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Question 19/15 - General characteristics of optical transport networks

(Continuation of Question 20/15, Study period 2000-2003)

Background and justification

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

SG 15 is continuing studies in the various Study Questions on the following aspects of optical transport networks, leading to a several series of published and planned Recommendations. These recommendations include aspects such as

(a) architecture;

(b) functional characteristics;

(c) structure and mapping aspects;

(d) management aspects; and

(e) physical layer characteristics.

The most established series of recommendations describes SDH networks. Another series of recommendations describes the OTN1. A third series of recommendations addresses ASON (Automatically Switched Optical Network). ASON, based on requirements in Recommendation G.807, includes: (a) distributed connection management; (b) automatic discovery; (c) optical route selection; (d) connection access control. In addition to these three series, metropolitan optical networks and studies on individual aspects of optical networks continue to be pursued.

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. It also 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. In particular with regards to the introduction of optical transport of Internet packets ("IP over Optical"), coordination with IP related groups (e.g. SG 13-IP Experts, IETF) shall be pursued. This should allow a proper integration of the indications coming from Internet experts and those related to optical networking, and eventually should ensure the mutual consistency of the standards prepared by the various bodies, on this subject.

In addition, some general aspects of the optical transport network including OTN and ASON, such as general terminology or reliability/availability, need to be captured.

Responsibility under this Question includes the following Recommendations:

G. 871: Framework of Optical Transport Network Recommendations

G.911: Parameters and calculation methodologies for reliability and availability of fibre optic systems


  • What characteristics of optical transport networks still need to be fully developed in the various network environments (e.g. metropolitan, backbone,...), in what Study Question and within what time schedule?
  • What aspects of optical transport networks, related to optical transport of IP-type traffic ("IP over Optical"), need to be assigned to what Study Question for timely development?

  • What enhancements to Rec. G.871 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?

Study items

Study items to be considered include the coordination in the following areas:

  • Automatically Switched Transport Network requirements aspects [SG 13]
  • Optical access networks [Q.2/15]
  • OTN & ASON functional characteristics [Q.9/15]
  • OTN & ASON structures and mapping [Q.11/15]
  • OTN & ASON architectural aspects [Q.12/15]
  • OTN synchronization characteristics [Q.13/15]
  • OTN & ASON management aspects [Q.14/15; SG4]
  • OTN physical layer characteristics [Q.15, 16, & 17/15]

Specific tasks

  • 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
  • Revise Recommendation G.871; as appropriate
  • Prepare possible new Recommendation(s) to address the above two tasks, and other items that may be identified (e.g. a vocabulary Recommendation), as required
  • Facilitate the update of Recommendation G.911 in the most appropriate technical Question as necessary


  • Other relevant Questions of SG 15
  • ITU-T SG13 Questions on IP and optical network requirements
  • ITU-T SG 4 Question on management and testing aspecting
  • IETF IP related networks and protocols
  • OIF related to optical networking

1 In this text, the Optical Transport Network (with capitalized first letters) or the acronym OTN, refers to the specific optical network based on the architecture defined in Recommendation G.872. While, optical transport networks (with the first letters in lower case) refers to a generic optical transport network.


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