Patent Grant
7000011
1. Field of Invention
The present invention pertains to the field of networks. More particularly, this invention relates to designing interconnect fabrics of networks.
2. Art Background
A wide variety of networks may be viewed as a set of source nodes that communicate with a set of terminal nodes via an interconnect fabric. For example, a storage area network may be arranged as a set of computers as source nodes which are connected to a set of storage devices as terminal nodes via an interconnect fabric that includes communication links and devices such as hubs, routers, switches, etc. Devices such as hubs, routers, switches, etc., are hereinafter referred to as interconnect devices.
The communication requirements of an interconnect fabric may be characterized in terms of a set of flow requirements. A typical set of flow requirements specify the required communication bandwidth from each source node to each terminal node. The design of an interconnect fabric usually involves selecting the appropriate arrangement of physical communication links and interconnect devices and related components that will meet the flow requirements.
Prior methods for designing interconnect fabrics are usually based on manual design techniques. Such manual techniques may be based on heuristics and/or prepackaged structures. Unfortunately, such techniques are usually error prone and may result in an over-provisioned interconnect fabric that is more expensive than needed to meet the flow requirements. Moreover, such techniques are usually time-consuming and may require expert intervention, thereby increasing design costs.
A method is disclosed for designing an interconnect fabric for communication between a set of source nodes and a set of terminal nodes. The method partitions the flow requirements of the interconnect fabric into flow-sets and merges the flow-sets to reduce port violations with respect to available ports on source and terminal nodes while taking into account costs and feasibility of implementation.
In one embodiment, the method includes the steps of determining an arrangement of flow-sets in the interconnect fabric in response to a set of flow requirements for the source and terminal nodes. The method also includes determining one or more port violations in the source and terminal nodes which are associated with the arrangement of flow-sets and then alleviating at least one of the port violations by merging a pair of the flow-sets. The step of alleviating may be performed iteratively while taking into account the feasibility and costs of merging pairs of flow-sets.
Other features and advantages of the present invention will be apparent from the detailed description that follows.
The present invention is described with respect to particular exemplary embodiments thereof and reference is accordingly made to the drawings in which:
At step 20, an arrangement of flow-sets in the interconnect fabric is determined in response to a set of flow requirements for the source and terminal nodes. In one embodiment, step 20 is performed by generating a flow-set for each flow specified in the flow requirements for the interconnect fabric.
Table 1 shows an example set of flow requirements for an interconnect fabric under design.
The flow requirements in this example specify three source nodes (source nodes 40–44 in the figure below) and three terminal nodes (terminal nodes 50–54 in the figures below). If an interconnect fabric is to meet the flow requirements, it must contain communication paths between all pairs of the source and terminal nodes 40–44 and 50–54 having positive flow requirements and must have sufficient bandwidth to support all of the flow requirements simultaneously.
In one embodiment, the source nodes 40–44 are host computers and terminal nodes 50–52 are storage devices and the bandwidth values a–h are numbers expressed in units of megabits per second.
In other embodiments, there may be multiple flow requirements between a given source and terminal node pair. In such embodiments, the cells of Table 1 would contain a list of two or more entries.
At step 22, port violations which are associated with the arrangement of flow-sets in the interconnect fabric are determined. Port violations are determined for each source node 40–42 and each terminal node 50–52. In general, the number of port violations for a node is equal to the sum, over all flow-sets, of the number of required physical communication links to the node from that flow-set, minus the number of available ports in the node because each flow-set may require one or more physical communication links to a given source or terminal node in the network. In this example, the number of port violations for a node is equal to the number of flow-sets connected to the node minus the number of available ports in the node because each flow-set is carried by one physical communication link in the interconnect fabric.
In this example, each source node 40–42 and each terminal node 50–52 has two available ports for connections to the interconnect fabric. Therefore, the source node 40 has a port violation of one since each of its three flow-sets requires one physical communication link to the source node 40 and the source node 40 has only two available ports. Similarly, the source nodes 42–44 have port violations of one and zero, respectively, and the terminal nodes 50–54 have port violations of zero, one, and one, respectively, in the interconnect fabric. In other examples, the number of available ports on the source nodes 40–42 and the terminal nodes 50–52 may differ and the number of physical communication links required by a flow-set on a given source or terminal node it connects to may exceed one.
At step 24, at least one of the port violations is alleviated by merging a pair of the flow-sets. Step 24 initially involves selecting the pair of flow-sets in the current interconnect fabric that are to be merged. Initially, a candidate pair of flow-sets is chosen that would alleviate the port violation on a node with the greatest port violation if merged. If there is more than one such candidate pair then one of the candidate pairs that alleviates a port violation on a node having the next greatest port violation is chosen from among them. If there is more than one such candidate pair then a pair of them that would be least costly to merge is chosen. The cost of merging two candidate pairs may be determined by choosing the least expensive interconnect device that is feasible for the merged flow-set.
In the current state of the example interconnect fabric shown in
The candidate pairs of flow-sets considered at step 24 must be feasible to merge. An example of a pair of flow-sets that is not feasible to merge is a pair for which an interconnect device of sufficient bandwidth is not available. For example, a flow-set having 60 units of bandwidth cannot be merged with a flow-set having 50 units of bandwidth if the highest bandwidth interconnect device available is 100 units. Another example of a pair of flow-sets that is not feasible to merge is a pair that would exceed the available ports on every available interconnect device of the resulting flow-set. Candidate pairs that are not feasible to merge are bypassed at step 24 in favor of other candidate pairs.
If port violations still exist in the interconnect fabric after step 24, then another candidate pair of flow-sets is selected and merged in a repeat of step 24. The method 200 loops through steps 22–24 in an iterative fashion until all port violations are eliminated or until no further merges are feasible.
Each flow-set has at most one interconnect device associated with it and all of the flows for the flow-set are routed through that interconnect device or a single communication link if possible. When a pair of flow-sets are merged, their existing interconnect devices, if any, are replaced by a single interconnect device which may be of a different type than the replaced interconnect devices. Usually, the interconnect device that results in the least expensive routing of the flows in the flow-set is chosen from among those interconnect devices that are feasible for the flow-set.
The flow requirements data 110 specifies the desired flow requirements for the interconnect fabric design 120. The desired flow requirements include a list of source nodes, a list of terminal nodes and one or more bandwidth requirements for each pairing of the source and terminal nodes.
The port availability data 112 specifies the number of communication ports available on each source node and each terminal node and each available interconnect device.
The available component data 114 specifies a list of available communication links that may be employed in the interconnect fabric design 120 and specifies the bandwidth provided by each and any other relevant constraints. There are numerous examples of available communication links including fiber optic links, fibre channel links, wire-based links, and links such as SCSI as well as wireless links. The available component data 114 also specifies a list of available interconnect devices such as switching hubs, repeaters, etc., and port bandwidth, device bandwidth, and other relevant information.
The cost data 116 specifies costs associated with the available communication links and interconnect devices that may be employed in the interconnect fabric design 120. The cost data 116 also specifies the costs of ports for source and terminal nodes and interconnect devices. Other relevant costs may also be indicated.
The interconnect fabric design 120 generated by the fabric design tool 100 includes a list of the physical communication links and interconnect devices and ports, etc. and may include cost data.
The foregoing detailed description of the present invention is provided for the purposes of illustration and is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. Accordingly, the scope of the present invention is defined by the appended claims.
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