被動式光纖網路之交錯式輪詢排程與其延遲之探討

Interleaved Polling and Its Delay Performance in Passive Optical Networks

毛普臻(Pu-Chen Mao)

指導教授 ： 吳和庭

國立臺北科技大學/電資學院/資訊工程系研究所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00297

摘要

隨著網際網路、多媒體技術的普及與進步，網路頻寬的需求也同時快速成長。為了應付使用者在頻寬上的需求，網路提供業者必須更新網路設備以及網路基礎設施。近年來，多數的骨幹網路已替換成頻寬較高的光纖傳輸媒介，然而，在存取網路部分的更換速度卻相對緩慢。現今存取網路大多數使用基於銅線的傳輸通道，這也是骨幹網路與存取網路之間頻寬瓶頸之主要來源。為了應付頻寬的成長，將銅線傳輸媒介更換為光纖電纜是必然的。被動式光纖網路技術如 EPON、GPON 提供了有效的解決方案。
本研究探討光纖網路終端機與光纖網路局端之不同距離對被動式光纖網路延遲的影響。本論文首先觀察因不等距離而造成的空閒時隙，並且使用一個優先分配最早空閒時隙的排程機制，和過去傳統的依序排程機制做延遲上的比較。我們再使用此機制延伸一個知名的線上交錯式排程演算法，IPACT，並觀察兩種機制的延遲比較。此論文也使用 MPCP 通訊協定中 GATE 訊息的四個 GRANT 欄位，將一個光纖網路終端機的傳輸時間分配分為最多四段更小的分配量填入空閒時隙，進一步觀察此機制對延遲效能的提升。我們再來使用了一個循環佇列切換的技巧，使 ONU 能夠紀錄封包延遲資訊，並且將這資訊傳送給 OLT。OLT 使用了收集到各 ONU 的封包延遲資訊後，透過一個頻寬分配機制可以進而降低網路封包的延遲時間。

關鍵字

交錯式排程 ； 長距離被動式光纖網路 ； 線上排程 ； 封包延遲

並列摘要

With advances in the World Wide Web and multimedia technologies requiring ever more network bandwidth, service providers have been upgrading network equipments and infrastructure to support the growing demand. While most of the media for backbone networks have been replaced by optical fiber over the years, progress in the access portion of the network is relatively slow in this regard. Due to the bottlenecks existing in copper-based access channels, upgrading the last (first) mile to optical fiber is inevitable. Passive optical network (PON) solutions such as EPON and GPON provide a cost effective approach to this problem.
This study investigates the effects of the variable distance of optical network units (ONUs) from the OLT on scheduling and delay performance in PONs. We observe the formation of idle time periods in the transmission channel caused by the heterogeneous distances from the optical line terminal (OLT), and attempt to allocate these time periods in an earliest first fashion by insertion of transmission windows into the gaps, as opposed to sequentially scheduling each ONU in traditional schemes. Comparison between a well known EPON scheduling algorithm, IPACT, and its extension using our allocation scheme is done from a delay performance perspective. We further extend this allocation scheme by utilizing the four grants available in the MPCP message and divide a single grant into four smaller grant segments, and observe the improvement in delay performance. In addition, a circular queue switching technique is employed at the ONUs to enable communication of packet delay information to the OLT. The OLT uses the delay information from ONUs in a bandwidth distribution scheme that reduces mean packet delays even further when paired with the insertion scheduling method.

並列關鍵字

long-reach EPON ； online scheduling ； heterogeneous propagation delay

參考文獻

[1] Paul Green Jr., “Fiber to the Home: The New Empowerment”, Wiley-Interscience, ISBN: 978-0-471-74247-0, 2006.

[2] Biswanath Mukherjee, “Optical Networks: The Road Ahead,” European Conference on Optical Communications (ECOC), Berlin, Germany, September 16-21, 2007, pp. 1-4.

[3] Kramer, G. Pesavento, G., “Ethernet passive optical network (EPON): building a next-generation optical access network,” IEEE Communications Magazine, Vol. 40, Issue 2, 2002, pp. 66-73.

[5] G. Kramer, B. Mukherjee, G. Pesavento, “IPACT: A Dynamic Protocol for an Ethernet PON (EPON),” IEEE Communications Magazine, Vol. 40, Issue 2, 2002, pp. 74-80.

[7] Ahmed Helmy, Habib Fathallah, and Hussein Mouftah, “Interleaved Polling Versus Multi-Thread Polling for Bandwidth Allocation in Long-Reach PONs,” IEEE/OSA Journal of Optical Communications and Networking, Volume: 4, Issue: 3, 2012, pp. 210-218.