RSVP之適應性訊息更新機制

Abstract

RSVP是一種用於IP網路上的信號傳遞協定，特別是設計在對於多媒體資料流路徑的建立與維護上。它允許使用者對於特定的資料流要求服務品質需求（QoS, Quality of Service），使得這資料流的特性符合使用者的需要。RSVP讓即時性（real-time）的資料也能在一般的IP網路上傳送，藉由保留一些固定的頻寬使得這些即時性的資料流能在一定的延遲之內送達目的地。RSVP會在資料流路徑上傳播這些資源保留（resource reservation）的訊息，在這路徑上的路由器將會設定相對的參數與狀態資料（state）使得此資料流得到品質保證的服務。RSVP會隨著網路的狀況來動態調整資料流走的路徑，所以它能夠適應網路路徑的變化。RSVP會間歇性的去對這種狀態資料作更新（refresh）的動作，然而在複雜又多變的網際網路中固定間隔的更新動作會造成一些問題，因為固定間隔的訊息更新將是不彈性的也沒有效率。 在我們的論文中，我們提出了一種使用乏晰技術的動態機制，它可以在RSVP狀態資料更新的機制中得到好處，使用動態機制來監控在路由器中的狀態資料數目以及每個交談（session）所要求的頻寬以決定一較適當的更新間隔，這將比傳統的RSVP所採用的固定間隔的更新時間來的有彈性。在這使用乏晰技術的動態機制中，包含了一個知識庫、兩個輸入的乏晰變數、以及一個輸出的乏晰變數。這種動態的調整更新間隔的機制對於多樣複雜的網際網路而言有很大的好處，傳統的固定間隔更新機制無法作調整所以無法適應不同特性、不同頻寬的網路，而且當路由器中的狀態資料增加得很快時，這傳統的機制也無法對此做出反應，除此之外，由於每個交談都可以擁有不同的頻寬要求，對於不同要求的交談我們也應該有不同的策略。這是傳統固定間隔更新機制無法做到的，同時，動態乏晰機制在效能上也會比傳統的來的好，由實驗結果顯示，這樣的機制的確能減少由RSVP所浪費的頻寬，我們比較了網路吞吐量以及封包延遲，都有良好的表現，因此適應性訊息更新機制能使得RSVP更有效率。

RSVP, a signaling protocol for IP unicast and multicast sessions, is designed to handle IP traffic streams generated by applications such as networked multimedia. It allows users to request quality-of-service (QoS) behavior for traffic streams across IP networks and provides an general facility for creating and maintaining distributed reservation state across a mesh of multicast or unicast delivery paths. RSVP enables real-time traffic to reserve resources necessary for consistent latency. RSVP can adjust and alter the path between RSVP end systems to recover from router changes. This behavior is called ``soft state." State is the information about a session that stored in the router. RSVP sends periodic refresh messages to keep these states alive. However, in the heterogeneous internet a regular refresh interval may be a problem for its inflexibility. In this thesis, we propose a fuzzy-based refresh mechanism for RSVP. We monitor the total number of states in the router and the resource reservation size (bandwidth reserved) of a specific session to decide an appropriate refresh interval rather than the fixed interval in conventional RSVP. The fuzzy refresh mechanism consists of a knowledge rule base that represents our experiences/policies and two linguistic input variables and one output linguistic variables. The dynamic adjustment of the refresh interval is a benefit for a heterogeneous inter-networking environment. The fixed timer-value fails because it adapts to neither the wide range of link speeds that exist in most wide-area internets nor fluctuations in the amount of states over time. In addition, sessions have different bandwidth (resource) reservations should have different treatments in the refresh interval. The simulation results show that the adaptive refresh mechanism could reduce the overhead caused by periodical refreshes and state deletion latency. Therefore the proposed adaptive refresh mechanism achieves better performances than the conventional RSVP in throughput and the packet delay. So that these improvements make RSVP more scalable and efficient.