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Question 3/15 – General characteristics of transport networks
(Continuation of Question 3/15)


Due to the widespread introduction of high bit-rate, Internet, and Ethernet services, the transport network is continuing to evolve worldwide based on optical and packet-based networking technologies. The transport network able to dynamically provide multiplexing, routing and transporting of optical channels carrying a variety of client signals is becoming reality. These new networking characteristics are being developed to improve management capabilities, expand service opportunities, and optimize transport of IP and other data traffic.

Recognizing that without a strong coordination effort there is the danger of duplication of work as well as the development of incompatible and non-interoperable standards, the WTSA-2000 designated Study Group 15 as Lead Study Group on Optical Technologies within ITU-T.

SG15 is continuing studies under various Questions on the following aspects of optical transport networks, leading to several series of published and planned Recommendations. These Recommendations include aspects such as:

  1. architecture;
  2. functional characteristics;
  3. structure and mapping aspects;
  4. management aspects; and
  5. physical layer characteristics.

Standardization topics to be coordinated include:

  • SDH networks
  • OTN networks
  • Packet-based transport networks, including Ethernet and MPLS-TP
  • Network management and control, including ASON (Automatically Switched Optical Network)

ASON, based on requirements in Recommendation G.8080, includes: (a) distributed connection management; (b) automatic discovery; (c) optical route selection; and (d) connection access control.

A coordination and communication activity among the involved Questions is fundamental in order to facilitate the most efficient completion of the work. This activity includes the identification of missing work areas and those that are overlapping, or potentially so, between multiple Questions or other standards groups. In case of a new work area, clarification of general requirements and framework by this Question would facilitate the work on specific aspects by relevant Questions. It includes encouraging the relevant work items in the most appropriate Questions, helping to define a suitable time schedule, and monitoring its development in a consistent way. For example, a new packet-based transport technology may be needed to support the Future Packet Based Network (FPBN) which is studied by Q.J/13.

In addition, some general aspects such as terminology or reliability/availability, need to be captured.

A communications, publicity, and promotion activity is also important to support the adoption of ITU-T Recommendations throughout the industry. External communications activities should aid in the consistency of Recommendations and other standards related to optical and packet-based transport technologies across the industry.

The following major Recommendations, in force at the time of approval of this Question, fall under its responsibility: G.871, G.780/Y.1351, G.870/Y.1352, G.8081/Y.1353, G.8001/Y.1354, G.8101/Y.1355.


What characteristics of optical and packet-based transport networks still need to be fully developed in the various network environments (e.g. metropolitan, backbone, etc.), in what Study Question and within what time schedule?

What aspects of optical and packet-based transport networks, related to optical transport of IP, Ethernet, or Storage Area Network traffic, need to be assigned to what Study Question for timely development?

What enhancements to OTNT SWP or what new Recommendation(s) or mechanisms are necessary to capture, within this framework, new or evolving aspects of optical transport networks, their general terminology, and reliability/availability characteristics?

What form of communication or publicity is prudent to enhance the use of and alignment with ITU-T standards in the area of optical and packet-based transport networks and technologies?

What are the general requirements for future packet-based transport technologies and with what framework should each aspect of these technologies be developed?

What coordination is needed to provide energy savings directly or indirectly in Information and Communication Technology (ICTs) or in other industries?

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

  • Coordination of work in the following areas:
    • Automatically Switched Transport Network requirements aspects (Q12/15)
    • Optical access networks (Q2/15)
    • OTN & ASON functional characteristics (Q9/15)
    • OTN & ASON structures and mapping (Q11/15)
    • OTN & ASON architectural aspects (Q12/15)
    • OTN synchronization characteristics (Q13/15)
    • OTN & ASON management aspects (Q14/15; SG4)
    • OTN physical layer characteristics (Q5, Q6, & Q7/15)
    • IP and NGN aspects (QE/13 (ex Q5/13), Q16/12, and Q17/12)
    • Packet Transport Networking (e.g., Ethernet and MPLS-TP) aspects (QE/13 (ex Q5/13), Q9/15, Q11/15, Q12/15, Q14/15)
    • OTN OAM for packet transport (Q10/15)


Tasks include, but are not limited to:

  • Develop, maintain, and regularly distribute a baseline overview/work plan that documents the work and time schedules of all major new optical transport network activities
  • Prepare possible new Recommendation(s) to address the tasks above, and other items that may be identified (e.g. a terminology Recommendation), as required
  • Harmonize and align related terminology definitions across Recommendations, striving for a single normative definition for each term
  • Maintain terminology Recommendations G.780/Y.1351, G.870/Y.1352, G.8081/Y.1353, & G.8001/Y.1354, creating amendments and corrigenda to correct and add new terms as necessary
  • Develop a revised version of Recommendation G.8101/Y.1355 “Terms and definition for MPLS-TP” to align with the MPLS-TP architecture and include the appropriate normative references to the MPLS-TP RFCs that are being developed to address the requirements of the transport network.
  • Develop Recommendations on general requirements and framework for packet-based and optical transport technologies.
  • Revise Recommendation G.871; as appropriate
  • Publicize results of ITU-T related to optical and packet-based transport networks and technologies in the form of press releases, brochures, etc. when appropriate.

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




  • All SDH, OTN, ASON, and packet-based transport related Recommendations.


  • Q2/15, Q6/15, Q7/15, Q9/15, Q10/15, Q11/15, Q12/15, Q13/15, Q14/15, Q15/15, Q12/13, Q20/13, Q11/12 and Q17/12.

Study Groups:

  • ITU-T SG13 on IP and NGN requirements
  • ITU-T SG12 on performance aspects
  • ITU-T SG2 on management aspects

Standardization bodies, forums and consortia:

  • IETF on IP-related networks and protocols
  • IEEE on Ethernet
  • MEF on Ethernet
  • OIF on optical networking


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Updated : 2008-12-23