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Scheme for Providing Fair Port ID Allocation in a Switch Fabric

IP.com Disclosure Number: IPCOM000012667D
Original Publication Date: 2003-May-19
Included in the Prior Art Database: 2003-May-19
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Abstract

A Fibrechannel Fabric may have the capability of assigning more than one address identifier (N_Port ID) to each N_Port to which it is attached. Additional N_Port IDs are assigned by the Fabric upon request from the attached N_Ports. Since the total number of N_Port IDs assignable by a Fabric is limited, a scheme which prevents any single N_Port from obtaining more than it's fair share of N_Port IDs is described. Use of the scheme described here also guarantees that each N_Port will be able to obtain a sufficient number of N_Port IDs in order to operate effectively.

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Scheme for Providing Fair Port ID Allocation in a Switch Fabric

  Reference - "Fibre Channel-Framing and Signalling (FC-FS)," American National Standards Institute, INCITS Project 1331-D."

A typical configuration consisting of a Fibre Channel Fabric and attached N_Ports is shown in the figure.

Figure

  Each N_Port in the figure requires at least one address identifier (N_Port ID) to identify it. The Fabric assigns this address identifier to the N_Port during initialization. If an N_Port is used by a single logical entity, then this single N_Port ID is sufficient. It the N_Port is used by multiple logical entities, such as A, B, and C in the lower left of the figure, however, it may be desirable to assign each logical entity a unique identity. In this case, the N_Port requests the Fabric to assign it additional N_Port IDs.

  Each N_Port ID assigned by the Fabric consumes resources within the fabric, and a problem can occur in the above configuration if the N_Port requests an unfair number of N_Port IDs. When this occurs, it is impossible for the fabric to assign additional N_Port IDs to other N_Ports due to lack of resources. The scheme described below provides the means for preventing one of the N_Ports from obtaining more than a predetermined number of N_Port IDs; it also ensures that each attached device is able to obtain a minimum number of N_Port IDs.

   To prevent the above problem, the fabric is configured with a table which specifies the maximum number of N_Port IDs which can be assigned to each attached N_Port. Optionally, data specifying a guaranteed minimum number of N_Port IDs which can be assigned to each N_Port can also be configured into the fabric. An example of such a table is shown below.

Col. 1 Col. 2 Col. 3

Table 1

  Each entry in the Table 1 can be identified by either an "N_Port Name" or a Fabric port number. (See column 1.) The N_Port Name is an 8-byte number which

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permanently and uniquely identifies one of the attached N_Ports. Since the N_Port Name identifies the attached N_Port, the number of N_Port IDs which can be assigned to an N_Port is the same, regardless of the port on the Fabric to which it is attached.

  If the entries in the table are identified by a Fabric port number instead of an N_Port Name, then the number of N_...