# Patent

## Title
Method and apparatus for detecting and removing orphaned primitives in a fibre channel network

## Abstract

A method and system for detecting orphaned CLS primitives in a fibre channel network having a fibre channel switch element coupled to an arbitrated loop is provided. The method includes, sending an OPN primitive to a switch element port's own AL_PA to open a connection with itself; and determining if a CLS primitive is received within a loop a latency period. If a CLS primitive is received within the latency period then the CLS primitive is classified as an orphan and the orphaned CLS primitive is removed by the switch element by enabling a firmware based removal feature. The switch element includes a port that arbitrates for the arbitrated loop ownership and sends an OPN primitive to its own AL_PA.

## Background
I. CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 USC Section 119(e), to the following provisional patent applications:

    
    
        Ser. No. 60/487,876 filed on Jul. 16, 2003;
        Ser. No. 60/487,887 filed on Jul. 16, 2003;
        Ser. No. 60/487,875 filed on Jul. 16, 2003;
        Ser. No. 60/490,747 filed on Jul. 29, 2003;
        Ser. No. 60/487,667 filed on Jul. 16, 2003;
        Ser. No. 60/487,665 filed on Jul. 16, 2003;
        Ser. No. 60/492,346 filed on Aug. 4, 2003; and
    
    


Ser. No. 60/487,873 filed on Jul. 16, 2003.
The disclosures of the foregoing applications are incorporated herein by reference in their entirety.


BACKGROUND
1. Field of the Invention
The present invention relates to networks, and more particularly to detecting and removing orphaned CLOSE (CLS) primitives in a fibre channel network.
2. Background of the Invention
Fibre channel is a set of American National Standard Institute (ANSI) standards, which provide a serial transmission protocol for storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users.
Fibre channel supports three different topologies: point-to-point, arbitrated loop and fibre channel fabric. The point-to-point topology attaches two devices directly. The arbitrated loop topology attaches devices in a loop. The fibre channel fabric topology attaches host systems directly to a fabric, which are then connected to multiple devices. The fibre channel fabric topology allows several media types to be interconnected.
Fibre channel is a closed system that relies on multiple ports to exchange information on attributes and characteristics to determine if the ports can operate together. If the ports can work together, they define the criteria under which they communicate.
In fibre channel, a path is established between two nodes where the path's primary task is to transport data from one point to another at high speed with low latency, performing only simple error detection in hardware.
In a Fibre Channel Arbitrated Loop as defined in the FC-AL standard, the Close (CLS) primitive is transmitted by ports involved in a connection (Loop circuit) to terminate the connection. In most connections, each port involved (i.e., either in the OPEN or OPENED state) should remove the CLS primitive from loop traffic when it is received. If for some reason a port does not remove the CLS primitive (e.g., device failure or extraction from the loop), the CLS primitive becomes “orphaned” (i.e., unclaimed) and continues to transit the loop indefinitely. The orphaned CLS primitive prevents any subsequent connections from being maintained, destroying the integrity of the loop. There is no FC-AL defined solution for this problem other than a total re-initialization of the loop.
Therefore, there is a need for a method and system that is capable of detecting orphaned CLS primitives and removing them from a loop.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method for detecting orphaned CLS primitives in a fibre channel network having a fibre channel switch element coupled to an arbitrated loop is provided. The method includes, sending an OPN primitive to a switch element port's own AL_PA to open a connection with itself; and determining if a CLS primitive is received within a loop latency period. If a CLS primitive is received within the latency period then the CLS primitive is classified as an orphan and the orphaned CLS primitive is removed by the switch element by enabling a firmware based removal feature.
In yet another aspect of the present invention, a method for removing orphaned CLS primitives in a fibre channel network having a switch element coupled to an arbitrated loop is provided. The method includes, detecting an orphaned CLS primitive; enabling a remove CLS primitive feature; and replacing the orphaned CLS primitive with a Current Fill Word. A switch element port sends an OPN primitive to itself; and if a CLS primitive is received within a loop a latency period it is classified as an orphan.
In yet another aspect of the present invention, a fibre channel switch element coupled to an arbitrated loop in a fibre channel network is provided. The switch element includes, a port that arbitrates for the arbitrated loop ownership and sends an OPN primitive to its own AL_PA; and if the port receives a CLS primitive within a certain latency period then the CLS primitive is classified as an orphan. A remove CLS primitive feature is enabled by firmware of the switch element and the orphan CLS primitive is replaced by a current fill word.
In another aspect of the present invention, a fibre channel based network is provided. The network includes a switch element coupled to an arbitrated loop, wherein the switch element includes a port that arbitrates for the arbitrated loop ownership and sends an OPN primitive to its own AL_PA; and if the port receives a CLS primitive within a certain latency period then the CLS primitive is classified as an orphan.
In one aspect of the present invention, by detecting and removing the CLS primitive, traffic disruption is minimized.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof concerning the attached drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing features and other features of the present invention will now be described with reference to the drawings of a preferred embodiment. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following Figures:
FIG. 1 shows a block diagram of a storage area network;
FIG. 2 shows a flow diagram for detecting a CLS primitive, according to one aspect of the present invention;
FIGS. 3 and 3A show flow diagrams for removing orphaned CLS primitives, according to one aspect of the present invention;
FIG. 4 shows a block diagram of a switch element, according to one aspect of the present invention;
FIGS. 5A and 5B (jointly referred to as FIG. 5) show a block diagram of a transmission protocol engine, according to one aspect of the present invention; and
FIGS. 6A and 6B show block diagrams for a diagnostic module and a SES module, according to one aspect of the present invention.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Definitions:
The following definitions are provided as they are typically (but not exclusively) used in the fibre channel environment, implementing the various adaptive aspects of the present invention.
“AL_PA”: Arbitrated loop physical address.
“Arbitrated Loop timeout value (AL_TIME)”: This value (typically 15 milliseconds) represents twice the worst case round trip latency for a very large loop.
“FC-AL”: Fibre channel arbitrated loop process described in FC-AL standard (incorporated herein by reference in its entirety).
“Fibre channel ANSI Standard”: The standard (incorporated herein by reference in its entirety)

    
    
        describes the physical interface, transmission and signaling protocol of a high performance serial link for support of other high level protocols associated with IPI, SCSI, IP, ATM and others.
    
    


“FC-1”: Fibre channel transmission protocol, which includes serial encoding, decoding and error control.
“FC-2”: Fibre channel signaling protocol that includes frame structure and byte sequences.
“FC-3”: Defines a set of fibre channel services that are common across plural ports of a node.
“FC-4”: Provides mapping between lower levels of fibre channel, IPI and SCSI command sets, HIPPI data framing, IP and other upper level protocols.
“LIP”: Loop initialization protocol primitive.
“L_Port”: A port that contains Arbitrated Loop functions associated with the Arbitrated Loop topology.
“SES”: SCSI Enclosure Services.
“TPE”: Transmission Protocol Engine, a controller that operates at the FC-1 level.
To facilitate an understanding of the preferred embodiment, the general architecture and operation of a fibre channel system will be described. The specific architecture and operation of the preferred embodiment will then be described with reference to the general architecture of the fibre channel system.
FIG. 1 is a block diagram of a fibre channel system 100 implementing the methods and systems in accordance with the adaptive aspects of the present invention. System 100 includes plural devices that are interconnected. Each device includes one or more ports, classified as node ports (N_Ports), fabric ports (F_Ports), and expansion ports (E_Ports). Node ports may be located in a node device, e.g. server 103, disk array 105 and storage device 104. Fabric ports are located in fabric devices such as switch 101 and 102. Arbitrated loop 106 may be operationally coupled to switch 101 using arbitrated loop ports (FL_Ports).
The devices of FIG. 1 are operationally coupled via “links” or “paths”. A path may be established between two N_ports, e.g. between server 103 and storage 104. A packet-switched path may be established using multiple links, e.g. an N-Port in server 103 may establish a path with disk array 105 through switch 102.
FIG. 4 is a block diagram of an 18-port ASIC FC element 400A (also referred to as system 400A) according to one aspect of the present invention. FC element 400A provides various functionality in an FC_AL environment, including without limitation, FC element 400A operates as a loop controller and loop switch using switch matrix 408, in accordance with the FC-AL standard.
FC element 400A of the present invention is presently implemented as a single CMOS ASIC, and for this reason the term “FC element” and ASIC are used interchangeably to refer to the preferred embodiments in this specification. Although FIG. 4 shows 18 ports, the present invention is not limited to any particular number of ports.
System 400A provides a set of port control functions, status indications, and statistics counters for monitoring the health of the loop and attached devices, diagnosing faults, and recovering from errors.
ASIC 400A has 18 ports where 16 ports are shown as numeral 405 while a host port 404 and cascade port 404A are shown separately for convenience only. These ports are generic to common Fibre Channel port types, for example, L_Ports.
For illustration purposes only, all ports are drawn on the same side of ASIC 400A in FIG. 4. However, the ports may be located on any side of ASIC 400A. This does not imply any difference in port or ASIC design. Actual physical layout of the ports will depend on the physical layout of the ASIC.
Each port has transmit and receive connections to switch matrix 408 and includes transmit protocol engine 407 and a serial/deserializer 406. Frames enter/leave the link 405A and SERDES 406 converts data into 10-bit parallel data to fibre channel characters.
Switch matrix 408 dynamically establishes a connection for loop traffic. Switch matrix 408 includes a global arbiter (hence switch matrix 408 is also referred to as SGA 408) that provides lower latency and improved diagnostic capabilities while maintaining full Fibre Channel Arbitrated Loop (FC-AL) compliance.
Switch matrix 408 provides a quasi-direct architecture in the form of a buffer-less Switch Matrix. Switch matrix 408 includes data multiplexers that provide a path to each port.
SGA 408 creates a direct loop connection between source and destination devices. This connection methodology avoids the delay associated with data having to pass from one disk drive member of the loop to the next until the data has completed traversing the loop.
System 400A includes plural 12C (12C standard compliant) interfaces 412-413 that allow system 400A to couple to plural 12C ports each having a master and slave capability.
System 400A also includes a general-purpose input/output interface (“GPIO”) 415. This allows information from system 400A to be analyzed by any device that can use GPIO 415. Control/Status information 419 can be sent or received through module 415. Timer module 411 is provided for monitoring plural operations.
System 400A also includes a SPI module 414 that is used for parallel to serial and serial to parallel transfer between processor 400 firmware and flash memory 421 in the standard Little Endian format.
System 400A also includes a Universal Asynchronous Receiver/Transmitter (“UART”) interface 418 that converts serial data to parallel data (for example, from a peripheral device modem or data set) and vice-versa (data received from processor 400) complying industry standard requirements.
System 400A can also process tachometer inputs (received from a fan, not shown) using module 417. Processor 400 can read the tachometer input via a tachometer rate register and status register (not shown).
System 400A provides pulse width modulator (“PWM”) outputs via module 416. Processor 400 can program plural outputs.
System 400A also includes two frame manager modules 402 and 403 that are similar in structure. Processor 400 can set both modules 402 and 403 into a data capture mode by using a control bit as described below with respect to FIGS. 7 and 8. Processor 400 can access runtime code from memory 420 and input/output instructions from read only memory 409.
Port Management Interface (PMIF) 401 allows processor 400 access to various port level registers, SerDes modules 406 and TPE Management Interfaces 509 (FIG. 5). PMIF 401 contains a set of global control and status registers, receive and transmit test buffers, and three Serial Control Interface (SCIF) controllers (not shown) for accessing SerDes 406 registers.
Module 402 (also referred to as the “diag module 402”) is a diagnostic module used to transfer diagnostic information between a FC-AL and the firmware of system 400A.
Diag module 402 is functionally coupled to storage media (via ports 405) via dedicated paths outside switch matrix 408 so that its connection does not disrupt the overall loop. Diag module 402 is used for AL_PA capture during LIP propagation, drive(s) (coupled to ports 405) diagnostics and frame capture.
Module 403 (also referred to as “SES module 403”) complies with the SES standard and is functionally coupled to host port 404 and its output is routed through switch matrix 408. SES module 403 is used for in-band management services using the standard SES protocol.
When not bypassed, modules 402 and 403 receive primitives, primitive sequences, and frames. Based on the received traffic and the requests from firmware, modules 402 and 403 maintain loop port state machine (LPSM) (615, FIG. 6B) in the correct state per the FC-AL standard specification, and also maintains the current fill word.
Based on a current LPSM 615 state (OPEN or OPENED State), modules 402 and 403 receive frames, pass the frame onto a buffer, and alert firmware that a frame has been received. Module 402 and 403 follow FC-AL buffer to buffer credit requirements.
Firmware may request modules 402 and 403 to automatically append SOF and EOF to the outgoing frame, and to automatically calculate the outgoing frame's CRC using CRC generator 612. Modules 402 and 403 can receive any class of frames and firmware may request to send either fibre channel Class 2 or Class 3 frames.
FIGS. 6A and 6B show block diagrams for module 402 and 403. It is noteworthy that the structure in FIGS. 6A and 6B can be used for both modules 402 and 403. FIG. 6B is the internal data path of a FC port 601 coupled to modules 402/403.
Modules 402 and 403 interface with processor 400 via an interface 606. Incoming frames to modules 402 and 403 are received from port 601 (which could be any of the ports 404, 404A and 405) and stored in frame buffer 607. Outgoing frames are also stored in frame buffer 607. Modules 402 and 403 have a receive side memory buffer based on “first-in, first-out” principle, (“FIFO”) (RX_FIFO) 603 and transmit side (TX_FIFO) FIFO 604 interfacing random access FIFO 605. A receive side FIFO 603 signals to firmware when incoming frame(s) are received. A transmit side FIFO 604 signals to hardware when outgoing frames(s) are ready for transmission. A frame buffer 607 is used to stage outgoing frames and to store incoming frames. Modules 602 and 602A are used to manage frame traffic from port 601 to buffers 603 and 604, respectively.
Modules 402 and 403 use various general-purpose registers 608 for managing control, status and timing information.
Based on the AL_PA, modules 402 and 403 monitor received frames and if a frame is received for a particular module (402 or 403), it will pass the frame onto a receive buffer and alert the firmware that a frame has been received via a receive side FIFO 603. Modules 402 and 403 follow the FC-AL buffer-to-buffer credit requirements using module 616. Modules 402 and 403 transmit primitives and frames based on FC-AL rules. On request, modules 402 and 403 may automatically generate SOF and EOF during frame transmission (using module 613). On request, modules 402 and 403 may also automatically calculate the Cyclic Redundancy Code (CRC) during frame transmission, using module 612.
Overall transmission control is performed by module 611 that receives data, SOF, EOF and CRC. A word assembler module 609 is used to assemble incoming words, and a fill word module 610 receives data “words” before sending it to module 611 for transmission. Transmit control module 614 is used by module 611 to perform transmit buffer control operations.
In one aspect of the present invention, SES 403 is used to detect if there is an orphaned CLS primitive on the loop and a TPE (407) to remove it. In order to detect an orphaned CLS primitive, SES 403 arbitrates for ownership of the loop and once it has obtained ownership, it establishes a connection with itself by sending an OPN primitive to its own AL_PA. Once the connection to itself is opened, if SES 403 receives a CLS primitive within the round trip latency time of the loop, then the CLS primitive is orphaned since SES 403 did not send it. In one aspect of the present invention, the loop latency time could be set (for example, 15 millisecond (AL_TIME)),or it could be determined through another mechanism, such as counting the time it takes for an OPN primitive that SES 403 sent to itself to traverse the loop.
In one aspect of the present invention, to remove an orphaned CLS primitive, system 400A firmware enables the “remove CLS” feature in the host port 404 TPE since all loop traffic enters through this port. The host port 404 TPE is set to remove a single CLS primitive. When a CLS primitive enters the host port 404 TPE, it is detected and removed by replacing it with a Current Fill Word (CFW) value. The detection process can then be repeated to determine if there are any more orphaned CLS primitives traversing the loop.
In yet another aspect of the present invention, system 400A firmware is used to remove an orphaned CLS primitive. Typically, LPSM 615 sends a CLS primitive after it receives a CLS primitive. In the present invention, after system 400A receives an orphaned CLS primitive, it transitions the LPSM 615 to a MONITORING State without sending a CLS primitive. The firmware inhibits sending the CLS primitive after it receives an orphaned CLS primitive. Thereafter, firmware requests to by-pass the L_Port and waits for LPSM 615 to be in a Monitoring state without sending a CLS, and requests to enable the affected L_Port.
System 400A firmware may use any method to transition LPSM 615 to the MONITORING state without sending a CLS.
FIG. 2 shows a flow diagram for detecting a CLS primitive, according to one aspect of the present invention. In step S200, SES module 403 arbitrates for loop ownership, per FC-AL standard.
In step S201, SES 403 sends an OPN primitive (as defined by FC standards) to its own AL_PA.
In step S202, SES 403 determines if it received a CLS primitive within a loop latency period. This could be pre-set by firmware or based on a real count of the time it takes for a value to traverse the loop.
In step S203, if a CLS primitive is received within the loop latency period, then the CLS is designated as “orphaned” and the process moves to FIG. 3 for removing the orphaned primitive.
FIG. 3 shows a flow diagram for removing orphaned CLS primitives. In step S300, firmware enables the CLS primitive removal feature.
In step S301, the TPE for host port 404 detects the orphaned CLS primitive.
In step S302, the CLS primitive is replaced by a current fill word.
The detection/removal process can be repeated to determine if there are any more orphaned CLS primitives. SES module 403 can be pre-programmed by processor 400 firmware to perform this operation frequently.
FIG. 3A shows another flow diagram to remove orphaned CLS primitives. In step S310, firmware of system 404A inhibits sending the CLS primitive, and then proceeds to step S311.
In step S311, system 400A firmware requests to bypass the L_Port. In step S312, firmware waits for the LPSM 615 to transition to a MONITORING State. When the LPSM 615 reaches a MONITORING State, in step S313, firmware requests to enable the L_Port, and normal network activity resumes.
It is noteworthy that the present invention is not limited to any particular method where LPSM 615 transitions to MONITORING state without sending a CLS primitive.
FIG. 5 shows a block diagram of the transmission protocol engine (“TPE”) 407. TPE 407 maintains plural counters/registers to interact with drives coupled to ports 405. Each TPE 407 interacts with processor 400 via port manager interface 401.
Each Fibre Channel port of system 400A includes a TPE module for interfacing to with SerDes 406. TPE 407 handles most of the FC-1 layer (transmission protocol) functions, including 10B receive character alignment, 8B/10B encode/decode, 32-bit receive word synchronization, and elasticity buffer management for word re-timing and TX/RX frequency compensation.
SerDes modules 406 handle the FC-1 serialization and de-serialization functions. Each SerDes 406 port consists of an independent transmit and receive node.
TPE 407 has a receive module 500 (that operates in the Rx clock domain 503) and a transmit module 501. Data 502 is received from SERDES 406 and decoded by decoding module 504. A parity generator module 505 generates parity data. SGA interface 508 allows TPE to communicate with switch 514 or switch matrix 408. Interface 508 (via multiplexer 507) receives information from a receiver module 506 that receives decoded data from decode module 504 and parity data from module 505.
Management interface module 509 interfaces with processor 400. Transmit module 501 includes a parity checker 511, a transmitter 510 and an encoder 512 that encodes 8-bit data into 10-bit data. 10-bit transmit data is sent to SERDES 406 via multiplexer 513.
In one aspect of the present invention, by detecting and removing the CLS primitive, traffic disruption is minimized.
Although the present invention has been described with reference to specific embodiments, these embodiments are illustrative only and not limiting. Many other applications and embodiments of the present invention will be apparent in light of this disclosure and the following claims.

## Claims

1. A method for detecting orphaned close (CLS) primitives in a fibre channel network having a fibre channel switch element coupled to an arbitrated loop, the method comprising:
sending an open (OPN) primitive from a switch element port to its own arbitrated loop physical address (AL_PA) to open a connection with itself; and
determining if a CLS primitive is received by the switch element port within a loop latency period; and
if a CLS primitive is received within the latency period, then the CLS primitive is classified as an orphan; wherein
the latency period is either set at a desired value or determined.

2. The method of claim 1, further comprising the step of removing the orphaned CLS primitive by enabling a firmware based removal feature.

3. The method of claim 2, wherein by removing the CLS primitive traffic disruption is minimized.

4. A method for removing orphaned close( CLS) primitives in a fibre channel network having a switch element coupled to an arbitrated loop, the method comprising:
detecting an orphaned CLS primitive in the loop;
enabling a remove CLS primitive feature; and
removing the orphaned CLS primitive by replacing it with a Current Fill Word.

5. The method of claim 4, wherein the step of detecting an orphaned CLS primitive includes a switch element port sending an open (OPN) primitive to itself and if a CLS primitive is received within a loop latency period then it is classified as an orphan.

6. The method of claim 5, wherein the orphaned CLS primitive is removed by the switch element by enabling a firmware based removal feature.

7. The method of Claim 4, wherein by removing the CLS primitive traffic disruption is minimized.

8. A switch element coupled to an arbitrated loop in a fibre channel network, the switch element for detecting orphaned close CLS) primitives, the switch element comprising:
a port for arbitrating for ownership of the arbitrated loop and for sending an open (OPN) primitive to its own arbitrated loop physical address (AL_PA) to open a connection with itself, the port being further for determining if a CLS primitive is received within a loop latency period;
wherein if the port receives a CLS primitive within the latency period then the CLS primitive is classified as an orphan, and the latency period is either set at a desired value or determined.

9. The switch element of claim 8, further comprising firmware for enabling a remove CLS primitive feature and for replacing the orphan CLS primitive by a current fill word.

10. The switch element of claim 8, wherein the firmware inhibits sending a response to the orphan CLS primitive.

11. A fibre channel based network, comprising:
a switch element coupled to an arbitrated loop, the switch element for detecting orphaned CLS primitives, wherein the switch element includes a port for ownership of the arbitrated loop and for sending an open (OPN) primitive to its own arbitrated loop physical address (AL_PA) to open a connection with itself, the port being further for determining if a CLS primitive is received within a loop latency period; and
wherein if the port receives a CLS primitive within the latency period then the CLS primitive is classified as an orphan, and the latency period is either set at a desired value or determined.

12. The switch element of claim 11, further comprising firmware for enabling a remove CLS primitive feature and for replacing the orphan CLS primitive by a current fill word.

13. The switch element of claim 11, wherein the firmware inhibits sending a response to the orphan CLS primitive.

14. The method of claim 2, wherein the step of removing the orphaned CLS primitive comprises replacing the orphaned CLS primitive with a Current Fill Word value.

15. The method of claim 1, wherein the latency period is determined by counting the time it takes for a primitive sent by the port to itself to traverse the loop.

16. The switch element of claim 8, wherein the latency period is determined by counting the time it takes for a primitive sent by the port to itself to traverse the loop.

17. The switch element of claim 11, wherein the latency period is determined by counting the time it takes for a primitive sent by the port to itself to traverse the loop.