bit-rate technologies (SDH, OTN), were enhanced and revised as implementations matured. Recommendations addressing packet based services and interfaces continued to be developed. Further work is expected on the transport of high speed Ethernet and Storage Area Networks (SAN), including Fibre Channel and Enterprise Systems CONnection (ESCON) flows.

Existing Recommendations may need to be enhanced to take into account new network features of Automatically Switched Optical Network (ASON).

The area of responsibility under this Question includes the specification of:

  • Transport signal structure
  • Adaptations of client signals into server transport layers
  • Interface characteristics for the transport and supervision of client signals

The following major Recommendations, in force at the time of approval of this Question, fall under its responsibility: G.703, G.704, G.707/Y.1322, G.709/Y.1331, G.7041/Y.1303, G.7042/Y.1305, G.7043/Y.1343, G.8040/Y.1340, X.85/Y.1321, X.86/Y.1323.


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

  • What enhancements should be made to the existing Recommendations or what new Recommendations should be developed
    • what enhancements should be made to the Optical Transport Network (OTN) hierarchy to accommodate higher speed Ethernet clients?
    • to reflect additional transport network applications (e.g. ASON) and interworking scenarios?
    • for networks optimized for transport of packet data, including packet over packet and circuit over packet adaptations and aspects related to connectionless layer networks?
  • What should be specified for the definition of new transport networks (including NGN), while insuring transverse compatibility and interworking with previously specified technologies?
  • What enhancements to existing Recommendations are required to provide energy savings directly or indirectly in Information and Communication Technologies (ICTs) or in other industries? What enhancements to developing or new Recommendations are required to provide such energy savings?


Tasks include, but are not limited to:

  • Maintenance of PDH, SDH, OTN and LAPS Recommendations
  • Evolution of GFP and LCAS related Recommendations
  • Further development of the OTN Interface Recommendation

NOTE: An up-to-date status of work under this Question is contained in the SG15 Work Programme at




  • G.783, G.798, G.806, G.872, G.957, G.959.1, G.8010, G.8021, G.8110.1, G.8121.


  • Q3/15, Q6/15, Q9/15, Q10/15, Q12/15, Q13/15, Q14/15, and Q15/15.

Study Groups:

  • ITU-T SG2 on network maintenance
  • ITU-T SG12 on network performance

Standardization bodies, forums and consortia:

  • MEF on Ethernet services Issues
  • IEEE 802.1 on Ethernet bridges
  • IEEE 802.3 on Ethernet transport and high speed Ethernet
  • IEEE 802.17 on Resilient Packet Rings
  • T11.3 on SAN flows transport
  • IETF ccamp on MPLS extensions
  • IETF pppext on IP transport
  • IETF mpls on MPLS transport
  • IETF PWE3 on packet/circuit over packet


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Updated : 2008-12-23