US20050041579A1 - Head of line blocking - Google Patents
Head of line blocking Download PDFInfo
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- US20050041579A1 US20050041579A1 US10/876,653 US87665304A US2005041579A1 US 20050041579 A1 US20050041579 A1 US 20050041579A1 US 87665304 A US87665304 A US 87665304A US 2005041579 A1 US2005041579 A1 US 2005041579A1
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- output
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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
- H04L49/505—Corrective measures
- H04L49/508—Head of Line Blocking Avoidance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L49/00—Packet switching elements
- H04L49/20—Support for services
- H04L49/201—Multicast operation; Broadcast operation
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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
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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
- H04L49/501—Overload detection
Definitions
- the present invention relates to network switching communication protocols generally and to prevention of head of line blocking in particular.
- a network switch creates a network among a plurality of end nodes, such as workstations, and other network switches connected thereto. Each end node is connected to one port of the network. The ports also serve to connect network switches together.
- Each end node sends packets of data to the network switch which the switch then routes either to another of the end nodes connected thereto or to a network switch to which the destination end node is connected. In the latter case, the receiving network switch routes the packet to the destination end node.
- Each network switch has to temporarily store the packets of data which it receives from the units (end node or network switch) connected to it while the switch determines how, when and through which port to retransmit the packets.
- Each packet can be transmitted to only one destination address (a “unicast” packet) or to more than one unit (a “multicast” or “broadcast” packet).
- the switch typically stores the packet only once and transmits multiple copies of the packet to some (multicast) or all (broadcast) of its ports. Once the packet has been transmitted to all of its destinations, it can be removed from the memory or written over.
- Switch 10 comprises a central queuing manager 12 , an output buffer 14 , and a multiplicity of output ports 16 .
- Switch 10 receives incoming data 18 which it stores until transmission as queued data 24 in output buffer 14 .
- switch 10 transfers the queued data 24 out of the relevant output port 16 as outgoing data 26 .
- Output buffer 14 is either a pooled buffer which services the entire switch 10 or a plurality of dedicated queues within buffer 14 , one queue per output port 16 .
- the exemplary switch 10 shown in FIG. 1 comprises a pooled output buffer 14 and two output ports 16 B and 16 C.
- Incoming data 18 comprises data packets 30 , 32 , 34 and 36 , which are designated for various destination ports 16 .
- Data 18 is received by manager 12 , which identifies the appropriate destination port 16 of the packets 30 , 32 , 34 , and 36 respectively, and dispatches them to the output buffer 14 .
- unicast data packets 32 and 36 are designated for port 16 C
- unicast data packet 30 is designated for port 16 B
- multicast packet 34 is designated for both ports 16 B and 16 C.
- Output buffer 14 stores the queued data 24 until the relevant port 16 is available, at which point, the outgoing data 26 is transferred to the relevant port 16 .
- Manager 12 is aware of the backup in the output buffer 14 , typically through a fullness sensor (not shown) measuring the fullness of output buffer 14 , and, accordingly, stops receiving incoming data 18 to switch 10 .
- switch 10 Although switch 10 no longer receives incoming data 18 , it continues to send outgoing data 26 , and thus, clears out the output buffer 14 . Once enough outgoing data 26 has been sent, output buffer 14 empties out and is again able to receive more data 24 . Manager 12 reopens inflow of data 18 to switch 10 .
- Manager 12 halts the incoming flow of data 18 . All data 18 incoming into switch 12 is halted and discarded, including unicast data packets 32 and 36 and multicast data packet 34 which are designated for the available port 16 C.
- a network switch which includes a plurality of output ports, at least one input port and a queuing manager.
- Each output port has a control unit associated therewith.
- the input port receives incoming data destined for various ones of the output ports.
- the queuing manager directs the incoming data to their destination output ports.
- Each control unit includes an output queue, a fullness/emptiness sensor and a head of line (HOL) mask.
- the output queue stores the incoming data destined for its associated output port.
- the sensor senses when the output queue reaches a fullness or an emptiness state.
- the HOL mask is connected to the output of the sensor and blocks inflow of the incoming data to the output queue when the sensor senses the fullness state and for enabling inflow when the sensor senses the emptiness state.
- control unit for an output port of a network switch as described hereinabove.
- a method of controlling flow within a network switch comprising the steps of sensing when an output queue of the network switch reaches a fullness or an emptiness state, blocking queueing of incoming data to the output queue when the fullness state is sensed, discarding of unicast packets destined to the full output port queue, avoiding queuing of multicast packets to said output port queue and enabling queueing when the emptiness state is sensed.
- FIG. 1 is a schematic illustration of a prior art network switching protocol
- FIG. 2 is a schematic illustration of a network switching protocol constructed and operative in accordance with a preferred embodiment of the present invention.
- FIG. 2 illustrates, in general terms, a portion of the data packet transfer process that takes place within the operations of a network switch 50 , constructed and operative in accordance with a preferred embodiment of the present invention.
- Switch 50 comprises many of the elements described in the prior art FIG. 1 .
- Elements of FIG. 2 which are similar to those of FIG. 1 have the same reference numerals.
- switch 50 comprises a plurality of: output queues 66 , head of line (HOL) masks 52 , fullness watermarks 60 , emptiness watermarks 62 and sensors 64 .
- HOL head of line
- the output queues 66 function similar to output buffer 14 in that the output queue 66 s temporarily store data 24 waiting for transmission to output ports 16 . However, in contrast to output buffer 14 , output queues 66 are dedicated to their associated output ports 16 , for example, output queue 66 B is dedicated to output port 16 B, and so.
- HOL masks 52 control data flow to their output queues 14 .
- FIG. 2 shows HOL masks 52 B and 52 C as logical switches and operative for output queues 14 B and 14 C, respectively.
- Each sensor 64 is dedicated to an associated output queue 66 and relays to manager 12 the fullness or emptiness state of that associated queue 14 .
- Each sensor 64 is a counter which has two thresholds, one associated with its fullness watermark 60 and one associated with its emptiness watermark 62 .
- Switch 50 receives, distributes, queues and sends data in a manner similar to that described for switch 10 . Additionally similar to switch 10 , from time to time one of the output ports 16 is busier than the other output ports 16 .
- the data 24 in one or more output queue 66 backs up and reaches the fullness threshold 60 of that queue 66 .
- queue 66 is almost full and temporarily can not receive any more data 24 .
- the associated sensor 64 notifies the state of fullness to its associated HOL mask 52 , which stops inflow of data to the almost full output queue 66 .
- the data 24 in output queue 66 B reaches almost fullness, it crosses the fullness threshold 60 B.
- Sensor 64 B notifies such to HOL mask 52 B which stops data flow to output queue 66 B.
- switch 50 continues to transfer incoming data 18 to the output queues 66 which are not affected by a backup. Hence, the data going to output queue 66 C will be received and its associated output port 16 C will continue to operate unhindered. However, incoming data 18 designated for port 16 B is discarded.
- data 18 comprises data packets 54 , 56 , and 58 .
- Packets 54 and 58 are unicast packets destined for ports 16 B and 16 C, respectively.
- Packet 56 is a multicast packet destined for both ports 16 B and 16 C. All packets 54 , 56 and 58 are received by switch 50 .
- Queuing manager 12 identifies the packets and distributes them to the appropriate output queues 66 ; unicast packet 54 to output queue 66 B, multicast packet 56 to output queues 66 B and 66 C, and unicast packet 58 to output queue 66 C.
- Multicast packet 56 and unicast packet 58 designated for output queue 66 C are properly queued for delivery. However, since output queue 66 B is full, HOL mask 52 B does not queue unicast packet 54 and multicast packet 56 designated for port 16 B, and thus, packet 54 is discarded, and packet 56 is queued only to output queue 66 C.
- Port 16 B continues transmitting data 26 B, until eventually the data 24 B in output queue 66 B reaches the emptiness watermark 62 signaling that output queue 66 B is almost empty. This information is relayed by sensor 64 B to HOL mask 52 B which, in turn, reopens inflow to its associated output queue 66 B, and data will again be queued to output queue 66 B. In this a manner, packets destined for output queues 66 which are not full are not affected by HOL blocking from other backed up output queues 66 .
Abstract
A network switch which includes a plurality of output ports, at least one input port and a queuing manager. Each output port has a control unit associated therewith. The input port receives incoming data destined for various ones of the output ports. The queuing manager directs the incoming data to their destination output ports. Each control unit includes an output queue, a fullness/emptiness sensor and a head of line (HOL) mask. The output queue stores the incoming data destined for its associated output port. The sensor senses when the output queue reaches a fullness or an emptiness state. The HOL mask is connected to the output of the sensor and blocks inflow of the incoming data to the output queue when the sensor senses the fullness state and for enabling inflow when the sensor senses the emptiness state.
Description
- The present invention relates to network switching communication protocols generally and to prevention of head of line blocking in particular.
- A network switch creates a network among a plurality of end nodes, such as workstations, and other network switches connected thereto. Each end node is connected to one port of the network. The ports also serve to connect network switches together.
- Each end node sends packets of data to the network switch which the switch then routes either to another of the end nodes connected thereto or to a network switch to which the destination end node is connected. In the latter case, the receiving network switch routes the packet to the destination end node.
- Each network switch has to temporarily store the packets of data which it receives from the units (end node or network switch) connected to it while the switch determines how, when and through which port to retransmit the packets. Each packet can be transmitted to only one destination address (a “unicast” packet) or to more than one unit (a “multicast” or “broadcast” packet). For multicast and broadcast packets, the switch typically stores the packet only once and transmits multiple copies of the packet to some (multicast) or all (broadcast) of its ports. Once the packet has been transmitted to all of its destinations, it can be removed from the memory or written over.
- Reference is now made to
FIG. 1 which schematically illustrates a portion of the data packet transfer process that takes place within the operations of anetwork switch 10.Switch 10 comprises acentral queuing manager 12, anoutput buffer 14, and a multiplicity of output ports 16. Switch 10 receivesincoming data 18 which it stores until transmission as queueddata 24 inoutput buffer 14. At the appropriate time, which is generally when the relevant output port 16 is available, switch 10 transfers thequeued data 24 out of the relevant output port 16 as outgoing data 26. -
Output buffer 14 is either a pooled buffer which services theentire switch 10 or a plurality of dedicated queues withinbuffer 14, one queue per output port 16. Theexemplary switch 10 shown inFIG. 1 comprises apooled output buffer 14 and twooutput ports - Incoming
data 18 comprisesdata packets Data 18 is received bymanager 12, which identifies the appropriate destination port 16 of thepackets output buffer 14. As an exampleunicast data packets port 16C,unicast data packet 30 is designated forport 16B andmulticast packet 34 is designated for bothports Output buffer 14 stores thequeued data 24 until the relevant port 16 is available, at which point, the outgoing data 26 is transferred to the relevant port 16. - Occasionally, one of the output ports 16 transfers at a faster pace than the other ports or, alternatively, receives more data than the other ports. For whatever reason, a condition may arise where the
data 24 for one of the output ports 16 backs up in theoutput buffer 14 creating a condition whereoutput buffer 14 is unable to receive more data.Manager 12 is aware of the backup in theoutput buffer 14, typically through a fullness sensor (not shown) measuring the fullness ofoutput buffer 14, and, accordingly, stops receivingincoming data 18 to switch 10. - All
incoming data 18 not received byswitch 10 is discarded, regardless of its destination output port 16. Not only is theincoming data 18 destined for the full output port discarded but theincoming data 18 destined for the available ports are also discarded. This problem is known as “Head of Line Blocking”. - Although
switch 10 no longer receivesincoming data 18, it continues to send outgoing data 26, and thus, clears out theoutput buffer 14. Once enough outgoing data 26 has been sent,output buffer 14 empties out and is again able to receivemore data 24.Manager 12 reopens inflow ofdata 18 to switch 10. - For example, if
port 16B is backed up, then theoutput buffer 14 will become full withqueued data 24B, whileoutput port 16C will still available to transmit.Manager 12 halts the incoming flow ofdata 18. Alldata 18 incoming intoswitch 12 is halted and discarded, includingunicast data packets multicast data packet 34 which are designated for theavailable port 16C. - It is an object of the present invention to prevent Head of Line Blocking as much as possible.
- There is therefore provided, in accordance with a preferred embodiment of the present invention, a network switch which includes a plurality of output ports, at least one input port and a queuing manager. Each output port has a control unit associated therewith. The input port receives incoming data destined for various ones of the output ports. The queuing manager directs the incoming data to their destination output ports. Each control unit includes an output queue, a fullness/emptiness sensor and a head of line (HOL) mask. The output queue stores the incoming data destined for its associated output port. The sensor senses when the output queue reaches a fullness or an emptiness state. The HOL mask is connected to the output of the sensor and blocks inflow of the incoming data to the output queue when the sensor senses the fullness state and for enabling inflow when the sensor senses the emptiness state.
- There is also provided, in accordance with a preferred embodiment of the present invention, a control unit for an output port of a network switch as described hereinabove.
- Finally, there is provided, a method of controlling flow within a network switch, the method comprising the steps of sensing when an output queue of the network switch reaches a fullness or an emptiness state, blocking queueing of incoming data to the output queue when the fullness state is sensed, discarding of unicast packets destined to the full output port queue, avoiding queuing of multicast packets to said output port queue and enabling queueing when the emptiness state is sensed.
- The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:
-
FIG. 1 is a schematic illustration of a prior art network switching protocol; and -
FIG. 2 is a schematic illustration of a network switching protocol constructed and operative in accordance with a preferred embodiment of the present invention. - Reference is now made to
FIG. 2 which illustrates, in general terms, a portion of the data packet transfer process that takes place within the operations of anetwork switch 50, constructed and operative in accordance with a preferred embodiment of the present invention.Switch 50 comprises many of the elements described in the prior artFIG. 1 . Elements ofFIG. 2 which are similar to those ofFIG. 1 have the same reference numerals. - In addition to the prior art elements,
switch 50 comprises a plurality of: output queues 66, head of line (HOL) masks 52, fullness watermarks 60, emptiness watermarks 62 and sensors 64. - The output queues 66 function similar to
output buffer 14 in that the output queue 66 s temporarily storedata 24 waiting for transmission to output ports 16. However, in contrast tooutput buffer 14, output queues 66 are dedicated to their associated output ports 16, for example,output queue 66B is dedicated tooutput port 16B, and so. - HOL masks 52 control data flow to their
output queues 14.FIG. 2 showsHOL masks output queues queue 14. Each sensor 64 is a counter which has two thresholds, one associated with its fullness watermark 60 and one associated with its emptiness watermark 62. -
Switch 50 receives, distributes, queues and sends data in a manner similar to that described forswitch 10. Additionally similar to switch 10, from time to time one of the output ports 16 is busier than the other output ports 16. - The
data 24 in one or more output queue 66 backs up and reaches the fullness threshold 60 of that queue 66. Hence queue 66 is almost full and temporarily can not receive anymore data 24. - The associated sensor 64 notifies the state of fullness to its associated HOL mask 52, which stops inflow of data to the almost full output queue 66. As an example, when the
data 24 inoutput queue 66B reaches almost fullness, it crosses thefullness threshold 60B.Sensor 64B notifies such toHOL mask 52B which stops data flow tooutput queue 66B. - Unlike in the prior art which halted all inflow of
data 18 to switch 10,switch 50 continues to transferincoming data 18 to the output queues 66 which are not affected by a backup. Hence, the data going tooutput queue 66C will be received and its associatedoutput port 16C will continue to operate unhindered. However,incoming data 18 designated forport 16B is discarded. - As a further example,
data 18 comprisesdata packets Packets 54 and 58 are unicast packets destined forports Packet 56 is a multicast packet destined for bothports packets switch 50.Queuing manager 12 identifies the packets and distributes them to the appropriate output queues 66; unicast packet 54 tooutput queue 66B,multicast packet 56 tooutput queues unicast packet 58 tooutput queue 66C.Multicast packet 56 andunicast packet 58 designated foroutput queue 66C are properly queued for delivery. However, sinceoutput queue 66B is full,HOL mask 52B does not queue unicast packet 54 andmulticast packet 56 designated forport 16B, and thus, packet 54 is discarded, andpacket 56 is queued only tooutput queue 66C. -
Port 16B continues transmittingdata 26B, until eventually thedata 24B inoutput queue 66B reaches the emptiness watermark 62 signaling thatoutput queue 66B is almost empty. This information is relayed bysensor 64B toHOL mask 52B which, in turn, reopens inflow to its associatedoutput queue 66B, and data will again be queued tooutput queue 66B. In this a manner, packets destined for output queues 66 which are not full are not affected by HOL blocking from other backed up output queues 66. - It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims that follow:
Claims (16)
1. (Cancelled).
2. A control unit for an output port of a network switch, the control unit comprising:
an output queue for storing incoming data destined for said output port;
a fullness/emptiness sensor for sensing when said output queue reaches a fullness or an emptiness state; and
a head of line (HOL) mask, in communication with the output of said sensor, for blocking inflow of said incoming data to said output queue when said sensor senses said fullness state and for enabling inflow when said sensor senses said emptiness state.
3. (Cancelled).
4. A method of controlling flow within a network switch, the method comprising the steps of:
sensing when an output queue of said network switch reaches a fullness or an emptiness state;
blocking queuing of incoming data to said output queue when said fullness state is sensed;
discarding unicast packets destined to said output queue; and
enabling queuing when said emptiness state is sensed.
5. A network switch comprising:
a plurality of output port means for outputting data, each having a means for controlling associated therewith;
at least one input port means for receiving incoming data destined for various ones of said output port means; and
means for directing said incoming data to their destination output port means;
wherein each means for controlling comprises:
means for storing said incoming data destined for its associated output port;
means for sensing when said means for storing reaches a fullness or an emptiness state; and
means, in communication with the output of said means for sensing, for preventing queuing of said incoming data to said means for storing when said means for sensing senses said fullness state and for enabling queuing when said means for sensing senses said emptiness state.
6. A control unit for an output port of a network switch, the control unit comprising:
means for storing incoming data destined for the output port;
means for sensing when said means for storing reaches a fullness or an emptiness state; and
means, in communication with the output of said means for sensing, for blocking inflow of said incoming data to said means for storing when said means for sensing senses said fullness state and for enabling inflow when said means for sensing senses said emptiness state.
7. A device for controlling flow within a network switch, the device comprising:
means for sensing when an output queue of said network switch reaches a fullness or an emptiness state;
means for blocking queuing of incoming data to said output queue when said fullness state is sensed;
means for discarding unicast packets destined to said output queue; and
means for enabling queuing when said emptiness state is sensed.
8. A method for controlling flow within a network switch, the network switch including a plurality of output ports each having a control unit associated therewith, including at least one input port for receiving incoming data destined for various ones of said output ports, and including a queuing manager for directing said incoming data to their destination output ports, wherein each control unit performs the method comprising:
sensing when an output queue, for storing incoming data and associated with an output port, reaches a fullness or an emptiness state;
preventing queuing of the incoming data to the output queue when the fullness state is sensed; and
enabling queuing of the incoming data to the output queue when the emptiness state is sensed.
9. A method for a control unit for an output port of a network switch, the method comprising:
sensing when an output queue, for storing incoming data destined for the output port, reaches a fullness or an emptiness state;
blocking inflow of the incoming data to the output queue when the fullness state is sensed; and
enabling inflow of the incoming data to the output queue when the emptiness state is sensed.
10. A device for controlling flow within a network switch, the device comprising:
a sensor, adapt to sense when an output queue of said network switch reaches a fullness or an emptiness state:
a blocking element, adapted to block queuing of incoming data to said output queue when said fullness state is sensed;
a device adapted to discard unicast packets destined to said output queue and adapted to enable queuing when said emptiness state is sensed.
11. A network switch, comprising:
a plurality of output port means for outputting data, each having means for controlling associated therewith;
at least one input port means for receiving incoming data destined for various ones of said output port means; and
means for directing said incoming data to their destination output port means, wherein each means for controlling comprises:
means for storing said incoming data destined for its associate output port means;
means for sensing when an output queue, for storing incoming data and associated with an output port means, reaches a fullness or an emptiness state;
means for preventing queuing of the incoming data to the output queue when the fullness state is sensed; and
means for enabling queuing of the incoming data to the output queue the emptiness state is sensed.
12. A control unit for an output port of a network switch, the control unit comprising:
means for sensing when an output queue, for storing incoming data destined for the output port, reaches a fullness or an emptiness state;
means for blocking inflow of the incoming data to the output queue when the fullness state is sensed; and
means for enabling inflow of the incoming data to the output queue when the emptiness state is sensed.
13. A network device comprising:
an output queue for storing incoming data destined for an associated output port;
a fullness/emptiness sensor for sensing when the output queue reaches a fullness or an emptiness state; and
a head of line (HOL) mask, in communication with the output of said sensor, for blocking inflow of the incoming data to said output queue when said sensor senses the fullness state and for enabling inflow when said sensor senses the emptiness state.
14. A network device comprising:
means for storing incoming data destined for an associated output port;
means for sensing when the means for storing reaches a fullness or an emptiness state; and
means, in communication with the output of the means for sensing, for blocking inflow of the incoming data to the means for storing when the means for sensing senses the fullness state and for enabling inflow when the means for sensing senses the emptiness state.
15. A network device comprising:
a plurality of output ports each having a control unit associated therewith;
at least one input port for receiving incoming data destined for various ones of said output ports; and
a queuing manager for directing said incoming data to their destination output ports;
wherein each control unit comprises:
an output queue for storing said incoming data destined for its associated output port;
a fullness/emptiness sensor for sensing when said output queue reaches a fullness or an emptiness state; and
a head of line (HOL) mask, connected to the output of said sensor, for preventing queuing of said incoming data to said output queue when said sensor senses said fullness state and for enabling queuing when said sensor senses said emptiness state.
16. A network device comprising:
a plurality of output port means for outputting data, each having a means for controlling associated therewith;
at least one input port means for receiving incoming data destined for various ones of said output port means; and
means for directing said incoming data to their destination output port means;
wherein each means for controlling comprises:
means for storing said incoming data destined for its associated output port;
means for sensing when said means for storing reaches a fullness or an emptiness state; and
means, in communication with the output of said means for sensing, for preventing queuing of said incoming data to said means for storing when said means for sensing senses said fullness state and for enabling queuing when said means for sensing senses said emptiness state.
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Cited By (8)
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US20030103517A1 (en) * | 2001-12-03 | 2003-06-05 | Rahul Saxena | Multicast and broadcast operations in ethernet switches |
US7403521B2 (en) * | 2001-12-03 | 2008-07-22 | Intel Corporation | Multicast and broadcast operations in ethernet switches |
US20080253371A1 (en) * | 2001-12-03 | 2008-10-16 | Rahul Saxena | Multicast and broadcast operations in ethernet switches |
US20060013135A1 (en) * | 2004-06-21 | 2006-01-19 | Schmidt Steven G | Flow control in a switch |
US20080019566A1 (en) * | 2006-07-21 | 2008-01-24 | Wolfgang Niem | Image-processing device, surveillance system, method for establishing a scene reference image, and computer program |
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Also Published As
Publication number | Publication date |
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IL125271A0 (en) | 1999-03-12 |
US6829245B1 (en) | 2004-12-07 |
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