Browsing by Author "Wei, HY"

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Assessing and improving TCP rate shaping over edge gateways
(2004-03-01)
Wei, HY
;
Tsao, SC
;
Lin, YD
;
資訊工程學系
;
Department of Computer Science
Computers installed with commercial/open-source software have been widely employed as organizational edge gateways to provide policy-based network management. Such gateways include firewalls for access control, and bandwidth managers for managing the narrow Internet access links. When managing the TCP traffic, pass-through TCP flows can introduce large buffer requirements, large latency, frequent buffer overflows, and unfairness among flows competing for the same queue. So, how to allocate the bandwidth for a TCP flow without the above drawbacks becomes an important issue. This study assesses and improves TCP rate shaping algorithms to solve the above problems through self-developed implementations in Linux, testbed emulations, live Internet measurements, computer simulations, modeling, and analysis. The widely deployed TCP Rate control (TCR) approach is found to be more vulnerable to Internet packet losses and less compatible to some TCP sending operating systems. The proposed PostACK approach can preserve TCR's advantages while avoiding TCR's drawbacks. PostACK emulates per-flow queuing, but relocates the queuing of data to the queuing of ACKs in the reverse direction, hence minimizing the buffer requirement up to 96 percent. PostACK also has 10 percent goodput improvement against TCR under lossy WAN environments. A further scalable design of PostACK can scale up to 750Mbps while seamlessly cooperating with the link-sharing architecture. Experimental results can be reproduced through our open sources: 1) tcp-masq: a modified Linux kernel, 2) wan-emu: a testbed for conducting switched LAN-to-WAN or WAN-to-LAN experiments with RTT/loss/jitter emulations.
Co-DRR: An integrated uplink and downlink scheduler for bandwidth management over wireless LANs
(2003)
Wei, HY
;
Chiang, CC
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Lin, YD
;
資訊工程學系
;
Department of Computer Science
Bandwidth management over wired bottleneck links has been an effective way to utilize network resources. For the rapidly emerging IEEE 802.11 Wireless LAN (WLAN), the limited WLAN bandwidth becomes a new bottleneck and requires bandwidth management. Most possible existing solutions only exclusively focus on optimizing multimedia traffic, pure downlink or pure uplink fairness, or are incompatible with IEEE 802.11. This study proposes a cooperative deficit round robin (co-DRR), an IEEE 802.11-compatible host-based fair scheduling algorithm based on the deficit round robin (DRR) and distributed-DRR (DDRR) schemes, to cooperate the uplink and downlink quantum calculations to simultaneously control uplink and downlink bandwidth. Co-DRR uses the standard PCF mode to utilize the contention-free period to compensate for the unfairness in the contention period. Numerical results demonstrate that: co-DRR can scale up to 100 mobile hosts even under high bit error rate (0.0001) while simultaneous achieving uplink/downlink long-term fairness (CoV<0.01) among competing mobile hosts.
Evaluation of bandwidth enforcement at edge devices
(2002)
Wei, HY
;
Lin, YD
;
資訊工程學系
;
Department of Computer Science
Bandwidth enforcement at edge devices can 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) sizing the TCP window could cause performance or fairness degradation even under slight packet loss rates; (2) narrowband rate enforcement is more difficult; (3) the voice quality over IP networks significantly depends on the packet sizes of all other traffic when using a narrowband (125kbps) access link. All test results are verified by the vendors and are reproducible through our open tools. Nowadays most benchmark reports are financed by vendors and may be biased, without practical testbeds. Guided by this neutral test, readers can obtain in-depth sights when examining such devices.
On shaping TCP traffic at edge gateways
(2004)
Wei, HY
;
Tsao, SC
;
Lin, YD
;
資訊工程學系
;
Department of Computer Science
Many security and QoS functions have been deployed at edge gateways to provide policy-based network management. For QoS functions, the bandwidth management system can manage the narrow WAN access links. When managing the TCP traffic, pass-through TCP flows can introduce large buffer requirement, latency, buffer overflows, and unfairness among flows competing for the same queue. This study evaluates possible TCP-aware approaches through self-developed implementations in Linux, testbed emulation, and live WAN measurement. The widely deployed TCP Rate control (TCR) approach is found to be more vulnerable to WAN packet losses and less compatible to several TCP sending operating systems. The proposed PostACK approach can preserve TCR's advantages while avoiding TCR's drawbacks. PostACK emulates per-flow queuing but relocates the queuing of data to the queuing of ACKs in the reverse direction, hence minimizes buffer requirement up to 96%. PostACK also has 10% goodput improvement against TCR under lossy WAN. Experimental results can be reproduced through our open sources: (1) tcp-masq: a modified Linux kernel; (2) wan-emu: a testbed for conducting switched LAN-to-WAN or WAN-to-LAN experiments with RTT/loss/jitter emulations.
Ordered lookup with bypass matching for scalable per-flow classification in layer 4 routers
(2001-04-01)
Lin, YD
;
Wei, HY
;
Wu, KJ
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資訊工程學系
;
Department of Computer Science
In order to provide different service treatments to individual or aggregated hows, layer 4 routers in Integrated Services networks need to classify packets into different queues. The classification module of layer 4 routers must be fast enough to support gigabit links at a rate of millions of packets per second. In this work, we present a new software method OLBM to lookup multiple fields of a packet, in a dynamically pre-defined order, against the classification database. This algorithm also uses a technique called bypass matching and can classify packets at a rate of well over one million packets per second while scaling to support more than 300k flows. Complexity analysis and experiment measurements are also presented in this study. (C) 2001 Elsevier Science B.V. All rights reserved.