Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/28—Flow control; Congestion control in relation to timing considerations
  • H04L47/283—Flow control; Congestion control in relation to timing considerations in response to processing delays, e.g. caused by jitter or round trip time [RTT]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/24—Traffic characterised by specific attributes, e.g. priority or QoS
  • H04L47/2441—Traffic characterised by specific attributes, e.g. priority or QoS relying on flow classification, e.g. using integrated services [IntServ]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/30—Flow control; Congestion control in combination with information about buffer occupancy at either end or at transit nodes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/10—Flow control; Congestion control
  • H04L47/32—Flow control; Congestion control by discarding or delaying data units, e.g. packets or frames
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L47/00—Traffic control in data switching networks
  • H04L47/50—Queue scheduling
  • H04L47/62—Queue scheduling characterised by scheduling criteria
  • H04L47/625—Queue scheduling characterised by scheduling criteria for service slots or service orders
  • H04L47/6275—Queue scheduling characterised by scheduling criteria for service slots or service orders based on priority

Definitions

• This mvention is related to network switches, and more specifically, frame forwarding techniques employed therein.
• Differentiated Services are a set of technologies proposed by the IETF (Internet Engineering Task Force) which would allow Internet and other IP-based network service providers to offer differentiated levels of service, for an additional charge, to individual customers and information streams provided thereto.
• the header of each frame which enters a network router contains a marker which indicates the level of service that the network router would apply to such frame during transmission.
• the network router then applies the corresponding differentiated grades of service to the various frame which enter on the various ports.
• service providers offer and provide to certain customers (not a hard and fast guarantee), a preferential grade of service for all frame traffic in accordance with the appropriate frame markers contained in the frame header.
• the more preferential grades of service offer lower frame latency (i.e., frame delay). During times of frame congestion, those preferentially-marked frames would receive preferential service.
• the present invention disclosed and claimed herein in one aspect thereof, comprises a frame scheduling and discard architecture in a Differentiated Services network environment.
• the architecture comprises a discard logic for discarding a frame from a stream of incoming frames of the network environment in accordance with a discard algorithm, the frame being discarded if a predetermined congestion level in the network environment has been reached, and a predetermined backlog limit of a queue associated with the frame, has been reached.
• Scheduling logic is also provided for scheduling the order in which to transmit one or more enqueued frames of the network environment.
• FIG. 1 illustrates a general block diagram of a frame forwarding system in accordance with a disclosed embodiment
• FIG. 2 illustrates a graph of congestion plane defined by the system of FIG. 1
• FIG. 3 illustrates. a block diagram of sample frame forwarding system in accordance with Table 1;
• FIG. 4 illustrates a graph of the sub-congestion planes in a WRED implementation.
• the disclosed novel scheme preferably combines both measurable Quality of Service (QoS) criteria, such as delay and bandwidth, as well as buffer management, in a unified approach for frame forwarding in a Differentiated Services environment.
• QoS Quality of Service
• the approach to QoS described herein is based upon several assumptions: that the offered traffic pattern is unknown, the incoming traffic is not policed or shaped (however, if the incoming traffic is policed or shaped, additional assurances about switch performance may be made), and the network manager knows the applications (or traffic types) utilized on the network, such as voice, file transfer, or web browsing, and their relative importance.
• shaped or “shaping” is defined as the process of controlling (or pacing) traffic flow to prevent overflow of a downstream device by limiting traffic flow to that which more closely matches the input bandwidth capabilities of the downstream device. Policing is similar to shaping, however, traffic that exceeds the configured rate is normally discarded, instead of being buffered. With this application knowledge, the network manager can then subdivide the applications into classes, and set up a service-level agreement with each.
• the service-level agreement for example, may consist of bandwidth or latency assurances per class.
• a class is capable of offering traffic that exceeds the contracted bandwidth.
• a well-behaved class offers traffic at a rate no greater than the agreed-upon rate.
• misbehaving class offers traffic that exceeds the agreed-upon rate.
• a misbehaving class is formed from an aggregation of misbehaving microflows. To achieve high link bandwidth utilization, a misbehaving class is allowed to use any idle bandwidth. However, such leniency must not degrade the QoS received by well-behaved classes.
• Table 1 illustrates a sample grid of six traffic types, where each type may have its own distinct properties and applications. Table 1. Sample Grid of Six Traffic Types
• the traffic types i.e., phone calls, circuit emulation, training videos, critical and non-critical interactive applications, web businesses, e-mails, file backups, and casual web browsing
• Class C 3 the highest priority transmission class, requires that all frames be transmitted in less than 1 ms, and receives 40 Mbps of the 100 Mbps of bandwidth (40%) at that port.
• Class C 2 the middle transmission priority class, receives 35 Mbps of the 100 Mbps total bandwidth (or 35%) at that port, and requires that all frames be transmitted in less than 4 ms.
• class C l5 the lowest transmission priority class, receives 25 Mbps of the 100 Mbps total bandwidth (or 25%) at that port, and requires that frames be transmitted in less than 16 ms, before dropping occurs. .
• each transmission class (C l5 C 2 , and C 3 ) has two subclasses; high-drop and low-drop.
• Well-behaved users should rarely.lose frames.
• poorly-behaved users i.e., users who send frames at too high of a rate
• Table 1 shows that the class applications, respective priorities, and delay and drop criteria, may be structured in any manner desired. For example, casual web browsing fits into the category of high-drop, high-latency-tolerant traffic, whereas VoIP phone calls fit into the category of low-drop, low-latency traffic.
• each 10/100 Mbps port supports three total classes (C l5 C 2 , and C 3 ).
• the queue of the higher class has the higher priority (i.e., C 2 has strict priority over C,). Again, this is just one example. Note that the disclosed architecture is compatible with IETF classes proposed by the Internet Engineering Task Force.
• FIG. 1 there is illustrated a block diagram which provides a high- level view of a disclosed embodiment.
• the disclosed novel forwarding mechanism comprises two intertwined parts: buffer management, which operates in accordance with a discard algorithm for determining the admittance or discarding of incoming frames; and transmission scheduling, for determining the sequence of frame departure.
• bandwidth, delay, and buffering are mathematically related by Bandwidth Received oc Queue Size/Delay Experienced.
• the unified scheme through scheduling and buffer management, controls the Delay Experienced and Queue Size. As a consequence of this fact and the mathematical relationship hereinabove, the unified scheme also modulates Bandwidth Received per class.
• a frame forwarding system 100 comprises a discard logic 102 operable in accordance with a discard algorithm which monitors an incoming bit stream 104.
• An output 106 of the discard logic 102 flows to one or more queues 108, 110 and 112 (also denoted as queues Q Q 2 ,— 5 Q n ) which correspond to respective classes C l5 C 2 ,...,C n of traffic.
• the queues 108, 110 and 112 temporarily store frames according to the class of frame traffic to which each is assigned, and each outputs frames to a multiplexer logic 114 for ultimate output at an output queue 116, which has total bandwidth capacity of K Mbps.
• class C l3 the lowest transmission priority class, has associated therewith a service-level agreement ⁇ ! which is defined by a delay bound parameter ( ⁇ x ) and a bandwidth parameter (r x ). If the number of frames enqueued in the queue 108 (also designated Q,) cannot be transmitted within the time designated by the delay parameter ( ⁇ , there is some probability that frames associated with that class will need to be dropped in order to prevent congestion.
• class C 2 the next highest transmission priority class, has associated therewith a service-level agreement S 2 which is defined by a delay bound parameter ( ⁇ 2 ) and a bandwidth parameter (r 2 ).
• the highest transmission priority class C n has associated therewith a service-level agreement S n which is defined by a delay bound parameter ( ⁇ and a bandwidth parameter (r n ). If the number of frames enqueued in the queue 112 (also designated Q cannot be transmitted within the time designated by the delay parameter ( ⁇ n ), there is some probability that frames associated with that class will need to be dropped in order to prevent congestion.
• the output queue 116 temporarily stores the frames received from the various class queues 108, 110 and 112, and outputs frames of the various classes C l3 C 2 ,...,C n to a port P (not shown).
• the multiplexer 114 is controlled by a scheduling logic 118 which determines the sequence of frame departure from the various class queues 108, 110 and 112.
• port P serves n service classes of traffic, labeled C Manual C 2 ,...,C n .
• the classes are defined such that the guaranteed maximum delay ⁇ 2 of class C, is greater than or equal to the guaranteed maximum delay ⁇ 2 of class C 2 , and that the guaranteed maximum delay ⁇ 2 of class C 2 is greater than or equal to the guaranteed maximum delay ⁇ 3 of class C 3 , and so on (i.e., ⁇ j > ⁇ 2 > ... > ⁇ chorus).
• the disclosed scheme advantageously simultaneously satisfies both the delay and bandwidth constraints of the service-level agreements S; for all i, regardless of the offered traffic pattern.
• Delay bounded scheduling is now discussed in the context of the 10/100 Mbps port having three delay-bounded classes (C 3 , C 2 , and C x ).
• C 3 , C 2 , and C x delay-bounded classes
• other implementations having more classes can be structured similarly.
• scheduling for bounded delay in the case of the 10/100 Mbps port of Table 1, each frame enqueued in the three transmission scheduling queues Q ! -Q 3 (of classes C 1; C 2 , and C 3 ) contains an arrival time stamp.
• the scheduling decision is made when a frame reaches the head-of-line (HOL) position in the queue, and according to the time stamp of the HOL frame of each queue.
• delay is defined to be the difference between the stamped arrival time of a job (or frame) and the current time. Obviously, if there are no frames awaiting transmission for a particular class, then that class cannot be selected.
• FIG. 2 there is illustrated the concept of a congestion plane 200 in Euclidean space, in accordance with a disclosed embodiment.
• Q x be the queue backlog (measured in total bytes) for the output port P for each service class awaiting forwarding.
• the congestion hyperplane 200 is spanned by the set of vectors ⁇ Q l5 Q 2 , Q 3 ,...,Q n ⁇ , and defined by equation
• the first condition indicates that the system 100 is congested, i.e., that the system 100 has surpassed the congestion plane 200.
• the second condition indicates that class has already accumulated a large backlog. Even if admitted, a frame belonging to class C ; has little chance of meeting its delay constraint, which is a consequence of the existing backlog and the minimum bandwidth assurances to other classes. Therefore, the incoming class i frame is discarded.
• FIG. 3 there is illustrated a block diagram of a sample frame forwarding system in accordance with Table 1.
• the frame forwarding system 300 (similar to system 100) has a 100 Mbps bandwidth, and utilizes the discard logic 102 which operates in accordance with the discard algorithm disclosed herein.
• the discard logic 102 monitors an incoming bit stream 302, and based upon predetermined criteria, discards selected frames 304 of the bit stream 302 into a discard bin 306 (shown for purposes of discussion, only).
• Admitted frames (307, 309, and 311) are then enqueued into respective classes of input queues (308, 310, and 312).
• input queue 308 is a class C ⁇ queue (the lowest transmission priority class) having a delay bound which requires that all frames 307 be transmitted in less than 16 ms, and where class C x becomes a misbehaving class by offering traffic which exceeds the agreed-upon rate of 25 Mbps, there is some probability that some of the incoming class frames will be dropped to prevent congestion.
• Input queue 310 is a class C 2 queue (the intermediate transmission priority class) having a delay bound which requires that all frames 309 be transmitted in less than 4 ms, and where class C 2 becomes a misbehaving class by offering traffic which exceeds the agreed-upon rate of 35 Mbps, there is some probability that some of the incoming class C 2 frames will be dropped to prevent congestion.
• input queue 312 is a class C 3 queue (the highest transmission priority class) having a delay bound which requires that all frames 311 be transmitted in less than 1 ms, and where class C 2 becomes a misbehaving class by offering traffic which exceeds the agreed-upon rate of 40 Mbps, there is some probability that some of the incoming class C 3 frames will be dropped to prevent congestion.
• class C 3 queue the highest transmission priority class
• Level 1 and Level 2 sub-congestion planes prevent congestion by randomly dropping a percentage of high-drop frames, while still largely sparing low-drop frames. This allows high-drop frames to be discarded early, as a sacrifice for low-drop frames.
• there will be some probability of dropping frames when the total available queue backlog N ranges from 120 to 200 KB, and any one of the class queues Q Q 3 has a backlog of buffered frames which meets or exceeds the respective queue limits of A, B, or C (in kilobytes).
• the low-drop-to-high-drop range varies from 0 to X%, respectively.
• the Level 2 sub-congestion plane 402 where 16Q 3 + 4Q 2 + Q x ⁇ 160 KB, and any one or more of the queues Q Q 3 exceeds its backlog limit (A, B, and C, respectively), the low-drop-to-high-drop range varies from Y% to Z%, respectively.
• the Level 3 congestion plane 200 where the congestion plane 200 is defined by 16Q 3 + 4Q 2 + Qi ⁇ 200 KB, both the low-drop and high-drop rules stipulate a drop of 100% of the frames.
• Level 3 of Table 3 follows the rules set forth hereinabove and given the bounded delay constraints in Figure 1. For example, according to the equations, a Class 2 frame is dropped, if and only if, 16Q 3 + 4Q 2 + Q x ⁇ 200 KB, and queue Q 2 exceeds a predetermined backlog limit, i.e., Q 2 > 17.5 KB. Level 1 and Level 2 define the sub-congestion planes (400 and 402, respectively) which were discussed hereinabove. For example, if 120 KB ⁇ 16Q 3 + 4Q 2 + Q x ⁇ 200 KB, and Q 2 > 17.5 KB, then dropping will still occur with some probability. Observe that frames may be identified as high-drop or low-drop, and assigned different drop probabilities within each category on each WRED level.
• every point on the congestion plane 200 defines a triple of queue lengths (Q l5 Q 2 , Q 3 ) that is sustainable, in the sense that all latency bounds can be satisfied if the corresponding queue lengths (Q l5 Q 2 , Q 3 ) remain steady at those values.
• one sustainable set of steady-state queue lengths, in KB is (50, 17.5, 5).

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• 2001
  • 2001-02-16 EP EP01909268A patent/EP1258115A1/de not_active Withdrawn
  • 2001-02-16 WO PCT/US2001/005014 patent/WO2001063858A1/en not_active Application Discontinuation
  • 2001-02-16 KR KR1020027011090A patent/KR20020079904A/ko not_active Application Discontinuation
  • 2001-02-16 AU AU2001237043A patent/AU2001237043A1/en not_active Abandoned
  • 2001-02-16 CN CNB018052460A patent/CN100568847C/zh not_active Expired - Fee Related
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