A New Available Bandwidth Measurement Method Based on Self-Loading Periodic Streams Yufeng Xiao, Shanzhi Chen, Xin Li, Yuhong Li Broadband Network Research Center, State Key Laboratory of Networking and Switching, Beijing University of Posts and Telecommunications, Beijing, China
[email protected] Abstract—We present a new available bandwidth measurement method based on Self-Loading Periodic Streams (SLoPS) in this paper. SLoPS sends probe stream at specific rate and estimates the available bandwidth from the inference of self-induced congestion. Contrary to traditional SLoPS method, the new method infers the congestion from a parameter named interval difference, not end-to-end delays. In probing scheme, the new method exponentially adjust probe rate to demarcate a rough bandwidth range and constringe the rate to available bandwidth value with quick search in the rough range. Since it uses only interval times of packets, our method does not require high timestamping accuracy nor synchronous at the sender and receiver. We test our method in controlled and reproducible environment using NS2, and the simulation experiments show our method is accurate, quick and non-intrusive. Keywords- available bandwidth; network measurement;
I.
INTRODUCTION
For many network applications, it is important to infer the available bandwidth of the network path. Knowledge of the available bandwidth can improve streaming applications such as VoIP, optimize routing decisions, enhance traffic engineering, and verify service level agreement. There are two ways to measure the available bandwidth. One way is direct probing [1], which bases on the assumption that the tight link bandwidth is known. Delphi is a tool worked in this way [1]. The other way is iterative probing, which based on the relation between the probing rate and available bandwidth. There are two types of tools work in this way, which named TOPP (Trains of Packet Pairs) and SLoPS. The TOPP not only estimate the available bandwidth, but also measure the capacity of the tight link. Pathload and Pathchirp are both SLoPS tools [2,3,4]. Pathload sends periodic packet streams while pathChirp sends chirp that composed of packets with exponentially increasing interarrivals between successive packets [1]. Additionally, to improve available bandwidth estimation, some models based on statistical analysis have been presented. For example, Haga proposed a model makes uses of three parameters composed of physical bandwidth, the available bandwidth and the weighted average of the packet size of the cross traffic [5]. .Although these tools can estimate the available bandwidth, they face the common problems as follows. Firstly, they sent
too many probing packets in measurement, which cost large amount of network resource. In low bandwidth network, the great mount of probing loads will influence the other traffic. Secondly, they take too much time to estimate the available bandwidth. Thirdly, they require the high resolution and accuracy in time-stamping probe packets for ensuring the accuracy, which make them face increasingly challenges as link speeds increase and network functionality grows more complex [6,7]. In this paper, we present a new method based on SLoPS. SLoPS sends probe stream at specifically rate and estimates the available bandwidth from the inference of self-induced congestion. Contrary to traditional SLoPS method, the new method infers the congestion from a parameter named interval difference, not end-to-end delays. In our method, a TCP connection is initially established between sender and receiver; through this connection, the sender of probe packet transfers message with the value of current sending interval to the receiver; getting the message, the receiver calculates the interval difference; through the TCP connection, the receiver returns a message with the value of interval difference to the sender; getting knowledge of the interval difference, the sender can determine whether the probe rate is beyond the available bandwidth and adjusts the range of probe rate. In probing scheme, the new method exponentially adjust the probe rate to demarcate a rough bandwidth range and constringe the rate to bandwidth value with quick search in the rough range. Thus, the probe rate can fast converge to the available bandwidth value. The algorithm for the calculation of interval difference and two algorithms for probing scheme will be detailed in following sections. The new method overcomes some of the common problems of existing bandwidth probing methods in this way: firstly, it requires fewer overheads than the other methods; secondly, with the aid of probing schemes, it provides a fast and some accurate available bandwidth estimation for short-term decisions; thirdly, it needs not to timestamp the packets, and has not the requirement of high time-stamping accuracy [6]. The rest of this paper is organized as follows. In Section II, we present our measurement method based on SLoPS. In Section III, we use the simulation experiments to verify the method. In Section IV, we summarize our work and give the direction of further job.
This research is supported by National Natural Science Foundation of China (60672086), the state 863 high-tech program of China (2006AA01Z229) and the Ministry of Education Foundation for Western Returned Chinese Scholars.
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Figure 1.
II.
1) CA – Rc ı R: Using the packet-pair property in the available bandwidth measurement, the sending interval of interpacket will be preserved over all links [8]. Then, there is the result that Ƹs is equal to Ƹr , expressed as Ƹs =Ƹr. 2) CA – Rc˘R: Using the following deduction, S ½ S ∆s = °° ∆ C − Rc R s R = = A ¾ S S S R ∆ r ° ∆r = = A C A − Rc °¿ C A − Rc
Measurement model
Then, there is the result that Ƹs is less than Ƹr.
THE NEW AVAILABLE BANDWIDTH MEASUREMENT METHOD BASED ON SLOPS
In the following section, we assume that the network path consists of N hops; the two ends of the path are called source end and destination end. Along this path, the probing streams are sent from source to destination. Our method consists of three algorithms: demarcating bandwidth range, approaching bandwidth value and determining the relation between sending interval and receiving interval. A. Available Bandwidth Definition The available bandwidth of a link is the unused capacity of the link during a certain period. If an end-to-end path consists of N links, the available bandwidth is the minimum available bandwidth of these links. The link with the minimum is called tight link. The formula below is a simple definition of the path available bandwidth:
A = min Ai i =1,..., N
(1)
Where Ai is the available bandwidth of ith link, A is the available bandwidth on the path. B. Measurement Model In the method, UDP packets are sent from a source node to a destination node along the end-to-end path. Initially, a TCP connection between the two ends is established to deliver message with the value of current sending interval, message with the value of interval difference, the abortion or finality of the measurement. In Fig. 1, R is the sending rate, A is available bandwidth of the path, Ƹs is the sending interval between the packets at the source, Ƹr is the receiving interval between the packets at the tight link, RC is the rate of cross traffic, S is the size of probing packets, and CA is the bandwidth of tight link of the end-to-end path. According to bottleneck principle [8], the Ƹ r will be preserved to the destination. The method is constructed on the fact: If available bandwidth is larger than the sending rate, the sending interval is equal to receiving interval; if available bandwidth is less than the sending rate, the sending interval will become less than receiving interval. This fact can be present in the expression: If CA – RCı R, then Ƹs = Ƹr; If CA – RC ˘ R, then Ƹs < Ƹr. We deduce it as below:
C A − Rc < R ∆ s C A − Rc = R ∆r
C A − Rc ½ < 1° R ° ∆s R , F(X ) = ® °¯0, Oi a ≤ R
3
C
C
C
cross traffic source
C
dst C
cross traffic source
Figure 3. The simulation network
If Ƹs
