適用於具延展性無線應用協定閘道器之高效率負載平衡策略

Abstract

叢集式架構適合用來建立一個具延展性、可靠性、及高效能的無線應用協定閘道器。然而，它需要一個有效率的負載平衡機制來分派行動用戶要求至叢集中能提供最佳服務的閘道器。此外，在無線應用協定模式中，行動用戶的連線時間無法預測與對閘道器產生的負載不均等，這兩者對閘道器間之負載平衡產生重大的影響。在本論文中，我們提出了一個負載平衡策略，此策略有三個特色：(1) 利用低運算及無額外通訊負擔的方式來估計每台閘道器的可能負載，(2) 使用非同步警訊機制來反應叢集中任何閘道器的使用率超過臨界值，(3) 明瞭無線應用協定。我們也提出一個具延展性無線應用協定閘道器 (SWG)，它包含一個無線應用協定指派器 (WAP dispatcher) 及由數個閘道器所組成的叢集。無線應用協定指派器是一個具有我們提出之負載平衡策略的前端負載分配器。為了避免無線應用協定指派器成為瓶頸，無線應用協定指派器在核心層分配行動用戶要求，且不處理從閘道器送至行動用戶的回應。實驗結果顯示，我們的SWG比LVS及Kannel閘道器擁有較佳的負載平衡效能、傳輸量與延遲。

Clustered architecture provides a promising way to build a scalable, reliable, and high-performance WAP gateway. However, it requires an efficient load balancing mechanism for assigning a request to a selected gateway of the cluster, which can offer the best service. In addition, unpredictable connection time and nonuniformity of the incoming load from different mobile clients in the WAP model are big obstacles to load balancing among real gateways. In this thesis, we propose a load balancing strategy that has the following features: (1) estimating the potential load of real gateways with low computation and no communication overhead, (2) asynchronous alarm sent when the utilization of a real gateway exceeds a critical threshold, and (3) WAP-awareness. We also propose a scalable WAP gateway (SWG) that consists of a {\it WAP dispatcher} and a {\it cluster of real gateways}. The WAP dispatcher is a front-end distributor with our load balancing strategy. To prevent the WAP dispatcher from becoming a bottleneck, the WAP dispatcher distributes mobile clients' requests in kernel space and does not process outgoing gateway-to-client responses. Experiment results show that our SWG has better load balancing performance, throughput, and delay compared to the LVS and the Kannel gateway.