WAN Optimization Device Lossless Failover via TCP State Mirroring
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Solution Overview
Problem
WAN optimization devices face data loss when they acknowledge data locally before it is received by the server, as this data cannot be recovered if the device fails.
Innovation Solution
Implementing a mechanism where WAN optimization devices delay acknowledging data until it is actually received from the target, while maintaining an open TCP window to prevent throttling issues, and using mirrored devices for redundancy to ensure rapid acknowledgement and lossless operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If WAN optimization devices do local TCP acknowledgement to improve flow, then throughput is improved, but data loss occurs if the device fails
Solution Approach 1:
The patent applies preliminary action by pre-synchronizing TCP state information between primary and secondary WAN optimization devices before failover occurs. The secondary device maintains up-to-date TCP state through continuous synchronization, so when failover happens, the secondary device can immediately continue data transmission without retransmitting previously acknowledged data, thus preventing data loss while maintaining high throughput
Solution Approach 2:
The patent uses copying by creating a redundant copy of the TCP state information in the secondary WAN optimization device. This copy is kept synchronized with the primary device through state synchronization mechanisms, allowing the secondary device to take over seamlessly upon primary device failure, ensuring both reliability and continuous high-speed data flow
2Reliability
If WAN optimization devices delay ACK to prevent data loss, then reliability is improved, but throughput decreases due to throttling
Solution Approach 1:
The patent segments the acknowledgment function into two independent parts: local ACK generation for throughput optimization and remote ACK verification for reliability. The local ACK is sent immediately to maintain high throughput, while a separate verification mechanism checks whether the remote end actually received the data, preventing data loss without throttling the overall transmission speed
Solution Approach 2:
The patent introduces an intermediary verification mechanism that mediates between the need for immediate ACK (for throughput) and actual data receipt confirmation (for reliability). This intermediary layer allows the system to send ACKs promptly while still verifying data delivery through additional confirmation protocols, resolving the contradiction between speed and reliability
3Reliability
If mirrored CNE/LDCM devices are used for redundancy, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the failover functionality into the standard TCP state synchronization process between primary and secondary devices. By combining redundancy with the existing state synchronization mechanism, the system achieves failure tolerance without requiring separate complex failover protocols, thus improving reliability while minimizing additional system complexity
Solution Approach 2:
The patent implements self-service by enabling the secondary WAN optimization device to automatically detect primary device failure and take over data transmission without manual intervention. The automatic failover mechanism monitors the primary device's health and seamlessly transitions to the secondary device when failure is detected, providing high reliability through automated operations rather than complex manual configuration
Data Source
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AI summary
The WAN optimization devices delay ACK until the ACK is actually received from the target while opening up the TCP window. When the ACK is received and forwarded, the TCP window is reduced in size. If there are mirrored WAN optimization devices, the original WAN optimization device sends the datagram across the WAN and at the same time sends the datagram to the mirroring WAN optimization device. When the mirroring WAN optimization device ACKs the mirrored datagram, the original WAN optimization device ACKs the host. When the ACK across the WAN is received, the mirroring WAN optimization device gets the ACK forwarded and deletes the mirrored datagram. On a loss of a device, the TCP connection transitions to the mirroring WAN optimization device, which closes the LAN TCP window and transmits all un-ACKed data. Then upon success the mirroring WAN optimization device reopens the LAN TCP window.