WO2000000899A2 - Flow control using output port buffer allocation - Google Patents
Flow control using output port buffer allocation Download PDFInfo
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- WO2000000899A2 WO2000000899A2 PCT/US1999/014207 US9914207W WO0000899A2 WO 2000000899 A2 WO2000000899 A2 WO 2000000899A2 US 9914207 W US9914207 W US 9914207W WO 0000899 A2 WO0000899 A2 WO 0000899A2
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- input port
- network switch
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/90—Buffering arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/10—Flow control; Congestion control
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/10—Flow control; Congestion control
- H04L47/13—Flow control; Congestion control in a LAN segment, e.g. ring or bus
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/10—Flow control; Congestion control
- H04L47/26—Flow control; Congestion control using explicit feedback to the source, e.g. choke packets
- H04L47/263—Rate modification at the source after receiving feedback
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L47/00—Traffic control in data switching networks
- H04L47/10—Flow control; Congestion control
- H04L47/30—Flow control; Congestion control in combination with information about buffer occupancy at either end or at transit nodes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/30—Peripheral units, e.g. input or output ports
- H04L49/3027—Output queuing
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/35—Switches specially adapted for specific applications
- H04L49/351—Switches specially adapted for specific applications for local area network [LAN], e.g. Ethernet switches
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/50—Overload detection or protection within a single switching element
Definitions
- This invention relates to information networks for computer systems and more specifically to a system for implementing flow control in an information network.
- Information networks transmit computer information such as computer data between various computer systems operably coupled to the information network.
- One type of information network is a local area network (LAN) utilizing a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) as specified by the IEEE standard 802.03, which is hereby incorporated by reference in its entirety.
- LAN local area network
- CSMA/CD Carrier Sense Multiple Access with Collision Detection
- One problem with an information network is how to regulate the information being transmitted on the network such that the amount of information being transmitted does not overload the network.
- Another problem is how to fairly allocate the network resources among a multitude of users operably coupled to the system.
- allocating portions of an output buffer of an information network switch among input ports of the information network switch advantageously provides a flow control method that fairly allocates network resources among the information packet generators and sinks operably coupled to the network.
- an information network switch in one aspect of the invention, includes a first input port for receiving information packets and a second input port for receiving information packets.
- the first input port has an enabled state and a disabled state
- the second input port has an enabled state and a disabled state.
- the information network switch also includes an output port for transmitting information packets.
- the output port includes a buffer for holding received information packets to be transmitted from the output port. A first portion of the buffer is allocated for holding information packets from the first input port and a second portion of the buffer is allocated for holding information packets from the second input port.
- the first input port transitions to the disabled state from the enabled state in response to a level of occupancy of the first portion of the buffer exceeding a first level.
- the second input port transitions ⁇ ???? ⁇ to the disabled state from the enabled state in response to a level of occupancy of the second portion of the buffer exceeding a first level.
- Steve The inventor suggests using the verb "transists” instead of using "transitions” as a verb.
- the invention includes a method of controlling the flow of information in an information network having an information network switch.
- the method includes allocating a first portion of a buffer of an output port of the information network switch for holding information packets received via a first input port of the information network switch and allocating a second portion of the buffer for holding information packets received via a second input port of the information network switch.
- the method also includes determining a level of occupancy of the first portion of the buffer and determining a level of occupancy of the second portion of the buffer.
- the method further includes providing a control signal to a first information packet source operably coupled to the first input port to inhibit the first information packet source from transmitting information packets to the first input port in response to the level of occupancy of the first portion of the buffer exceeding a first level.
- the method also includes providing a control signal to a second information packet source operably coupled to the second input port to inhibit the second information packet source from transmitting information packets to the second input port in response to the level of occupancy of the second portion of the buffer exceeding a first level
- an information network switch in another aspect of the invention, includes an output port for transmitting information packets to an information packet destination operably coupled to the output port.
- the output port includes a buffer for holding information packets to be transmitted to the information packet destination.
- the output port has a non hold state and a hold state. In the non hold state, the output port transmits information packets in the output buffer to the information packet destination.
- the output port transitions to the hold state from the non hold state in response to the information network switch receiving a control signal provided by the information packet destination.
- the output port In the hold state, the output port has a first sub- state and a second sub-state, in a first sub-state, the output port transmits information packets in the output buffer to the information packet destination. In the second sub-state, the output port does not transmit information packets to the information packet destination.
- the output port transitions to the first sub-state from the second sub-state in response to the level of occupancy of the buffer exceeding a first level.
- an information network switch in another aspect of the invention, includes a plurality of input ports for receiving information packets from information packet sources and a plurality of output ports for transmitting information packets received from the input ports to information packet destinations.
- Each output port includes a buffer for holding received information packets to be transmitted from the output port.
- the information network switch also includes means for implementing an allocated usage of each output port among the input ports.
- Figure 1 shows one embodiment of an information network that allows for the transmission of information packets among information generators and information sinks operably coupled to the network.
- Figure 2 shows one embodiment of an information network switch.
- Figure 3 shows one embodiment of an output port of an information network switch according to the present invention.
- Figures 4A, 4B, and 4C set forth one embodiment of a system for implementing flow control in an information network.
- Figures 5A, 5B, and 5C set forth one embodiment of a system for implementing flow control that enables the system set forth in Figures 4A, 4B, and 4C to implement buffer sharing without overloading the output buffer.
- Figures 6A and 6B set forth one embodiment of a system for implementing flow control in an information network.
- Figure 1 shows one embodiment of an information network that allows for the transmission of information packets among information generators and information sinks operably coupled to the network.
- information network 101 is a computer Local Area Network (LAN) employing CSMA/CD conforming to the IEEE 802.3 standard.
- Information generators are devices that generate information that is transmitted in information packets on information network 101.
- An information sink is a device that receives and uses the information in the information packets generated by the generators.
- the information contained in the information packets are computer data that is used by an information sink. Examples of information generators and sinks include computer workstations (such as 107), terminals (such as 105, 109, and 111), and desktop computers (such as 113).
- An information network allows for these information generators/sinks to be operably coupled to exchange information among each other.
- Other types of information generators and/or sinks include notebook computers, mainframes, servers, other types of computer systems, printers, scanners, or other devices capable of generating or receiving information over an information network.
- the information packets are information frames conforming to the IEEE 802.3 standard.
- each frame contains a preamble field, a start of frame delimiter field, a destination address field, a source address field, a length of data field, a data field which contains the information to be sent to the destination, a pad field, and a checksum field.
- the information generators/sinks (105 107, 109, 111, and 113) are operably coupled to each other via information network switches (121, 122, and 123) and network links (such as 131, 133, 135, 136, and 137).
- An information network switch is an information packet routing device that routes packets received via the input ports of the switch to the output ports as per information included in the information packet.
- Each information network switch includes a plurality of input ports (input ports 1 through N, as designated in Figure 1 by the in-going arrows) for receiving information packets from information packet sources operably coupled to the input ports via network links.
- An information packet source may include an information packet generator such as terminal 105 or another switch (switch 121 is an information packet source for input portN of switch 122).
- Each information network switch also includes a plurality of output ports (output ports 1 through N, as designated by the outgoing arrows) for transmitting information packets to information packet destinations via network links operably coupled to the output ports.
- An information packet destination may include an information sink such as terminal 111 or another information network switch (switch 123 is an information packet destination for output port 3 of switch 121).
- the switches, information packet generators, and information packet sinks are operably coupled to one another via network links.
- These network links may include twisted pair cable, coaxial cable, fiber optic cable, or other mechanisms for transmitting information packets.
- the links are full duplex links or are bi-directional. Information packets can be exchanged in both directions between one switch and another switch or generator/sink.
- switches 121 and 123 are operably coupled via link 131 in which information packets are provided from switch 121 to switch 123 via link 131 A of link 131 and packets are provided from switch 123 from switch 121 via link 13 IB of link 131.
- the links in the network may have a different data transmission rates with some links having, for example, data transmission rates of 10 Megabits per second (Mbs), 100 Mbs, or 1 Gigabits per second (Gps).
- FIG 2 shows one embodiment of an information network switch.
- Information network switch 201 is similar to information network switches 121, 122, and 123.
- Each output port of switch 201 includes an output buffer (buffers 1, i and N are shown in Figure 2) for holding received information packets to be transmitted to an information packet destination via the respective output port.
- the output buffers are FIFO buffers, wherein each output port transmits information packets held in its respective output buffer in the FIFO order.
- Switch 201 includes a switching fabric 205 that is used in selectively interconnecting each input port with each output port of the information network switch. Upon receiving an information packet via one of the input ports 1 through N, the switch 205 determines whether the packet is a valid packet and whether the information packet is to be transmitted from any or all of the output ports 1 through N.
- information network switch 201 includes a switch processing engine 215 such as a microprocessor and/or hardwired circuitry, for determining whether an information packet is valid and for determining to which of the output port(s) the received information packets are to be routed.
- the information network switch may also be referred to as a switch, hub, gateway, router, concentrator, or other term.
- the network switch is a non blocking output buffered switch.
- FIG. 3 shows one embodiment of an output port of an information network switch according to the present invention.
- Output port 301 includes FIFO output buffer 305, a buffer counter 307 and buffer counters 1 through N. Information packets received from the input ports of the switch that are to be transmitted from the output port 301 are admitted into buffer 305.
- Buffer counter 307 provides a counter signal that, in the embodiment shown, is indicative of the level of occupancy of the buffer 305. With each information packet that is admitted into the buffer, buffer counter 307 is incremented by one. For each information packet held in the buffer 305 that is transmitted from output port 301, buffer counter 307 is decremented by one. Thus, the value of the counter indicates of the number of information packets in buffer 307 which, in the embodiment shown, is indicative of the level of occupancy of the buffer.
- Output port 301 also includes a plurality of counters (1 through N) that, in the embodiment shown, enable a portion of the output buffer 305 to be allocated to each of the input ports of the information network switch.
- Each counter provides a counter signal that, in the embodiment shown, is indicative of the level of occupancy of a corresponding allocated portion of buffer 305.
- counter 2 provides a counter signal that is indicative of the number of information packets in buffer 305 that were received from input port
- each output port of a switch includes one buffer counter and a counter for each input port of the switch.
- the counter signals from the buffer are provided to the switch processing engine 215.
- each counter shown in Figure 3 includes a hardwired, up/down counter.
- each counter is implemented by a microprocessor and a memory.
- network 101 incorporates a Media Access Control (MAC) sub-layer.
- the MAC sub-layer allows for the utilization of a control packet such as the MAC control frame named PAUSE.
- a PAUSE frame is provided to an information packet source by a downstream destination to inhibit transmission of information packets such as information frames by the information packet source to the downstream destination for a specified period of time.
- the PAUSE frame contains a PAUSE opcode field and a time parameter field which contains a time parameter specifying an amount of time (in units of 64 bytes transmission time on a specified link) that an upstream information packet source must hold its transmission activity.
- a PAUSE(t) frame is a control frame containing t as its time parameter.
- a PAUSE(l) frame provided to the upstream source by the downstream destination will inhibit the upstream information source from transmitting for 51.2 microseconds. If the PAUSE frame has a time parameter equal to zero (PAUSE (0)), the upstream information packet source will immediately be enabled to transmit information packets.
- An indefinite pause control frame PAUSE (co)
- PAUSE co
- control packets have non preemptive priority over information packets and are not sensitive to flow control. For example, the transmission of an information packet cannot be interrupted for the transmission of a control packet. Also, the receipt of a PAUSE frame does not inhibit the receiving switch from transmitting a PAUSE frame over the blocked link.
- FIGS. 4A, 4B, and 4C set forth one embodiment of a system for implementing flow control in an information network utilizing the allocation of output buffers of the output ports among the input ports of the switches.
- the system is executed by the switch processing engines of the information network switches of the information network.
- buffer allocation each input port of an information network switch is allocated a portion of the output buffer of each output port of the switch.
- the switch provides a control signal to the upstream sources operably coupled to the input port to inhibit information packet transmissions to the input port.
- Such a system advantageously allows for a fair usage of the output ports of a switch among all input ports of the switch.
- each input port of the network switch has an ENABLED state 403 and a DISABLED state 407.
- an input port of a switch transitions to the
- the information network switch provides a control signal such as a control packet (like the PAUSE ( ⁇ ) frame or an equivalent PAUSE frame) to the information packet sources operably coupled to the input port to inhibit the information packet sources from transmitting information packets to the input port.
- a control signal such as a control packet (like the PAUSE ( ⁇ ) frame or an equivalent PAUSE frame) to the information packet sources operably coupled to the input port to inhibit the information packet sources from transmitting information packets to the input port.
- the input port transitions to the ENABLED state 403 in response to the level of occupancy of the portion of the output buffer allocated to the input port decreasing below a second level or second threshold level.
- the switch provides a control signal such as a control packet (like the PAUSE(O) frame) to the upstream information packet source to enable the information packet source to transmit information packets to the input port.
- the level of occupancy of an allocated portion of an output buffer is measured in terms of the number of packets in the buffer that were received from the input port.
- the counter of the output port associated with the specific input port is decremented by one to indicate that the level of occupancy of the allocated portion of the buffer has decreased due to an information packet received from the specific input port being transmitted from the output port.
- the counter of the output port associated with the specific input port is incremented by one to indicate that the level of occupancy of the allocated portion of the buffer has increased due to an information packet received from the specific input port being admitted into the output buffer.
- terminal 109 would transmit the packet to input port N of switch 121.
- Switch 121 would route the packet to output port 3 of switch 121 where the packet would be admitted into the output buffer of output port 3.
- the packet would then be transmitted by the output port 3 of switch 121 to input port 3 of switch 123 via link 131A.
- Switch 123 would route the information packet to output port 1 of switch 123 where the information packet would be admitted into the output buffer of output port 1 of switch 123.
- the counter of output port 1 associated with input port 3 of switch 123 is incremented by one to indicate that the level of occupancy of the portion of the buffer of output port 1 allocated to input port 3 has increased due to the inputting of the received packet.
- the counter of output port 1 associated with input port 3 is decremented by one to indicate the decrease in the level of occupancy of the portion of the buffer allocated to input port 3.
- the switch when the input port is in the ENABLED state 403, the switch is in a wait for packet state 411. Upon the receipt and admittance of an information packet from an input port, a determination is made (415) of whether the level of occupancy of the portion of the output buffer allocated to the input port has exceeded a first level. If the first level has been exceeded, the input port transitions to the DISABLED state. If the first level has not been exceeded, the switch returns to the wait for packet state 411.
- a counter is used to determine whether the level of occupancy of the portion of the output buffer allocated to the input port has exceeded a first level, wherein the input port transitions to the DISABLED state 407 in response to the counter providing a signal indicating that the level of occupancy has exceeded the first level.
- the switch processing engine of the switch executes a software routine stored in a memory of the switch processing engine that checks the level of occupancy of a portion of the buffer allocated to a specific input port each time an information packet has been received from the specific input port and has been admitted in the output buffer. The switch processing engine checks the level of occupancy by reading the counter signal from an associated hardware counter or by reading a signal indicative of a count stored in a memory location.
- the frequency at which the switch processing engine checks the counter signal is dependent upon the level of occupancy of the allocated portion of the buffer. If the level of occupancy of the allocated portion of a buffer is at zero, then the switch processing engine may wait an amount of time before checking the counter, wherein the amount of time is the minimal amount of time needed for the allocated portion of the buffer to reach the first level.
- the output port when the input port is in the DISABLED state, the output port continues transmitting information packets in its output buffer.
- the level of occupancy of the portion of the buffer allocated to the specific input port has decreased below a second threshold level, the input port transitions to the ENABLED state.
- switch 123 in response to the level of occupancy of the portion of the output buffer of output port 1 of switch 123 allocated to input port 3 of switch 123 exceeding the first level, switch 123 provides a PAUSE ( ⁇ ) control frame to switch 121 to inhibit the transmission of information packets via output port 3 of switch 121.
- This PAUSE ( ⁇ ) control frame is provided to switch 121 via output port 3 of switch 123 and link 13 IB.
- switch 121 places output port 3 of switch 121 in a hold state wherein no information frames are transmitted from output port 3 of switch 121.
- switch 123 During the time when input port 3 of switch 123 is in the DISABLED state, output port 1 of switch 123 is transmitting the information packets held in its output buffer to terminal 1 1 1.
- switch 123 provides via its output port 3 and link 13 IB, a PAUSE(O) control frame to the input port 3 of switch 121 to enable output port 3 to transmit information packets to input port 3 of switch 123.
- one advantage of the present invention is that heavy traffic via one input port to a specific output port will not block the other input ports from receiving information packets to be transmitted from that output port.
- a counter is used to determine whether the level of occupancy of the portion of the output buffer allocated to the input port has decreased below a second level, wherein the input port transitions to the ENABLED state 403 in response to the counter providing a signal indicating that the level of occupancy has decreased below the second level.
- the switch processing engine of the switch executes a software routine stored in a memory of the switch processing engine that checks the level of occupancy of a portion of the buffer allocated to a specific input port each time an information packet received from an input port and has been transmitted from the output buffer.
- the switch processing engine checks the level of occupancy by reading the counter signal from an associated hardware counter or by reading a signal indicative of a count stored in a memory location.
- the switch of the input port discards information packets received via the input port in the DISABLED state (operation 423). In some embodiments, the switch discards all information packets received from the input port in the DISABLED state received after a specific period of time from when the PAUSE ( ⁇ ) frame or other control signal was transmitted to the upstream source to inhibit the transmission of information packets to the input port. In other embodiments, the switch would accept a specific number packets received via the input port after the PAUSE ( ⁇ ) frame or other control signal was provided before discarding information packets received from the disabled input port.
- the switch of the input port in the DISABLED state would not discard the packet if the buffer of the output port had available space. Such a condition would occur when only one source is transmitting information packets to the output port at a given time and the level of occupancy of the remaining allocated portions are at low levels.
- the switch would not discard information packets received via the disabled input port if the level of occupancy of the portion of the output buffer allocated to the disabled input port is below the first level. Such a condition may occur after the input port has become disabled for a length of time where some of the packets received from the disabled input port have been transmitted from the output buffer but not enough for the level of occupancy to decrease below the second level.
- An input port of a switch may transition to the DISABLED state from the E ABLED state in response to the level of occupancy of a portion of an output buffer allocated to the input port of any output port of the switch exceeding a first level.
- first level for each output port buffer may be at different levels with respect to each other.
- first levels for the different allocated portions of an output buffer may also vary with respect to each other. For example, the "first level” for the portion of the output buffer allocated to input port 1 may be twice as large as the "first level” for the portion allocated to input port 2.
- a switch transitions to the DISABLED state in response to the level of occupancy of an output buffer of a specific output port exceeding a first level, then the input port will not transition back to the ENABLED state unless the level of occupancy of the output buffer of the specific output port decreases below the second level. If an input port is in a DISABLED state due to the level of occupancy of an allocated portion of an output buffer of a first output port exceeding a first level and if the level of occupancy of a portion of a buffer of a second output port exceeds a first level, then the input port would transition to the ENABLED state in response to the level of occupancy of the allocated portions of both the first and second output ports decreasing below the second levels.
- the first level (the level of occupancy of an allocated portion exceeded for the transition of an input port from an ENABLED state to a DISABLED state) is higher than the second level (the level of occupancy that is decreased below for the transition of the input port to the ENABLED state from the DISABLED state).
- Having the first level be a higher level than the second level provides the buffer allocation flow control system of the information network switch with a hysteresis feature. This hysteresis feature reduces the number of control packets provided over the network to inhibit (and then enable) an upstream source in providing information packets when the input port transitions back and forth between the DISABLED and ENABLED states.
- the hysteresis feature also reduces the amount of threshing (multiple transitions across a threshold in quick succession) that can result during a busy period of a switch. Threshing makes it harder on a switch to recover from an extra load. Consequently, increasing the distance between the first level and the second level reduces the number overhead of control packets transmitted and reduces problems due to threshing. However, increasing the distance between the first level and the second level increases the amount of time that the upstream source is in a hold state and correspondingly the opportunity for information packets to be discarded by the upstream source due to the upstream device's output buffer overflowing.
- the portions of an output buffer allocated to the various input ports of a switch may be mutually exclusive from each other. For example, if the output buffer holds 100 packets and there are 10 input ports, then the allocated portion for each input port in a mutually exclusive allocation system would be 10 packets per input port.
- an allocated buffer portion for an input port of a switch may be "shared" by other portions of the output buffer allocated to other input ports of the switch.
- the total amount of buffer space of the allocated portions exceeds the total amount of buffer space in the output buffer.
- each input port is guaranteed a minimum amount of buffer space in an output buffer with the rest of the buffer space being usable by all of the input ports.
- Mi represents the amount of output buffer space (denoted in the number of packets) guaranteed for input port i.
- M represents the total buffer space (denoted in the number of packets) that is guaranteed for all of the input ports wherein:
- B represents the total buffer space (denoted in the number of packets) in the output buffer.
- the allocated portion of an output buffer for input port i may exceed the guaranteed portion of the buffer for input port i.
- f the sharing factor and Hi represents the maximum buffer space (denoted in the number of packets) of the output port that can hold information packets received from input port i.
- f 1
- each allocated portion of the buffer is mutually exclusive with the other allocated portions and thus no sharing takes place.
- the sharing of buffer space among the allocated portions of the output buffer advantageously allows the switch to respond to changes in the packet load received by the input ports.
- each input port of a switch is connected to information sources that infrequently transmit a large number of packets over a short time period.
- a sharing factor of greater than one a buffer may overflow without the occupancy level of any allocated portion of the buffer exceeding a first level.
- Figures 5 A, 5B, and 5C set forth one embodiment of a system for implementing flow control that enables the system set forth in Figures 4A, 4B, and 4C to implement buffer sharing without causing overflow of the output buffer.
- Output buffer overflow for an output port implementing buffer sharing is prevented by inhibiting the information packet sources operably coupled to an information switch from providing information packets to the input ports of the information switch when the level of occupancy of the output buffer has exceeded a particular level.
- each output port of an information switch has an ON state and an OFF state, the output port of a switch transition from the ON state 503 to the OFF state 507 in response to the level of occupancy of the output buffer of the output port exceeding a first level or threshold.
- the switch provides a control packet such a PAUSE ( ⁇ o) frame to each upstream information source operably coupled to an input port of the switch to inhibit the upstream information sources from transmitting information packets to the switch.
- the output port of a switch transitions from the OFF state 507 to the ON state 503 in response to level of occupancy in the output buffer of the output port decreasing below a second level.
- the switch provides a control packet such as the PAUSE(O) frame to each information source coupled to an input port of the switch to enable the information source to transmit information packets.
- information packets held in the output buffer are transmitted to information destinations via the output port (operation 513 in the ON state).
- an output port is in the ON state 503
- information packets from all of the input ports are admitted into the output buffer (except from those input ports in the DISABLED state).
- the level of occupancy of an output buffer is measured in terms of the number of packets in the buffer.
- the buffer counter (such as buffer counter 307 of Figure 3) is incremented by one.
- the level of occupancy of the output buffer as indicated by the counter signal exceeds the first level, the output port transition to the OFF state 507.
- the switch when the output port is in the ON state 503, the switch is in a wait for packet state 511. Upon the receipt and admittance of an information packet from any input port of the switch, a determination is made (515) of whether the level of occupancy of the output buffer has exceeded a first level. If the first level has been exceeded, then the output port transitions to the OFF state. If the first level has not been exceeded, the switch returns to the wait for packet state 51 1. In one embodiment, a counter is used to determine whether the level of occupancy of the output buffer has exceeded a first level, wherein the output port transitions to the OFF state 507 in response to the counter providing a signal indicating that the level of occupancy has exceeded the first level.
- the switch processing engine of the switch executes a software routine stored in a memory of the switch processing engine that checks the level of occupancy of the buffer each time an information packet has been received and has been admitted in the output buffer.
- the frequency at which the switch processing engine checks the level occupancy during a particular time is dependent upon the level of occupancy of the buffer at that particular time. The lower the level, the less often the buffer is checked.
- output port 1 of switch 123 transitions to an OFF state from the ON state in response to the level of occupancy of the output buffer of output port 1 exceeding the first threshold level.
- switch 123 provides a PAUSE (oo) frame to both switch 121 and to desktop computer 113 to inhibit these upstream sources from transmitting information packets to the input ports of switch 123.
- the PAUSE ( ⁇ ) frame is provided to switch 121 via output port 3 of switch 123, link 131 B, and input port 3 of switch 121.
- the PAUSE (oo) is provided to desktop computer 113 via output port N of switch 123 and link 137B.
- output port 1 of switch 123 While output port 1 of switch 123 is in the OFF state, information packets held in the output buffer of output port 1 are transmitted to terminal 111. In response to the level of occupancy of the output buffer of output port 1 of switch 123 decreasing below a first level, output port 1 of switch 123 transitions to the ON state wherein a control packet such as the PAUSE(O) frame is provided to switch 121 and desktop computer 113.
- a control packet such as the PAUSE(O) frame is provided to switch 121 and desktop computer 113.
- a counter is used to determine whether the level of occupancy of the output buffer has decreased below a second level, wherein the output port transitions to the ON state 503 in response to the counter providing a signal indicating that the level of occupancy has decreased below the second level.
- the switch processing engine of the switch executes a software routine stored in a memory of the switch processing engine that checks the level of occupancy of the buffer each time an information packet has been transmitted from the output buffer.
- the switch processing engine checks the level of occupancy by reading the counter signal from an associated hardware counter or by reading a signal indicative of a count stored in a memory location.
- the first level at which the level of occupancy of an output buffer exceeds for the transition of an output port from an ON state to the OFF state is higher than the second level at which the level of occupancy decreases below for the transition of the output port to the ON state from the OFF state.
- This hysteresis feature reduces the number of control packets provided over the network to inhibit and then enable upstream sources in providing information packets when the output port transitions back and forth between the ON and OFF states.
- the hysteresis feature also reduces the amount of threshing that can result during a busy period of a switch. Consequently, increasing the distance between the first level and the second level reduces the number overhead of control packets transmitted and reduces problems due to threshing. However, increasing the distance between the first level and the second level increases the amount of time that the upstream devices are in hold states and correspondingly the opportunity for information packets to be discarded by the upstream devices due to the output buffers of the upstream devices overflowing.
- the switch of the output port discards the received information packets that are to be routed to the output port (operation 523).
- the switch discards all information packets received after a specific period of time from when the PAUSE (oo) frame or other control packet was provided to all information packet sources to inhibit the transmission of information packets to the input ports of the switch.
- the switch would accept a specific number packets received via the input ports after the PAUSE (oo) frames or other control packets were provided before discarding information packets from the input ports.
- the delay discard feature is implemented to where Coff number of packets will be accepted from each input port before any frame is discarded.
- Coff represents the upper bound of time (denoted in the number of packets) between the transmitting of the control packet to an upstream source and when that control packet takes affect on the upstream source to inhibit the transmission of information packets.
- H is the number of packets in the output buffer at which the output port transitions to the OFF state.
- L 0.8H wherein L is the number of packets in the output buffer at which the output port transitions to the ON state and wherein Li is the number of packets in an allocated portion of a buffer at which an input port transitions to a disabled state.
- Placing an upstream source in a hold state with a control packet such as the PAUSE ( ⁇ ) inhibits the upstream source from transmitting information packets.
- a control packet such as the PAUSE ( ⁇ ) inhibits the upstream source from transmitting information packets.
- the PAUSE (oo) frame inhibits the transmission of all information packets by the upstream source regardless of whether any of the packets are to be routed to the congested output port.
- output port 1 transitions to the OFF state where switch 123 provides a PAUSE (oo) frame to switch 121 to inhibit output port 3 of switch 121 from transmitting information packets to input port 3 of switch 123. Even if no information packets in the output buffer of output port 3 of switch 121 are to be routed to output port 1 of switch 123, output port 3 of switch 121 is inhibited from transmitting information packets in its output buffer.
- PAUSE PAUSE
- inhibiting output port 3 of switch 121 from transmitting causes output port 3 to become congested to where switch 121 provides PAUSE (oo) frames to all upstream sources operably coupled to its input ports. Consequently, implementing flow control to enable an efficient operation for one switch may cause other upstream sources in the computer network to become congested and therefore lead to the discarding of information packets.
- Figures 6A and 6B set forth a system for implementing flow control that allows upstream sources to minimize the amount of congestion in the computer network due to a downstream output port becoming congested.
- the upstream information packet source transmits information packets to the downstream destinations operably coupled to the upstream source.
- a control signal such as control packet (like a PAUSE (oo) frame) to inhibit transmission (such as when an input port of a downstream destination transitions to a DISABLED state or when an output port of a down stream destination transitions to an OFF state)
- the upstream source transitions to a HOLD state 607.
- the upstream source transitions to the NO HOLD state from the HOLD state in response to receiving a control signal such as a control packet (like the PAUSE(O) frame) to enable the upstream source to transmit information packets or in response to the expiration of the time period of the control packet that placed the upstream source in the HOLD state (such as when the upstream source is placed in a HOLD state with a PAUSE(l) frame).
- a control signal such as a control packet (like the PAUSE(O) frame) to enable the upstream source to transmit information packets or in response to the expiration of the time period of the control packet that placed the upstream source in the HOLD state (such as when the upstream source is placed in a HOLD state with a PAUSE(l) frame).
- the upstream source determines whether the level of occupancy of the output buffer of the upstream source is above a first level. If the level of occupancy is not above the first level, the upstream source enters a NON TRANSMITTING sub-state 614. In the NON TRANSMITTING sub-state 614, the upstream source does not transmit information packets to the downstream destination that provided the control packet to inhibit the upstream source (617).
- the upstream source transitions to a TRANSMITTING sub-state 613 wherein the upstream source disregards the control packet provided by the downstream destination and transmits information packets to the downstream destination.
- a TRANSMITTING sub-state 613 after each packet has been transmitted from the output buffer in operation 615, a determination is made in 621 of whether the level of occupancy of the output buffer of the upstream source has decreased below the second level. If the level of occupancy has not decreased below the second level, then the buffer remains in the TRANSMITTING sub-state.
- the upstream source transitions to the NON TRANSMITTING sub-state 614.
- the level of occupancy of the output buffer is determined with the use of a counter such as counter 307 of Figure 3.
- NON TRANSMITTING sub-state 614 for each packet admitted into the output buffer of the upstream source, a determination is made in 623 of whether the level of occupancy of the output buffer of the upstream source exceeds the first level. If the level of occupancy does not exceed the first level, then the upstream source remains in the NON TRANSMITTING sub-state 614. If the level of occupancy exceeds the first level after the packet has been admitted into the output buffer of the up stream source, then the upstream source transitions to the TRANSMITTING sub-state 613.
- switch 123 if output 1 of switch 123 becomes congested, switch 123 provides PAUSE (oo) frames to Desktop computer 113 and to switch 121 to inhibit the transmission of information packets by desktop computer 113 and output port 3 of switch 121. If the level of occupancy of the output buffer for output port 3 of switch 121 is above a first level, then output port 3 of switch 121 transitions to a TRANSMITTING sub-state where switch 121 ignores the PAUSE (oo) frame provided by switch 123 and transmits the packets in the output buffer of output port 3 to input port 3 of switch 123.
- Switch 123 discards the information packets received from switch 121 that are to be routed to output port 1 of switch 123 and provides the information packets that are to be routed to output ports 2, 3, and N to those output ports.
- output port 3 of switch 121 transitions to the NON TRANSMITTING state where output port 3 does not transmit information packets in its buffer.
- An information network that includes switches whose output ports have TRANSMITTING and NON TRANSMITTING sub-states in the HOLD state advantageously allows for the output buffers of upstream switches to be selectively used as additional storage for a downstream output buffer that has become congested during those instances when the network, as a whole, is lightly loaded.
- Such a system also prevents a single downstream congested output port of a switch from inhibiting the flow of information packets in the network that are not destined for the congested output port.
- the system set forth in Figures 6A and 6B may result in the discarding of information packets that are to be routed to the congested output port, the method reduces the discarding of information packets that are to be routed to uncongested output ports.
- the level of occupancy of a buffer may be measured in other units other than by the number of information packets in a buffer.
- the level of occupancy may be measured in terms of the number of bytes of the buffer being occupied by information packets versus the total number of bytes of the buffer. For example, if the size of the buffer is 4K bytes and only 2 Kbytes of memory hold information packets, then only one half of the buffer is being utilized at that moment.
- each output port would include mechanisms for determining the size in bytes (or other units of data) of the information packets held in the output buffer, or include mechanisms for determining the amount of buffer space in bytes that is being used to hold information packets. Such a system would be advantageous where the size of the information packets vary widely.
- control signals may be provided by a down stream switch to an upstream source to place the upstream source in a HOLD state when an input port of the down stream switch is transitioning between ENABLE/DISABLE states or when an output port of the down stream switch is transitioning between an ON/OFF states.
- the system may have a dedicated line for conveying a discrete control signal indicating to the upstream source to either transmit or not to transmit information packages.
Abstract
Description
Claims
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AU49600/99A AU4960099A (en) | 1998-06-30 | 1999-06-25 | Flow control using output port buffer allocation |
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US09/107,881 US6252849B1 (en) | 1998-06-30 | 1998-06-30 | Flow control using output port buffer allocation |
US09/107,881 | 1998-06-30 |
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US7286547B2 (en) | 2002-05-09 | 2007-10-23 | Broadcom Corporation | Dynamic adjust multicast drop threshold to provide fair handling between multicast and unicast frames |
US7764704B2 (en) | 2002-05-09 | 2010-07-27 | Broadcom Corporation | Dynamic adjust multicast drop threshold to provide fair handling between multicast and unicast frames |
Also Published As
Publication number | Publication date |
---|---|
EP1092301A2 (en) | 2001-04-18 |
JP2002519912A (en) | 2002-07-02 |
AU4960099A (en) | 2000-01-17 |
WO2000000899A3 (en) | 2000-05-04 |
US6252849B1 (en) | 2001-06-26 |
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