Mirrored WAN Optimization Devices Lossless Failover
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Solution Overview
Problem
In wide area network (WAN) optimization, data acknowledged by a local WAN optimization device is lost if the device fails, as the data cannot be recovered due to the lack of effective failover mechanisms for mirrored devices.
Innovation Solution
The implementation of mirrored CNE/LDCM devices, where the host CNE/LDCM device sends datagrams to both the WAN and a mirroring device, allowing the mirroring device to acknowledge and forward acknowledgments, ensuring data integrity and failover by transitioning the TCP connection and reopening the LAN TCP window upon successful transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a local WAN optimization device does a local TCP acknowledgement, then LAN-like performance is achieved, but data loss occurs if the device fails
Solution Approach 1:
The patent creates a mirror copy of the WAN optimization device that maintains identical state. When the primary device sends a local ACK, the mirror device simultaneously receives a copy of the data and can independently ACK. This copying mechanism ensures that if the primary device fails, the mirror device can take over without data loss, resolving the contradiction between fast local ACKing and data integrity.
Solution Approach 2:
The mirror device performs preliminary actions by receiving and buffering copies of data in advance before the primary device potentially fails. This preliminary data reception and buffering ensures that when failover occurs, the mirror device already has the necessary data to continue transmission without loss, maintaining both speed and reliability.
2Reliability
If data is buffered at the local WAN optimization device for later delivery, then data loss is prevented on failure, but device complexity increases
Solution Approach 1:
The patent segments the buffering function by distributing it across two separate devices - the primary WAN optimization device and the mirror device. Each device maintains its own buffer independently, eliminating the need for complex inter-device buffer coordination. This segmentation reduces individual device complexity while maintaining overall system reliability through redundancy.
3Reliability
If mirrored devices are implemented for failover, then data loss is prevented, but inter-device messaging overhead increases
Solution Approach 1:
The patent extracts the critical failover messaging from the general data flow by implementing separate, dedicated control channel communication between primary and mirror devices. This extraction allows minimal, essential state synchronization messages to be transmitted independently from data traffic, reducing overall messaging overhead while maintaining reliable failover capability.
Data Source
AI summary
If there are mirrored WAN optimization devices, a master WAN optimization device sends a datagram received from a source across the WAN and sends a copy of the datagram to a mirroring WAN optimization device. When the mirroring WAN optimization device ACKs the mirrored datagram, the master WAN optimization device ACKs the host. When the master WAN optimization device receives the ACK from the WAN, the ACK is forwarded to the mirroring WAN optimization device, which deletes the mirrored datagram. Alternatively, the mirroring WAN optimization device can receive the datagram from the source, store it and forward it to the master WAN optimization device, which sends the datagram across the WAN and sends an ACK to the host. When the ACK from the WAN is received, the master WAN optimization device forwards the ACK to the mirroring WAN optimization device, when then deletes the mirrored datagram.