網路頻寬管理器產品功能與效能評比-NCTU.doc

On Evaluating Policy-Based Bandwidth Management Devices Huan-Yun Wei Ying-Dar Lin Department of Computer and Information Science National Chiao Tung University, Hsinchu, Taiwan Tel: +886-3-5712121-ext56667 FAX: +886-3-5721490 Email: {hywei,ydlin}@.tw Policy-based bandwidth management defines how to allocate bandwidth resources according to organizational policy rules. Enterprises often employ such policy-based devices at their organizational edges to manage the narrow but expensive Internet access links. This work designs a novel testbed and uses it to evaluate the functionality and performance of many such devices, including six commercial products and one open source solution. Their policy rules can be categorized into (1) class-based rule; (2) connection rule within a class; (3) bandwidth borrowing rule among classes. The testbed mimics the real-life Internet with heterogeneous Internet delays/delay jitters/packet loss rates, and evaluates the effectiveness of policy enforcement of the above three policy types in terms of accuracy, fairness, stability, robustness, bandwidth borrowing, and voice over IP (VoIP) quality. The test results reveal that (1) explicitly sizing the TCP window could cause performance or fairness degradation even under slight packet loss rates; (2) the open source solution can compete with commercial products in accurately limiting flow aggregates; (3) the voice qualities over IP networks significantly depends on the packet sizes of all other traffic when using a narrowband (125kbps) access link. Keywords: policy-based, bandwidth management, TCP, testbed, emulator 1. Introduction Internet services provide an economic and convenient system to carry out business, such as efficient information exchange among branch offices, or efficient customer/provider access to the services. However, the importance of the services varies, and enterprises often fail to effectively utilize the narrow but expensive WAN link bandwidth. For in