Express Forwarding in Wireless Mesh Networks
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Solution Overview
Problem
Wireless mesh networks experience significant latency due to multi-hop paths, which is not adequately addressed by existing mechanisms, particularly in scenarios involving Voice Over Internet Protocol (VoIP) and multimedia applications that require stringent Quality of Service (QoS) with short end-to-end delays.
Innovation Solution
Implementing express forwarding techniques, such as maintaining a timer (NAV) for nodes, designating frames as time-sensitive QoS (TSQ) with incremented duration fields, and using residual lifetime or time-to-live based mechanisms to prioritize and efficiently forward frames, ensuring reduced delay and increased throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If frame-by-frame reservation is used in wireless LANs, then channel access flexibility is improved, but end-to-end delay increases due to repeated contention and reservation overhead in multi-hop scenarios
Solution Approach 1:
The patent applies preliminary action by having the source node perform start-to-finish reservation for the entire multi-hop transmission path before actual data transmission begins. The source node reserves channels at all intermediate forwarding nodes and the destination node in advance, eliminating the need for repeated contention and reservation at each hop during data transmission. This pre-reservation approach significantly reduces end-to-end delay while maintaining channel access flexibility.
2Loss of time
If start-to-finish reservation is used for entire transmission sequences, then end-to-end delay is reduced, but channel utilization efficiency deteriorates when reservations are denied or time remains reserved after transmission completion
Solution Approach 1:
The patent applies dynamics by making the reservation mechanism adaptive rather than static. The source node dynamically adjusts reservation duration based on actual transmission needs, and intermediate nodes can dynamically release reserved channels when not needed. The system transitions from rigid start-to-finish reservation to a flexible approach where reservations can be partially released or adjusted, optimizing channel utilization while maintaining low latency for active transmissions.
Solution Approach 2:
The patent applies discarding and recovering by allowing unused reserved time slots to be released back to the channel pool for other uses. When transmission sequences complete early or reservations are denied, the remaining reserved time is discarded and made available for other transmissions, improving overall channel utilization efficiency while preserving the low-latency benefits for active QoS traffic.
3Reliability
If conventional 802.11e mechanisms are used for single-hop transmissions, then QoS requirements are met for single hop, but latency requirements are not satisfied in multi-hop wireless mesh networks
Solution Approach 1:
The patent introduces an intermediary mechanism where the source node acts as a coordinator that performs centralized start-to-finish reservation for all intermediate forwarding nodes and the destination. This intermediary approach extends QoS guarantees beyond single-hop to multi-hop scenarios by coordinating channel reservations across the entire transmission path, ensuring that each hop has pre-secured access rights and avoiding cumulative contention delays that would otherwise violate latency requirements.
Data Source
AI summary
A method, apparatus and computer program product for the express forwarding are presented. A timer (NAV) is maintained at each respective node of a wireless LAN. A frame is designated as a TSQ frame to be express forwarded from a first node to a second node. A duration field of the frame is incremented by a first predetermined time increment (DT0) before the TSQ frame is forwarded and the TSQ frame is forwarded by the first node to the second node. A response is received from the second node wherein non-forwarding neighboring nodes each set their NAV according to a value equal to the duration field of the response. The second node attempts transmission of the TSQ frame when acknowledgement of receipt of the TSQ frame is complete.