Abstract:
Disclosed is a method of controlling an ingress transmission capacity of an interchassis switch includes comparing the ingress transmission capacity to a threshold capacity; and controlling, using a controller external to the interchassis switch, the ingress transmission capacity responsive to the ingress transmission capacity comparing step.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present invention is related to co-pending patent application 10/465,108 entitled “Interchassis Switch Controlled Ingress Transmission Capacity.” 
   FIELD OF THE INVENTION 
   The present invention relates generally to controlling ingress transmission capacity of a switch, and more specifically to controlling a maximum ingress transmission capacity of an interchassis switch used in a blades and chassis server. 
   BACKGROUND OF THE INVENTION 
   A blade and chassis configuration for a computing system includes one or more processing blades within a chassis. Also within the chassis are one or more integrated network switches that couple the blades together into an interchassis network as well as providing access to network connections exiting the chassis. Each blade has one or more network interface connections (NICs) for communicating with NICs incorporated into the switches. 
   In many implementations, an ingress transmission capacity into any individual switch exceeds the switch egress transmission capacity. The transmission capacity is a function of link speed and link load factor of the aggregated, active NICs. While an interchassis switch often includes an internal buffer that helps to moderate the effects of capacity mismatches, this internal buffer contributes to the final cost and complexity of the blades and chassis server. 
   Even with an internal buffer, the interchassis switch is always subject to buffer overruns because the NICs are able to transmit packets into receive buffers of the interchassis switch at a higher rate than the interchassis switch can transmit them out of outbound chassis buffers. The size of the buffer only affects how long a capacity mismatch can be sustained, but it does not eliminate buffer overrun conditions. 
   The buffer overrun condition results in dropped packets at the interchassis switch. The solution for a dropped packet is to cause such packets to be retransmitted by the original blade. Detecting these dropped packets and getting them retransmitted increases network latency and diminishes overall effective capacity. This problem is not unique to the Ethernet protocol and can also exist with other communications protocols. 
   In some implementations, network transmission capacity of a switch is consolidated into trunks in which two or more channels are combined to provide greater bandwidth. Trunking may be performed across multiple switches or multiple servers. Accordingly, what is needed is a method for decreasing the probability of buffer overruns and improving overall effective capacity of an interchassis network while being easily managed for different network configurations. The present invention addresses such a need. 
   SUMMARY OF THE INVENTION 
   Disclosed is a method of controlling an ingress transmission capacity of an interchassis switch includes comparing the ingress transmission capacity to a threshold capacity; and controlling, using a controller external to the interchassis switch, the ingress transmission capacity responsive to the ingress transmission capacity comparing step. 
   By controlling the maximum ingress transmission capacity, packets are not dropped which thereby significantly decreases network latency and improves network capacity. The controller is able to communicate with each switch and with other controllers in other servers to better manage the server, multiple switches in a server, and multiple servers sharing limited communications bandwidth. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram of a blade and chassis computing system; and 
       FIG. 2  is schematic block diagram of an ingress transmission capacity control process. 
   

   DETAILED DESCRIPTION 
   The present invention relates to controlling a maximum ingress transmission capacity of an interchassis switch used in a blades and chassis server. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein. 
     FIG. 1  is a schematic block diagram of a preferred implementation for a blade and chassis computing system  100 . System  100  includes a chassis  105 , one or more blades  110 , and one or more interchassis switches  115  coupled to blades  110  by an interchassis network  120 , with a management module  122  coupled to each blade  110  and each switch  115 . Switches  115  are also coupled to an extrachassis communications system  125  by an extrachassis network  130 . Each blade  110  has one or more network interface connections (NICs)  135  that couple it to one or more switches  115 . In the preferred embodiment, each chassis  105  includes up to fourteen blades  110  and up to four switches  115 , with one NIC  135  per blade  110  per switch  115  (i.e., there is one NIC  135  for every switch  115  on each blade  110 ) with each switch  115  including a NIC for each blade  110 . Each switch  115  defines one interchassis network  120 , so there are as many interchassis networks  120  and extrachassis networks  130  as there are switches  115 . In other implementations of the present invention, a different number of blades  105 , switches  115  and/or NICs  135  may be used depending upon the particular needs or performance requirements. The preferred embodiment advantageously uses a single management module  122  for each server  100 . 
   Each switch  115  includes a buffer  150 , a central processing unit (CPU)  155  (or equivalent) and a non-volatile memory  160 . Buffer  150  holds incoming packets and outgoing packets, with switch  115  and buffer  150  controlled by CPU  155  as it executes process instructions stored in memory  160 . Each interchassis network  120  has, using the switch as the reference frame, a maximum ingress transmission capacity and a maximum egress transmission capacity. The ingress transmission capacity is the aggregate capacity of all active links on network  120  into a particular switch  115  and the egress transmission capacity is the aggregate capacity of all active links on network  130  out of a particular switch  115 . 
   Capacity of a network is a function of the link speed of the network elements and the load factor of those elements. It is known that link connections may have one or more discrete connection speeds (e.g., 10 Mb/sec, 100 Mb/sec and/or 1 Gb/sec), and it is known that the link speed may be auto-negotiated upon first establishing active devices at each end of the link (IEEE 802.3 includes a standard auto-negotiation protocol suitable for the present invention, though other schemes may also be used). The speed parameters of at least one of the devices may be statically defined so as to predetermine the result of a negotiation using that device. Typically, each detected link device is always connected and auto-negotiated at the greatest speed mutually supported. It is anticipated that a NIC  135  will be developed having a variable connection speed over some specified range. The present invention is easily adapted for use with such NICs  135  when they become available. 
   Management module  122  is configured to control each NIC  135  of each blade  110  and switch  115 , with the control implemented through the blade/switch, a software driver for the NIC, and/or firmware of the NIC. In contrast to the related application referenced above, the present invention may be implemented with less costly interchassis switches  115 , and one management module  122  may be used for a plurality of interchassis switches  115 , and coordinate ingress transmission capacity with knowledge of macroscopic system configurations of the enterprise. Further, in the related application, a maximum ingress transmission capacity was preferably established using discrete, standard link speed values for NICs  135 . Management module  122  may be configured to provide more control over the NICs, and may provide for more granularity over NIC  135  functions, including link speed. Also, management module  122  may change link speed without necessarily breaking established links and reestablishing a link at a new desired link speed. Management of server  100  and monitoring of ingress transmission capacity relative to egress transmission capacity of the switches and servers in an enterprise is managed more easily by use of management module  122  that is logically accessible from outside server  100 . Further, in some implementations, it may be desirable to provide for a master management module that communicates and controls all management modules  122  of servers  100  in an aggregation of servers in an enterprise. 
   The present invention controls, per server  100  and per switch  115 , the maximum ingress transmission capacity of each interchassis network  120  in response to the current ingress transmission capacity and the egress transmission capacity, on per switch  115  basis, a per server  100  basis, and/or aggregation of servers  100  basis. The preferred embodiment is implemented in each server  100  and dynamically controls maximum ingress transmission capacity by reducing/increasing link speeds and/or reducing/increasing the number of link connections. The link speeds are set either on a per NIC  135  basis, uniformly for all active NICs  135 , or selectively, based upon different classifications of NICs  135 . The maximum ingress transmission capacity may be changed periodically or it may change automatically in response to changes in the egress transmission capacity or the current ingress transmission capacity as compared to the current effective egress transmission capacity. 
   In operation, there are several factors that are used to calculate a preferred setting for NIC operation capacity (NICset):
         BCap—aggregate capacity of all active blade links to the interchassis switch (N×NICset) (i.e., the ingress transmission capacity)   NCap—aggregate capacity of all active extrachassis network links to the interchassis switch (i.e., the egress transmission capacity)   NICset—capacity of a single NIC (BCap/N)   N—number of NICs attached to the interchassis switch   LoadFactor—the average load or utilization factor, between 0 and 1, of the blade links       

   NCap is, in the preferred embodiment, assumed to be a fixed value determined by a number of external network links and their available peak capacity, while BCap and LoadFactor are taken as adjustable parameters. LoadFactor varies depending upon several well-known factors, including type(s) of application(s) and time of time-of-day. For example, an aggregate NCap of 2 gigabits/second could support up to 10 internal 1 gigabit/second links (BCap=10 gigabits/second) if the LoadFactor is 0.2 or less. However, if 14 internal links were active, the overall BCap would be reduced to achieve the desirable operational range. 
   The preferred embodiment adjusts BCap by controlling N and/or NICset. Management module  122  may set individual NIC rates to the same value (NICset) so that the aggregate N×NICset is less than or equal to the desired BCap/LoadFactor value. Management module  122  may reduce the maximum number (N) of active blades  105  allowed such that Nmax×NICset is less than or equal to the required BCap/LoadFactor value. Management module  122  may allocate NIC bandwidth using classes of NICs or other prioritization systems. For example, a first set M of NICs may have a first value for NICset1 with remaining NICs having NICset2 so that (M×NICset1)+(Nmax−M)×NICset2) is less than BCap/LoadFactor, based upon apriori knowledge of blade application requirements or similar blade-dependent factors. 
   Management module  122  sets and enforces NICset based upon each NIC  135  and/or switch  115  and/or server  100  dependent upon the NIC and/or switch and/or server design and capability. For example, most Ethernet NICs support both 100 Mbps and 1 Gbps rates at the physical link level. Using these two discrete link speeds, a NIC can be selectively set to either 100 Mbps or 1 Gbps via the IEEE 802.3 standard auto-negotiation. Currently, this standard does not permit a link speed to be changed after it is initially set, therefore the preferred embodiment will disconnect and auto-negotiate a new appropriate rate for an active link that is to be changed. Management module  122  is able to query each blade  110  and switch  135  to recieve its configuration and operating parameters relevant to the present invention, and in addition, each management module  122  is able to communicate with management modules  122  of other servers  100  to coordinate bandwidth usage across all servers. 
   However as discussed above, rates other than 10, 100, 1000 Mbps (e.g., 500 Mbps) could be enforced by management module  122  via appropriate driver code or firmware within NICs and/or NIC driver software on the blades and switch, with the 802.3 standard used to auto-negotiate the NIC link speed NICset, or management module  122  directly controlling or setting the desired value for NICset for each NIC or set of NICs. This setting can be accomplished with or without the need to disconnect and reconnect to alter link speed (dynamic configuration). 
     FIG. 2  is a schematic block diagram of a preferred embodiment for an ingress transmission capacity control process  200  implemented by management module  122 . Process  200  is initialized at step  205  and then, at step  210 , determines the egress transmission capacity (NCap) of extrachassis network  130 . 
   Next at step  215 , process  200  determines the blade NIC capacity (BCap) and process tests, at step  220 , whether BCap should be adjusted. In making this determination, process  200  tests whether NCap is less than LoadFactor times BCap. 
   When NCap is less than LoadFactor times BCap, process  200  advances to step  225  to determine an appropriate interchassis link rate for one or more of NICs  135 . Process  200  determines a value for NICset such that BCap is greater than or equal to NCap divided by LoadFactor. Process  200  may establish all NICsets to a single value, all NICsets of particular priority or class to the same value or within predetermined ranges appropriate for the priority or class, or establish NICset differently for each NIC. After step  225 , process  200  sets the interchassis link rate NICset at step  230 . 
   Thereafter, process  200  tests, at step  235 , whether a chassis change has been made. These changes include changes to NCap, BCap, or the LoadFactor. If no change is detected, process  200  returns to step  235  to continually test for a configuration change. When a change is detected, process  200  returns to step  210  as described above. 
   When the test at step  220  is negative and NCap is greater than or equal to BCap times LoadFactor, process  200  performs the test at step  235  as described above. In this preferred embodiment, process  200  determines a desired setting for NICset when NCap is too low relative to BCap times LoadFactor. When NCap increases or LoadFactor decreases or BCap falls far enough below NCap, management module  122  may increase BCap while preserving the desired relationship between NCap and BCap. 
   Depending upon specific implementations and application requirements, process  200  may be adapted and modified without departing from the present invention. For example, process  200  may disable one or more selected NICs and inhibit reconnection as discussed above. In some implementations, certain blades may have a higher priority than other blades. In these cases, process  200  can selectively restrict NICset or disconnect NICs of lesser priority blades. Also, the BCap may be tuned using dynamic information relating to the LoadFactor of the ingress transmission capacity. 
   Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.