1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T Y.1540 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1 (01/2016) SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Quality of service a
2、nd network performance Internet protocol data communication service IP packet transfer and availability performance parameters Amendment 1: New Appendix IX Explanation of TCP-based measurement inadequacy to meet normative requirements Recommendation ITU-T Y.1540 (2011) Amendment 1 ITU-T Y-SERIES REC
3、OMMENDATIONS GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS GLOBAL INFORMATION INFRASTRUCTURE General Y.100Y.199 Services, applications and middleware Y.200Y.299 Network aspects Y.300Y.399 Interfaces and protocols Y.400Y.499 Numbering, addressing and naming
4、 Y.500Y.599 Operation, administration and maintenance Y.600Y.699 Security Y.700Y.799 Performances Y.800Y.899 INTERNET PROTOCOL ASPECTS General Y.1000Y.1099 Services and applications Y.1100Y.1199 Architecture, access, network capabilities and resource management Y.1200Y.1299 Transport Y.1300Y.1399 In
5、terworking Y.1400Y.1499 Quality of service and network performance Y.1500Y.1599 Signalling Y.1600Y.1699 Operation, administration and maintenance Y.1700Y.1799 Charging Y.1800Y.1899 IPTV over NGN Y.1900Y.1999 NEXT GENERATION NETWORKS Frameworks and functional architecture models Y.2000Y.2099 Quality
6、of Service and performance Y.2100Y.2199 Service aspects: Service capabilities and service architecture Y.2200Y.2249 Service aspects: Interoperability of services and networks in NGN Y.2250Y.2299 Enhancements to NGN Y.2300Y.2399 Network management Y.2400Y.2499 Network control architectures and protoc
7、ols Y.2500Y.2599 Packet-based Networks Y.2600Y.2699 Security Y.2700Y.2799 Generalized mobility Y.2800Y.2899 Carrier grade open environment Y.2900Y.2999 FUTURE NETWORKS Y.3000Y.3499 CLOUD COMPUTING Y.3500Y.3999 INTERNET OF THINGS AND SMART CITIES AND COMMUNITIES General Y.4000Y.4049 Definitions and t
8、erminologies Y.4050Y.4099 Requirements and use cases Y.4100Y.4249 Infrastructure, connectivity and networks Y.4250Y.4399 Frameworks, architectures and protocols Y.4400Y.4549 Services, applications, computation and data processing Y.4550Y.4699 Management, control and performance Y.4700Y.4799 Identifi
9、cation and security Y.4800Y.4899 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T Y.1540 (2011)/Amd.1 (01/2016) i Recommendation ITU-T Y.1540 Internet protocol data communication service IP packet transfer and availability performance parameters Amendment 1 New Appe
10、ndix IX Explanation of TCP-based measurement inadequacy to meet normative requirements Summary Amendment 1 to Recommendation ITU-T Y.1540 adds Appendix IX, which clarifies the Recommendations status as a measurement method by comparing the TCP protocol to the requirements given in clause 6.12 of the
11、 Recommendation. Readers of the Recommendation may find it useful to understand the implications of the normative requirements given in clause 6.12 when considering measurement methodologies, especially those based on available implementations of the TCP protocol. While TCP-based measurements are co
12、nsidered useful for informative surveys of user experience, they do not constitute the basis for standard metrics, methods of measurement or numerical objectives. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T I.380 1999-02-26 13 11.1002/1000/4573 1.0 ITU-T Y.1540 1999-02-2
13、6 13 11.1002/1000/5302 2.0 ITU-T Y.1540 2002-12-14 13 11.1002/1000/6189 2.1 ITU-T Y.1540 (2002) Amd. 1 2003-08-01 13 11.1002/1000/6975 3.0 ITU-T Y.1540 2007-11-13 12 11.1002/1000/9270 3.1 ITU-T Y.1540 (2007) Amd.1 2009-03-19 12 11.1002/1000/9727 4.0 ITU-T Y.1540 2011-03-01 12 11.1002/1000/11079 4.1
14、ITU-T Y.1540 (2011) Amd.1 2016-01-21 12 11.1002/1000/12761 * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T Y.1540 (2011)/Amd.
15、1 (01/2016) FOREWORD The International Telecommunication Union (ITU) is the United 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 responsi
16、ble for studying technical, 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-
17、T study groups which, in turn, 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
18、basis with ISO and IEC. NOTE 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 mandat
19、ory provisions (to ensure, e.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
20、 use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTSITU 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
21、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 property, pr
22、otected by patents, which 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 2016 All rights reserved. No par
23、t of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T Y.1540 (2011)/Amd.1 (01/2016) 1 Recommendation ITU-T Y.1540 Internet protocol data communication service IP packet transfer and availability performance parameters Amendment 1 Ne
24、w Appendix IX - Explanation of TCP-based measurement inadequacy to meet normative requirements (This appendix does not form an integral part of this Recommendation.) IX.1 Introduction Readers of this Recommendation may find it useful to understand the implications of the normative requirements in cl
25、ause 6.12 of the Recommendation when considering measurement methodologies, especially those based on available implementations of the TCP protocol. While TCP-based measurements are considered useful for informative surveys of user experience, they do not constitute the basis for standard metrics, m
26、ethods of measurement or numerical objectives. Comparison of TCP protocol with the requirements of clause 6.12 in this appendix clarifies its status as a measurement method. IX.2 Comparison with normative requirements The requirements in clause 6.12 are organized in two numbered lists. The first req
27、uirement list is for all parameters, and the second list is for parameters that assess the ability to sustain a given IP packet transfer rate. For the first list of requirements (all parameters): 1) Regarding the required accounting for packet delivery into the network and successful transfer: Some
28、versions of TCP may make available the count of re-transmitted segments during a connection (through a management interface), but retransmissions are based on the adaptive retransmission time out (RTO), not on whether the packets were actually lost, or are acknowledged after the time out expires, or
29、 whether an ACK was lost following successful delivery. TCP receivers do not distinguish whether the original or retransmitted (or both) packets arrive successfully. Furthermore, different TCP congestion control algorithms vary in their methods to achieve fairness to other flows and throughput, resu
30、lting in a larger number of lost packets when aggressive algorithms are used, or resulting in unnecessarily lower sending rates when packet losses are incorrectly interpreted as a signal of congestion (note the fixed mapping of packet loss interpreted as congestion in TCP flow control). 2) Regarding
31、 the required ability to measure partial paths: TCPs congestion control is highly sensitive to round-trip-time (RTT) in non-linear and sometimes unexpected ways. Thus, a TCP-based measurement on a partial path (EL or NS) will not typically predict the performance of a complete path, and TCPs depende
32、nce on RTT is one key reason. For the list of requirements for assessment of sustained packet rate: 1) Regarding the required description of the traffic pattern offered to the network: TCP slow-start and congestion avoidance phases determine the sending pattern, and these patterns vary widely accord
33、ing to the conditions on the path, especially the presence of cross-traffic and characteristics of any bottlenecks encountered. Thus, the pattern is difficult or impossible to constrain or predict with TCPs flow control operating. 2 Rec. ITU-T Y.1540 (2011)/Amd.1 (01/2016) 2) Regarding the requireme
34、nt to limit traffic rate to less than the capacity of connecting links: TCPs flow control continues to test for available capacity, assuming that conditions may change. It is not practical to limit a TCP sender to an exact capacity using the parameters available, partly due to the variation of RTT d
35、uring the life of a TCP connection. In other words, TCP can always send traffic at a rate that exceeds connecting links. Note that all difficulties caused by TCP flow control are further exacerbated by operating multiple simultaneous TCP connections, each independently evaluating their connection on
36、 the same path. In conclusion, the transport protocol is determined and implemented in user hosts, and outside the purview of IP-based packet transfer service providers. Standard assessments of the service provider performance should avoid the contribution of layers that are chosen by others and mus
37、t meet the normative requirements of clause 6.12 of this Recommendation. Printed in Switzerland Geneva, 2016 SERIES OF ITU-T RECOMMENDATIONS Series A Organization of the work of ITU-T Series D General tariff principles Series E Overall network operation, telephone service, service operation and huma
38、n factors Series F Non-telephone telecommunication services Series G Transmission systems and media, digital systems and networks Series H Audiovisual and multimedia systems Series I Integrated services digital network Series J Cable networks and transmission of television, sound programme and other
39、 multimedia signals Series K Protection against interference Series L Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant Series M Telecommunication management, including TMN and network maintenance
40、 Series N Maintenance: international sound programme and television transmission circuits Series O Specifications of measuring equipment Series P Terminals and subjective and objective assessment methods Series Q Switching and signalling Series R Telegraph transmission Series S Telegraph services te
41、rminal equipment Series T Terminals for telematic services Series U Telegraph switching Series V Data communication over the telephone network Series X Data networks, open system communications and security Series Y Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities Series Z Languages and general software aspects for telecommunication systems
