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Question 9/15 - Transport equipment and network protection/restoration

(Continuation of Question 9/15)

Background and justification

Two key technologies are driving the development of transport equipment and standards:

  • The explosive growth of the Internet and other packet based traffic carried over networks
  • The development of OTN provides the ability to dramatically increase the bandwidth that can be carried over networks

Responsibilities under this Question include the following areas of standardisation related to these new technologies:

  • Specification of all equipment functions and supervision processes related to the OTN and SDH layer networks
  • Specification of Adaptation Functions and Supervision Processes for transport of packet traffic (e.g., IP, ATM, MPLS) via the SDH or OTN layer networks
  • Specification of survivability capabilities and development of a strategy for multi-layer survivability interactions
  • Examining the impact on synchronization layer functions, which may differ for transport of different client layers (e.g., IP traffic)

Recommendations related to transport technologies (e.g., SDH, PDH, OTN) used in the access environment and not covered by other Questions of ITU-T SG 15, such as Flexible Multiplexers, are also covered by this Question. Responsibility under this Question includes the following draft or published Recommendations:

G.681: Functional characteristics of interoffice and long-haul line systems using optical amplifiers, including optical multiplexing

G.705: Characteristics of Plesiochronous Digital Hierarchy (PDH) Equipment Functional Blocks

G.781: Synchronisation Layer Functions

G.783: Characteristics of Synchronous Digital Hierarchy (SDH) Equipment Functional Blocks

G.798: Characteristics of Optical Transport Network (OTN) Equipment Functional Blocks

G.806: Characteristics of Transport Equipment – Description Methodology and Generic Functionality

G.841: Types and Characteristics of SDH Network Protection Architectures

G.842: Interworking of SDH network protection architectures


  • What equipment functions must be specified to enable compatible transport equipment in inter-office and long distance networks, including evolution to the optical transport network?
  • What additional characteristics of transport equipment should be recommended to provide enhanced survivability capabilities and a cohesive strategy for multi-layer survivability interactions?
  • What considerations are necessary for equipment optimised for transport of IP-type traffic?

Study items

Study items to be considered include:

  • Completion of equipment Recommendations for the OTN (OTN equipment in this context relates to equipment functions and the assembly of optical components and sub-systems)
  • Equipment Recommendations to provide enhanced survivability capabilities and a cohesive strategy for multi-layer survivability interactions. This includes revisions needed to Recommendations G.841 and G.842. These Recommendations will cover SDH and OTN layer protection, as well as multi-layer survivability, including interactions with protection at packet layers
  • Specifications of Equipment functions necessary to implement an Automatically Switched Optical Network (ASON)
  • Enhancements to SDH equipment characteristics or network protection protocols to support paths with longer delay times, such as satellite systems, submarine cable systems, radio relay systems or systems with numerous regenerators
  • Enhancements to the transport equipment Recommendations in order to meet the needs of the access network
  • Enhancements required to the transport equipment Recommendations in order to meet the needs of the GII and transport of Internet and other packet based traffic. This includes examining the impact, if any, on synchronisation layer functions
  • Incorporating the impact of recent technological developments into equipment Recommendations
  • Clarification and resolution of technical issues in current and draft Recommendations

Specific tasks

  • Revise Recs. G.781, G.841, G.842 as required
  • Complete Rec. G.798 by 2001
  • Develop additional Recommendations from progress on the above study points


  • Other relevant Question of SG 15 on optical networks, digital hierarchy and management and digital hierarchies
  • ITU-T SG 4 on TMN
  • ITU-T SG 13 on Transport Network Architectures
  • ITU-R SG 4 on Satellite systems
  • ITU-T SG7 on aspects related to mapping of IP structured signals
  • ITU-R SG 9 on Radio-relay systems
  • IETF
  • ATIS Committee T1X1
  • ETSI


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