WO2006067768A1 - Procede et systeme destines a reconstruire des exigences de bande passante de flux de trafic avant la formation tout en observant passivement le trafic forme - Google Patents

Procede et systeme destines a reconstruire des exigences de bande passante de flux de trafic avant la formation tout en observant passivement le trafic forme Download PDF

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Publication number
WO2006067768A1
WO2006067768A1 PCT/IE2004/000175 IE2004000175W WO2006067768A1 WO 2006067768 A1 WO2006067768 A1 WO 2006067768A1 IE 2004000175 W IE2004000175 W IE 2004000175W WO 2006067768 A1 WO2006067768 A1 WO 2006067768A1
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traffic
aggregate
sub
analysing
aggregates
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PCT/IE2004/000175
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English (en)
Inventor
Raymond Russell
Dmitri Botvich
Donal O'sullivan
Matthew Charles Davey
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Corvil Limited
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Priority to PCT/IE2004/000175 priority Critical patent/WO2006067768A1/fr
Priority to US11/722,699 priority patent/US20080137533A1/en
Publication of WO2006067768A1 publication Critical patent/WO2006067768A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/12—Network monitoring probes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/10—Active monitoring, e.g. heartbeat, ping or trace-route
    • H04L43/106—Active monitoring, e.g. heartbeat, ping or trace-route using time related information in packets, e.g. by adding timestamps

Definitions

  • the present invention relates to communication networks and specifically to packet based data communication networks.
  • the invention relates to a method for quality of service measurement of traffic aggregates before shaping on the basis of passive traffic observations obtained post shaping.
  • a communication network is a collection of network elements interconnected so as to support the transfer of information from a user at one network node to a user at another.
  • the principal network elements are links and switches.
  • a link transfers a stream of bits from one end to another at a specified rate with a given bit error rate and a fixed propagation time.
  • rate at which a buffer is served is the service capacity, measured in bits per second.
  • Other common terms for service capacity are link-rate and bandwidth. The most important links are:
  • Switch a device that transfers bits from its incoming links to its outgoing links.
  • the name "switch" is used in telephony, while in computer communications, the device that performs routing is called a router; the terms are used interchangeably in this specification.
  • the receiver of each incoming link writes a packet of bits into its input buffer; the transmitter of each outgoing link reads from its output buffer.
  • the switch transports packets from an input buffer to the appropriate output buffer.
  • FIG. 1 An schematic example of such a network arrangement is shown in Figure 1 where a router 100 including an input buffer 110 and an output buffer 120 is used to couple one or more incoming links 130 with one or more outgoing links 140.
  • the quality of a communications network service varies greatly with the state of the network. To make packet-switched networks economically viable, it is necessary to be able to guarantee quality while reducing capital investment and operating expenses.
  • Degradation in the perceived quality of a service can often be traced back to loss or delay of data packets at a node or switch in the network. User satisfaction can be guaranteed by managing loss and delay of packets at those nodes where congestion can occur.
  • Loss and delay of data packets at a node in the network arise from the queuing of packets in the buffers of switches or routers. Buffers are required to cope with fluctuations in the bit-rate on incoming links. However, if the buffers are too small, packets will be lost as a result of buffer overflow; if the buffers are too large, some packets will experience unacceptable delays. For a given buffer-size, loss and delay can be reduced by increasing the capacity of the outgoing link. To eliminate packet loss entirely, it would be necessary to increase the capacity of the outgoing link to equal the sum of the capacities of the incoming links. This is prohibitively expensive. Nevertheless, it is a strategy employed sometimes by network operators who take a conservative view on assuring network quality of service.
  • QoS Quality of Service
  • BWR Bandwidth Requirement
  • a traffic aggregate is any grouping of network traffic.
  • An aggregate is usually defined using a packet filter.
  • a traffic aggregate may be defined by a variety of different parameters including the source, destination and type of traffic.
  • the traffic aggregate may be real in the sense that it could define all traffic arriving through a particular router.
  • a traffic aggregate could be artificial in the sense, for example, that it could comprise traffic being analysed for a possible reconfiguration on the network rather than a current implementation.
  • a traffic aggregate may be defined to investigate the possibility of changing router configuration or to investigate the possibility of installing a new router to handle some traffic from one or more existing routers.
  • the shaping of the aggregates is caused by, inter-alia, queuing, packet delay and jitter at routers, arising from a number of different reasons.
  • queuing packet delay and jitter at routers
  • packet delay packet delay and jitter at routers
  • router/switch internal procedures influence delays and jitter also. It is important to emphasize that by shaping, is meant practically everything that influences packet jitter and packet losses.
  • Traffic measurement typically involves using counters to record values such as, for example, the number of data packets and the volume of data moving along a link. These counters are periodically inspected and the values used in the measurement of statistical characteristics regarding the performance of the network. It will be appreciated that a variety of different statistical measurement techniques are available. Nonetheless, because of shaping effects the statistical characteristics of traffic aggregates are significantly changed when traffic aggregates traverse through network. These statistical characteristics include the statistical Quality of Service (QoS) parameters such as the Essential Bandwidth with loss and/or delay targets.
  • QoS Quality of Service
  • Specific statistical descriptors for the assignee/applicant of the present invention include CORVILTM traffic descriptors (CTD's) and CORVILTM essential bandwidth.
  • the so-called essential bandwidth is also sensitive to shaping as the peak rate used in its calculation is very sensitive to traffic shaping.
  • a description of the concept of essential bandwidth is contained in F.P.Kelly, S.Zachary and I.Zeidens, editors, Stochastic Networks: Theory and Applications, Royal Statistical Society Lecture Notes Series, Chapter 8, pp.141 -168, Oxford University Press, 1996, the entire contents of which are hereby incorporated by reference. It will be appreciated that a variety of different traffic descriptors and bandwidth measurement tools are employed by different suppliers and the present invention should not be construed as being limited to any particular method of calculation or implementation. As result of shaping the QoS related statistical characteristics of the same traffic aggregate are different before and after shaping, or more generally at different measurement points (i.e. the location of probes at different routers/switches).
  • the probe is located after router R1.
  • router R1 We are interested in the essential bandwidth measurements before router R1, i.e. on links (R2, R1), (R3, R1), (R4, R1).
  • the problem could be solved by increasing the number of locations with probes, i.e. such that there was a probe at each point of interest, there are both economic and technical reasons why this may not be possible or practical.
  • the cost of deploying probes in order to make QoS measurements may be uneconomic or certain areas of the network may be inaccessible to the company seeking to deploy the probes.
  • a first embodiment of the invention provides a method of analysing a traffic aggregate of packets in a network comprising the steps of: separating the traffic aggregate into a series of individual co-temporal sub- aggregates; and performing a measurement using the individual sub- aggregates of the series to obtain a statistical measure for the traffic aggregate.
  • the method may comprise the initial step of identifying the traffic aggregate.
  • This identification may be performed using a packet filter.
  • the method of separating the traffic aggregate is suitably selected so as to provide statistical independence vis a vis the sub-aggregates.
  • One method which provides statistical independence is the separating step is the use of a hash function to determine the appropriate sub-aggregate for a packet.
  • the hash function has x possible results where x is the number of sub-aggregates.
  • One possible hash function uses modulo division performed on the weighted sum of a plurality of fields from the packet header for of individual packets.
  • the plurality of fields may include one or more of the following: Source IP address, Source port number, destination IP address, destination port number and the TOS field.
  • the step of performing a measurement may comprises the steps of: calculating individual cumulant generating functions for each sub-aggregate, and summing the calculated individual cumulant generating functions to provide a combined cumulant generating function. This combined function provides a statistical measure for the traffic aggregate.
  • the step of performing a measurement using the individual sub-aggregates may comprise the step of time-shift multiplexing the sub-aggregates together to produce a reconstructed traffic aggregate, and performing a calculation on the reconstructed traffic aggregate to produce a traffic estimate.
  • each sub-aggregate is time-shifted by a different amount.
  • the method may additionally comprise the step of estimating a traffic congestion state on the network to provide an indicator for the reliability of the traffic estimate. This traffic congestion state may be calculated by determining a load level for the traffic.
  • the congestion state estimation also applies where there are a number of intervening points between the location of the point of measurement for the traffic aggregate and the actual traffic aggregate itself, in this case the traffic congestion state is determined at each of said intervening points.
  • a second embodiment of the invention provides a system for analysing traffic in a network comprising: a traffic aggregator for identifying a traffic aggregate of interest, a sub-aggregator for separating the traffic aggregate into a series of individual sub-aggregates, where each sub-aggregate and the aggregate are co-temporal, and a traffic measurement module for performing a measurement using the individual sub-aggregates of the series to obtain a statistical measure for the traffic aggregate.
  • the traffic aggregator comprises a packet filter.
  • the sub-aggregator may be adapted to separate the traffic aggregate with substantially statistical independence between sub- aggregates. The Separation may be through the use of a hash function for each packet in the aggregate.
  • the hash function suitably has x possible results where x is the number of sub-aggregates.
  • the hash function may comprise the implementation of a modulo division performed on the weighted sum of a plurality of fields from the packet headers of individual packets.
  • the plurality of fields include one or more of the following: source IP address, source port number, destination IP address, destination port number and the TOS field.
  • the traffic measurement module may be adapted to perform the steps of: calculating individual cumulant generating functions, and summing the calculated individual cumulant generating functions to provide a combined cumulant generating function which may function as a statistical measure for the traffic aggregate.
  • the traffic measurement module is adapted to calculate the individual cumulant generating functions using many sources asymptotics.
  • the traffic measurement module may be adapted to time-shift multiplex the sub-aggregates together to produce a reconstructed traffic aggregate and further adapted to calculate a traffic estimate from the reconstructed traffic aggregate.
  • the traffic measurement module is adapted to apply a different time shift to each sub- aggregate.
  • a congestion state module may be included to provide an indicator of the traffic congestion on the network.
  • the traffic congestion module may be adapted to determine said indicator by determining a load level for the traffic. In situations where there are a number of intervening points between the location of the point of measurement for the traffic aggregate and the actual traffic aggregate itself, the traffic congestion module may be adapted to determine said indicator by determining the traffic congestion state at each of said intervening points.
  • Figure 1 is a typical example of a router in a packet based network
  • Figure 2 is an exemplary first scenario where the present invention may be employed
  • Figure 3 is an exemplary second scenario where the present invention may be employed
  • Figure 4 is a further exemplary scenario where the present invention may be employed.
  • Figure 5 is a system according to an embodiment of the present invention
  • Figure 6 is a method according to an embodiment of the present invention
  • Figure 7 is a method according to another embodiment of the present invention
  • Figure 8 is a method according to a further embodiment of the present invention.
  • the present invention may be implemented in a number of different schemes including as part of a router ⁇ switch, for simplicity however the present invention will be described with reference to implementation as a passive probe tapped to a link of interest in a communications network.
  • the probe itself may be of any conventional design, since the invention lies in the method of analysis and not the method of acquisition.
  • the probe may be used to extract information from packets passing over the link, with the identification of the traffic aggregate and subsequent steps of the method being performed elsewhere on the basis of the information extracted by the probe.
  • the system 500 is shown as comprising a number of distinct modules. However, it will be appreciated that this is merely for the purposes of explaining the system. In practise, the elements and functionality of the system may be implemented within one or more systems in either software or hardware or a combination thereof.
  • the system comprises a probe 504 which is adapted to examine individual packets as they pass along a network path (link) 502.
  • the probe may be a standalone probe or, for example, integrated within the functionality of another network device, e.g. a router.
  • the probe suitably comprises a traffic aggregator adapted to identify and extract a traffic aggregate of interest. There are a variety of different methods for identifying a traffic aggregate, the most common of which is a packet filter 506.
  • the packet filter inspects the headers of packets and applies a filter function to identify an aggregate of interest.
  • the aggregate of interest is defined by the packet filter parameters.
  • the contents per se of the packets is not of significant interest. Instead, the size and quantity of packets is generally of more interest as these parameters are used to perform a measurement of the traffic.
  • the packet filter may be adapted to supply information on the packets rather than the packets themselves to subsequent parts of the system.
  • the packets (or as explained information regarding the packets) for the aggregate of interest are passed to a sub-aggregator 510, the function and operation of which will now be explained.
  • a key idea behind the present invention is related to the observation of the present inventors that if an aggregate is split into a number of individual sub-aggregates then individual sub-aggregates are likely to be less shaped than the aggregate. Accordingly, the inventors have applied this so that the traffic aggregate passed from the traffic aggregator to the sub-aggregator 510 is separates into a series of sub- aggregates. Some exemplary methods of operation of the traffic aggregator are explained below.
  • a sub-aggregate of a traffic aggregate consists of a portion of packets from the aggregate.
  • the number of sub-aggregates should be large enough for statistical purposes (ranges discussed below). It is also preferable that the individual sub-aggregates are sufficiently active and in particular it would be undesirable to have one sub-aggregate that dominates, for example in that sense it takes more than 50% of aggregate load.
  • the individual sub-aggregates and the aggregate are co- temporal. By co-temporal is meant that the period of measurements for the individual sub-aggregates and the aggregate are the same. Thus, for example, if the period of measurement for an aggregate is five minutes, the period of measurement for each of the individual sub-aggregates is also effectively the same five minutes.
  • the method of the invention commences with the probe identifying an aggregate of interest (Step 600). As described above, this may be by means of a packet filter.
  • traffic of the aggregate is examined and separated into sub-aggregates (step 602) by the sub-aggregator 510.
  • the sub-aggregator preferably employs an efficient method for sub-aggregation. It is advantageous, if the sub-aggregator only requires information which readily available to the probe, namely, the information contained in the packet headers.
  • the method of separating the traffic aggregate is selected so as to substantially provide statistical independence vis a vis the sub-aggregates. It will be appreciated that the term substantially is used as there may be some limited statistical independence between sub-aggregates which for most purposes may be ignored. Similarly, care should be taken in selecting the method of separating the traffic aggregate to ensure it is performed on a flow level, i.e.
  • the number of sub-aggregates is determined, typically this would be a predefined figure.
  • a suitable range for selection of M from is between 5 and 30, with the preferable range being between 10 and 20.
  • the individual sub-aggregates are indexed, e.g. from 0 to M-1.
  • a function (H) which we will refer to as a hash function, provides an integer value from 0 to M-1 for a packet, which in turn allows an individual packet to be assigned to a sub-aggregate having the index of that integer.
  • the hash function may be implemented within the sub-aggregator.
  • the hash function comprises a modulo division performed on the weighted sum of a plurality of fields from the packet header for an item function.
  • the plurality of fields may include one or more of the following: Source IP address, Source port number, destination IP address, destination port number and the TOS (Type of Service) field.
  • H(packet) [a1 * source_IP_address + a2 * source_port_number + a3 * destination_IP_address + a4* destination_port_number + a5 * TOSJield] (modulo M) , where integer numbers a1 , a2, a3, a4, a5 are chosen appropriately and fixed.
  • One possible way to choose a1-a5 is to use sufficiently large different prime numbers, for example greater than 1000000.
  • packets from a flow will be always assigned to the same sub-aggregate as source_IP_address, source_port_number, destination_IP_address, destination_port_number, TOS_field are identical for packets of same TCP or UDP flows. It will also be appreciated that individual packets are each assigned to only one sub-aggregate. Once the packets have been assigned to a sub-aggregate, the sub- aggregates are directed to a traffic measurement module.
  • the traffic measurement module may employ a number of different methods to perform a measurement (Step 604) on the individual sub-aggregates of the series to obtain a statistical measure for the traffic aggregate.
  • a first one of these methods uses a many sources asymptotics [or simply MSA] method described in the following documents; D. Botvich and N. Duffield. Large deviations, the shape of the loss curve, and economies of scale in large multiplexers. Queueing Systems, 20: 293 - 320, 1995, A. Simonian and J.
  • the traffic measurement module suitably comprises a number of counters for each sub-aggregate. At the start of the process, these counters are created (if in software) and initialised (step 700). Suitably, the traffic measurement module employs two counters for each sub-aggregate: a first counter for recording the number of packets in a particular sub-aggregate and the second counter for recording the volume of data in the packets of the sub-aggregate. In operation, as packets arrive and are assigned to a sub-aggregate, the traffic measurement module updates the counters (step 702) for relevant sub-aggregate.
  • the method of updating counters may be described generally as follows:
  • step 700 Initialise all sub-aggregates counters (step 700) for all aggregates by 0, including packet counter and volume counter.
  • additional information including for example the arrival time of the last packet, as this additional information may be useful for performance optimisation purposes in some traffic measurement schemes.
  • Step 704 Periodically, the counters for each sub-aggregate are inspected (Step 704). From the values obtained, statistical measures may be calculated for each sub-aggregate. It will be appreciated, the step of updating the counters continues during the period of measurement, whereas the inspection of the counters and calculation of statistical measures occurs on a periodic basis, for example, every 5mSec. The results for the individual sub-aggregates may be combined (step 706) to produce an indication for the traffic prior to shaping.
  • the above method provides a measure of the traffic before shaping in certain circumstances the results may be unreliable.
  • the accuracy of the estimations produced by the method of the invention depends on many factors, including traffic load conditions, network topology, schedulers used and QoS targets.
  • traffic load conditions when the invention method does not produce reliable (i.e. accurate) estimations of the essential bandwidth.
  • the invention method does not produce reliable (i.e. accurate) estimations of the essential bandwidth.
  • the invention method does not produce reliable (i.e. accurate) estimations of the essential bandwidth.
  • the invention method does not produce reliable (i.e. accurate) estimations of the essential bandwidth.
  • the invention method does not produce reliable (i.e. accurate) estimations of the essential bandwidth.
  • the invention method does not produce reliable (i.e. accurate) estimations of the essential bandwidth.
  • the traffic will be shaped at routers R1 and R2.
  • the method for calculating the essential bandwidth measurement is substantially identical to a 1 -layer scenario, the reliability of the results will be different.
  • an optional congestion state module may be employed within the system of the invention to provide an indication as to the reliability of traffic measurements.
  • the congestion state module suitably accepts as an input information from the traffic measurement module regarding the volume of data being transmitted over a particular link or links and, depending on the type of queuing schedulers involved, the essential bandwidth measurements.
  • the congestion state module may also require information to be entered by a user. This information may, for example, include the types of routers and the queuing techniques employed on particular links. Alternatively, it will be appreciated by those skilled in the art, that this information may be obtainable automatically. For example, if a router has a feature allowing for its interrogation by an external system. The exact method employed by the congestion state module will now be explained in greater detail.
  • the method may be (by experiment) taken as reliable (i.e. the estimation error is less than 5-10%) if: load at router R 1 ⁇ 80% (1 )
  • the load is measured as the ratio of the mean rate to link rate and multiplied by 100%. As an aside, it will be appreciated that in a well designed network the load would never normally exceed 50%.
  • the measurements in this scenario are not reliable (e.g. errors are often more than 20-50% or even more) if the router is in a second region where: load at router Ri is > 90%.
  • the boundary case is the third region, when: 80% ⁇ load at router R 1 ⁇ 90% (3) may also be usefully treated as being unreliable, although the estimation error is typically within 20%.
  • the first region (case 1) where the essential bandwidth estimations are reliable may be referred to as sub-critical, when it is unreliable (case 2) as the super-critical region and intermediate (case 3) as the critical region.
  • case 2 when it is unreliable
  • case 3 the critical region.
  • the process of the determination when the essential bandwidth estimations are reliable as the congestion state evaluation and describing the corresponding congestion states as sub-critical, super-critical and critical, respectively. It will be appreciated that there is no precise boundary for deciding between what is sub-critical, super-critical and critical as the selection of a boundary between these regions is a somewhat subjective rather than an objective test.
  • the evaluation of the traffic aggregate congestion state is a significant part of the present invention as it allows the methods to be applied with some certainty as to the reliability of the results.
  • the traffic aggregate congestion state is associated with a particular traffic aggregate. Each traffic aggregate is defined at certain point in the network, whereas (in the case of a single probe) all traffic aggregates are observed at the same point where the probe is located. It will be appreciated that the congestion state is a dynamic object, which changes constantly over time. To account for this, the congestion state is evaluated periodically, for example, every 1 to 5 minutes.
  • a primary aggregate is a traffic aggregate which represents the total traffic of a particular traffic class at some node. The same procedure may be applied to the primary aggregate as is applied as to any traffic aggregate of interest.
  • the method of the present invention is reliable for a broad range of different network load conditions.
  • the inventors of the present invention have defined critical parameters that are important means to determine the congestion state and have accounted for the fact that the critical parameters may be different for different types of schedulers. Using these critical parameters, the inventors have derived algorithms to determine the traffic aggregate congestion state, i.e. is it sub-critical, critical or super-critical.
  • the information regarding the configuration of routers on a network is however generally known to the person responsible for the network and thus may be entered manually into the congestion state module. Alternatively, some of this information may be available via interaction with the individual routers.
  • the output from the congestion state module may be passed directly to a user identifying whether the results coming from the system are reliable. Alternatively, the output may be passed as an indicator of reliability to the traffic measurement system, which may be adapted to take the reliability indicator into account when presenting results to a user.
  • Different schedulers e.g. FIFO, Priority Queue, WFQ
  • WFQ Priority Queue
  • mean rate load may be viewed as the critical parameter and accordingly the essential bandwidth load may be viewed as not critical.
  • essential bandwidth load may be viewed as the critical parameter when dealing with lowest priority traffic class.
  • the mean rate load is its critical parameter.
  • WFQ Weighted Fair Queue
  • the reliable regime for the method of the present invention method (as described above) is the so-called sub-critical regime. It may be characterized as follows: FIFO Queue less than 80% of mean rate load;
  • the essential bandwidth load is determined by taking into account traffic from the traffic class of interest as well as all traffic of higher priorities classes.
  • the unreliable regime for operation of the method of the present invention is the so-called super-critical regime, which may be characterized as follows: FIFO Queue more than 90% of mean rate load; Priority Queue
  • essential bandwidth load is also determined by taking into account traffic from the traffic class of interest as well as all traffic of higher priorities classes. Weighted Fair Queue If both the critical parameters are more 80% then it is typically unsafe;
  • the boundary between safe and unsafe regimes is relatively small.
  • the congestion state is critical when mean rate load is about 80%-90%.
  • the invention method degrades gracefully under unsafe conditions (i.e. when the critical parameter is larger the safe threshold, i.e. 80%).
  • the method of the present invention provides reliable estimation for a particular traffic aggregate of the essential bandwidth if the traffic aggregate is in the sub-critical congestion state during the measurement period.
  • the method may be taken as reliable if on the path of the aggregate (aggregate path) all nodes for all traffic classes involved in the aggregate of interest are in sub-critical congestion state. It will be appreciated that this condition is simpler and more efficient to check.
  • the method for doing performing such a check will now be described in greater detail.
  • a characterization will be provided for when a particular traffic class at a particular node in 1 -layer scenario is sub-critical or supercritical.
  • a characterization for when the whole path is sub- critical or super-critical will be developed (a multi-layer scenario) .
  • the aggregate path includes all network nodes that the aggregate traffic passes through, i.e. between the point where the aggregate is defined and the point, where the probe is located.
  • the aggregate path is A-B-C.
  • the corresponding ports at A, B and C must be sub-critical for all traffic classes involved in the aggregate.
  • the invention method is reliable for the traffic aggregate. But if at least one node is "congested” (i.e. in the super-critical or critical congestion state) then the method of measurement of the present invention is likely to be unreliable for the traffic aggregate. For this reason, it can be said that the traffic aggregate congestion state is super-critical if at least one node is in not sub-critical congestion state.
  • the traffic classes involved in the aggregate are applied according to the queuing scheduling hierarchy. It can be noted that if all traffic classes at a node involved in the aggregate are "not congested” then the invention method is reliable. Alternatively, if at least one traffic class at a node involved in the aggregate is "congested” then the estimations can be not reliable. For this reason, it may be said that the traffic aggregate congestion state is super-critical if at least one class involved in the aggregate is in not sub- critical congestion state.
  • the estimations for an aggregate of interest using the invention method may be considered reliable knowledge of the following may be required: aggregate path; traffic classes involved in the aggregate; congestion states for all traffic classes involved in the aggregate for each node on the aggregate path;
  • the so-called primary aggregates are used that are simply total traffic associated with a particular traffic class at a particular node.
  • schedulers including the FIFO queue, Priority scheduler and WFQ scheduler. It will be appreciated that further rules may be developed for other schedulers.
  • the FIFO queue case is the simplest case to consider as in this case there is only one traffic class. Similarly, there is also only one primary aggregate P which represents the total traffic entering the FIFO queue.
  • the algorithm for testing the congestion state of traffic in FIFO configured router may be simply stated as:
  • the FIFO queue is sub-critical if: Mean_rate(P) / Link_Rate * 100% ⁇ 80%.
  • the FIFO queue is super-critical if:
  • the Priority queue case is more complicated than FIFO case. A simpler case having two priority classes will first be explained and then a more general case of priority queue with N traffic classes developed.
  • the Algorithm for the two priority class scheme may be stated as:
  • the higher priority traffic class is sub-critical if: Mean_rate(P H ) / Link_Rate * 100% ⁇ 80%.
  • N priority traffic classes will now be considered.
  • N primary aggregates P,- , / 1 , ..., N, associated with each traffic class, respectively: highest priority primary aggregate (P 1 ) and lowest priority primary aggregate (PN).
  • the priority traffic class / (1 ⁇ / ⁇ N) is sub-critical if:
  • the lowest priority traffic class N is sub-critical if:
  • the WFQ scheduler case is a bit more complicated than the case of the Priority scheduler. Initially the simpler case with two classes will be described followed by the general case of N traffic classes.
  • the algorithm may be stated as follows: The traffic class / is sub-critical if:
  • the traffic class / is sub-critical if: Mean_rate(P ⁇ / (Link_Rate * W 1 ) * 100% ⁇ 80%. or
  • the overall algorithm for the evaluation of the traffic aggregate congestion state in multi-layer scenarios is relatively straightforward.
  • the method begins with an evaluation of all nodes on the traffic aggregate path starting from the end (i.e. from the node attached to the probe) and along the path until the start. At each node we need to evaluate all traffic classes contributing to the traffic aggregate. If at some node at least one of traffic classes involved in the traffic aggregate is not sub-critical then the traffic aggregate congestion state is said to be super-critical and no further use of the algorithm is required. Otherwise the traffic aggregate congestion state is determined as sub-critical.
  • the mean rate load may be taken as the ratio of the mean rate of total traffic to the link rate multiplied by 100%
  • the Essential bandwidth load may be taken as the ratio of the essential bandwidth (for a particular QoS target) of total traffic to the link rate multiplied by 100%
  • the class mean rate load may be taken as the ratio of the mean rate of the total class traffic to the link rate divided by class weight and multiplied 100%.
  • a second alternative method for the performing an estimate (e.g. a measurement of essential bandwidth) based on traffic aggregates before shaping will now be described.
  • This method is also based on the splitting an aggregate into sub-aggregates.
  • the splitting of an aggregate into sub- aggregates is done in exactly the same way as in the previous method.
  • the difference between this second method and the first described above is in how the measurement using the individual sub-aggregates of the series is performed to obtain a statistical measure for the traffic aggregate, i.e. how the sub- aggregates and their counters are used.
  • the alternative method does not reconstruct the MSA CGFs at all. The method will now be described in detail. As in the previous approach aggregate traffic is split into several sub- aggregates.
  • the sub-aggregates are multiplexed together, with each sub- aggregate offset by some time constant. It is important that the time offsets of different sub-aggregates should be different.
  • the choice and application of time constants may be performed in several different ways.
  • T 0 50ms is offset time or some other value.
  • T 0 50ms is offset time or some other value.
  • the reconstructed traces or measurements may be used as an approximation of the traffic aggregate before shaping.
  • These reconstructed traces, or measurements may be supplied to a bandwidth requirement estimator (as known from the prior art) in order to determine the bandwidth required to satisfy QoS.
  • these reconstructed traces, or measurements may be supplied to a Bandwidth Estimator. If the Bandwidth of the reconstructed traffic exceeds that of the observed shaped traffic, then it is a strong indication that the required bandwidth exceeds the shaping rate.
  • the Offset Method may be implemented in a number of different ways. However a particularly efficient algorithm will now be described, with reference to Figure 8. This algorithm minimizes the memory requirements and is easily extended to reconstruct different numbers of sub-aggregates and different offsets.
  • a current slot number p may then be used to keep reference to current slot in the circular buffer.
  • a total reconstructed aggregate counter C r may then be used to supply measurements to a Bandwidth Estimator.
  • the implementation of the algorithm may be as follows:
  • step 802 retrieve the value in slot p of the buffer and increase C 7 - by it;
  • the counter C r is used for bandwidth estimation (Step 808).
  • the counter C r comprises two counters, the first measuring the volume of data, and the second measuring the quantity of data packets. Insert the measurement from the 1 st sub-aggregate into slot p, replacing any value already in slot p.
  • an important advantage of the invention is that the method and probes are passive, i.e. they do not generate any additional traffic but only inspect packets, classify packets, update counters and make the essential bandwidth measurements.
  • the present invention does not require any artificially generated traffic.
  • the methodology of the present invention can be used in a traffic analysing tool placed at any node or location in a data network within any device, including for example a router, and used to effectively monitor the traffic in another location.
  • the subsequent analysis of the traffic can be used for a plurality of different purposes for example in weighted scheduler arrangements to determine the optimum weights to assign to each buffer, or as a parameter to describe traffic in a network.
  • a traffic descriptor could for example include a relationship between the service rate and quality of service achieved at that service rate.
  • a plurality of traffic analysers according to the invention can be implemented across a data network and used to create an analysis of traffic across the entire network.
  • rules can be applied such that different types of data for example Voice Data, Internet Traffic etc., can be analysed using the technique of the present invention and then treated differently depending on the output of the analysis.
  • the techniques of the present invention may by modified in a number of differing fashions depending on the applications and level of accuracy required in the calculation.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)

Abstract

La présente invention concerne des procédés de mesure du trafic sur un réseau. Une difficulté avec la mesure du trafic sur un réseau est que, fréquemment, le trafic a été formé avant d'atteindre le point de mesure. La présente invention concerne l'obtention d'une mesure du trafic formé avant la formation sur la base d'observations passives du trafic formé. Plus particulièrement, l'invention concerne un procédé destiné à analyser un agrégat de trafic de paquets dans un réseau et consistant à séparer l'agrégat de trafic en une série de sous-agrégats co-temporels individuels et à réaliser une mesure au moyen des sous-agrégats individuels de cette série en vue de l'obtention d'une mesure statistique pour l'agrégat de trafic.
PCT/IE2004/000175 2004-12-23 2004-12-23 Procede et systeme destines a reconstruire des exigences de bande passante de flux de trafic avant la formation tout en observant passivement le trafic forme WO2006067768A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/IE2004/000175 WO2006067768A1 (fr) 2004-12-23 2004-12-23 Procede et systeme destines a reconstruire des exigences de bande passante de flux de trafic avant la formation tout en observant passivement le trafic forme
US11/722,699 US20080137533A1 (en) 2004-12-23 2004-12-23 Method and System for Reconstructing Bandwidth Requirements of Traffic Stream Before Shaping While Passively Observing Shaped Traffic

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030145232A1 (en) * 2002-01-31 2003-07-31 Poletto Massimiliano Antonio Denial of service attacks characterization
US20040125797A1 (en) * 2002-12-27 2004-07-01 Raisanen Vilho I. Flow labels
US20040136379A1 (en) * 2001-03-13 2004-07-15 Liao Raymond R Method and apparatus for allocation of resources

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040136379A1 (en) * 2001-03-13 2004-07-15 Liao Raymond R Method and apparatus for allocation of resources
US20030145232A1 (en) * 2002-01-31 2003-07-31 Poletto Massimiliano Antonio Denial of service attacks characterization
US20040125797A1 (en) * 2002-12-27 2004-07-01 Raisanen Vilho I. Flow labels

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