1Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
Ongoing Research in
Communication Technology Laboratory
Prof. Tak-Shing Peter Yum ( 任德盛 教授 )
Information Engineering DepartmentThe Chinese University of Hong Kong
2Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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)
3Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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 im
proper response to congestion
4Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
5Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
6Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
7Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
8Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
9Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
OVSF Code Assignment Schemes – 1
Orthogonal variable-spreading-factor(OVSF) codes are the basic resource units for assignment in UTRA-TDD and FDD systems
10Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
11Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
12Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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 boundarie
s when necessary.
13Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
14Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
Internet Content Adaptation Protocol – 2
Our Approach Attach application servers to proxies through ICAP
ICAP Protocol
Internet
Client
Cl ient
Proxy Caching Server(ICAP Cl ient)
OriginalServer
TranscoderAd Insertion
LanguageTranslation
ICAP Servers(Value-added
Service)
OriginalServer
OriginalServer
Network Edge
15Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
16Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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
17Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
Offline Routing for RPR – 1
The topology of IEEE 802.17 Resilient Packet Ring (RPR) is as follows
Outer ri ngcontrol
I nner ri ngdata
Outer ri ngdata
I nner ri ngcontrol
18Prof. Tak Shing Yum ( 任德盛 ), IE, CUHK
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