Method and system for reducing latency and congestion in fibre channel switches

• US 7,522,522 B2
• Filed: 07/20/2004
• Issued: 04/21/2009
• Est. Priority Date: 07/21/2003
• Status: Expired due to Fees

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: QLogic Corporation (Marvell Technology Group Limited)
• Inventors: Dropps, Frank R., Verba, Craig M.
• Primary Examiner(s): Yao; Kwang B
• Assistant Examiner(s): Lai; Andrew
• Application Number:
  US10/894,595
• Publication Number:
  US 20050018603A1
• Time in Patent Office: 1,736 Days
• Field of Search: 370/229, 370/230, 370/230.1, 370/235, 370/235.1, 370/236
• US Class Current: 370/230.1
• CPC Class Codes: H04L 12/10 Current supply arrangements
• CPC Class Codes: H04L 45/00 Routing or path finding of packets in data switching networks routing or path finding in wireless networks H04W40/00
• CPC Class Codes: H04L 45/20 Hop count for routing purposes, e.g. TTL
• CPC Class Codes: H04L 45/60 Router architectures
• CPC Class Codes: H04L 49/101 using crossbar or matrix
• CPC Class Codes: H04L 49/25 Routing or path finding in a switch fabric
• CPC Class Codes: H04L 49/3009 Header conversion, routing tables or routing tags
• CPC Class Codes: H04L 49/357 Fibre channel switches

Abstract

A method and system for routing fiber channel frames using a fiber channel switch element is provided. The switch element includes, a port with a buffer having more than one memory slot for receiving fiber channel frames, wherein the port tracks a relative age of a first memory slot with respect to at least another memory slot; and frames are transmitted from a memory slot based on the relative age. The method includes, determining a relative age of a first memory slot with respect to at least another memory slot; and transmitting a frame from a memory slot based on the relative age. The method also includes, sending frames that have resided in a memory slot for a greater period compared to frames residing in at least another memory slot; and setting age bits in plural memory slots when frames are written and the relative age is determined based on the age bits. An aging table may be used to store the age bits of the plural memory slots.

Claims

1. A method for routing fibre channel frames using a fibre channel switch element having a plurality of ports, each port including a receive segment for receiving a fibre channel frame and a transmit segment for transmitting a fibre channel frame, comprising:

storing a relative age of a first fibre channel frame with respect to a second fibre channel frame;

wherein the first fibre channel frame and the second fibre channel frame are received by the receive segment of a port from among the plurality of ports; and

the first frame is stored in a first memory slot of a receive buffer having a plurality of memory slots and the second frame is stored in a second memory slot of the receive buffer;

wherein the relative age is stored in an aging table and the relative age indicates how long a fibre channel frame has been waiting at a memory slot compared to other fibre channel frames that are waiting in other memory slots at any given time;

determining if more than one transmit segment is requesting fibre channel frames stored in the plurality of memory slots;

if only one transmit segment requests a fibre channel frame stored at a memory slot, then routing the frame to the transmit segment without using the aging table;

if more than one transmit segment is requesting fibre channel frames then using the aging table to determine which fibre channel frame is the oldest among the plurality of fibre channel frames stored in the plurality of memory slots;

transmitting the oldest fibre channel frame from a memory slot based on the relative age obtained from the aging table; and

setting age bits in the aging table when fibre channel frames are written in the receive segment; and

the relative age for a fibre channel frame is determined based on a value of the age bits;

wherein the aging table includes a grid having a plurality of rows and a plurality of columns and the grid stores the age bits, and wherein each row and column of the aging table is identified by a memory slot number.

2. The method of claim 1, wherein the aging table is stored within a receive buffer of the receive segment for each of the plurality of ports.

3. The method of claim 1, wherein an age bit value stored at a grid location indicates an age of a fibre channel frame stored at a memory slot with respect an age of another frame stored at another memory slot.

4. A fibre channel switch element for routing fibre channel frames, comprising:

a plurality of ports, each port having a receive segment for receiving a fibre channel frame and a transmit segment for transmitting a fibre channel frame, where each receive segment includes a buffer having a plurality of memory slots for receiving the fibre channel frames,

wherein each port includes an aging table for storing relative age of a frame stored at a memory slot and the relative age indicates how long a fibre channel frame has been waiting at a memory slot compared to how long other fibre channel frames are waiting in other memory slots at any given time; and

wherein before transferring a fibre channel frame, the receive segment of the port determines if more than one transmit segment is requesting fibre channel frames stored in the plurality of memory slots; and

if only one transmit segment requests a fibre channel frame stored at a memory slot, then the frame is routed without using the aging table;

but if more than one transmit segment is requesting fibre channel frames then the receive segment uses the aging table to determine which fibre channel frame is the oldest among the plurality of fibre channel frames stored in the plurality of memory slots; and

the oldest fibre channel frame is transmitted from a memory slot based on the relative age obtained from the aging table, wherein age bits are set when fibre channel frames are written in the receive segment of each port and the relative age for the fibre channel frames is determined based on a value of the age bits;

wherein the aging table includes a grid having a plurality of rows and plurality of columns; and

the grid stores the age bits, and wherein each row and column of the aging table is identified by a memory slot number.

5. The switch element of claim 4, wherein the aging table is stored within a receive buffer of the receive segment for each of the plurality of ports.

6. The switch element of claim 4, wherein an age bit value stored at a grid location indicates an age of a fibre channel frame stored at a memory slot with respect an age of another frame stored at another memory slot.

7. A method for routing fibre channel frames using a fibre channel switch element having a plurality of ports, each port including a receive segment for receiving a fibre channel frame and a transmit segment for transmitting a fibre channel frame, comprising:

storing a relative age of a first fibre channel frame with respect to a second fibre channel frame;

wherein the first fibre channel frame and the second fibre channel frame are received by the receive segment of a port from among the plurality of ports; and

the first frame is stored in a first memory slot of a receive buffer having plurality of memory slots and the second frame is stored in a second memory slot of the receive buffer;

wherein the relative age is stored in an aging table and the relative age indicates how long a fibre channel frame has been waiting at a memory slot compared to other fibre channel frames that are waiting in other memory slots at any given time;

determining if more than one transmit segment is requesting fibre channel frames stored in the plurality of memory slots;

if only one transmit segment requests a fibre channel frame stored at a memory slot, then routing the frame to the transmit segment without using the aging table;

if more than one transmit segment is requesting fibre channel frames then using the aging table to determine which fibre channel frame is the oldest among the plurality of fibre channel frames stored in the plurality of memory slots; and

transmitting the oldest fibre channel frame from a memory slot based on the relative age obtained from the aging table;

wherein if there are N number of memory slots, then (N*N)−

N)/2 bits are used to populate the aging table.

8. A fibre channel switch element for routing fibre channel frames, comprising:

a plurality of ports, each port having a receive segment for receiving a fibre channel frame and a transmit segment for transmitting a fibre channel frame, where each receive segment includes a buffer having a plurality of memory slots for receiving the fibre channel frames,

wherein each port includes an aging table for storing a relative age of a frame stored at a memory slot and the relative age indicates how long a fibre channel frame has been waiting at a memory slot compared to how long other fibre channel frames are waiting in other memory slot at any given time; and

wherein before transferring a fibre channel frame, the receive segment of the port determines if more than one transmit segment is requesting fibre channel frames stored in the plurality of memory slots; and

if only one transmit segment requests a fibre channel frame stored at a memory slot, then the frame is routed without using the aging table;

but if more than on transmit segment is requesting fibre channel frames then the receive segment uses the aging table to determine which fibre channel frame is the oldest among the plurality of fibre channel frames stored in the plurality of memory slots; and

the oldest fibre channel frame is transmitted from a memory slot based on the relative age obtained from the aging table;

wherein if there are N number of memory slots, then ((N*N)−

N)/2) bits are used to populate the aging table.

9. A port for a switch element operationally coupled to a network for sending and receiving network frames, comprising:

a receiving segment for receiving a network frame;

a transmit segment for transmitting a network frame;

wherein the receive segment includes;

(a) a buffer having a plurality of memory slots for receiving the network frames; and

(b) an aging table for storing a relative age of a network frame stored at a memory slot and the relative age indicates how long a network frame has been waiting at a memory slot compared to how long other network frames are waiting in other memory slots from among the plurality of memory slots, at any given time;

wherein before transferring a network frame, the port determine if more than one transmit segment is requesting network frames stored in the plurality of memory slots; and

if only one transmit segment requests a network frame stored at a memory slot, then the network frame is routed without using the aging table;

but if more than one transmit segment is requesting network frames then the receive segment uses the aging table to determine which network frame is the oldest among the plurality of network frames stored in the plurality of memory slots; and

the oldest fibre channel frame is transmitted from a memory slot based on the relative age obtained from the aging table, wherein age bits are set in the aging table when network frames are written in the receive segment and the relative age for the network frames is determined based on a value of the age bits, and wherein the aging table includes a grid having a plurality of rows and a plurality of columns identified by memory slot numbers and the grid stores the age bits.

10. A port for a switch element operationally coupled to network for sending and receiving network frames, comprising:

a receive segment for receiving a network frame;

a transmit segment for transmitting a network frame;

wherein the receive segment includes;

(a) a buffer having a plurality of memory slots for receiving the network frames; and

(b) an aging table for storing a relative age of a network frame stored at a memory slot and the relative age indicates how long a network frame has been waiting at a memory slot compared to how long other network frames are waiting in other memory slots from among the plurality of memory slots, at any given time;

wherein before transferring a network frame, the port determines if more than one transmit segment is requesting network frames stored in the plurality of memory slots; and

if only one transmit segment requests a network frame stored at a memory slot, then the network frame is routed without using the aging table;

but if more than one transmit segment is requesting network frames then the receive segment uses the aging table to determine which network frame is the oldest among the plurality of network frames stored in the plurality of memory slots; and

the oldest fibre channel frame is transmitted from a memory slot based on the relative age obtained from the aging table, wherein age bits are set in the aging table when network frames are written in the receive segment of the relative age for the network frames is determined based on a value of the age bits, wherein if there are N number of memory slots, then ((N*N)−

N)/2 bits are used to populate the aging table.