Electrical computers and digital data processing systems: input/ – Access arbitrating
Reexamination Certificate
1998-05-12
2001-11-06
Lee, Thomas (Department: 2182)
Electrical computers and digital data processing systems: input/
Access arbitrating
C710S241000, C710S120000, C709S238000, C709S249000, C370S398000, C370S462000
Reexamination Certificate
active
06314488
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to fibre channel communication systems and, more particularly, to a method and system for segmenting a fibre channel arbitrated loop that achieves improved performance and manageability over prior art methods and systems.
BACKGROUND OF THE INVENTION
In recent years several technical developments have converged to a bigger than ever need for extremely fast data links. High performance computers have become the focus of much attention in the data communications industry. Performance improvements have spawned increasingly data-intensive and high-speed networking applications, such as multimedia and scientific visualization. However, the existing network interconnects between computers and I/O devices are unable to run at the speeds needed.
One approach to provide fast data links, called fibre channel, provides a practical, inexpensive, yet expandable means of quickly transferring data between workstations, mainframes, supercomputers, desktop computers, storage devices, displays and other peripherals. Fibre channel is the general name of an integrated set of standards being developed by the American National Standards Institute (ANSI). Fibre channel attempts to combine the best of channel and network methods of communication into a new I/O interface that meets the needs of both channel users and network users.
Fibre channel allows for an active intelligent interconnection scheme, called a fabric, to connect devices. In a fibre channel system a port simply manages a simple point-to-point connection between itself and the fabric. Since a fibre channel system relies on ports logging in with each other and the fabric, it is irrelevant whether the fabric is a circuit switch, an active hub or a loop. The topology can be selected depending on system performance requirements or packaging options. Possible fibre channel topologies include point-to-point, crosspoint switched or arbitrated loop.
In a fibre channel arbitrated loop, a shared media exists amongst participating end stations and storage devices, for example. In the fibre channel arbitrated loop, a switched media device enables multiple end stations to have simultaneous conversations. To date however, no fibre channel arbitrated loop provides multiple conversations in the arbitrated loops. In these loops with the shared media device, only one pair may have a conversation at a given time.
Existing fibre channel arbitrated loop technologies have limited bandwidth because the bandwidths are shared among all of the participants in the loop. This limits the conversations to only one conversation at a time. As a result, latency occurs within the fibre channel arbitrated loop, which latency can be detrimental to various applications.
A problem associated with latency can be seen in the example of a database application. For example, if a database application is to scale, in the sense that there are more processors in the loop to achieve performance, there is a latency of somewhere in the vicinity of 10-100 microseconds. In a fibre channel arbitrated loop, if one frame time is 20 microseconds, there may be the need to wait for five frames in front of a given frame in order to conduct a conversation. If this occurs, latency extending beyond the 100 microseconds rule occurs, which violates the database application latency limit.
During arbitrated in a fibre channel arbitrated loop, when one individual arbitrates and wins a loop, it sends data to another end station. As long as an end station sends data, it owns the arbitrated loop and no other end station may use the loop. Depending on the amount of data being sent and its data flow rate, the sending station could continuously consume loop resources. This would prevent other end stations from using the loop until the transmission from the end station consuming loop resources was completed. This idea of “fairness” has both to do with how long an end station uses the loop and how frequently the user has access to the loop.
With existing fibre channel arbitrated loop technology, up to 126 devices may be used. This, in most cases, does not occur. Instead most systems use on the order of eight to ten devices. There is no system, however, that practically provides the ability to have multiples of eight to ten devices within an arbitrated loop. Nor is there a device that permits the aggregation of arbitrated loop stations or stations. With the current technology, arbitrated operates only within one loop.
SUMMARY OF THE INVENTION
In light of the above, a need exists for a method and system for segmenting a fibre channel arbitrated loop communications network that eliminates or substantially reduces latency and unfairness, as well as provides increased performance and overall flexibility relative to prior art fibre channel arbitrated loop operational methods and systems.
According to one aspect of the present invention, there is provided a segmented storage and communication system for a fibre channel communications system that includes a segmentation router comprising a plurality of ports. Control instructions associate with the segmentation router to establish the segmentation router as a master router. This occurs by initializing each of at least a predetermined subset of the plurality of ports on the fibre channel arbitrated loop that are part of the segmentation router. This causes the segmentation router to win the LISM process performed by the fibre channel arbitrated loop. The control instructions further include instructions for transmitting loop initialization frames to the fibre channel arbitrated loop from each of the ports, beginning with LIPA frames. In the LIPA frames, all but the LIPA frame range of address bits are set to 1. This prevents other network loop ports attached to a router other than the master router from acquiring a duplicate address. This establishes a plurality of sub-loops each associated with a predetermined set of physical addresses.
A technical advantage that the present invention provides is the ability to segment a given fibre channel arbitrated loop into a number of separate loops. This permits users on end stations at separate segments to have conversations within a local segment and receive, for example, the benefit of 100 megabytes per second data flow, i.e., full band width operation in the fibre channel at the different segmented loops. Thus, as long as a given segment is not crossed it is possible, using the present invention, to provide multiplicative bandwidth within a single channel fibre channel arbitrated loop. This overcomes the latency problem that exists in current fibre channel arbitrated loop technology.
Another technical advantage that the present invention provides is the ability to segment the fibre channel arbitrated loop so that multiple conversations may occur simultaneously. This allows end stations that otherwise would not have access to the loop to have access to their defined subsegment. Thus, even in the instance of an unfair station consuming a disproportionate amount of time in the fibre channel arbitrated loop, other stations may communicate using the segmented loop.
The present invention also provides the technical advantage of permitting a topology that supports a wide array of infrastructure components making the segmentation transparent to the user while at the same time increasing the fairness and reducing latency among devices.
The present invention provides the technical advantage of a much less expensive solution than using a switchboard for multiple simultaneous conversations. Moreover, the installed base of infrastructure components in an arbitrated loop cannot readily employ switchboards or other switches. Segmenting the fibre channel arbitrated loop according to the teachings of the present invention provides a topology supporting all the infrastructure components that is completely transparent to the user.
REFERENCES:
patent: 5751715 (1998-05-01), Chan et al.
patent: 5768551 (1998-06-01), Bleiweiss et al.
patent: 6055228 (2000-04-01), DeKoning et al.
pat
Crossroads Systems Inc.
Du Thuan
Gra Car Ware and Freidenrich
Lee Thomas
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