Network Working Group P. Kim Internet-Draft Korea Polytechnic University Intended status: Experimental H. Han Expires: September 1, 2010 KUT February 28, 2010 A Mechanism for Available Capacity Estimation draft-pskim-ippm-capaest-00.txt Abstract In this draft, a mechanism for available capacity estimation of an end-to-end path is proposed to improve the estimation accuracy compared with the existing IGI(Initial Gap Increasing)/PTR(Packet Transmission Rate) mechanism. The proposed mechanism defines three cases of the difference between the average output gap and the input gap, and then reflects fully them, while the existing mechanism reflected only two cases. Since three cases are handled respectively by appropriate corresponding manners, the proposed mechanism can be expected to reduce the detection error for the turning point. Therefore, the end-to-end available capacity can be estimated more accurate than the existing mechanism. 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Copyright Notice Kim & Han Expires September 1, 2010 [Page 1] Internet-Draft A Mechanism for Available Capacity Estimation Feb 2010 Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Proposed Scheme . . . . . . . . . . . . . . . . . . . . . . . 3 2.1 IGI/PTR Mechanism . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Measuring Bottleneck Link Capacity . . . . . . . . . . . . . 4 2.3 Estimating Available Path Capacity . . . . . . . . . . . . . 5 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 4. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Normative References . . . . . . . . . . . . . . . . . . 7 4.2. Informative References . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction Understanding the dynamic properties of the end-to-end IP performance metrics, such as capacity, delay, jitter, packet loss, is beneficial for the proper resource management in existing wired and emerging wireless Internet services[IEEE21][FMIPv6-MIH]. The increasing trend in the wireless Internet services means that the requested performance for a certain service might not be guaranteed, not only because of the air interface bandwidth limitation, but also due to a limitation in the transport network's available capacity. Measuring IP performance metrics is a very challenging task due to the heterogeneity of the current systems and the different traffic characteristics of different data flows[RFC2330]. In the recent decade, the IP Performance Metrics (IPPM) working group defined a set of standard metrics and has developed schemes for accurately measuring these performance metrics. Among them, this draft considers the available capacity measurement[RFC5136]. The available capacity of an end-to-end path is its remaining capacity, that is, the amount of traffic that can be sent along the path without congesting it. This available capacity between two hosts is an important network parameter for improving Quality of Service (QoS) in many distributed applications, such as the overlay construction of peer to peer system, optimization of resource utilization, Kim & Han Expires September 1, 2010 [Page 2] Internet-Draft A Mechanism for Available Capacity Estimation Feb 2010 optimization of dynamic server selection, socket buffer sizing, admission control, and congestion control. Therefore, recently, the area of end-to-end available capacity estimation has attracted considerable interest. As a result, several mechanisms for the available capacity estimation have been developed based on active measurements[Hu]. Among existing mechanisms for available capacity estimation, the IGI(Initial Gap Increasing)/PTR(Packet Transmission Rate) mechanism has been proposed recently[Hu]. The ultimate objective is to experimentally determine the input gap value at some point for which the average output gap is equal to the input gap. At this point, the probing packets are considered to interleave nicely with the competing traffic, and the average rate of the packet train equals the available capacity on the bottleneck link. This point is called the "turning point". At the turning point, the input gap value for which the average output gap is equal to the input gap is the right value to use for estimating the available capacity. However, there are some issues in the existing IGI/PTR mechanism. After performing a measurement, three cases can be defined according to the difference between the average output gap and the input gap. These three cases have respectively different relationship between the average rate of the probing packet train and the available capacity. However, the existing mechanism did not reflect fully these three cases in order to reduce the detection latency of the turning point. That is, two of three cases are handled in the same way, which can introduce the detection error for the turning point since these two cases handled in the same way are absolutely different. Thus, the available capacity can be estimated inaccurately although the measurement latency can be reduced. Therefore, to reduce the detection error of the turning point and enhance the accuracy of the available capacity estimation, a new mechanism is proposed based on the IGI/PTR mechanism. The proposed mechanism reflects fully three cases, while the existing mechanism reflected only two cases. Since three cases are handled respectively by appropriate corresponding manners, the proposed mechanism can be expected to reduce the detection error for the turning point. Therefore, the end-to-end available capacity can be estimated more accurate than existing mechanism. In order to verify the proposed mechanism and to compare with the existing mechanism, experiments are performed, which shows the proposed mechanism is more accurate than the existing mechanism. 2. Proposed Mechanism 2.1 Existing IGI/PTR Mechanism More recently, the IGI(Initial Gap Increasing)/PTR(Packet Kim & Han Expires September 1, 2010 [Page 3] Internet-Draft A Mechanism for Available Capacity Estimation Feb 2010 Transmission Rate) mechanism was proposed for the available capacity estimation and shown to be much faster than existing mechanisms with similar measurement accuracy but with shorter measurement latency. This mechanism is based on a single-hop gap model that captures the relationship between the competing traffic and the probing packet train. As a sequence of probing packet trains from the source travel through the network, packets belonging to the competing traffic may be inserted between them, thus increasing the gap at the destination. As a result, the average output gap value at the destination may be a function of the competing traffic rate, making it possible to estimate the amount of competing traffic. That is, the average output gap can be used to determine the competing traffic capacity and hence the available capacity on the end-to-end path assuming that the bottleneck link capacity along the end-to-end path is known. At some point, the average output gap equals the input gap as gaps in a probing packet train increase. This point is called the "turning point". At the turning point, the input gap value for which the average output gap is equal to the input gap is the right value to use for estimating the available capacity. However, there are some issues in the existing IGI/PTR mechanism. After performing the measurement, three cases are defined according to the difference between the average output gap and the input gap. These three cases mean that the average output gap at the destination is (a) larger than, (b) equal to, (c) less than the input gap at the source. These three cases have respectively different relationship between the average rate of the probing packet train and the available capacity. However, the existing mechanism did not reflect fully these three cases in order to reduce the measurement latency. That is, both (b) and (c) cases are handled in the same way, which can introduce the detection error for the turning point since (b) and (c) cases are absolutely different. Therefore, the available capacity can be estimated inaccurately although the measurement latency can be reduced. In this draft, a new mechanism for available capacity estimation mechanism is proposed to improve the estimation accuracy compared with the existing mechanism. As mentioned before, since (b) and (c) cases handled in the same way are absolutely different, they should be handled by respectively. 2.2 Measuring Bottleneck Link Capacity As shown in [Hu], the end-to-end available capacity is defined as the difference between the bottleneck link capacity along an end-to-end path and the competing traffic. The bottleneck link capacity in the path determines the end-to-end capacity which is the maximum IP layer rate that the path can transfer from source to Kim & Han Expires September 1, 2010 [Page 4] Internet-Draft A Mechanism for Available Capacity Estimation Feb 2010 destination. In other words, the capacity of a path establishes an upper bound on the IP layer throughput that a user can expect to get from that path. There are diverse measurement mechanisms for the bottleneck link capacity. Therefore, the bottleneck link capacity can measured from one of existing mechanisms. 2.3 Estimating Available Path Capacity There are several important probing parameters such as probing packet size, number of probing packet in packet train, and input gap to get correct measurement. Among them, input gap in a probing packet train is the most important parameter to control for accurate available capacity estimation. The source sends a sequence of probing packet trains with adjusting input gap. The difference between the average output gap and the input gap is observed for each train. Then, the turning point is detected for estimating the available capacity. (a) Detection of turning point After performing a measurement, three cases are defined according to the difference between the average output gap and the input gap. Three cases are called 'Red', 'Yellow', 'Green' cases which have respectively different relationship between the average rate of the probing packet train and the available capacity as follows: - Red : The average rate of the packet train is more than the available capacity with the following condition: average output gap > input gap + delta/2. - Yellow : The average rate of the packet train is similar to the available capacity with the following condition: |average output gap - input gap | < delta. - Green : The average rate of the packet train is less than the available capacity with the following condition: average output gap < input gap - delta/2. Above three cases are handled respectively as follows: (1) Handling of 'Red' case The measurement is repeated with the increased input gap. After then, three cases observed once again. For each case, the measurement is repeated with adjusting input gap as follows: Kim & Han Expires September 1, 2010 [Page 5] Internet-Draft A Mechanism for Available Capacity Estimation Feb 2010 - Red : increased input gap - Yellow : same input gap as previous measurement - Green : decreased input gap In the existing mechanism, the measurement is repeated with the same input gap as previous measurement for 'Green' case. (2) Handling of 'Yellow' case The measurement is repeated with the same input gap as previous measurement. After then, three cases are observed once again and then handled respectively as follows: - Red : measurement with increased input gap - Yellow : measurement finished (turning point detected) - Green : measurement with decreased input gap In the existing mechanism, the measurement is finished for 'Green' case. (3) Handling of 'Green' case The measurement is repeated with the decreased input gap. In the existing mechanism, the measurement is repeated with the same input gap in this case. After then, three cases are observed once again and then handled respectively as follows: - Red : measurement with increased input gap - Yellow : measurement finished (turning point detected) - Green : measurement with decreased input gap In the existing mechanism, the measurement is finished for 'Green' case. As shown in three cases, the proposed mechanism handles 'Yellow' and 'Green' cases respectively while the existing mechanism handles them in the same way. (b) Computing available capacity When the turning point is detected, the measurement is finished and then the end-to-end available capacity can be estimated as follows. The end-to-end available capacity is obtained by subtracting the competing traffic capacity from the bottleneck link capacity. As mentioned before, the bottleneck link capacity can be measured from one of existing mechanisms. Then, the competing traffic capacity can be computed using the average output gap and the input gap at the turning point, and the bottleneck link capacity. Kim & Han Expires September 1, 2010 [Page 6] Internet-Draft A Mechanism for Available Capacity Estimation Feb 2010 3. IANA Considerations This document has no IANA actions. 4. References 4.1. Normative References [RFC2330] V. Paxson, G. Alimes, J. Mahdavi and M. Mathis, "Framework for IP Performance Metrics," IETF RFC 2330, May 1998. [RFC5136] P. Chimento, J. Ishac, "Defining Network Capacity," IETF RFC 5136, Feb 2008. 4.2. Informative References [IEEE21] IEEE802.21/D09.00, "Draft standard for local and metropolitan area networks : Media independent handover services," Feb 2008. [FMIPv6-MIH] Q. B. Mussabbir, W. Yao, "Optimized FMIPv6 handover using IEEE 802.21 MIH services in vehicular networks," IEEE Trans. on Vehicular Technology, Vol. 56, No. 6, pp. 3397~3407, 2007. [Hu] N. Hu and P. Steenkiste, "Evaluation and characterization of available bandwidth probing techniques," IEEE JSAC, Vol. 21, No. 6, pp. 879-894, 2003. Author's Address Pyungsoo Kim Department of Electronics Engineering, Korea Polytechnic University, 2121 Jungwang-Dong, Shiheung City, Gyeonggi-Do 429-793 KOREA Phone: +82 31 8041 0489 EMail: poongdou@gmail.com Youn-Hee Han KUT Gajeon-Ri, 307, Byeongcheon-Myeon Cheonan, Chungnam KOREA Phone: +82 41 560 1486 Email: yhhan@kut.ac.kr Kim & Han Expires September 1, 2010 [Page 7]