1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T E.681TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2001) SERIES E: OVERALL NETWORK OPERATION, TELEPHONE SERVICE, SERVICE OPERATION AND HUMAN FACTORS Traffic engineering Traffic engineering for IP-networks Traffic engineering methods for IP access ne
2、tworks based on hybrid fiber/coax system ITU-T Recommendation E.681 ITU-T E-SERIES RECOMMENDATIONS OVERALL NETWORK OPERATION, TELEPHONE SERVICE, SERVICE OPERATION AND HUMAN FACTORS INTERNATIONAL OPERATION Definitions E.100E.103 General provisions concerning Administrations E.104E.119 General provisi
3、ons concerning users E.120E.139 Operation of international telephone services E.140E.159 Numbering plan of the international telephone service E.160E.169 International routing plan E.170E.179 Tones in national signalling systems E.180E.189 Numbering plan of the international telephone service E.190E
4、.199 Maritime mobile service and public land mobile service E.200E.229 OPERATIONAL PROVISIONS RELATING TO CHARGING AND ACCOUNTING IN THE INTERNATIONAL TELEPHONE SERVICE Charging in the international telephone service E.230E.249 Measuring and recording call durations for accounting purposes E.260E.26
5、9 UTILIZATION OF THE INTERNATIONAL TELEPHONE NETWORK FOR NON-TELEPHONY APPLICATIONS General E.300E.319 Phototelegraphy E.320E.329 ISDN PROVISIONS CONCERNING USERS E.330E.349 INTERNATIONAL ROUTING PLAN E.350E.399 NETWORK MANAGEMENT International service statistics E.400E.409 International network man
6、agement E.410E.419 Checking the quality of the international telephone service E.420E.489 TRAFFIC ENGINEERING Measurement and recording of traffic E.490E.505 Forecasting of traffic E.506E.509 Determination of the number of circuits in manual operation E.510E.519 Determination of the number of circui
7、ts in automatic and semi-automatic operation E.520E.539 Grade of service E.540E.599 Definitions E.600E.649 Traffic engineering for IP-networks E.650E.699 ISDN traffic engineering E.700E.749 Mobile network traffic engineering E.750E.799 QUALITY OF TELECOMMUNICATION SERVICES: CONCEPTS, MODELS, OBJECTI
8、VES AND DEPENDABILITY PLANNING Terms and definitions related to the quality of telecommunication services E.800E.809 Models for telecommunication services E.810E.844 Objectives for quality of service and related concepts of telecommunication services E.845E.859 Use of quality of service objectives f
9、or planning of telecommunication networks E.860E.879 Field data collection and evaluation on the performance of equipment, networks and services E.880E.899 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. E.681 (10/2001) i ITU-T Recommendation E.681 Traffic engineer
10、ing methods for IP access networks based on hybrid fiber/coax system Summary This Recommendation describes generic preferred methods for the traffic control and dimensioning of IP-access networks based on hybrid fiber/coax (HFC) system, taking into account the capabilities and limitations of the cab
11、le-modem based access technology. The main focus is on the provision over HFC system of IP telephony service in an integrated voice/data environment. Factors affecting system capacity for the support of voice connections are described. Topics discussed include the dimensioning of a single upstream c
12、hannel, upstream channel pooling, and interoperability between DOCSIS 1.0 and DOCSIS 1.1. Source ITU-T Recommendation E.681 was prepared by ITU-T Study Group 2 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 October 2001. ii ITU-T Rec. E.681 (10/2001) FOREWORD The International
13、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, operating and tariff questions and issuing Recommendations on
14、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 approval of IT
15、U-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 “Administration“ is us
16、ed for conciseness to indicate 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 t
17、akes no position concerning the 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 received notice of intellectual propert
18、y, protected by patents, 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 b
19、e reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. E.681 (10/2001) iii CONTENTS Page 1 Scope 1 2 References. 1 2.1 Normative references 1 2.2 Non-normative references 2 3 Definitions 2 4 Abbreviations 2 5 Introduction 2 6 Grade of Service parameters. 4 7 T
20、raffic engineering considerations . 4 7.1 Factors affecting upstream capacity . 4 7.1.1 Channel characteristics. 5 7.1.2 Protocol features. 5 7.1.3 Propagation delay . 5 7.2 Protocol for upstream transmission 5 8 Dimensioning of a single upstream 6 8.1 Voice capacity 6 8.2 Available capacity for dat
21、a. 6 9 DOCSIS 1.0 and DOCSIS 1.1 interoperability 7 10 Upstream channel pooling 8 10.1 Immediate upstream channel change 8 10.2 Voice slot jitter . 8 10.3 Assignment algorithms. 8 11 History 10 Appendix I Example calculation of upstream channel capacity. 10 Appendix II Example of jitter window. 11 I
22、TU-T Rec. E.681 (10/2001) 1 ITU-T Recommendation E.681 Traffic engineering methods for IP access networks based on hybrid fiber/coax system 1 Scope This Recommendation describes generic preferred methods for the traffic control and dimensioning of IP-access networks based on hybrid fiber/coax (HFC)
23、system, taking into account the capabilities and limitations of the cable-modem based access technology. It contains relevant traffic principles for the planning, operation, and management of HFC-based IP-access networks so that quality of service (QOS) objectives to customers can be met. For traffi
24、c engineering, this Recommendation assumes that the network is available: that is, it does not consider network equipment in a failure state. The first release of this Recommendation is only concerned with the provision over HFC system of IP telephony service in an integrated voice/data environment.
25、 While the impact of voice service on the capacity available for data is considered, traffic-engineering methods for TCP/IP-supported data services such as web-browsing, email, file transfer, and high-speed data access are for further study. Other services such as video telephony, video-on-demand, a
26、re also for further study. 2 References 2.1 Normative 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 publication, the editions indicated were valid. All Recomme
27、ndations 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 of the currently valid ITU-T Recommendations is regularly p
28、ublished. ITU-T Recommendation E.526 (1993), Dimensioning a circuit group with multi-slot bearer services and no overflow inputs. ITU-T Recommendation E.651 (2000), Reference connections for traffic engineering of IP access networks. ITU-T Recommendation E.721 (1999), Network grade of service parame
29、ters and target values for circuit-switched services in the evolving ISDN. ITU-T Recommendation E.726 (2000), Network grade of service parameters and target values for B-ISDN. ITU-T Recommendation G.114 (2000), One-way transmission time. ITU-T Recommendation G.711 (1988), Pulse code modulation (PCM)
30、 of voice frequencies. ITU-T Recommendation G.728 (1992), Coding of speech at 16 kbit/s using low-delay code excited linear prediction. ITU-T Recommendation J.112 (1998), Transmission systems for interactive cable television services. 2 ITU-T Rec. E.681 (10/2001) 2.2 Non-normative references The fol
31、lowing references are listed here for information: DOCSIS 1 Data-Over-Cable Service Interface Specifications, Radio Frequency Interface Specification 1.0, SP-RFI-I05-991105, Cable Television Laboratories, Inc., November 1999. DOCSIS 2 Data-Over-Cable Service Interface Specifications, Radio Frequency
32、 Interface Specification 1.1, SP-RFIv1.1-I07-010829, Cable Television Laboratories, Inc., August 2001. DOCSIS 3 Data-Over-Cable Service Interface Specifications, Cable Modem to Customer Premises Equipment Interface Specification, SP-CMCI-I05-001215, Cable Television Laboratories, Inc., December 2000
33、. 3 Definitions This Recommendation defines the following terms: 3.1 A cable modem (CM) is a modulator-demodulator at subscriber locations intended for use in conveying data communications on a cable television system. 3.2 A cable modem termination system (CMTS), located at the cable television syst
34、em headend or distribution hub, provides complementary functionality to the cable modems to enable data connectivity to a wide-area network. 3.3 A fiber node is a point of interface between a fiber trunk and the coaxial distribution. 3.4 A hybrid fiber/coax (HFC) system is a broadband bi-directional
35、 shared-media transmission system using fiber trunks between the headend and the fiber nodes, and coaxial distribution from the fiber nodes to the customer locations. 4 Abbreviations This Recommendation uses the following abbreviations: CM Cable Modem CMTS Cable Modem Termination System CPE Customer
36、 Premises Equipment GoS Grade of Service HFC Hybrid Fiber/Coax system IP Internet Protocol MTA Multi-media Terminal Adapter QoS Quality of Service TCP Transmission Control Protocol 5 Introduction This Recommendation uses the reference architecture of IP access networks based on hybrid fiber/coax sys
37、tems as specified in 7.1/E.651. For convenience, Figure 7-1/E.651 is reproduced below as Figure 5-1. ITU-T Rec. E.681 (10/2001) 3 T0209350-02MTACPEMTACPEPSTN/ISDNcable cablefiberphonephoneEdgerouterCablemodemterminationsystemIP corenetworkPSTN/ISDNgatewayFibernodeCablemodemCablemodemHFC-based IPacce
38、ss networklocalIPFigure 5-1/E.681 Reference architecture of an HFC-based IP access network This figure shows an HFC-based IP-access network with cable modems (CMs) located at customer premises connected to a cable modem termination system (CMTS) at the head-end. The HFC distribution plant includes f
39、iber links between a CMTS and a fiber node, with the latter performing optical/electrical conversion. Coaxial cable is used to connect multiple customer premises in close proximity to the fiber node. Customer-premises equipment, such as a personal computer, can interface directly with a CM. An ordin
40、ary telephone is usually interfaced through a multi-media terminal adapter (MTA) to a CM. The MTA may be integrated with the CM. Through a managed local IP network and an edge router, an HFC-access network is connected to an IP core network for either Internet access or all-IP end-to-end telephone c
41、alls. Connection is also provided via a gateway for interworking with PSTN/ISDN for telephone calls. The edge router may be integrated with the CMTS and routes the traffic over the local IP network. It may also perform traffic policing and, optionally, admission control functions. The local IP netwo
42、rk contains all the network elements/servers required for connection management and call processing. A CMTS and a CM transfer IP traffic by using the Data-Over-Cable Service Interface Specifications, Radio Frequency Interface Specification, Version 1.1 DOCSIS 2. This specification is commonly referr
43、ed to as DOCSIS 1.1. An earlier version, DOCSIS 1.0 DOCSIS 1, was originally developed to support best-effort high-speed data service. Traffic engineering issues related to the interoperability between these two versions is addressed in clause 9. 4 ITU-T Rec. E.681 (10/2001) 6 Grade of Service param
44、eters In this clause, GoS parameters that are relevant for traffic engineering purposes are listed. Their definitions and target values are the subject of a future Recommendation. For IP telephony, the following traffic GoS parameters at the call level are recommended: 1) probability of call blockin
45、g; 2) post-selection delay; 3) answer-signal delay; 4) call-release delay. NOTE 1 These parameters are functionally similar to the corresponding ones specified in ITU-T Recs E.721 and E.726. NOTE 2 In the context here, answer-signal delay is functionally equivalent to post pick-up delay. That is, th
46、e interval from the time when the terminating phone is picked up (after ringing) to the time when the end-to-end voice path to the originating phone is established. This interval is specified to avoid the “clipped hello“. After call establishment, for information transfer, the term packet refers to
47、a packet containing one or more voice samples. In this phase, the following traffic GoS parameters are recommended: 1) speech transmission delay (including packetization delay and one-way packet transfer delay); 2) packet delay variation, also referred to as jitter; 3) packet loss (average and burst
48、 loss). NOTE 3 These parameters are functionally similar to the corresponding cell-level GoS parameters specified in ITU-T Rec. E.726. 7 Traffic engineering considerations In an HFC system, two-way interactivity is accomplished by augmenting a cable-TV broadcast network with a return path in the ups
49、tream direction (i.e. a path from the customer to the network). However, due to the relatively small part of the spectrum allocated for upstream use (for compatibility with TV broadcasts) and the noise characteristics therein, the bandwidths available in the two directions are asymmetrical with the upstream bandwidth being much more limited than the downstream. Because of this asymmetry, a CMTS usually associates one downstream channel with multiple (typically up to eight) upstream channels. However, a CM can only access one
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