Source: http://www.google.com.tw/patents/US7961621
Timestamp: 2013-05-20 22:32:57
Document Index: 542274760

Matched Legal Cases: ['Application No. 200680032204', 'Application No. 200580035946', 'Application No. 200580034646', 'Application No. 200580035946', 'Application No. 200580034955', 'Application No. 200580034955', 'Application No. 200580034647', 'Application No. 200580034647', 'Application No. 200580034646', 'Application No. 200580034647', 'Application No. 05810800', 'Application No. 05812799', 'Application No. 08728248', 'Application No. 05810244', 'Application No. 05810800', 'Application No. 08728248']

�M�Q US7961621 - Methods and devices for backward congestion notification - Google �M�Q�j�M �Ϥ� �a�� Play YouTube �s�D Gmail ���ݵw�� ��h »�i���M�Q�j�M | �������� | �n�J�i���M�Q�j�M�M�QThe present invention provides improved methods and devices for managing network congestion. Preferred implementations of the invention allow congestion to be pushed from congestion points in the core of a network to reaction points, which may be edge devices, host devices or components thereof. Preferably,...http://www.google.com.tw/patents/US7961621?utm_source=gb-gplus-share�M�Q US7961621 - Methods and devices for backward congestion notification���}��US7961621 B2�X���������v�ӽЮѽs��11/248,933�o�G���2011�~6��14���ӽФ��2005�~10��11�� �u���v���2005�~10��11����L���}�M�Q��CN101253729AEP1935137A2US20070081454US20110273983WO2007050250A2WO2007050250A3�o��HValentina AlariaAndrea BaldiniDavide BergamascoFlavio BonomiRong Pan��M�Q�v�HCisco Technology, Inc. ���M�Q������370/236��ڱM�Q������H04J3/14 �X�@����H04L47/30H04L47/10H04L47/263 �ڬw������H04L47/26AH04L47/10H04L47/30�ѦҤ��m�M�Q�ޥ� (104)�D�M�Q�ޥ� (101)�Q�H�U�M�Q�ޥ� (4)�~���s�����M�Q�ӼЧ� ���M�Q�ӼЧ��M�Q����T�� �ڬw�M�Q��Methods and devices for backward congestion notificationUS 7961621 B2�K�n The present invention provides improved methods and devices for managing network congestion. Preferred implementations of the invention allow congestion to be pushed from congestion points in the core of a network to reaction points, which may be edge devices, host devices or components thereof. Preferably, rate limiters shape individual flows of the reaction points that are causing congestion. Parameters of these rate limiters are preferably tuned based on feedback from congestion points, e.g., in the form of backward congestion notification (��BCN��) messages. In some implementations, such BCN messages include congestion change information and at least one instantaneous measure of congestion. The instantaneous measure(s) of congestion may be relative to a threshold of a particular queue and/or relative to a threshold of a buffer that includes a plurality of queues.
26. The method of claim 2, wherein the threshold queue level decreases as a number of active virtual output queues (��VOQs��) in a buffer of the congestion point increases and wherein the threshold queue level increases as the number of active VOQs in the buffer decreases.
CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to U.S. patent application Ser. No. 11/155,388 entitled ��ACTIVE QUEUE MANAGEMENT METHODS AND DEVICES�� and filed on Jun. 16, 2005 (the ��AQM Application��), which is hereby incorporated by reference for all purposes.
BACKGROUND OF THE INVENTION Congestion avoidance techniques are essential to the operation of networks and network devices. One such technique known in the art as ��Random Early Discard�� or ��RED�� is described in a publication by S. Floyd and V. Jacobson entitled ��Random Early Detection Gateways for Congestion Avoidance, �� (Transactions on Networking, August 1993), which is hereby incorporated by reference for all purposes.
FIG. 1A includes graph 100 that illustrates how RED works. For each incoming packet, the average queue length is calculated. (Please note that the terms ��packet�� and ��frame�� may be used interchangeably herein.) If the average queue length is below a predefined minimum threshold 102, the packet is accepted and stored in the output queue for transmission. If the average queue size is above the minimum threshold 102 but below a predefined maximum threshold 104, a packet marking probability is computed and the packet gets marked according to this probability. The marking probability is proportional to the average queue size. Therefore, when the queue is larger, there is a higher probability for an incoming packet to be marked. Finally, if the average queue size is above the maximum threshold 104, all incoming packets are marked until the average queue size falls again below the maximum threshold 104.
It is responsibility of the transport protocol to take the appropriate countermeasures when it detects packets marked by RED. One explicit method of marking packets in this context is described in RFC 3168, ��The Addition of Explicit Congestion Notification (ECN) to IP�� (K. Ramakrishnan et al., September 2001), which is hereby incorporated by reference. When TCP is being used in the absence of an explicit method of marking packets, packets can only be ��marked�� by discarding them, with TCP interpreting the loss of packets as a congestion indication. When packet drops are detected, TCP sources immediately reduce their transmission rate, causing a reduction of the traffic volume at the congested router(s). Discarding packets is also a useful means to control average queue size when non-reactive transport protocols such as UDP are exploited.
Some exemplary high-speed, low latency networks having relatively small buffers, which will be referred to herein as Data Center Ethernet (��DCE��) or the like, are described in U.S. patent application Ser. No 11/084,587, entitled ��Ethernet Extension for the Data Center�� and filed on Mar. 18, 2005, to U.S. patent application Ser. No 11/078,992, entitled ��Fibre Channel Over Ethernet�� and filed on Mar. 10, 2005 and to U.S. patent application Ser. No 11/094,877, entitled ��Network Device Architecture for Consolidating Input/Output and Reducing Latency�� and filed on Mar. 30, 2005, (the ��DCE Applications��), all of which are incorporated by reference for all purposes.
More advanced congestion control mechanisms tailored for networks characterized by operational parameters similar to DCE have been considered. One such mechanism is Fibre Channel Congestion Control (��FCC��), a congestion management mechanism for Fibre Channel networks that is described in co-pending U.S. patent application Ser. No 10/777,886, entitled ��End-to-End Congestion Control in a Fibre Channel Network�� and filed on Feb. 11, 2004, which is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/026,583, entitled ��Methods and Apparatus for Network Congestion Control�� and filed on Dec. 18, 2001, both of which are incorporated herein by reference for all purposes.
SUMMARY OF THE INVENTION The present invention provides improved methods and devices for managing network traffic. Preferred implementations of the invention allow congestion to be pushed from congestion points in the core of a network to reaction points, which may be edge devices, host devices or components thereof. Preferably, rate limiters shape individual flows of the reaction points that are causing congestion. Parameters of these rate limiters are preferably tuned based on feedback from congestion points, e.g., in the form of backward congestion notification (��BCN��) messages. In some implementations, such BCN messages include congestion change information and at least one instantaneous measure of congestion. The instantaneous measure(s) of congestion may be relative to a threshold of a particular queue and/or relative to a threshold of a buffer that includes a plurality of queues.
The feedback information may comprise an instantaneous measure of congestion and congestion change information. The instantaneous measure of congestion and the congestion change information may be determined with reference to a predetermined threshold of a queue. The predetermined threshold may decrease as a number of active virtual output queues (��VOQs��) in a buffer of a congestion point increases and the first predetermined threshold may increase as the number of active VOQs in the buffer decreases.
FIG. 4 illustrates an exemplary Rate Limited Tag (��RLT��) frame format.
The present invention provides congestion management methods and devices that are particularly suitable for network devices, such as switches and routers. Some aspects of the present invention are particularly suitable for implementing a Data Center Ethernet (��DCE��) solution, which simplifies the connectivity of data centers and provides a high bandwidth, low latency network for carrying Ethernet and storage traffic. Some exemplary DCE methods and devices are described in the DCE Applications, which have been incorporated by reference herein. However, the present invention has wide applicability outside of the DCE context and is suitable for Fibre Channel networks, IP networks, etc, potentially any kind of packet switched network.
In this example, core switch 140 is a ��congestion point�� that detects the congestion condition. According to preferred implementations of the invention, as soon as a congestion point detects congestion, it starts sending explicit feedback messages to the reaction points associated with the traffic flows causing such congestion. Such feedback messages will sometimes be referenced herein as backwards congestion notification (��BCN��) messages, BCN frames, or the like. In some such implementations, the feedback message is an Ethernet frame, which may have a format similar to that of the frame depicted in FIG. 3.
In this example, core switch 140 causes ��slow-down�� BCN messages 180 and 190 to be sent towards end nodes 115 and 135. These messages will also be referred to herein as a ��negative BCN feedback messages�� or the like. Such messages (and other BCN messages that are described below) are processed at ��reaction points,�� where congestion mitigation measures are put into place. The reaction points could be edge switches 110 and 130, or, in some implementations, end nodes 115 and 135.
The processing of a negative BCN feedback message will result in the instantiation of a filter/rate limiter (or a further slow down of the one(s) already instantiated, if any) at the reaction point. The purpose of the rate limiter is to slow down a congesting traffic flow to mitigate congestion at the core switch. If congestion should improve (or dissipate completely), ��speed-up�� messages (also referred to herein as ��positive BCN feedback messages�� or the like) will cause the rate limiters to increase their rate to avoid wasting bandwidth at the congestion point.
However, core switch 140 has detected congestion. First, core switch 140 has sent negative BCN feedback message 220 to a reaction point (edge switch 110), indicating that edge switch 110 should slow down its rate of transmission. Preferably, negative BCN feedback message 220 includes sufficient detail to allow edge switch 110 to identify a particular traffic flow (i.e., a layer 2 flow, a layer 3 flow, or a layer 4 flow) that needs to be slowed. A BCN frame is generated by a congestion point by sampling incoming traffic, e.g., as described below. In this example, core switch 140 has subsequently sent a ��stop�� BCN message 230 to edge switch 110. As described in more detail below, a ��stop�� BCN message 230 will cause a reaction point to stop transmitting data (preferably on a specified data flow) for a period of time.
One exemplary BCN frame is depicted in FIG. 3. BCN frame 305 has a Destination Address (��DA��) 310 that is equal to the Source Address of the sampled frame. BCN frame 305 also has a Source Address (��SA��) 315 equal to an address (here a MAC address) associated with the congestion point. This allows BCN Frame 220 to be routed back to the source of the traffic causing congestion (in this example, to edge switch 110 ) with a valid source address.
Field 340 indicates a congestion point identifier (��CPID��). A primary purpose of the CPID is to identify a congested entity in the network. In this example, the congested entity is a queue of core switch 140. This information is sent to a reaction point in order to create an association between the congested entity and the reaction point.
The contents of timestamp field 350 and unit field 352 are copied from the homonymous fields of a Rate Limited Tag (��RLT��) of the sampled frame. RLTs will be described below with reference to FIGS. 2B and 4. If the sampled frame does not carry such a tag, timestamp field 350 and unit field 352 are set to zero.
FIG. 5 illustrates an example of an extended BCN frame 505 that may be used in networks employing MAC-in-MAC encapsulation. Such methods may be implemented, for example, according to a conventional MAC-in-MAC scheme as described in IEEE standard draft 802.1ah or according to novel methods described in U.S. patent application Ser. No 11/152,991, entitled ��FORWARDING TABLE REDUCTION AND MULTIPATH NETWORK FORWARDING�� and filed on Jun. 14, 2005, both of which are hereby incorporated by reference.
When edge switch 110 receives a BCN frame from congestion point 140 and such message is intended to cause a congestion mitigation action to be undertaken on a particular data flow (e.g., the installation of a rate limiter or the slowing down of an existing one), edge switch 110 stores a CPID in a local register associated with such data flow. All the frames 240 belonging to that flow that are subsequently injected by edge switch 110 in the network will carry a Rate Limited Tag (��RLT��) containing the CPID.
Timestamp field 425 may be used to estimate the round trip time between the reaction point and the congestion point with which it is associated. Each time a reaction point inserts an RLT tag in a frame it is going to transmit, the current value of a local free running timer is copied into timestamp field 425. Unit field 427 indicates the time units used by the free running timer. The resolution of this free running timer may be, for example, a value in the range 1 �gs to 100 �gs. As noted above, when a frame having an RLT tag is sampled by a congestion point, the contents of timestamp field 425 and unit field 427 are copied and inserted in timestamp field 350 and unit field 352 of a BCN frame generated by the congestion point.
In this implementation, when the queue length is above Qeq, the Congestion Point will generate either a regular BCN feedback message or a ��stop�� BCN feedback message irrespective of the CPID field in the RLT tag. In this example, if the length of queue 605 is ��Qeq and is ��Qsc, a negative BCN feedback message is generated whether or not the packet carries an RLT tag, and whether or not the CPID of the RLT tag (if any) matches the congestion point ID. A ��stop�� BCN feedback message is generated when the length of the queue is >Qsc.
In this example, a BCN feedback message includes two fields, Qoff and Qdelta. Qoff is an instantaneous measure of congestion, which in this example is the offset of the current queue length with respect to the equilibrium threshold Qeq. Here, Qoff is saturated at +Qeq and −Qeq. Here, a BCN feedback message also includes congestion change information. Here, the congestion change information is Qdelta, which is the change in length of the queue since the last sampled frame. In this example, Qdelta is saturated at +2 Qeq and −2 Qeq. When Qdelta saturates, the Q bit in the BCN Frame is set. A ��stop�� BCN feedback message is indicated by zero values for Qoff and Qdelta. In fact, since a BCN message is not generated when a frame is sampled and Qoff and Qdelta are both zero, this combination may be used to identify a ��stop�� BCN message.
FIG. 7 illustrates the structure of the data paths of a reaction point according to some implementations of the invention. This process may be implemented, for example, in an ingress port of an edge switch or in an egress port of the network interface card (��NIC��) of a host device. Data path 705 represents a condition of the reaction point before any BCN frames have been received indicating congestion that pertains to this reaction point, e.g., as in the state of edge device 110 in FIG. 2A. In data path 705, un-tagged data frames, like those of data frames 210 of FIG. 2A, are transmitted by the reaction point.
After BCN frames have been received indicating congestion that pertains to this reaction point (e.g., as in the state of edge device 110 in FIG. 2B), a set of filters 720, F1 through Fn, divert the traffic that matches a particular filtering criterion (e.g., L2 SA-DA, L3 SA-DA, etc.) from data path 705 to a set of queues. Traffic is drained from such queues by a set of corresponding rate limiters 740, R1 through Rn, whose rate is controlled by the BCN Frames coming from congestion points. Besides controlling the rate of traffic, in this implementation the rate limiters also cause an RLT tag to be added to all the frames they transmit in order to elicit feedback from the congestion points. To ensure that the feedback is generated only by the congestion point that originally caused the instantiation of the filter, the RLT tag contains the identity of such congestion point (��CPID��). Congestion points should include their identity in every BCN Frame they generate, so that each of filters 720 may be associated with individual congestion points.
Fb=(Qoff−w�PQdelta) Equation (1)
IfFb>0R=R +Gi�PFb�PRu Equation(2)IfFb<0R=R�P(1−Gd�P|Fb|) Equation(3)
A limited number of filters/rate limiters may be available. There may be cases when all the filters have been used and a BCN message is received which should cause the instantiation of a new filter/rate limiter pair. In such cases, a number of actions may be taken, e.g.: (1) aggregate all the filters/rate limiters in a single filter/rate limiter that controls the entire traffic originated by and end system; (2) aggregate filters/rate limiters in an ��intelligent�� way, e.g., use the same filter/rate limiter for all the traffic flows sharing the same destination address, etc; or (3) aggregate filters/rate limiters in a ��less intelligent�� way, e.g., use the same filter/rate limiter for all the traffic flows sharing the same bucket based on an hash function of the frame header.
When a congestion point is subject to severe congestion, it may send a ��stop�� BCN feedback message. Such a message is also referred to herein as a ��BCN0�� message or the like because in some implementations a ��stop�� BCN feedback message is a BCN message with Qoff=0 and Qdelta=0.
Referring now to graph 805 of FIG. 8, transmission rates are indicated with respect to vertical axis 810 and time is indicated with respect to horizontal axis 815. When a rate limiter receives a ��stop�� BCN feedback message (at time 825), in some implementations of the invention it sets its current rate 820 to 0 and starts a timer, e.g., a random timer whose range is determined by time Tmax (e.g., 10 us). When the timer started by the BCN0 message expires, the rate limiter is set to operate at a minimum rate 835, which is a minimum rate Rmin in this example (e.g., 1/10 of line rate). This should restart the traffic flow towards the congestion point and trigger�Xhopefully positive�Xfeedback. In this example, the slow restart leads to positive feedback from the congestion point at time 840 and a subsequent increase in R to rate 845.
Fb sat = - 2 �P ( Qdelta 2 + w �P Qdelta ) The rate adjustment is then performed as usual, i.e.:
If Fbsat>0 R=R+Gi�PFbsat�PRu If Fbsat<0 R=R�P(1−Gd�P|Fbsat) The saturation feedback generates a rate adjustment twice as big as the maximum rate adjustment.
FIG. 9 depicts core switch 900 having an input buffer 905 for port 902. Core switch 900 is a congestion detection point. Here, input buffer 905 is shared by a number of output queues 910. When the overall occupancy of buffer 905 reaches a predetermined level, ��slow down�� or ��stop�� BCN indications will result, even when no individual queue is experiencing congestion.
In this example, when the occupancy of buffer 905 increases beyond mild congestion threshold (��Bmc��), the Mbit will be set in the BCN frame (e.g., in reserved area 335 of frame 305 (see FIG. 3)). The reaction point (e.g., an edge switch) will detect that the M bit has been set and will double the effect of any negative feedback. Positive feedback sent from a congestion point according to the condition of an individual queue with the M bit set will be ignored.
When the severe congestion threshold (��Bsc��) is crossed, the S bit will be set in the BCN frame. If the reaction point detects that the S bit has been set, the reaction point will translate any corresponding BCN indication to be a ��stop�� BCN indication and will respond accordingly.
The interfaces 1068 are typically provided as interface cards (sometimes referred to as ��line cards��). Generally, interfaces 1068 control the sending and receiving of data packets over the network and sometimes support other peripherals used with the network device 1060. Among the interfaces that may be provided are Fibre Channel (��FC��) interfaces, Ethernet interfaces, frame relay interfaces, cable interfaces, DSL interfaces, token ring interfaces, and the like. In addition, various very high-speed interfaces may be provided, such as fast Ethernet interfaces, Gigabit Ethernet interfaces, ATM interfaces, HSSI interfaces, POS interfaces, FDDI interfaces, ASI interfaces, DHEI interfaces and the like.
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