1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.983.4TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2001) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital sections and digital line system Optical line systems for local and access networks A broadband optical access
2、system with increased service capability using dynamic bandwidth assignment ITU-T Recommendation G.983.4 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 ANALO
3、GUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 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 COORD
4、INATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TESTING EQUIPMENTS G.500G.599 TRANSMISSION MEDIA 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 c
5、able systems G.910G.919 Digital sections at hierarchical 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 Di
6、gital section and digital transmission systems for customer access to ISDN G.960G.969 Optical fibre submarine cable systems G.970G.979 Optical line systems for local and access networks G.980G.989 Access networks G.990G.999 For further details, please refer to the list of ITU-T Recommendations. ITU-
7、T Rec. G.983.4 (11/2001) i ITU-T Recommendation G.983.4 A broadband optical access system with increased service capability using dynamic bandwidth assignment Summary This Recommendation specifies requirements for adding Dynamic Bandwidth Assignment (DBA) functionality to the Broadband Optical Acces
8、s Systems defined in ITU-T Rec. G.983.1. The use of DBA functionality enables dynamic sharing of upstream bandwidth. This dynamic sharing uses upstream bandwidth more efficiently and enables additional services flexibility. This Recommendation captures specifications for DBA operation and for DBA-re
9、lated communication between the OLT and the ONUs/ONTs. Source ITU-T Recommendation G.983.4 was prepared by ITU-T Study Group 15 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 November 2001. ii ITU-T Rec. G.983.4 (11/2001) FOREWORD The International Telecommunication Union (ITU)
10、 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, operating and tariff questions and issuing Recommendations on them with a view to standardi
11、zing 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 approval of ITU-T Recommendations is covere
12、d 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 “Administration“ is used for conciseness to indicat
13、e both a telecommunication administration and a recognized operating agency. 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 t
14、he evidence, 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,
15、which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2002 All rights reserved. No part of this publication may be reproduced or utilized
16、in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU. ITU-T Rec. G.983.4 (11/2001) iii CONTENTS Page 1 Introduction 1 1.1 Scope 1 1.2 Background. 1 1.2.1 Bandwidth assignment in non-DBA G.983.1 systems 1 1.2.2 Enhancing t
17、he bandwidth assignment on G.983.1 PON systems . 2 1.2.3 Effectiveness of dynamic bandwidth assignment . 2 1.2.4 General DBA approaches 3 1.2.5 Features and Migration scenarios for DBA. 4 1.2.6 Requirements for this Recommendation . 4 1.2.7 Layered architecture 4 1.3 Architectural Drawing 5 1.4 T-CO
18、NT priority hierarchy 6 1.5 Objectives . 7 2 References 7 3 Abbreviations . 8 4 Definitions 10 5 Architecture of the optical access network. 12 5.1 Network architecture 12 5.1.1 FTTCab/C/B scenario . 13 5.1.2 FTTH scenario. 13 5.1.3 DBA installations Scenario for FTTx . 14 5.2 Reference configuratio
19、n . 14 5.2.1 Service node interface . 15 5.2.2 Interface at the reference points S/R and R/S 15 5.3 Functional blocks 15 5.3.1 Optical line termination. 15 5.3.2 Optical network unit/optical network termination 16 5.3.3 Optical distribution network 16 5.4 ONU/ONT functional block . 17 5.4.1 NSR-ONU/
20、ONT functional block. 17 5.4.2 SR-ONU/ONT functional block 18 5.5 Optical Line Termination functional block 19 5.5.1 Non-DBA-OLT functional block 19 5.5.2 DBA-OLT functional block 20 5.6 Optical distribution network functional block 21 5.6.1 Passive optical elements 21 iv ITU-T Rec. G.983.4 (11/2001
21、) Page 5.6.2 Optical interfaces. 22 6 Services. 23 7 User network interface and service node Interface 24 8 Optical network requirements 24 8.1 Layered structure of the optical network 24 8.2 Physical medium dependent layer requirements for the ATM-PON . 25 8.3 Transmission convergence layer require
22、ments for the ATM-PON 25 8.3.1 Point-to-multipoint capacities for downstream and upstream. 25 8.3.2 Maximum payload capacities for downstream and upstream . 25 8.3.3 Downstream interface . 25 8.3.4 Upstream interface 25 8.3.5 Transport specific TC interface. 25 8.3.6 ATM specific TC functions. 47 8.
23、3.7 OAM functions 47 8.3.8 Messages in the PLOAM channel. 52 8.3.9 Automatic protection switching 59 8.4 Ranging method 59 8.4.1 Scope of the applied ranging method 59 8.4.2 Features of ranging method for DBA 59 8.4.3 Phase relation specification between downstream and upstream 59 8.4.4 Definition o
24、f messages used in the ranging protocol 59 8.4.5 Ranging procedure 59 8.4.6 Ranging time requirements . 64 8.5 Handshake procedures 64 8.5.1 Overall handshake procedure 64 8.5.2 Negotiated parameters. 64 8.5.3 Detailed procedures. 65 8.6 Operations for creation and deletion of T-CONTs. 68 8.6.1 Requ
25、irements for operations of T-CONT status change. 68 8.6.2 Operations for creation of T-CONTs 68 8.6.3 Operations for deletion of T-CONTs 72 8.6.4 Impact by T-CONT status change. 74 9 Operations Administration and Maintenance (OAM) functionality 75 10 Performance 75 11 Environmental condition 75 12 S
26、afety 75 ITU-T Rec. G.983.4 (11/2001) v Page Appendix I Algorithm for DBA 76 I.1 Algorithms for detecting ONU/ONT status for SR-ONU/ONT. 76 I.2 Algorithms for monitoring cell streams at OLT from NSR-ONUs/ONTs. 76 I.3 Algorithms to update bandwidth 76 I.5 Algorithms for grant assignment 79 I.6 Contro
27、l allowing for Upstream Congestion of the OLT NNI 79 Appendix II Options for minislot format and negotiating procedures . 80 II.1 Extended T-CONT reporting options. 80 II.1.1 Report type field 80 II.1.2 Reporting capability 80 II.1.3 Usage of extended reporting types 81 ITU-T Rec. G.983.4 (11/2001)
28、1 ITU-T Recommendation G.983.4 A broadband optical access system with increased service capability using dynamic bandwidth assignment 1 Introduction 1.1 Scope This Recommendation describes enhanced capabilities for flexible optical access networks based on ITU-T Rec. G.983.1. Specifically, this Reco
29、mmendation describes the functions that extend ITU-T Rec. G.983.1 to enable Dynamic Bandwidth Assignment (DBA). The requirements and specifications preserve backward compatibility and interoperability with the current G.983.1 systems, including management systems. This Recommendation includes: Perfo
30、rmances objectives (for example bandwidth assignment delay, maximum waiting time). Application functionality (for example dynamic bandwidth assignment for bursty traffic and for ONU/ONT aggregated traffic composed of different traffic classes). Fairness criteria and protocols (for example dynamic ba
31、ndwidth assignment based on ONU/ONT status reporting, dynamic bandwidth assignment based on OLT monitoring, dynamic bandwidth assignment based on a combination of reporting and monitoring). Backwards compatibility and interoperability that allows legacy OLTs and ONUs/ONTs to operate in systems where
32、 DBA is employed. It is anticipated that the introduction of DBA functionality into B-PON systems will increase efficiency and therefore lower the cost of providing broadband services. 1.2 Background 1.2.1 Bandwidth assignment in non-DBA G.983.1 systems The current method for bandwidth assignment vi
33、a grant control on ITU-T G.983.1 systems is described below. ITU-T Rec. G.983.1 specifies a flexible access platform to provide broadband services through passive optical networks. It defines physical and link layer requirements. Traffic is conveyed in the passive optical network in the following fr
34、ame formats. The upstream traffic from the ONUs/ONTs to the OLT is transferred in a frame of 53 timeslots (cellslots). Each timeslot consists of three bytes of PON layer overhead and an ATM cell or a PLOAM cell. The upstream bandwidth is shared among the associated ONUs/ONTs. The OLT controls each u
35、pstream transmission from the ONUs/ONTs on a timeslot-by-timeslot basis. This is accomplished by sending data grants in downstream PLOAM cells. PLOAM data grant cells are sent in the downstream direction to all ONUs/ONTs. The data grants are addressed to specific ONUs/ONTs and contain parameters tha
36、t include the number of upstream data grants and the timeslots for the grants that are assigned to the individual ONU/ONT. Currently the grants are assigned in a static manner. 2 ITU-T Rec. G.983.4 (11/2001) 1.2.2 Enhancing the bandwidth assignment on G.983.1 PON systems In ITU-T Rec. G.983.1, the O
37、LT grant generation and distribution are updated when a new connection is provisioned on a PON or an existing connection is removed from a PON. However, there are also other occasions when bandwidth is reassigned. Once the bandwidth is provisioned, the OLT will continuously send the assigned grants
38、to the associated ONUs/ONTs; subsequently, the OLT will receive corresponding user cells in the upstream. This current granting mechanism is most efficient for real time traffic. For example, real time traffic (represented by circuit emulation services) is a typical application that is provided over
39、 an ATM DBR Class 1 service connection. This service will generate a well-behaved traffic pattern and can be readily accommodated using the static bandwidth assignment method. However, ITU-T Rec. G.983.1 is intended to enable a wide range of broadband services, including those that do not have a con
40、stant bit rate. For example, the Internet connects to many bursty traffic sources, which are best accommodated by ATM SBR Class 2 or GFR, which have less rigid requirements on cell transfer delay and cell delay variation. Mapping these non-real-time services into a fixed bandwidth channel prevents t
41、he ONUs/ONTs on a PON from dynamically sharing the upstream PON bandwidth. For these non-real-time traffic types, the ability to assign bandwidth dynamically is expected to provide higher efficiency than the current static granting mechanisms. 1.2.3 Effectiveness of dynamic bandwidth assignment A Dy
42、namic Bandwidth Assignment (DBA) mechanism improves the efficiency of the PON upstream bandwidth by dynamically adjusting the bandwidth among the ONUs/ONTs in response to ONU/ONT bursty traffic requirements. The practical benefits of DBA are twofold. First, the network operators can add more subscri
43、bers to the PON due to more efficient bandwidth use. Second, the subscribers can enjoy enhanced services, such as those requiring bandwidth peaks that would extend beyond the traditional fixed allocation. A comparison between the current static mechanism and DBA is shown in Figure 1. Three ONUs/ONTs
44、 are represented and labelled No. 1, No. 2 and No. 3. ONU/ONT No. 1 requires constant bit rate traffic such as DBR Class 1, which is carried efficiently using the static bandwidth assignment method. ONU/ONT No. 2 and ONU/ONT No. 3, however, both have bursts of traffic; traffic from ONU/ONT No. 3 als
45、o has delay requirements. With static bandwidth allocation (shown in Figure 1 a), traffic from ONU/ONT No. 2 would be lost and traffic from ONU/ONT No. 3 would be delayed. The efficiency of DBA is shown in Figure 1 b), where ONU/ONT No. 3 is dynamically assigned enough bandwidth to carry its traffic
46、 burst, followed by ONU/ONT No. 2 being dynamically assigned sufficient bandwidth for its traffic. ITU-T Rec. G.983.4 (11/2001) 3 T1546240-02Original trafficONU/ONT #2Lost traffic in #2Delayed traffic in #3a) Transfer by Static bandwidth assignmentb) Transfer by DBAConstant bit rate trafficBursty tr
47、affic Bursty and delay sensitive traffic ONU/ONT #2ONU/ONT #3ONU/ONT #1ONU/ONT #2ONU/ONT #3ONU/ONT #1ONU/ONT #3ONU/ONT #1Figure 1/G.983.4 Comparison between the current mechanism and DBA 1.2.4 General DBA approaches Two different DBA mechanisms are summarized below. Method one is referred to as “idl
48、e cell adjustment“. In this approach, the OLT monitors the bandwidth used by each of the ONUs/ONTs. If the utilization exceeds a predefined threshold, then additional bandwidth will be assigned if it is available. In this approach, no bandwidth resources are needed for the ONU/ONT to report status;
49、the OLT infers individual ONU/ONT bandwidth needs from the current utilization. However, a possible drawback of this approach would be slow reaction to ONUs/ONTs requesting upstream bandwidth. Method two is called “buffer status reporting“. ONUs/ONTs using this approach report the status of their buffers by using mini-slots. The OLT reassigns the bandwidth according to the ONU/ONT reports. 4 ITU-T Rec. G.983.4 (11/2001) 1.2.5 Features and Migration scenarios for DBA Other features of DBA include the ability to accommodate sever
