1、 International Telecommunication Union ITU-T G.984.7TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2010) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Optical line systems for local and access networks Gigabit-capable passive opt
2、ical networks (GPON): Long reach Recommendation ITU-T G.984.7 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
3、 INDIVIDUAL 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 TELEPHON
4、Y G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 General G.900G.909 Parameters for optical fibre cable systems G.910G.919 Digital sections at hierarchi
5、cal bit rates based on a bit rate of 2048 kbit/s G.920G.929 Digital line transmission systems on cable at non-hierarchical bit rates G.930G.939 Digital line systems provided by FDM transmission bearers G.940G.949 Digital line systems G.950G.959 Digital section and digital transmission systems for cu
6、stomer access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989Access networks G.990G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6
7、000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.984.7 (07/2010) i Recommendation ITU-T G.984.7 Gigabit-capable passive optical netwo
8、rks (GPON): Long reach Summary Recommendation ITU-T G.984.1 defines the maximum differential distance between any two ONUs on the passive optical network (PON) as 20 km and the GPON logical reach has been defined as 60 km. However, based on practical deployment experience, it has been found that a d
9、ifferential distance of 40 km ranging from 0 to 40 km, 20 to 60 km, or distances in between allows significant flexibility in PON deployment and offers many benefits including the ability to serve sparsely populated areas in an efficient manner. The present Recommendation describes the necessary req
10、uirements for GPON to support the differential distance of 40 km. History Edition Recommendation Approval Study Group 1.0 ITU-T G.984.7 2010-07-29 15 Keywords Differential distance, GPON, quiet window. ii Rec. ITU-T G.984.7 (07/2010) FOREWORD The International Telecommunication Union (ITU) is the Un
11、ited Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recomme
12、ndations 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 turn, produce Recommendations on these topics. The ap
13、proval 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. NOTE In this Recommendation, the expression “Administr
14、ation“ 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.g., interoperability or applicability) and compli
15、ance 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 suggest that compliance with the Recommendation is
16、 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 evidence, validity or applicability of claimed Int
17、ellectual 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, which may be required to implement this Recommendatio
18、n. 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 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without
19、 the prior written permission of ITU. Rec. ITU-T G.984.7 (07/2010) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations and acronyms 1 5 Conventions 1 6 Overview 2 7 Physical layer requirements 4 7.1 Spectral width . 4 7.2 Attenuation range . 4 7.3 ODN topology 4 8 GPON Transm
20、ission convergence layer requirements . 5 8.1 OLT side considerations . 5 8.2 ONU side considerations 5 Rec. ITU-T G.984.7 (07/2010) 1 Recommendation ITU-T G.984.7 Gigabit-capable passive optical networks (GPON): Long reach 1 Scope This Recommendation contains the set of G-PON physical media-depende
21、nt requirements and transmission convergence layer requirements that allow extending the maximum differential fibre distance of a G-PON system to 40 km versus the conventional 20 km differential fibre distance, as required by Recommendation ITU-T G.984.1. This Recommendation introduces additional ca
22、pabilities to the ITU-T G.984-series Recommendations and does not replace other Recommendations in the series. The appropriate ITU-T G.984-series Recommendations should be selected for the intended application and distance requirements. 2 References The following ITU-T Recommendations and other refe
23、rences contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to inv
24、estigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of 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 s
25、tatus of a Recommendation. ITU-T G.984.1 Recommendation ITU-T G.984.1 (2008), Gigabit-capable passive optical networks (GPON): General Characteristics. ITU-T G.984.2 Recommendation ITU-T G.984.2 (2003), Gigabit-capable Passive Optical Networks (GPON): Physical Media Dependent (PMD) layer specificati
26、on. ITU-T G.984.3 Recommendation ITU-T G.984.3 (2008), Gigabit-capable Passive Optical Networks (GPON): Transmission convergence layer specification. 3 Definitions This clause is intentionally left blank. 4 Abbreviations and acronyms GPON Gigabit-capable Passive Optical Network ODN Optical Distribut
27、ion Network OLT Optical Line Terminal ONU Optical Network Unit PLOAM Physical Layer Operations, Administration and Maintenance PON Passive Optical Network 5 Conventions This clause is intentionally left blank. 2 Rec. ITU-T G.984.7 (07/2010) 6 Overview Figure 6-1 shows the construction of a quiet win
28、dow for the serial number acquisition in the ITU-T G.984 GPON system, where all ONUs are within the 20 km fibre reach. The quiet window in this case must accommodate the 200 s variation of the round-trip propagation delay (0 to 200 s), the 2 s variation of the ONU processing time (34 to 36 s), and t
29、he 48 s ONU random delay (0 to 48 s) (see clause 10.4.2 of ITU-T G.984.3). Therefore, the minimum size of the quiet window is 250 s. For the sake of specificity, assume that the OLT does not start the quiet window construction until the transmission of the serial number request grant. (See clause 10
30、.4.5 of ITU-T G.984.3 for the discussion of the alternatives.) In this case, the OLT employs the pre-assigned delay, which is not less than the combined variation of round-trip propagation delay and ONU processing time (202 s). The minimum offset of the quiet window at the OLT (i.e., the time to ear
31、liest arrival of the serial number response after transmission of a serial number request grant) can be determined as 236 s, a sum of the pre-assigned delay and the minimum ONU response time. G.984.7(10)_F6-1OLT20 kmGTC frame N GTC frame + 1N GTC frame + 2N GTC frame + 3NQuiet window offset, 236 sSN
32、 request:StartTime = 0Quiet window, 250 sPossible SN responsetransmissionPropagation delay Propagation delayPre-assigned delay, 202 sMinONUresp.timeMaxrandomdelayEmptyBWmapFigure 6-1 Construction of GPON quiet window with the 0 to 20 km distance range Figure 6-2 shows the quiet window construction f
33、or serial number acquisition in a GPON system where the fibre distances of all ONUs vary between 20 km and 40 km. The maximum differential fibre distance is the same as in the example above, i.e., 20 km. Since ONUs design and protocol parameters depend on fibre distance only, through the maximum dif
34、ferential fibre distance, they too remain the same. The minimum quiet window size in this case is also 250 s. On the other hand, the round-trip propagation delay now varies from 200 to 400 s, and the minimum round-trip propagation contributes to the quiet window offset, which becomes 436 s. Rec. ITU
35、-T G.984.7 (07/2010) 3 G.984.7(10)_F6-2OLT40 km20 kmGTC frame N GTC frame + 1N GTC frame + 2N GTC frame + 3N GTC frame + 4N GTC frame + 5NQuiet window offset, 436 sSN request:StartTime = 0Quiet window, 250 sPossible SN responsetransmissionPropagation delay Propagation delayPre-assigned delay,202 s1:
36、 Minimum ONU response time2: Maximum random delayEmptyBWmap12Figure 6-2 Construction of GPON quiet window with the standard differential distance and 20 km to 40 km distance range In a GPON system with extended differential reach (an EDR GPON system) the differential fibre distance is increased so t
37、hat the ONUs could be placed anywhere between 0 and 40 km. This increases the variation of round-trip propagation delay to 400 s (ranging from 0 to 400 s). Therefore, the size of the quiet window that the OLT has to open for serial number acquisition in such a system, with other parameters being inv
38、ariant, must be at least 450 s. Figure 6-3 shows the construction of the quiet window for EDR GPON. Following the pattern adopted earlier, the pre-assigned delay is assumed to be equal to the combined variation of round-trip propagation delay and ONU processing time, i.e., 402 s. The offset of the q
39、uiet window in this case is can be determined as 436 s. G.984.7(10)_F6-3OLT40 km20 kmGTC frame N GTC frame + 1N GTC frame + 2N GTC frame + 3N GTC frame + 4N GTC frame + 5N GTC frame + 6NQuiet window offset, 436 sSN request:StartTime = 0Quiet window, 450 sPossible SN responsetransmissionPropagation d
40、elay Propagation delayPre-assigned delay,402 s1: Minimum ONU response time2: Maximum random delayEmptyBWmapEmptyBWmapPartiallyemptyBWmap12Figure 6-3 Construction of GPON quiet window with proposed extended differential distance (0 to 40 km) 4 Rec. ITU-T G.984.7 (07/2010) Note that serial number acqu
41、isition requires a broadcast PLOAM grant, and that multiple ONUs may attempt to respond. The random delay (0.48 s) helps to reduce the probability of collision. When the OLT opens a quiet window for ranging, it uses a unicast grant with no possibility of contention, so that the minimum quiet window
42、sizes are 202 s for the case of the 20 km differential fibre distance case and 402 s for the 40 km differential fibre distance case. 7 Physical layer requirements 7.1 Spectral width ITU-T G.984.2 defines certain PMD specifications for the OLT and ONU. For a GPON system operating at 2488 Mbps downstr
43、eam rate and 1244 Mbps upstream rate, the 20 dB spectral width was originally specified as 1 nm. In order to serve ONUs deployed 0-40 km, 20-60 km or at distances in between with a 40 km differential distance from the OLT, the OLT laser 20 dB spectral width needs to be less than or equal to 0.6 nm.
44、7.2 Attenuation range An EDR GPON system shall employ the optical components and maintain the optical power levels consistent with one of the standard attenuation range classes: Class B+, Class C, and Class C+. It shall support the maximum fibre distance and the maximum differential fibre distance a
45、s specified in the following table. Table 1 Physical medium dependant layer parameters of ODN Attenuation class Attenuation range, dB Max physical reach, km Max differential fibre distance, km Class B+ 13-28 40 40 Class C 15-30 40 40 Class C+ 17-32 60 40 7.3 ODN topology The ODN shall be based on IT
46、U-T G.652 fibre and shall possess the topology, including the location and degree of the power splitter and possible use of passive optical attenuators, to ensure that the minimum loss requirement is met for each ONU. An ODN accommodating the differential fibre reach approaching 40 km may employ an
47、unbalanced cascade of splitters, where the shortest fibre branches experience the highest degree of split. An example of a Class B+ ODN supporting 13-28 dB attenuation range with maximum physical reach of 40 km and differential fibre reach of 40 km is shown in Figure 2.1. In this example, the ONUs w
48、ith shorter fibre distance experiences the higher degree of split than the remote ONUs. Specifically, assuming, in the first approximation, 3.5 dB attenuation per binary split and 0.4 dB per kilometre of fibre, one can obtain for the group of near ONUs the total attenuation of 17.5 dB and for the gr
49、oup of remote ONUs the total attenuation of 26.5 dB, both values being within the allowed window for the class. Other topologies may be possible, provided the ODN meets the specifications given in ITU-T G.984.2. Rec. ITU-T G.984.7 (07/2010) 5 .G.984.7(10)_F7-140 km1:21:16 1 km1:4Figure 7-1 An example of Class B+ ODN supporting the differential fibre reach of 40 km 8 GPON Transmission convergence layer requirements 8.1 OLT side considerations At the serial number acquisition and ranging phases of t
