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