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Prof. Tak Shing Yum ( ), IE, CUHK 1 Ongoing Research in Communication Technology Laboratory Prof. Tak-Shing Peter Yum ( ) Information Engineering Department The Chinese University of Hong Kong

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Prof. Tak Shing Yum ( ), IE, CUHK 2 Outline Internet Congestion Control (Cun-Qing Hua) Peer-to-Peer Network (Li Zhang) Internet Content Adaptation Protocol (Wing-Lam Tam) Wireless Communication OVSF Code Assignment Schemes (Yang Yang) Cell Sectoring for CDMA Systems (Fang-Zhong Shen) Routing Offline Routing for RPR (Cheng Li)

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Prof. Tak Shing Yum ( ), IE, CUHK 3 Congestion Control 1 Host-based Congestion Control Based on packet loss detection: e.g. TCP Tahoe, Reno and NewReno Based on end-to-end delay variance: e.g. TCP Vegas and Tri-S Advantages Easy to implement Easy for decentralized resource allocation Weakness long response delay (at least one round trip time) Limited information collected solely from end hosts may lead to improper response to congestion

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Prof. Tak Shing Yum ( ), IE, CUHK 4 Congestion Control 2 Case study: TCP Vegas The TCP Vegas flows passing through multiple congested links tend to be unfairly treated due to the cumulative nature of round trip time Router-based Congestion Control Routers monitor the network state and notify the end hosts in case of congestion by dropping or marking packets: e.g. RED, BLUE, ECN

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Prof. Tak Shing Yum ( ), IE, CUHK 5 Congestion Control 3 Our solution: The Joint Congestion Control (JCC) It unifies the efforts of end hosts and routers to provide proactive and accurate congestion control Basic Idea The source sends probing packets to collect the state of the most congested link along the path, and with which to adjust the congestion window Properties Lower variance of throughput Lower packet loss rate Fairer resource allocation

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Prof. Tak Shing Yum ( ), IE, CUHK 6 Peer-to-Peer Network 1 Traditional C/S Model P2P network: every node can take the roles of both server and client intermittently connected edge devices (PC, PDA, WAP Phones) can receive information from and provide information to the Internet Takes advantage of edge device resources Storage and processing capability of edge devices Content of edge devices Human presence at edge devices

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Prof. Tak Shing Yum ( ), IE, CUHK 7 Peer-to-Peer Network 2 Typical Problems A distributed naming scheme for nodes and files A distributed file indexing scheme Server selection A distributed routing protocol (reverse anycast) Security and authentication

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Prof. Tak Shing Yum ( ), IE, CUHK 8 Peer-to-Peer Network 3 Our work Architecture and topology Architecture design: Distributed, Centralized and Augmented Network partitioning Server selection Network distance Measures Routing rules Delay and throughput Analysis

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Prof. Tak Shing Yum ( ), IE, CUHK 9 OVSF Code Assignment Schemes 1 Orthogonal variable-spreading-factor(OVSF) codes are the basic resource units for assignment in UTRA-TDD and FDD systems

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Prof. Tak Shing Yum ( ), IE, CUHK 10 OVSF Code Assignment Schemes 2 Nonrearrangeable and rearrangeable code assignment schemes Our solution: Compact Assignment (CA) and Rearrangeable Compact Assignment (RCA) Both schemes can leave the resulting code tree as flexible as possible (in supporting multi-rate traffic classes) after each code assignment Analytical and simulation results show both schemes can offer the blocking, throughput and fairness performance very close to the theoretical bounds Compared with other schemes, CA and RCA have the combined advantage of simple, efficient, stable and fair Generalization: optimize the assignment to match the traffic rate distribution

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Prof. Tak Shing Yum ( ), IE, CUHK 11 Cell Sectoring for CDMA Systems 1 Problem Cell sectoring is used to reduce the co-channel interference However, it works inefficiently when addressing hot-spot scenarios. Some congested sectors may have outages, while the lightly loaded sectors may have spare capacity Solution Dynamic cell sectoring, i.e., adaptively changing the sector pattern according to the traffic can solve the problem

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Prof. Tak Shing Yum ( ), IE, CUHK 12 Cell Sectoring for CDMA Systems 2 Three Aspects How to produce dynamic sector patterns? Circular Array Beamforming networks with Butler Matrix Dynamic Cell Sectoring Algorithms MinTTP Sectoring based on Shortest Path Algorithm PE Sectoring based on Greedy Algorithm How to keep the optimality of the sectoring at all times Resectoring: Detect the traffic and readjust the sector boundaries when necessary.

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Prof. Tak Shing Yum ( ), IE, CUHK 13 Internet Content Adaptation Protocol 1 Objective Develop Web services for customizing content Language Translation Advertisement Insertion Conventional Approach Proprietary API Single-source solution, creating programming and testing complexities Problems of scalability, flexibility, reusability

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Prof. Tak Shing Yum ( ), IE, CUHK 14 Internet Content Adaptation Protocol 2 Our Approach Attach application servers to proxies through ICAP

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Prof. Tak Shing Yum ( ), IE, CUHK 15 Internet Content Adaptation Protocol 3 Internet Content Adaptation Protocol Open protocol Enables communication between edge content devices (web caches and Internet content origin servers) and application servers for content adaptation Part of an evolving architecture that promotes Web scalability by better facilitating distribution and caching

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Prof. Tak Shing Yum ( ), IE, CUHK 16 Internet Content Adaptation Protocol 4 Work Involved: Development of the ICAP protocol core Architecture design Software implementation Development of the ICAP-enabled e-services Content filter and transcoder for WAP phones Advertisement insertion server Performance analysis of ICAP-enabled proxy ICAP overhead System scalability, efficiency Caching performance

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Prof. Tak Shing Yum ( ), IE, CUHK 17 Offline Routing for RPR 1 The topology of IEEE 802.17 Resilient Packet Ring (RPR) is as follows

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Prof. Tak Shing Yum ( ), IE, CUHK 18 Offline Routing for RPR 2 Objective Design the link capacity dimensioning for this system Problems Given: Traffic matrix, Ring topology, utility function Maximize the system revenue or throughput while maintain fairness among the competing flows Given: Traffic matrix, utility function Link capacity dimensioning Solutions: Linear programming Non-linear programming with convex objective function and linear constraints