Interconnect system for fiber channel arbitrated loop...

Details Interconnect system for fiber channel arbitrated loop... Interconnect system for fiber channel arbitrated loop...

2000-07-06

2002-10-22

Chin, Wellington (Department: 2665)

Multiplex communications

Pathfinding or routing

C370S360000, C370S401000, C370S422000, C709S233000, C709S249000, C710S106000, C710S120000

Reexamination Certificate

active

06470007

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to input/output channel and networking systems, and more particularly to methods of using a Fibre Channel fabric or intelligent bridging hub to interconnect Fibre Channel Arbitrated Loops composed of private loop devices (i.e., devices which do not support direct fabric attachment).
BACKGROUND OF THE INVENTION
Fibre Channel is an American National Standards Institute (ANSI) set of standards which describes a high performance serial transmission protocol which supports higher level storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre Channel was created to merge the advantages of channel technology with network technology to create a new I/O interface which meets the requirements of both channel and network users. Channel technology is usually implemented by I/O systems in a closed, structured and predictable environment, whereas network technology usually refers to an open, unstructured and unpredictable environment.
Advantages of Fibre Channel typically include the following. First, it achieves high performance, which is a critical in opening the bandwidth limitations of current computer to storage and computer to computer interfaces at speeds up to 1 gigabit per second or faster. Second, utilizing fiber optic technology, Fibre Channel can overcome traditional I/O channel distance limitations and interconnect devices over distances of 6 miles at gigabit speeds. Third, it is high level protocol independent, enabling Fibre Channel to transport a wide variety of protocols over the same media. Fourth, Fibre Channel uses fiber optic technology which has a very low noise properties. Finally, cabling is simple in that Fibre Channel typically replaces bulky copper cables with small lightweight fiber optic cables.
Fibre Channel supports three different topologies: point-to-point, Arbitrated Loop and fabric attached. The point-to-point topology attaches two devices directly. The Arbitrated Loop topology attaches devices in a loop. The fabric attached topology attaches a device directly to a fabric.
The Arbitrated Loop topology was initially designed to provide a lower cost interconnect than fabrics and to provide more interconnect than point-to-point topologies. The Arbitrated Loop topology was created by separating the transmit and receive fibers associated with each loop port and connecting the transmit output of one loop port to the receive input of the next loop port. Typically, characteristics of the Arbitrated Loop topology include: first it, allows up to 126 participating node ports and one participating fabric port to communicate, second, each node port implements a route filtering algorithm, and third, all ports on a single loop have the same upper 16 bits of the 24-bit NL_Port address identifier.
There are two classifications of devices on an Arbitrated Loop: private loop devices and public loop devices. Public loop devices attempt a Fabric Login (FLOGI) upon initialization. Public loop devices also are cognizant of all twenty four bits of the 24-bit NL_Port native port address identifier. Public loop devices will open the fabric port at Arbitrated Loop Physical Address (ALPA, bits
7
to
0
) zero when the domain and area (bits
23
to
8
) do not match their domain and area. Private loop devices use only the lower eight bits of the ALPA and can only communicate within the local loop.
Generally, the disadvantages of the Arbitrated Loop topology include: first, it is a blocking topology, that is, only a single connection between a pair of nodes is allowed at any point in time (excluding the broadcast mode). Second, device buffering occurs in each device as it has a six word buffer, creating a delay of up to 225 nanoseconds. This delay is additive with each device in the loop. The delay creates overhead for the communicating devices when a large number of devices are connected to a loop. Third, distance also adds delay to a loop and is additive for each device. For copper medium there is a 4 nanosecond delay per meter and for optical medium there is a 5 nanosecond delay per meter. Fourth, robustness is an issue since all devices are on one loop any device failure will cause the entire loop to fail or reset. Fifth, the total bandwidth available is limited to the bandwidth of the loop itself. Finally, device failure is an issue since while frames are being transmitted, a timeout in an upper level protocol may occur, thereby disrupting the applications.
Loop devices are typically interconnected on an Arbitrated Loop with a hub, see
FIG. 22
numeral
678
. The hub is a passive device, that is a loop exists within the hub
674
,
675
,
676
,
677
,
679
. A hub in most cases maintains the loop's integrity when devices are removed, powered off, or fail by using a port bypass circuit
674
,
675
,
676
,
677
. Hubs simply receive and redrive the signals to individual devices.
There are many disadvantages which result when interconnecting private loop devices with hubs: First, hubs do not address the blocking nature of the loop topology. Second, jitter is propagated from bypassed nodes. This additive affect causes loop instability when a large number of devices are interconnected. Third, when data is currently being transferred and a device attached to a hub is powered off or fails, the loop could be reset which is destructive to the communicating devices. Fourth, if a device is inserted into a live loop the loop will be reset which is destructive to the communicating devices.
The majority of initial Fibre Channel equipment deployment utilizes the Arbitrated Loop topology with hubs as the interconnect. These environments are experiencing all the previously defined problems inherent in both Arbitrated Loop topology and with hub deployment. The blocking nature of the Arbitrated Loop is limiting the number of devices on a loop. The distance and delay parameters are also creating more overhead for the loop. Finally the loop is being reset by single devices.
As such, it is the goal of this invention to provide apparatus and methods which solve or mitigate these problems.
SUMMARY OF THE INVENTION
This invention relates to methods and apparatus for Fibre Channel interconnection of a plurality of private loop devices through a Fibre Channel private loop device interconnect system. In the preferred embodiments, the Fibre Channel private loop device interconnect system is a fabric or an intelligent bridging hub. Through these methods and apparatus, multiple Fibre Channel Arbitrated Loops, the loops containing one or more private loop devices, may be interconnected even though on separate Arbitrated Loops.
In the preferred embodiment, an interconnection system is provided for connecting a plurality of physically separate Fibre Channel Arbitrated Loops, the loops either containing, or being adapted to contain, one or more private loop devices. The apparatus preferably includes at least a first Arbitrated Loop containing, or adapted to contain, one or more private loop devices, and at least a second Arbitrated Loop, either containing, or adapted to contain, one or more private loop devices. The Arbitrated Loops are interconnected via a Fibre Channel private loop device interconnect system which is disposed between the Arbitrated Loops.
In one embodiment, a Fibre Channel fabric is disposed between the Arbitrated Loops, and includes a routing filter which filters incoming Arbitrated Loop physical addresses (ALPAs) to determine which Fibre Channel frames must attempt to be routed through the fabric. Thus, by disposing routing information regarding private loop devices within the Fibre Channel private loop device interconnect system, multiple Arbitrated Loops containing private loop devices may be interconnected.
Any type of private loop device, consistent with the apparatus and methods stated herein, may be utilized in conjunction with this system. Examples of private loop devices include storage devices, such as tape drives, JBODs and RAID subsystems, host systems, and other connections within a system, such as bri

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