Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1998-08-03
2001-12-04
Ngo, Ricky (Department: 2664)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S412000
Reexamination Certificate
active
06327243
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to packet routing systems and, more specifically, to a system for providing a seamless switchover from a primary packet routing device to a secondary packet routing device.
BACKGROUND OF THE INVENTION
Information systems have evolved from centralized mainframe computer systems supporting a large number of users to distributed computer systems based on local area network (LAN) architectures. As the cost-to-processing-power ratios for desktop PCs and network servers have dropped precipitously, LAN systems have proved to be highly cost effective. As a result, the number of LANs and LAN-based applications has exploded.
A consequential development relating to the increased popularity of LANs has been the interconnection of remote LANs, computers, and other equipment into wide area networks (WANs) in order to make more resources available to users. However, a LAN backbone can transmit data between users at high bandwidth rates for only relatively short distances. In order to interconnect devices across large distances, different communication protocols have been developed. These include packet switching protocols, such as X.25, ISDN, frame relay, and ATM, among others.
Packet switching involves the transmission of data in packets through a network. Each block of end-user data that is to be transmitted is divided into packets. A unique identifier, a sequence number and a destination address are attached to each data packet. The packets are independent and may traverse the data network by different routes. The packets may incur different levels of propagation delay, or latency, caused by physical paths of different length. The packets may also be held for varying amounts of delay time in packet buffers in intermediated switches in the network. The packets may also be switched through differing numbers of packet switches as they traverse the network, wherein each switch has an associated processing delay caused by error detection and correction.
As a result, the packets may arrive out-of-order at the destination node. However, the destination node uses the identification and sequencing information in each data packet to assemble the data packets back in the proper order before continuing to process the original end-user data block.
To enhance the reliability of a packet switched network, it is common practice to build the packet switches as redundant devices. Each packet switch contains a primary (also called “master” or “active”) packet routing engine that ordinarily performs packet routing and a secondary (also called “slave” or “standby”) packet routing engine that takes over from the primary packet routing engine upon failure or upon the occurrence of certain selected events.
However, the switchover (or failover) from a primary to a secondary packet routing engine is frequently a disruptive event. At the time of switchover, the primary packet routing engine typically contains unprocessed data packets in input buffers, processed data packets in output buffers, and in-process data packets that are currently being processed by the control processor of the primary packet routing engine. Since the in-process data may affect the contents of both the input buffers and the output buffers, the loss of this in-process data during switchover to the secondary causes service disruptions.
There is therefore a need in the art for an improved redundant data packet switch that provides a more seamless switchover from a primary packet routing engine to a secondary packet routing engine. In particular, there is a need in the art for an improved redundant data packet switch in which the secondary packet routing engine is able to identify in-process data held in the primary packet routing engine and is able to correctly re-process such in-process data after a switch-over has occurred.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in a packet switched network, a redundant switch comprising a primary controller capable of routing data packets from an input interface to an output interface of the redundant switch and a secondary controller capable of performing data packet routing tasks performed by the primary controller after a switchover event. According to one embodiment of the present invention, the primary controller comprises: 1) an inbound queue capable of storing data packets inbound to the redundant switch; 2) an outbound queue capable of storing data packets outbound from the redundant switch; and 3) a control processor capable of processing a first data packet stored in the inbound queue and assigning an identifier to the first data packet, wherein the control processor further assigns the identifier to a second data packet, the second data packet associated with the first data packet and stored in one of the inbound queue and the outbound queue, wherein the first data packet is removed from the inbound queue only upon completion of all processing associated with the first data packet and wherein a removal of the first data packet from the inbound queue enables the second data packet to be transferred to the secondary controller during a switchover.
The above-described embodiment introduces a novel and advantageous feature of the present invention. During normal operation and during a switchover operation, the primary controller does not allow the second data packet in the outbound queue to be transferred or processed in any way until processing of the first data packet is complete and the first data packet is removed from the inbound queue, thereby preventing erroneous redundant data transfers. If the second data packet were transferred before all processing of the first data packet were complete, the secondary controller would regenerate the second data packet after a switchover and the second data packet would be transferred to its final destination twice. Hence, the second data packet is never accessed until after first data packet is completely processed and removed from the inbound queue. Additionally, the second data packet in the outbound queue is discarded if the first data packet is still in the inbound queue at switchover time, since the secondary controller will regenerate the second data packet after transfer of the first data packet.
According to one embodiment of the present invention, input interface is switchable between the primary controller and the second controller.
According to another embodiment of the present invention, the output interface is switchable between the primary controller and the second controller.
According to still another embodiment of the present invention, the redundant switch further comprises an intersystem queue capable of transferring data packets from the primary controller to the second controller.
According to yet another embodiment of the present invention, the control processor transfers the second data packet from the outbound queue to the intersystem queue during a failover if the control processor determines that no data packet in the inbound queue is assigned the identifier also assigned to the second data packet.
According to a further embodiment of the present invention, the control processor reads the first data packet from the inbound queue.
According to a still further embodiment of the present invention, a reading of the first data packet by the control processor does not remove the first data packet from the inbound queue.
According to a yet further embodiment of the present invention, a plurality of data packets stored in the inbound queue and in the outbound queue may not be transferred to the secondary controller until a parent data packet from which the plurality of data packets are derived is removed from the inbound queue.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Addit
Han John C.
Ngo Ricky
Samsung Electronics Co,. Ltd.
Tran Phuc
LandOfFree
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