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Question 6/15 – Characteristics of optical systems for terrestrial transport networks
(Continuation of Question 6/15)


Optical fibre networks are deployed in telecommunication systems worldwide. Structural reforms leading to increased privatisation of telecommunications networks create an operating environment requiring optical networking and interconnection among different carriers. Simultaneously, there is occurring a rapid evolution toward a packet-based (IP type) infrastructure and a future Next Generation Network (NGN) supporting multiple integrated services. These developments are being fuelled by customer demand for ever higher bit rate data services, high-speed Internet access, and other innovative services. It leads to a push for higher bit-rate (Terabit/s) optical transport systems in the intra-office, inter-office and long distance networks of the various network operators.

Together with the continuing use of the Synchronous Digital Hierarchy (SDH) worldwide, network operators are deploying an Optical Transport Network (OTN). The OTN utilises the technologies of time-division multiplexing (TDM) and Wavelength-Division Multiplexing (WDM); new technologies such as advanced modulation formats may be expected in the future. Specifications are needed for physical layer interfaces of WDM systems, including the OTN, to enable the evolution of the intra-office, inter-office and long distance networks to support the ubiquitous availability of next-generation high-bandwidth services. To the greatest extent possible, these specifications should enable transverse compatibility (black-box and/or black-link) in a multi-vendor, multi-network-operator environment.

The following major Recommendations, in force at the time of approval of this Question, fall under its responsibility: G.664, G.955, G.957, G.959.1, G.691, G.692, G.693, G.694-series, G.695, G.696.1, G.697, G.698.1, G.698.2, G.680, G.640, G.911.


What system aspects and physical layer characteristics are necessary to enable longitudinally compatible and transversely compatible optical systems in intra-office, inter-office and long distance networks?

What enhancements to existing draft or published Recommendations and what new Recommendations are necessary to specify interfaces for single and multichannel optical transport systems for bit rates above 100 Gbit/s?

What systems and physical layer considerations are necessary for optical transport systems optimized for packet data transport (e.g. IP over WDM) and NGN applications?

What enhancements should be made to existing draft or published Recommendations to reflect technological developments?

What enhancements can be made to existing draft or published Recommendations to further reduce the power consumption of optical fibre communication systems?

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

  • General considerations for optical systems used to transport SDH, OTN and Ethernet signals using several types of single-mode fibre
  • Statistical and semi-statistical power budget approaches
  • Optical link and optical interface parameters for SDH and OTN systems to enable transverse compatibility
  • Optical frequency plan, including optical supervisory channel wavelength, for WDM systems
  • Optical aspects of TDM and WDM systems such as:
    • Optical power levels including safety aspects and automatic gain control
    • Dispersion accommodation techniques
    • Polarisation mode dispersion system penalty
  • Clarification and resolution of technical issues in current and draft Recommendations
  • Specifications to enable transverse compatibility in single-channel and multichannel optical systems
  • System models, reference configurations and reference points to support alternative optical interface specification methodologies
  • Descriptive methodology for classifying application code structures of optical interfaces to be standardised (e.g. increasingly complicated systems with various dispersion accommodation techniques, line codes, etc.)
  • Parallel and serial transmission of higher bitrates (e.g. above 100 Gbit/s)
  • Specifications of interfaces inside a black link
  • Evaluation of the quality of an optical channel end-to end enabling routing decisions in an All Optical Network (AON) (e.g. cumulated effects of degradations, transients, etc)
  • Alternative modulation formats including but not limited to:
    • Return-to-Zero (e.g. RZ, CS-RZ etc.)
    • Phase Shaped Binary Transmission (PSBT) or duo-binary
    • Phase Modulation (e.g. PSK, QPSK, DPSK, DQPSK etc.)
    • Polarisation multiplexing
    with a view of developing multi-vendor interoperable optical interfaces using some of these formats where appropriate
  • PMD at higher orders, such as 2nd order, at 40G and higher bit rates
  • PMD mixing with PDL, SPM, XPM and CD
  • Enhanced dispersion management techniques for high-performance systems
  • Enhanced optical monitoring
  • Coherent detection, for bit rates at 40 Gbit/s and beyond and Optical Circuit / Packet / Burst Switching towards IP-over-DWDM
  • Characteristics of TDM line systems up to or above 40 Gbit/s and their upgrade by WDM
  • Optical interface specifications for metro applications
  • Optical interface specifications for long haul multi-span applications
  • Utilisation of Optical Add-Drop Multiplexers (OADMs) and Optical cross-Connects (OXCs) with or without wavelength converter, also considering evolution towards transversely compatible interfaces for an All Optical Network (AON)
  • Concatenation of the transfer functions of different optical Network Elements (NEs)
  • Application of forward error correction (FEC) techniques to terrestrial optical transmission systems (e.g. to enhance system margin or to relax optical parameter specifications)
  • Use of new types of optical amplifiers with changes in systems wavelengths and/or power levels
  • Application of additional passive and active dispersion accommodation techniques (e.g. adaptive chromatic dispersion compensators)
  • Single and Multichannel Polarization Mode Dispersion (PMD) compensation in optical systems
  • Enhanced statistical design approaches
  • Characteristics of optical systems optimized for data transport, e.g. IP, SDH, ATM and Ethernet over an OTN
  • Availability/reliability aspects of optical systems


Tasks include, but are not limited to:

  • Enhance Recommendations G.664, G.955, G.957, G.959.1, G.691, G.692, G.693, G.694-series, G.695, G.696.1, G.697, G.698.1, G.698.2, G.680. G.640
  • Develop new Recommendations or combine existing Recommendations from progress on the above study points
  • Complete and update the text of G.Sup39

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




  • G.65x series, G.66x series, G.671.


  • Q2/15, Q3/15, Q5/15, Q7/15, Q8/15, Q9/15, Q11/15 and QL/9.

Study Groups:

  • ITU-T SG13 on NGN, data-centric networks
  • ITU-T SG12 network performance objectives.

Standardization bodies, forums and consortia:

  • IEC SC86C on system measurement test methods and on optical amplifier test methods
  • OIF on optical systems interfaces
  • IEEE 802.3 on optical systems interfaces.


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Updated : 2008-12-09