全光近屬封包交換 IP-over-WDM 網路之訊務控制技術與效能分析

Abstract

對於IP-over-WDM網路而言，全光近屬封包交換網路(OCPS)技術已設計來克服全光封包交換的限制。藉由使用內頻控制進行叢集交換，同時採用訊務控制強化技術，以提供高頻寬使用率與服務品質保證。在此篇論文裡，先簡單介紹全光近屬封包交換網路技術，接著提出所設計的服務品質強化訊務控制機制，於入口路由器做封包集結動作時，提供延遲等級區分與遺失等級區分技術，以應用於全光近屬封包交換網路上。根據這兩個目的，此機制可稱之為(psi,tou)封包排程器/流量調節器，其中psi與tou分別代表最大的叢集大小與最長叢集組合時間。為了提供延遲等級區分，IP封包資料流選定一個延遲相關之權重，(psi,tou)封包排程器根據這些權重與大小為psi的虛擬視窗，集結封包為叢集。每個延遲等級之延遲保證上限，可以藉由正式規範的逐步服務曲線來量化。為了提供遺失等級區分，(psi,tou)流量調節器分配較大的叢集尺寸給較高遺失優先權等級者，以促進訊務調節效果。為了檢查此效果與遺失表現之關係，此論文分析並導出了(psi,tou)流量調節器的輸出程序，封包輸入流則模組化為具有批次輸入的雙態Markov Modulated Bernoulli Process。分析結果顯示(psi,tou)流量調節器的叢集輸出間距時間的變化程度的減少，與叢集大小是有關的。最後，此論文做了個模擬實驗，環境設定為24節點的美國ARPANET網路與16節點的4x4-torus網路，並比較全光近屬封包交換技術與全光叢集交換技術之遺失率表現。模擬結果顯示，透過叢集尺寸調整，(psi,tou)流量調節器可以有效的區分遺失等級，與使用外頻控制與偏移時間服務品質策略之全光叢集交換技術相比，全光近屬封包交換技術可以呈現優越的封包遺失率予高優先權等級，與較佳的遺失訊務等級區分。

For IP-over-WDM networks, Optical Coarse Packet Switching (OCPS) has been proposed to circumvent optical packet switching limitations by using in-band-controlled per-burst switching and advocating traffic control enforcement to achieve high bandwidth utilization and Quality-of- Service (QoS). In this thesis, we first introduce the OCPS paradigm. Significantly, we present a QoS-enhanced traffic control scheme exerted during packet aggregation at ingress nodes, aiming at providing delay and loss class differentiations for OCPS networks. Serving a dual purpose, the scheme is called (psi,tou)-Scheduler/Shaper, where psi and tou are the maximum burst size and burst assembly time, respectively. To provide delay class differentiation, for IP packet flows designated with delay-associated weights, (psi,tou)-Scheduler performs packet scheduling and assembly into bursts based on their weights and a virtual window of size psi. The guaranteed delay bound for each delay class is quantified via the formal specification of a stepwise service curve. To provide loss class differentiation, (psi,tou)-Shaper facilitates traffic shaping with larger burst sizes assigned to higher loss priority classes. To examine the shaping effect on loss performance, we analytically derive the departure process of (psi,tou)-Shaper. The aggregate packet arrivals are modeled as a two-state Markov Modulated Bernoulli Process (MMBP) with batch arrivals. Analytical results delineate that (psi,tou)-Shaper yields substantial reduction, proportional to the burst size, in the coefficient of variation of the burst inter-departure time. Furthermore, we conduct extensive simulations on a 24-node ARPANET network and a 16-node 4x4-torus network to draw packet loss comparisons between OCPS and Just-Enough-Time (JET)-based OBS. Simulation results demonstrate that, through burst size adjustment, (psi,tou)-Shaper effectively achieves differentiation of loss classes. Essentially, compared to JET-based OBS using out-of-band control and offset-time-based QoS strategy, OCPS is shown to achieve invariably superior packet loss probability for a high priority class, facilitating better differentiation of loss traffic classes.