Method and system for managing traffic in fibre channel systems

Abstract

Method and system for routing fiber channel frames using a fiber channel switch element is provided. The method includes, inserting a time stamp value in a fiber channel frame that is received at a receive segment of the fiber channel switch element; determining if a timeout occurs after a frame arrives at a receive buffer; and processing the frame if the timeout occurred. The method also includes, determining if a delta time value, which provides an accumulated wait time for a frame, is present in frame data; subtracting the delta time stamp value from a global time stamp value and using the resulting time stamp value to determine frame timeout status in the fiber channel switch element. A timeout checker circuit declares a timeout after comparing a time stamp value that is inserted in a fiber channel frame with a programmed time out value and global counter value.

Description

BACKGROUND

1. Field of the Invention

The present invention relates to fibre channel systems, and more particularly, to determining frame time out to minimize frame latency and reduce congestion.

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.

Fibre channel fabric devices include a node port or “N_Port” that manages fabric connections. The N_port establishes a connection to a fabric element (e.g., a switch) having a fabric port or F_port. Fabric elements include the intelligence to handle routing, error detection, recovery, and similar management functions.

A fibre channel switch is a multi-port device where each port manages a simple point-to-point connection between itself and its attached system. Each port can be attached to a server, peripheral, I/O subsystem, bridge, hub, router, or even another switch. A switch receives messages from one port and automatically routes it to another port. Multiple calls or data transfers happen concurrently through the multi-port fibre channel switch.

Fibre channel switches use memory buffers to hold frames received and sent across a network. Associated with these buffers are credits, which are the number of frames that a buffer can hold per fabric port.

Frames enter a fabric switch element at a given time, but for whatever reason may be stalled in the switch element. This can cause congestion and frame latency causing degradation in the overall performance of the network.

A fibre channel fabric is required to either deliver or discard a frame within certain duration, known as RA_TOV (per fibre channel standard, FC-FS). Error recovery procedures depend on this aspect. Conventional fibre channel switch elements do not know how long a frame has taken to traverse other switch elements in the fabric before arriving at a local switch element.

Therefore, what is required is a method and system for switch elements to track the total time a frame has been in the fabric and declare a time-out if the frame has not been delivered/processed in time.

SUMMARY OF THE PRESENT INVENTION

In one aspect of the present invention, a method for routing fibre channel frames using a fibre channel switch element is provided. The method includes,

inserting a time stamp value in a fibre channel frame that is received at a receive segment of the fibre channel switch element; determining if a timeout occurs after a frame arrives at a receive buffer; and

processing the frame if the timeout occurred.

The method also includes, determining if a delta time value, which provides an accumulated wait time for a frame, is present in frame data; subtracting the delta time stamp value from a global time stamp value and using the resulting time stamp value to determine frame timeout status in the fibre channel switch element.

In another aspect of the present invention, a fibre channel switch element for routing fibre channel frames is provided. The fibre channel switch element includes a receive and transmit segment for receiving and transmitting fibre channel frames, wherein the receive and transmit segments include a timeout checker circuit that declares a timeout after comparing a time stamp value that is inserted in a fibre channel frame with a programmed time out value and a global counter value. The programmed time out value is used to declare a major or minor timeout.

Also, a fibre channel frame received by the receive segment includes a delta time value, which specifies an accumulated elapsed time for a frame in transit. If an incoming frame includes the delta time feature then the delta time value is subtracted from the global counter value, wherein the result of the subtraction becomes the delta time value for the frame when the frame moves from the receive segment to the transmit segment.

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. 1A shows an example of a Fibre Channel network system;

FIG. 1B shows an example of a Fibre Channel switch element, according to one aspect of the present invention;

FIG. 1C shows a block diagram of a 20-channel switch chassis, according to one aspect of the present invention;

FIG. 1D shows a block diagram of a Fibre Channel switch element with sixteen GL_Ports and four 10 G ports, according to one aspect of the present invention;

FIGS. 2A/2B (jointly referred to as FIG. 2) show another block diagram of a Fibre Channel switch element with sixteen GL_Ports and four 10 G ports, according to one aspect of the present invention;

FIGS. 3A/3B (jointly referred to as FIG. 3) show a block diagram of a GL_Port, according to one aspect of the present invention;

FIGS. 4A/4B (jointly referred to as FIG. 3) show a block diagram of XG_Port (10 G) port, according to one aspect of the present invention;

FIGS. 5A-1/5A-2 (referred to herein as FIG. 5A) show a schematic with a timestamp feature, according to one aspect of the present invention;

FIG. 5B shows a schematic of time out checker circuit, according to one aspect of the present invention; and

FIG. 6 shows a flow diagram for managing frame time outs and reducing congestion, 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.

“Delta Time Value”: A value inserted in the fibre channel frame that denotes the total time a frame has spent while he frame is in transit from a source port to a destination port.

“D_ID”: 24 bit fibre channel header field that contains destination address.

“Domain_Id”: The high 8 bits of a 24 bit fibre channel address that identifies a switch within a fabric.

“EOF”: End of Frame, defined by Fibre Channel standards.

“E-Port”: A fabric expansion port that attaches to another Interconnect port to create an Inter-Switch Link.

“F-Port”: A port to which non-loop N_Ports are attached to a fabric and does not include FL_ports.

“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.

“FC-FS”: Fibre channel standard, incorporated herein by reference in its entirety, for framing and signaling, including frame structure, basic link maintenance and login, and sequence and exchange operation, incorporated herein by reference in its entirety.

“FC-GS-3”: Fibre channel specification incorporated herein by reference in its entirety for fabric servers and includes zoning.

“Fabric”: The structure or organization of a group of switches, target and host devices (NL_Port, N_ports etc.).

“Fabric Topology”: This is a topology where a device is directly attached to a fibre channel fabric that uses destination identifiers embedded in frame headers to route frames through a fibre channel fabric to a desired destination.

“FL_Port”: A L_Port that is able to perform the function of a F_Port, attached via a link to one or more NL_Ports in an Arbitrated Loop topology.

“Global Time Value”: means a time value with respect to a switch element (for example, an ASIC) and not the entire fabric.

“Hard Zoning”: This restricts access to certain ports by filtering frames.

“Inter-Switch Link”: A Link directly connecting the E_port of one switch to the E_port of another switch.

Port: A general reference to N. Sub.—Port or F.Sub.—Port.

“L_Port”: A port that contains Arbitrated Loop functions associated with the Arbitrated Loop topology.

“N-Port”: A direct fabric attached port.

“NL_Port”: A L_Port that can perform the function of a N_Port.

“S_ID”: 24 bit fibre channel header field that contains the source address of a frame.

“SOF”: Start of Frame, defined by Fibre Channel standards.

“Switch”: A fabric element conforming to the Fibre Channel Switch standards.

“Time Out”: A duration that has exceeded or is equal to a certain threshold value. This indicates that a frame has been waiting for processing for more than a desired time period within a fibre channel switch element.

Fibre Channel System:

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. 1A 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. 1A 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.

Fabric Switch Element

FIG. 1B is a block diagram of a 20-port ASIC fabric element according to one aspect of the present invention. FIG. 1B provides the general architecture of a 20-channel switch chassis using the 20-port fabric element. Fabric element includes ASIC 20 with non-blocking fibre channel class 2 (connectionless, acknowledged) and class 3 (connectionless, unacknowledged) service between any ports. It is noteworthy that ASIC 20 may also be designed for class 1 (connection-oriented) service, within the scope and operation of the present invention as described herein.

The fabric element of the present invention is presently implemented as a single CMOS ASIC, and for this reason the term “fabric element” and ASIC are used interchangeably to refer to the preferred embodiments in this specification. Although FIG. 1B shows 20 ports, the present invention is not limited to any particular number of ports.

ASIC 20 has 20 ports numbered in FIG. 1B as GL0 through GL19. These ports are generic to common Fibre Channel port types, for example, F_Port, FL_Port and E-Port. In other words, depending upon what it is attached to, each GL port can function as any type of port. Also, the GL port may function as a special port useful in fabric element linking, as described below.

For illustration purposes only, all GL ports are drawn on the same side of ASIC 20 in FIG. 1B. However, the ports may be located on both sides of ASIC 20 as shown in other figures. 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 GL0-GL19 has transmit and receive connections to switch crossbar 50. One connection is through receive buffer 52, which functions to receive and temporarily hold a frame during a routing operation. The other connection is through a transmit buffer 54.

Switch crossbar 50 includes a number of switch crossbars for handling specific types of data and data flow control information. For illustration purposes only, switch crossbar 50 is shown as a single crossbar. Switch crossbar 50 is a connectionless crossbar (packet switch) of known conventional design, sized to connect 21×21 paths. This is to accommodate 20 GL ports plus a port for connection to a fabric controller, which may be external to ASIC 20.

In the preferred embodiments of switch chassis described herein, the fabric controller is a firmware-programmed microprocessor, also referred to as the input/out processor (“IOP”). IOP 66 is shown in FIG. 1C as a part of a switch chassis utilizing one or more of ASIC 20. As seen in FIG. 1B, bi-directional connection to IOP 66 is routed through port 67, which connects internally to a control bus 60. Transmit buffer 56, receive buffer 58, control register 62 and Status register 64 connect to bus 60. Transmit buffer 56 and receive buffer 58 connect the internal connectionless switch crossbar 50 to IOP 66 so that it can source or sink frames.

Control register 62 receives and holds control information from IOP 66, so that IOP 66 can change characteristics or operating configuration of ASIC 20 by placing certain control words in register 62. IOP 66 can read status of ASIC 20 by monitoring various codes that are placed in status register 64 by monitoring circuits (not shown).

FIG. 1C shows a 20-channel switch chassis S2 using ASIC 20 and IOP 66. S2 will also include other elements, for example, a power supply (not shown). The 20 GL ports correspond to channel C0-C19. Each GL port has a serial/deserializer (SERDES) designated as S0-S19. Ideally, the SERDES functions are implemented on ASIC 20 for efficiency, but may alternatively be external to each GL port.

Each GL port has an optical-electric converter, designated as OE0-OE19 connected with its SERDES through serial lines, for providing fibre optic input/output connections, as is well known in the high performance switch design. The converters connect to switch channels C0-C19. It is noteworthy that the ports can connect through copper paths or other means instead of optical-electric converters.

FIG. 1D shows a block diagram of ASIC 20 with sixteen GL ports and four 10 G (Gigabyte) port control modules designated as XG0-XG3 for four 10 G ports designated as XGP0-XGP3. ASIC 20 include a control port 62A that is coupled to IOP 66 through a PCI connection 66A.

FIG. 2 shows yet another block diagram of ASIC 20 with sixteen GL and four XG port control modules. Each GL port control module has a Receive port (RPORT) 69 with a receive buffer (RBUF) 69A and a transmit port 70 with a transmit buffer (TBUF) 70A, as described below in detail. GL and XG port control modules are coupled to physical media devices (“PMD”) 76 and 75 respectively.

Control port module 62A includes control buffers 62B and 62D for transmit and receive sides, respectively. Module 62A also includes a PCI interface module 62C that allows interface with IOP 66 via a PCI bus 66A.

XG_Port (for example 74B) includes RPORT 72 with RBUF 71 similar to RPORT 69 and RBUF 69A and a TBUF and TPORT similar to TBUF 70A and TPORT 70. Protocol module 73 interfaces with SERDES to handle protocol based functionality.

GL Port:

FIGS. 3A-3B (referred to as FIG. 3) show a detailed block diagram of a GL port as used in ASIC 20. GL port 300 is shown in three segments, namely, receive segment (RPORT) 310, transmit segment (TPORT) 312 and common segment 311.

Receive Segment of GL Port:

Frames enter through link 301 and SERDES 302 converts data into 10-bit parallel data to fibre channel characters, which are then sent to receive pipe (“Rpipe” may be referred to as Rpie 1 and/or Rpipe 2) 303A via a de-multiplexer (DEMUX) 303. Rpipe 303A includes, parity module 305 and decoder 304. Decoder 304 decodes 10B data to 8B and parity module 305 adds a parity bit. Rpipe 303A also performs various Fibre Channel standard functions such as detecting a start of frame (SOF), end-of frame (EOF), Idles, R_RDYs (fibre channel standard primitive) and the like, which are not described since they are standard functions.

Rpipe 303A connects to smoothing FIFO (SMF) module 306 that performs smoothing functions to accommodate clock frequency variations between remote transmitting and local receiving devices.

Frames received by RPORT 310 are stored in receive buffer (RBUF) 69A, (except for certain Fibre Channel Arbitrated Loop (AL) frames). Path 309 shows the frame entry path, and all frames entering path 309 are written to RBUF 69A as opposed to the AL path 308.

Cyclic redundancy code (CRC) module 313 further processes frames that enter GL port 300 by checking CRC and processing errors according to FC_PH rules. The frames are subsequently passed to RBUF 69A where they are steered to an appropriate output link. RBUF 69A is a link receive buffer and can hold multiple frames.

Reading from and writing to RBUF 69A are controlled by RBUF read control logic (“RRD”) 319 and RBUF write control logic (“RWT”) 307, respectively. RWT 307 specifies which empty RBUF 69A slot will be written into when a frame arrives through the data link via multiplexer 313B, CRC generate module 313A and EF module 314. EF (external proprietary format) module 314 encodes proprietary (i.e. non-standard) format frames to standard Fibre Channel 8B codes. Mux 313B receives input from Rx Spoof module 314A, which encodes frames to a proprietary format (if enabled). RWT 307 controls RBUF 69A write addresses and provides the slot number to tag writer (“TWT”) 317.

RRD 319 processes frame transfer requests from RBUF 69A. Frames may be read out in any order and multiple destinations may get copies of the frames.

Steering state machine (SSM) 316 receives frames and determines the destination for forwarding the frame. SSM 316 produces a destination mask, where there is one bit for each destination. Any bit set to a certain value, for example, 1, specifies a legal destination, and there can be multiple bits set, if there are multiple destinations for the same frame (multicast or broadcast).

SSM 316 makes this determination using information from alias cache 315, steering registers 316A, control register 326 values and frame contents. IOP 66 writes all tables so that correct exit path is selected for the intended destination port addresses.

The destination mask from SSM 316 is sent to TWT 317 and a RBUF tag register (RTAG) 318. TWT 317 writes tags to all destinations specified in the destination mask from SSM 316. Each tag identifies its corresponding frame by containing an RBUF 69A slot number where the frame resides, and an indication that the tag is valid.

Each slot in RBUF 69A has an associated set of tags, which are used to control the availability of the slot. The primary tags are a copy of the destination mask generated by SSM 316. As each destination receives a copy of the frame, the destination mask in RTAG 318 is cleared. When all the mask bits are cleared, it indicates that all destinations have received a copy of the frame and that the corresponding frame slot in RBUF 69A is empty and available for a new frame.

RTAG 318 also has frame content information that is passed to a requesting destination to pre-condition the destination for the frame transfer. These tags are transferred to the destination via a read multiplexer (RMUX) (not shown).

Transmit Segment of GL Port:

Transmit segment (TPORT) 312 performs various transmit functions. Transmit tag register (TTAG) 330 provides a list of all frames that are to be transmitted. Tag Writer 317 or common segment 311 write TTAG 330 information. The frames are provided to arbitration module (“transmit arbiter” (“TARB”)) 331, which is then free to choose which source to process and which frame from that source to be processed next.

TTAG 330 includes a collection of buffers (for example, buffers based on a first-in first out (“FIFO”) scheme) for each frame source. TTAG 330 writes a tag for a source and TARB 331 then reads the tag. For any given source, there are as many entries in TTAG 330 as there are credits in RBUF 69A.

TARB 331 is activated anytime there are one or more valid frame tags in TTAG 330. TARB 331 preconditions its controls for a frame and then waits for the frame to be written into TBUF 70A. After the transfer is complete, TARB 331 may request another frame from the same source or choose to service another source.

TBUF 70A is the path to the link transmitter. Typically, frames don't land in TBUF 70A in their entirety. Mostly, frames simply pass through TBUF 70A to reach output pins, if there is a clear path.

Switch Mux 332 is also provided to receive output from crossbar 50. Switch Mux 332 receives input from plural RBUFs (shown as RBUF 00 to RBUF 19), and input from CPORT 62A shown as CBUF 1 frame/status. TARB 331 determines the frame source that is selected and the selected source provides the appropriate slot number. The output from Switch Mux 332 is sent to ALUT 323 for S_ID spoofing and the result is fed into TBUF Tags 333.

TxMUX 339 chooses which data path to connect to the transmitter. The sources are: primitive sequences specified by IOP 66 via control registers 326 (shown as primitive 339A), and signals as specified by Transmit state machine (“TSM”) 346, frames following the loop path, or steered frames exiting the fabric via TBUF 70A.

TSM 346 chooses the data to be sent to the link transmitter, and enforces all fibre Channel rules for transmission. TSM 346 receives requests to transmit from loop state machine 320, TBUF 70A (shown as TARB request 346A) and from various other IOP 66 functions via control registers 326 (shown as IBUF Request 345A). TSM 346 also handles all credit management functions, so that Fibre Channel connectionless frames are transmitted only when there is link credit to do so.

Loop state machine (“LPSM”) 320 controls transmit and receive functions when GL_Port is in a loop mode. LPSM 320 operates to support loop functions as specified by FC-AL-2.

IOP buffer (“IBUF”) 345 provides IOP 66 the means for transmitting frames for special purposes.

Frame multiplexer (“Frame Mux”) 336 chooses the frame source, while logic (TX spoof 334) converts D_ID and S_ID from public to private addresses. Frame Mux 336 receives input from Tx Spoof module 334, TBUF tags 333, and Mux 335 to select a frame source for transmission.

EF (external proprietary format) module 338 encodes proprietary (i.e. non-standard) format frames to standard Fibre Channel 8B codes and CRC module 337 generates CRC data for the outgoing frames.

Modules 340-343 put a selected transmission source into proper format for transmission on an output link 344. Parity 340 checks for parity errors, when frames are encoded from 8B to 10B by encoder 341, marking frames “invalid”, according to Fibre Channel rules, if there was a parity error. Phase FIFO 342A receives frames from encode module 341 and the frame is selected by Mux 342 and passed to SERDES 343. SERDES 343 converts parallel transmission data to serial before passing the data to the link media. SERDES 343 may be internal or external to ASIC 20.

Common Segment of GL Port:

As discussed above, ASIC 20 include common segment 311 comprising of various modules. LPSM 320 has been described above and controls the general behavior of TPORT 312 and RPORT 310.

A loop look up table (“LLUT”) 322 and an address look up table (“ALUT”) 323 is used for private loop proxy addressing and hard zoning managed by firmware.

Common segment 311 also includes control register 326 that controls bits associated with a GL_Port, status register 324 that contains status bits that can be used to trigger interrupts, and interrupt mask register 325 that contains masks to determine the status bits that will generate an interrupt to IOP 66. Common segment 311 also includes AL control and status register 328 and statistics register 327 that provide accounting information for FC management information base (“MIB”).

Output from status register 324 may be used to generate a Fp Peek function. This allows a status register 324 bit to be viewed and sent to the CPORT.

Output from control register 326, statistics register 327 and register 328 (as well as 328A for an X_Port, shown in FIG. 4) is sent to Mux 329 that generates an output signal (FP Port Reg Out).

Output from Interrupt register 325 and status register 324 is sent to logic 335 to generate a port interrupt signal (FP Port Interrupt).

BIST module 321 is used for conducting embedded memory testing.

XG Port

FIGS. 4A-4B (referred to as FIG. 4) show a block diagram of a 10 G Fibre Channel port control module (XG FPORT) 400 used in ASIC 20. Various components of XG FPORT 400 are similar to GL port control module 300 that are described above. For example, RPORT 310 and 310A, Common Port 311 and 311A, and TPORT 312 and 312A have common modules as shown in FIGS. 3 and 4 with similar functionality.

RPORT 310A can receive frames from links (or lanes) 301A-301D and transmit frames to lanes 344A-344D. Each link has a SERDES (302A-302D), a de-skew module, a decode module (303B-303E) and parity module (304A-304D). Each lane also has a smoothing FIFO (SMF) module 305A-305D that performs smoothing functions to accommodate clock frequency variations. Parity errors are checked by module 403, while CRC errors are checked by module 404.

RPORT 310A uses a virtual lane (“VL”) cache 402 that stores plural vector values that are used for virtual lane assignment. In one aspect of the present invention, VL Cache 402 may have 32 entries and two vectors per entry. IOP 66 is able to read or write VL cache 402 entries during frame traffic. State machine 401 controls credit that is received. On the transmit side, credit state machine 347 controls frame transmission based on credit availability. State machine 347 interfaces with credit counters 328A.

Also on the transmit side, modules 340-343 are used for each lane 344A-344D, i.e., each lane can have its own module 340-343. Parity module 340 checks for parity errors and encode module 341 encodes 8-bit data to 10 bit data. Mux 342B sends the 10-bit data to a Tx SMF (transmit side smoothing FIFO) module 342 that handles clock variation on the transmit side. SERDES 343 then sends the data out to the link.

Time Stamp Features:

In one aspect of the present invention, frame data when received by RPORT 310 is provided a time stamp based on a Global Real Time counter value. The time stamp value is compared to a time out value to determine if a frame has timed out. If all copies of the received frames are moved out of switch element 20 before a time out occurs, nothing happens. IOP 66 can use time stamp information to prioritize frame processing.

If a frame times out before copies are sent to all destinations, the frame is tagged by RBUF 69A as having timed out. When a destination requests a copy of the frame, it is notified of the time out. The destination then reads the frame and disposes the frame according to a programmable policy, for example, Class 3 frames are tossed and Class 2 frames are sent to IOP 66 so that an F_BSY signal can be sent to the sender.

Various types of time out values may be used to determine if a frame has timed out. For example, a major or minor time out value may be used. If a minor time out has occurred for a frame then the frame is still kept in RBUF 69A or TBUF 70A. Minor time out can be programmed to any value. In one aspect, the minor time out value may be in the range of 0 milliseconds to 66.975 seconds in 1.02 millisecond increments.

In one aspect of the present invention, minor time out is determined in RPORT 310/TPORT 312 by comparing the frame's time stamp located in bits 16 to 31 of the EOF to the sum of a current Global Real Time counter value (507) (i.e. global with respect to ASIC 20) and a minor time out value (503).

If a major time out occurs then it denotes that a frame has resided in RBUF 69A longer than a “major time out value”. In this case the frame is rejected and the RBUF 69A slot is cleared. Major time out value (504) can be programmed. In one aspect, the major time out value may be in the range of 0 to 66.975 seconds in 1.02 milliseconds.

In one aspect of the present invention, if a major time out occurs but a read window is open (i.e., the frame is being read) and/or there are active read requests, then the read requests may be completed. If after the read window ends and there are no active read requests and destination bits are set, then the frame is tossed and a log error is generated.

It is noteworthy that although two time out categories have been described above (major and minor), the present invention is not limited to any particular number or value of time outs. For example, various (more than 2) incremental time out values may be used to trigger any action/inaction with respect to a frame. Also, any time out value may be programmed for such action/inaction.

GL Port Receive Side Time Out Processing:

FIG. 5A shows a schematic with GL_Port and XG_Port using the time stamp features, according to the adaptive aspects of the present invention. For RPORT 310, frame data 500 is received. A time stamp (501A) based on global real time counter value 507 (also referred to herein as value 507) is inserted in EOF 509. The output of Mux 501 (i.e. 501A) is then sent to RBUF 69A (or CBUF 62D).

When a frame lands into RBUF 69A, the time stamp 501A is extracted from the last word of the frame and loaded into a holding register (not shown). In one example, if RBUF 69A can hold 16 frames, there are 16 holding registers. In one aspect of the present invention, the time stamp could also be read from the RBUF 69A, eliminating the need for the holding registers.

The time stamp value 501A is sent to a time out checker circuit 506 (described below) through Mux 505A (output of Mux 505A is shown as 521). Time out checker circuit 506 also receives a time out value (major time out value 504 and minor time out value 503) via Mux 505 and value 507. Time out circuit 506 (described below in detail with respect to FIG. 5B) compares the time stamp 501A with the time out values(504 and 503) and counter value 507. If a time out occurs a status 506A is set in RBUF 69A. Frame information 500A is sent to TPORT 312 via cross-bar 50 and includes a time stamp and time out status flag.

Time out state machine 502 monitors the time stamps of all the frames in RBUF 69A. State machine 502 sets a status flag if a time out occurs, which notifies a destination that requests a “timed out” frame.

Although the term “state machine” has been used for various components, it is not intended to limit the adaptive aspects of the present invention. Other hardware (for example, micro-controllers, or processors)/firmware components may be used to achieve similar functionality as the state machines referenced in the various parts of this specification

GL Port Transmit Side Time Out Processing:

When a frame (500B) lands in TBUF 70A, the time stamp value 521A is extracted and held. A time out value 503A is sent to the time out checker circuit 506. Time stamp 521A is compared to the sum global real-time counter value 507 and time out value 503A. If a time out occurs then the status 506D is sent to TBUF 70A. A frame that has timed out may be rejected based on a programmed rejection policy. If no time out occurs then the frame is sent via path 506B. Frame data may also be sent (re-vectored) to a CPORT, shown as 506C.

XG Port Time Out Processing:

As shown in FIG. 5A, frame data 508 is received by RPORT 310A. Frame data may have a “delta time” feature/parameter/value (used interchangeably), which specifies the accumulated elapsed time for a frame. This feature is enabled by signal/command (the term is used interchangeably) 516 that is received from control register 326.

The delta time feature is configured on both ends of a communicating link. The feature would be negotiated at switch login time. This feature is very useful for E_Ports between switches, but can be used on any port type.

If signal 516 is enabled, then frame data 508 is expected to include the delta time value. The delta time value may be inserted in the EOF word on a 10 Gigabyte fibre channel link. Byte 3 uniquely identifies the word as an EOF. The other 3 bytes define the EOF type. By compressing the EOF type into a one byte EOF code, two bytes are available for the delta time value. Hence, in one aspect of the present invention, the delta time value may be received between 0 and 1 bytes of EOF word.

A similar feature may be used on a 1/2/4/8 Gigabyte FC link with some modification to the frame. This could be inserted in any fabric extension header or a delta time value may be inserted in the frame or a special word before or after the frame.

RPORT 310A includes logic 510 that receives frame data 508 with the delta time value and global real-time counter value 507. The output 510A of logic 510 provides the relative time stamp for port 310A by subtracting the delta time value in 508 from counter value 507. The new value 510A replaces the delta time value in frame 508 when the frame moves from RPORT 310A to TPORT 312A. In one aspect of the present invention, logic 510 may be a 16-bit subtractor.

Mux 501 receives input 508 (if no delta time feature is enabled) and 511A (if delta time feature is enabled) and moves the frame data with time stamp 511B (similar to GL_Port described above) to RBUF 69A. This adjusted time stamp value accounts for the delta time elapsed, if the delta time feature is enabled. The time out checker circuit 506 as described above with respect to GL_Port processes the time stamp value 511B.

TPORT 312A has two modes of operation when delivering frames. In the normal mode, the EOF compressed code is replaced by the standard Fibre Channel version of EOF (32 bit value). Frame 512A enters TBUF 70A and if signal 518 is not active (i.e. there is no delta time feature), the frame is processed similar to TPORT 312 (i.e. 515 is similar to 506B and 512 is similar to 506C).

In the second mode if signal 518 is active, then the upper 16 bits of the standard EOF are replaced by a delta time value. When the frame 512A arrives at TPORT 312A, the upper 16 bits are interpreted as the real time stamp value when the frame entered the switch. Time stamp value 520A is subtracted from value 507 by logic 520. The resultant value 513 is placed in the upper 16 bits of the EF word, as shown in FIG. 5A and data 517 with the new delta time stamp is transmitted.

Time out Checker Circuit 506:

FIG. 5B shows a schematic of time out checker circuit 506, according to one aspect of the present invention. Time out value 522 (similar to time out values 503, 503A and 504) is sent to logic 523 that also receives a frame's time stamp value 529 (similar to 501A, 511B, or 521A).

For illustration purposes only, if there are 16 frames in RBUF 69A, then 16 time stamps are multiplexed down to one time stamp at input Mux 501. A 4-bit select for Mux 501 is created by a free running counter that may be master cleared to a “0000” value and counts up at every clock. At a value of “1111”, the counter resets to “0000”. A new time stamp value is multiplexed in every clock and each time stamp value is seen once every 16^th clock. The selected time stamp 529 is sent to logic 523 that adds the time out value 522.

Time stamp value 529 is also sent to rollover logic 527 where the time stamp value 529 is compared to global real-time counter value 507. If the time stamp value 529 is greater than 507, a rollover value 527A is generated.

Rollover logic 527 is used to accommodate the situation where global real-time counter value 507 reaches its maximum value (for example a maximum 16 bit value) and then rolls over to zero. Since the frame time stamp is obtained from the global real-time counter value 507, the time stamp value 529 will be less than or equal to a current value of 507. The global real time counter value 507 will be less than the frame's time stamp value 529 when the counter has rolled over. Therefore. the time stamp value 529 is compared with value 507 by logic 527 for as long as a frame remains in TBUF 70A. If logic 527 detects a counter rollover situation, then the rollover state is captured and held by module 526. This affects a frame time out comparison that is performed by logic 525 and generates frame time out signal 528 that indicates if a frame has timed out.

Logic 525 compares value 507 and frame time out value 524A. Time out value 524A is a sum of time out value 522 and frame time stamp 529. In one example, if both 522 and 529 are 16-bit values, then the sum will create a 17-bit value (524A). In order to compare this 17-bit sum with value 507, another bit is concatenated. The rollover state described above is used as the most significant bit with value 507. This represents the 17^th bit in a 17-bit value derived from a 16-bit counter.

The foregoing example is only to illustrate the adaptive aspects of the present invention and not to limit the invention to any particular counter size, or a particular bit size for the various inputs (for example, 522 and 529).

FIG. 6 shows a flow diagram for managing frame time outs and reducing congestion, according to one aspect of the present invention.

In step S600, frame data (500/508 for RPORT segment and 500B/512A for TPORT segment) is received.

In step S601, a time stamp (501A and 511B) based on global real time counter value 507 (also referred to herein as value 507) is inserted in EOF 509. If a delta time value is present, then the frame time stamp value is subtracted from value 507 and the resultant value (510A) replaces the delta time value in frame 508 when the frame moves from RPORT 310A to TPORT 312A.

In step S602, the process determines if a time out has occurred. This is performed by time out checker circuit 506, that has been described above with respect to FIGS. 5A and 5B. If a time out has not occurred, then time out state machine 502, in step S603, continues to monitor RBUF 69A or TBUF 70A depending upon the location of the frame.

In step S604, the process determines if the time out is minor or major. If the time out is minor, then in step S605, the frame processing continues and a flag is set.

If the time out is major, then in step S606, the process determines if there are any read requests in process (or pending read requests). If there are read requests in process/pending, then in step S607, those read requests are completed.

In step S609, the process determines if all destinations have been processed. If yes, then the process stops in step S610. If all destinations have not been processed, then the process moves to step S608.

If there are no read requests, then in step S608, the frames are rejected, based on a programmable policy or otherwise.

In one aspect of the present invention, the delta time feature allows for accurate timing of frames without the need to synchronize timers or counters on both sides of the FC links.

It is noteworthy that the present invention provides end to end frame timing (i.e. from the time a frame enters a fabric to the time the frame leaves the fabric) without a requirement for synchronizing time between individual switch elements.

In one aspect of the present invention, overall congestion is reduced because frames time out can be monitored and frames that are stalled can be removed.

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 routing fibre channel frames using a fibre channel switch element, comprising: inserting a time stamp value in a fibre channel frame that is received at a received segment of the fibre channel switch element;determining if a minor time out of the frame has occurred by comparing the time stamp value to a global counter value and a minor time out value; andprocessing the frame if the time out has occurred;wherein if a major time out occurs while the frame is being read, then the frame read is completed; orif a major time out occurs when there is at least one active read request, then the read request is completed.

2. The method of claim 1, wherein the step of determining if a minor time out of the frame has occurred is performed by a time out checker circuit that extracts the time stamp value from the frame.

3. The method of claim 2, wherein a fibre channel switch element processor programs the minor time out value.

4. The method of claim 1, wherein if a minor time out occurs, the receive segment sets a status flag for a transmit segment of the switch element.

5. The method of claim 1, wherein end to end frame timing is provided, without synchronizing plural switch elements of a fabric.

6. The method of claim 1, further comprising the step of determining if a major time out of the frame has occurred by comparing the time stamp value to a global counter value and a major time out value.

7. The method of claim 6, wherein the step of determining if a major time out of the frame has occurred is performed by a time out checker circuit that extracts the time stamp value from the frame.

8. The method of claim 7, wherein a fibre channel switch element processor programs the major time out value.

9. A fibre channel switch element for routing fibre channel frames, comprising: a receive and transmit segment configured to receive and transmit fibre channel frames, anda time out checker circuit configured to declare a major time out after comparing a time stamp value in a fibre channel frame with a programmed major time out value and a global counter value;wherein if a major time out occurs while the frame is being read, then the frame read is completed; orif a major time out occurs when there is at least one active read request, then the read request is completed.

10. The switch element of claim 9, wherein if a major time out occurs and the frame is not being read, then the switch element tosses the frame.

11. The switch element of claim 9, wherein end to end frame timing is provided, without synchronizing plural switch elements of a fabric.

12. The switch element of claim 9, wherein the time out checker circuit is further configured to declare a minor time out after comparing the time stamp value with a programmed minor time out value and the global counter value.

13. The switch element of claim 12, wherein the switch continues processing the frame if a minor time out occurs.

14. The switch element of claim 9, wherein if a major time out occurs and the there are no active read requests, then the switch element tosses the frame.

15. A method for routing fibre channel frames using a fibre channel switch element, comprising: inserting a time stamp value in a fibre channel frame that is received at a receive segment of the fibre channel switch element;determining if a delta time value, which provides an accumulated elapsed time for the frame, is present in the frame's data;if the delta time value is present in the frame's data, subtracting the delta time value from a global time value to determine an adjusted relative time stamp value;using the adjusted relative time stamp value to determine if the frame has timed out after the frame arrives at a receive buffer; andprocessing the frame if the time out occurs;wherein if a major time out occurs while the frame is being read, then the frame read is completed; orif a major time out occurs when there is at least one active read request, then the read request is completed.

16. The method of claim 15, wherein the adjusted relative time stamp value is inserted into the frame.

17. The method of claim 15, wherein a delta time value is computed by subtracting the frame's time stamp value from a global counter value and the time stamp value is inserted into the frame before the frame is transmitted.

18. A fibre channel switch element for routing fibre channel frames, comprising: a receive and transmit segment configured to receive and transmit fibre channel frames; anda time out checker circuit configured to declare a frame time out after comparing a relative time stamp value in a fibre channel frame with a programmed time out value and a global counter value;wherein the relative time stamp value is calculated using a delta time value from the frame, which specifies an accumulated elapsed time for the frame;wherein if a major time out occurs while the frame is being read, then the frame read is completed; orif a major time out occurs when there is at least one active read request, then the read request is completed.

19. The switch element of claim 18, wherein an adjusted relative time stamp value is calculated by subtracting the delta time value from a global counter value.