1、 International Telecommunication Union ITU-T G.680TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2007) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Transmission media and optical systems characteristics Characteristics of optical systems Physical transfer functions of
2、optical network elements ITU-T Recommendation G.680 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUA
3、L CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.4
4、99 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 General G.600G.609 Symmetric cable pairs G.610G.619 Land coaxial cable pairs G.620G.629 Submarine cables G.630G.639 Free space optical systems G.640G.649 Optical fibre cables G.650G.659 Characteristics of optical components and sub
5、systems G.660G.679 Characteristics of optical systems G.680G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS
6、G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.680 (07/2007) i ITU-T Recommendation G.680 Physical transfer functions of optical
7、network elements Summary ITU-T Recommendation G.680 defines a “degradation function“ of optical network elements (ONEs) such as photonic cross-connects (PXCs), optical add-drop multiplexers (OADMs), etc. making up an optical network. This is done in terms of a list of parameters which characterize p
8、hysical impairments such as optical noise, chromatic dispersion, etc., and is intended to be independent from the network architecture that the devices are deployed in. For each kind of ONE considered in this Recommendation, the general functional description and the reference diagram is provided. P
9、rinciples for calculating the effect of cascading multiple ONEs on the degradation of the optical signal quality are given and example transfer parameter values for OADMs and PXCs are also provided. This version of the Recommendation covers the situation where the optical path between two consecutiv
10、e electrical regenerators is composed of dense wavelength division multiplexing (DWDM) line segments from a single vendor and OADMs and PXCs from other vendors. Source ITU-T Recommendation G.680 was approved on 29 July 2007 by ITU-T Study Group 15 (2005-2008) under the ITU-T Recommendation A.8 proce
11、dure. ii ITU-T Rec. G.680 (07/2007) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical,
12、 operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in tu
13、rn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOT
14、E In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e
15、.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not s
16、uggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the e
17、vidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, whic
18、h may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2008 All rights reserved. No part of this publication ma
19、y be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.680 (07/2007) iii CONTENTS Page 1 Scope 1 2 References. 2 3 Definitions 3 3.1 Terms defined elsewhere 3 3.2 Terms defined in this Recommendation. 4 4 Abbreviations 4 5 Classification of optical networ
20、k elements. 6 6 Reference points . 6 7 Functional description of the optical network elements (ONEs) 8 7.1 Functional description of a DWDM line segment 8 7.2 Functional description of an OADM (optical add/drop multiplexer). 8 7.3 Functional description of a PXC (photonic cross-connect) 9 7.4 Functi
21、onal description of an AOWC (all-optical wavelength converter) 11 7.5 Functional description of an OA (optical amplifier) 11 7.6 Functional description of an optical 3R regenerator 11 7.7 Functional description of an optical 2R regenerator 11 8 ONE transfer parameters 11 8.1 DWDM line segment transf
22、er parameters 12 8.2 OADM transfer parameters 12 8.3 PXC transfer parameters. 16 8.4 AOWC transfer parameters 19 8.5 OA transfer parameters. 19 8.6 Optical 3R transfer parameters. 19 8.7 Optical 2R transfer parameters. 19 9 Impact of the combination of cascaded optical transfer functions on line sys
23、tem performance 19 9.1 Impact of cascaded ONEs on line system OSNR. 19 9.2 Impact of cascaded ONEs on line system residual dispersion . 20 9.3 Impact of cascaded ONEs on line system PMD and PDL . 22 9.4 Impact of cascaded ONEs on line system channel ripple. 24 9.5 Impact of cascaded ONEs on line sys
24、tem transients 25 9.6 Impact of the channel uniformity of cascaded ONEs on line system performance 28 10 Calculation method to combine the system penalty contribution from the impact of the parameters. 30 iv ITU-T Rec. G.680 (07/2007) Page Appendix I Example transfer parameter values 32 I.1 Example
25、1 Values for a re-configurable OADM without amplifiers 32 I.2 Example 2 A second set of values for a re-configurable OADM without amplifiers 32 I.3 Example 3 Values for a re-configurable OADM with amplifiers . 33 I.4 Example 4 A second set of values for a re-configurable OADM with amplifiers 35 I.5
26、Example 5 Values for a PXC with add/drop functions and amplifiers . 37 Appendix II Examples of the effects of cascading ONEs. 40 II.1 Example of the impact of cascaded ONEs on line system OSNR . 40 II.2 Example of the impact of cascaded ONEs on line system residual dispersion 41 II.3 Examples of the
27、 impact of cascaded ONEs on line system PMD and PDL. 43 II.4 Examples of the impact of cascaded ONEs on line system channel ripple 44 II.5 Example of the impact of cascaded ONEs on line system transients. 46 II.6 Example of the impact of the channel uniformity of cascaded ONEs on line system perform
28、ance. 50 Appendix III Example application of this Recommendation 53 III.1 Procedure 53 III.2 An example of this procedure. 54 Appendix IV The users of this Recommendation. 56 IV.1 Introduction 56 IV.2 The actors in the use of this Recommendation. 56 IV.3 Example of the activities of the actors . 56
29、Bibliography. 58 ITU-T Rec. G.680 (07/2007) v Introduction The present optical transport networks (OTN) are evolving towards optical networks with an ever decreasing number of O/E/O conversions within their boundaries. The two main reasons for this evolution are the following: i) DWDM systems are be
30、coming capable of transporting light signals for some thousands of kilometres without electrical regeneration; ii) Photonic cross-connects (PXC) and optical add/drop multiplexers (OADMs) are becoming available with capacity, space requirements, power consumption, reliability and cost, suitable for t
31、heir use in the telecommunication networks. This evolution will lead to the deployment of a domain of optical transparency that can be large enough to ensure that all the potential routes of the backbone network of a medium size country (optical paths up to around 2000 km) could be realized all opti
32、cally. ITU-T Rec. G.680 (07/2007) 1 ITU-T Recommendation G.680 Physical transfer functions of optical network elements 1 Scope The scope of this Recommendation is to define a “degradation function“ of the optical network elements (DWDM line segment, PXC, OADM, etc.) between points MPI-SMand MPI-RM(F
33、igures 6-1 to 6-3) in terms of ASE, non-linear impairment, chromatic dispersion, PMD, etc., independently from the network architecture/structure/configuration that the system is deployed in. These degradation functions are the basis for guidelines found in clause 8 for the consequence of the cascad
34、ing of optical network elements (not including DWDM line segments for Situation 1 as described below) within an optical transmission system in order to assess the degradation of the signal quality due to the optical path between the ingress and egress 3R electrical regenerators. This version of the
35、Recommendation covers the reference situation: Situation 1 The optical path between two consecutive 3R regenerators is composed of DWDM line segments from a single vendor and OADMs and PXCs from another vendor as shown in Figure 1-1. The information in this Recommendation (when taken together with t
36、he corresponding parameters from the DWDM line segments including any non-linear effects) enables the evaluation of the impact on line system performance of the combination of transfer parameters related to the cascaded ONEs inserted in the optical route. .G.680(07)_F1-1PXCLine segment vendor 1PXC v
37、endor 2OADMOADM vendor 3Line segment vendor 1Line segment vendor 1Line segment vendor 1Line segment vendor 1Line segment vendor 1Figure 1-1 Illustration of Situation 1 A future revision of the Recommendation is expected to cover the reference situation: Situation 2 The optical path between two conse
38、cutive 3R regenerators is composed of DWDM line segments from different vendors and OADMs and PXCs from different vendors as shown in Figure 1-2. This will enable the degradation of the signal quality due to the optical path for an arbitrary route through an all-optical network (or sub-network) cons
39、isting of optical network elements including DWDM line segments to be assessed thereby enabling routing decisions in an all-optical network (or sub-network) to be made. 2 ITU-T Rec. G.680 (07/2007) .G.680(07)_F1-2PXCLine segment vendor 1PXC vendor 2OADMOADM vendor 8Line segment vendor 3Line segment
40、vendor 4Line segment vendor 5Line segment vendor 6Line segment vendor 7Figure 1-2 Illustration of situation 2 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of p
41、ublication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list o
42、f the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.652 ITU-T Recommendation G.652 (2005), Characteristics of a single-mode optical fibre and ca
43、ble. ITU-T G.661 ITU-T Recommendation G.661 (2007), Definition and test methods for the relevant generic parameters of optical amplifier devices and subsystems. ITU-T G.662 ITU-T Recommendation G.662 (2005), Generic characteristics of optical amplifier devices and subsystems. ITU-T G.663 ITU-T Recom
44、mendation G.663 (2000), Application related aspects of optical amplifier devices and subsystems. ITU-T G.665 ITU-T Recommendation G.665 (2005), Generic characteristics of Raman amplifiers and Raman amplified subsystems. ITU-T G.666 ITU-T Recommendation G.666 (2005), Characteristics of PMD compensato
45、rs and PMD compensating receivers. ITU-T G.667 ITU-T Recommendation G.667 (2006), Characteristics of adaptive chromatic dispersion compensators. ITU-T G.671 ITU-T Recommendation G.671 (2005), Transmission characteristics of optical components and subsystems. ITU-T G.694.1 ITU-T Recommendation G.694.
46、1 (2002), Spectral grids for WDM applications: DWDM frequency grid. ITU-T G.709 ITU-T Recommendation G.709/Y.1331 (2003), Interfaces for the Optical Transport Network (OTN). ITU-T G.959.1 ITU-T Recommendation G.959.1 (2006), Optical transport network physical layer interfaces. ITU-T Rec. G.680 (07/2
47、007) 3 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined in ITU-T G.661: channel addition/removal (steady-state) gain response; channel gain; channel input power range; channel output power range; channel signal-spontaneous noise figure; input (or output)
48、 power change; input reflectance; maximum reflectance tolerable at input; maximum reflectance tolerable at output; maximum total output power; multichannel gain variation (inter-channel gain difference); multichannel gain-change difference (inter-channel gain-change difference); multichannel gain ti
49、lt (inter-channel gain-change ratio); optical signal-to-noise ratio (OSNR); output reflectance; rate of change of power; total input power range; transient duration; transient gain increase; transient gain reduction. This Recommendation uses the following term defined in ITU-T G.663: amplified spontaneous emission (ASE) (see “noise accumulation“). This Recommendation uses the following terms defined in ITU-T G.671: adjacent channel isolation; channel ext
