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Efficient multimedia distribution architecture using anycast Hsu-Yang Kung a, * , Chung-Ming Huang b , Hao-Hsiang Ku b , Ching-Yu Lin a a Department of Management Information Systems, National Pingtung University of Science and Technology, Pingtung, Taiwan b Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan Received 28 January 2006; received in revised form 17 August 2006; accepted 20 August 2006 Available online 20 September 2006 Abstract This study proposes the anycast-based multimedia distribution architectures with application-level context-aware capability to specify the most suitable server for various application domains. The following three architectures, namely the identical, heterogeneous, and semi-heterogeneous candidate architectures, are specified for different application purposes. (i) The identical candidate architecture, in which multiple servers provide clients with the same contents, is highly reliable and suitable for real-time streaming applications. (ii) The heterogeneous candidate architecture, in which different servers provide clients with different contents, provides better service diver- sity than the identical candidate architecture, and is suitable for non-sequential content service. (iii) The semi-heterogeneous candidate architecture, comprising one main server and multiple proxy servers, in which the main server stores the completed contents and proxy servers store some portions of information sessions, has the best system performance, and works well under high network traffic loads. To obtain quick and smooth multimedia distribution, the server selection criteria should consider not only the nearest server, but also the network traffic loads and the popularity of requested content, i.e., context-aware considerations. The proposed architectures based on the characteristics of IPv6 anycast and context-aware operations attempt to find the most suitable server/proxy. Finally, the system perfor- mance of each of the three proposed architectures is analyzed and evaluated, and compared with the non-anycast architecture. Simula- tion results also indicate that the semi-heterogeneous architecture is adaptive in face of changing conditions. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Multimedia distribution; Context-aware; Anycast; Proxy 1. Introduction The increasing popularity of Internet multimedia applications has led to a requirement for large network bandwidth and many IP addresses. Consequently, IPv4 addresses are not enough to support all services and multi- media applications require large network bandwidth. The lack of sufficient IP addresses and network bandwidth become increasingly serious as the use of wireless and mobile communications rises. The IPv6 protocol has been proposed to increase the number of Internet addresses and improve the network bandwidth usage [1–3]. Anycast is a new method of addressing in IPv6 for server-based communications. Any- cast addressing is a service-oriented architecture that provides a point-to-point service [4,5]. In anycast address- ing, all server candidates are assigned with the same any- cast address and clients request multimedia distribution services from all server candidates using the same anycast address. The clients can automatically obtain connections from the nearest network server among all server candi- dates without knowing their actual IP addresses [6]. For example, anycast addressing can select the nearest web server or proxy server on an economic basis, and may reduce the bandwidth consumption, especially in wireless/ mobile communications [7,8]. However, searching the route with the fewest hop counts is not always suitable for all network situations or all application domains. That is, the nearest media server is not always the most suitable server [9–11]. 0140-3664/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2006.08.022 * Corresponding author. Tel.: +886 8 770 3202; fax: +886 8 774 0306. E-mail address: [email protected] (H.-Y. Kung). www.elsevier.com/locate/comcom Computer Communications 30 (2007) 288–301

Efficient multimedia distribution architecture using anycast

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Page 1: Efficient multimedia distribution architecture using anycast

www.elsevier.com/locate/comcom

Computer Communications 30 (2007) 288–301

Efficient multimedia distribution architecture using anycast

Hsu-Yang Kung a,*, Chung-Ming Huang b, Hao-Hsiang Ku b, Ching-Yu Lin a

a Department of Management Information Systems, National Pingtung University of Science and Technology, Pingtung, Taiwanb Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan

Received 28 January 2006; received in revised form 17 August 2006; accepted 20 August 2006Available online 20 September 2006

Abstract

This study proposes the anycast-based multimedia distribution architectures with application-level context-aware capability to specifythe most suitable server for various application domains. The following three architectures, namely the identical, heterogeneous, andsemi-heterogeneous candidate architectures, are specified for different application purposes. (i) The identical candidate architecture, inwhich multiple servers provide clients with the same contents, is highly reliable and suitable for real-time streaming applications. (ii)The heterogeneous candidate architecture, in which different servers provide clients with different contents, provides better service diver-sity than the identical candidate architecture, and is suitable for non-sequential content service. (iii) The semi-heterogeneous candidatearchitecture, comprising one main server and multiple proxy servers, in which the main server stores the completed contents and proxyservers store some portions of information sessions, has the best system performance, and works well under high network traffic loads.To obtain quick and smooth multimedia distribution, the server selection criteria should consider not only the nearest server, but also thenetwork traffic loads and the popularity of requested content, i.e., context-aware considerations. The proposed architectures based on thecharacteristics of IPv6 anycast and context-aware operations attempt to find the most suitable server/proxy. Finally, the system perfor-mance of each of the three proposed architectures is analyzed and evaluated, and compared with the non-anycast architecture. Simula-tion results also indicate that the semi-heterogeneous architecture is adaptive in face of changing conditions.� 2006 Elsevier B.V. All rights reserved.

Keywords: Multimedia distribution; Context-aware; Anycast; Proxy

1. Introduction

The increasing popularity of Internet multimediaapplications has led to a requirement for large networkbandwidth and many IP addresses. Consequently, IPv4addresses are not enough to support all services and multi-media applications require large network bandwidth. Thelack of sufficient IP addresses and network bandwidthbecome increasingly serious as the use of wireless andmobile communications rises.

The IPv6 protocol has been proposed to increase thenumber of Internet addresses and improve the networkbandwidth usage [1–3]. Anycast is a new method of

0140-3664/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.comcom.2006.08.022

* Corresponding author. Tel.: +886 8 770 3202; fax: +886 8 774 0306.E-mail address: [email protected] (H.-Y. Kung).

addressing in IPv6 for server-based communications. Any-cast addressing is a service-oriented architecture thatprovides a point-to-point service [4,5]. In anycast address-ing, all server candidates are assigned with the same any-cast address and clients request multimedia distributionservices from all server candidates using the same anycastaddress. The clients can automatically obtain connectionsfrom the nearest network server among all server candi-dates without knowing their actual IP addresses [6]. Forexample, anycast addressing can select the nearest webserver or proxy server on an economic basis, and mayreduce the bandwidth consumption, especially in wireless/mobile communications [7,8]. However, searching theroute with the fewest hop counts is not always suitablefor all network situations or all application domains. Thatis, the nearest media server is not always the most suitableserver [9–11].

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The most suitable media server should be selectedaccording to the required contents, network loads, andoperation loads of servers [12,13]. Restated, a suitablemedia server is determined based on context-aware opera-tions [10,14,15]. This study proposes a novel concept ofapplication-level context-awareness with provision of any-cast capability. The context-aware agent is designed to dis-cover the network traffic loads, and to consider thepopularity of requested contents to determine the mostsuitable server/proxy. For various application domains,this study proposes three context-aware anycast architec-tures, namely the identical, heterogeneous, and semi-heter-ogeneous candidate architecture. The performance costfunction and the characteristics comparison for the pro-posed architectures are also determined to indicate themost appropriate application domain for various context-aware and anycast-based architectures. Simulation resultsshow the system performance and distinction of the pro-posed architectures.

The rest of this study is organized as follows. Section 2describes related works about anycast techniques andapplications. Section 3 describes the system architecturesof context-aware anycast. Section 4 describes the systemperformance definition and comparison. Section 5 discussesthe testing and analysis of different architectures. Finally,Section 6 concludes this study.

2. Related works

The anycast techniques can be classified into two catego-ries, which are the network-layer anycast and the applica-tion-layer anycast [3]. Some researchers have designedand developed application-layer architectures to realizethe anycast services, e.g., AL-DHAD [16] and MMTP[17]. The objective of anycast services is to select the suit-able server to achieve the load balance technique [18]. Any-casting is a service-oriented network protocol, where anidentical address can be assigned to multiple nodes provid-ing a specific service. The anycast address is assigned on atype-of-service (TOS) basis [18]. Yu et al. [18] defined thearchitecture of application-layer anycast shown in Fig. 1.

Router

AnycastResolver

Internet

yreu

Q ts

a cy n

A

Client

esno

pse

R t s

a cyn

A

Server

Server

Fig. 1. Transitional application-layered anycast architecture.

Fig. 1 illustrates that a client tries to find a suitable serverfrom the candidate servers. The client sends an anycastquery to the anycast resolver to determine the most suitableserver among the candidate servers.

Ballani and Francis [19] proposed the proxy IP anycastservice (PIAS) to increase the transmission performanceunder anycast communication. PIAS advertises an IP any-cast address on behalf of the group members and tunnelsanycast packets to those members. PIAS also considersthe scalability for group communication. Ratnasamyet al. [20] defined the application-level redirection and net-work-level redirection strategies using anycast techniques.This paper also discussed the involvements of technicaland economic issues using anycast-based internet architec-ture. Hashim and Manan [21] proposed an active anycastRTT-based sever selection technique for real-time trans-mission issue.

Anycast technique can apply on the wireless and mobilenetworks to increase the transmission efficiency. Dow et al.[22] designed and implemented the anycast communicationprotocol for the mobile ad hoc network. This study pro-posed an anycast address mapper and a clustering architec-ture to achieve the anycast address assignment in theMANET environment. Chi et al. [23] and Chang et al.[24] proposed the anycast architecture for mobile IP envi-ronment. These two studies designed the control procedureand related control messages in mobile IP anycast environ-ment and proved their feasibility and performance efficien-cy. Hashimto et al. [25] described the IPv6 anycastapproach for IPv6 networks. This study proposed the map-ping policy to achieve the IPV6 anycast translation.

All of above studies are for the specific network environ-ment and application services. Most of these studies did notconsider the multimedia distribution problem. They alsoignored the transmission delay and the performance evalua-tion issues. In this paper, three different multimedia distribu-tions are proposed and discussed with detail transmissiontime diagrams and control procedures. Moreover, the per-formances evaluation shows that the proposed distributionarchitectures have better transmission performance thanthe traditional anycast architecture.

3. System architectures of context-aware anycast

This section describes the system design and controlprocedures of the proposed context-aware anycastarchitectures.

3.1. The identical candidate architecture

Fig. 2 depicts the identical candidate architecture, whichconsists of multiple servers with the same contents. The ori-ginal idea of identical candidate architecture comes formRFC 1546 [3] and the related research [8]. This architectureis suitable for real-time streaming applications with theheavily-accessed content. Clients obtain the multimediaservice from the most suitable content server. Fig. 3

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Fig. 2. System architecture of the identical candidate architecture.

Client Agent Servers (With Same Contents)

4. Assign_a_Elect_Server

1. Request_a_Elect_Server (Anycast)

5. Request_Connection (Unicast)

6. ACK_Connected

7. Request_Related_Contents

8. Request_Disconnect_Message

9. ACK_Disconnected_Message

Candidate Servers Elect Server

2. Detect_Message (contents, server load, network load)

3. ACK_Detect_Message

... (To transmit related contents form the elect server)

Contents

Fig. 3. Control procedure of the id

290 H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301

illustrates the control procedure of the identical candidatearchitecture. The control procedure is as follows.

(i) The client transmits an anycast request message tothe context-aware agent.

(ii) The agent determines the most suitable server, whichis called an elect serve. Elect server is the suitableserver selected form all candidate servers based onthe network conditions including the lowest networkand processing loads.

(iii) The client obtains the connection and downloads themedia contents from the elect server.

3.2. The heterogeneous candidate architecture

entical candidate architecture.

Fig. 4 depicts the heterogeneous candidate architecture,in which each server possesses different segments of themultimedia contents, and provides clients with differentcontents. This architecture is suitable for non-sequentialservices. For example, a user visits a museum with a non-sequential visiting route, i.e., each visiting point is indepen-dent and therefore provides different content segments forthe visitor. Fig. 5 shows the control procedure of the heter-ogeneous candidate architecture. The control procedure isas follows.

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Fig. 4. System architecture of the heterogeneous candidate architecture.

Client Agent Servers (Different Contents)

4. Assign_a_Elect_Server

1. Request_a_Elect_Server (Anycast)

5. Request_Connection (Unicast)

6. ACK_Connected

7. Request_Related_Contents

8. Response_Contents

19. Request_Disconnect_ Message

20. Disconnected_Message

14. ACK_Connected

15. Request_Related_Content (cont.)16. Response_Related_Content (cont.)17. Request_Disconntented_ Message

18.Disconnected_Message

13. Request_Connect (Unicast)

Candidate Servers Elect Server A Elect Server B

2. Detect_Message (contents, server load, network load)

3. ACK_Detect_Message

9. Request_Context_Aware_ Service

12. Assign_a_Elect_Server

(To transmit contents form the elect server B)...

10. Detect_Message (contents, server load, network load)

11. ACK_Detect_Message

(To transmit contents form the elect server A)...

Contents

Contents

Fig. 5. Control procedure of the heterogeneous candidate architecture.

H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301 291

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292 H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301

(i) The client transmits an anycast request message tothe context-aware agent.

(ii) According to the client requests, the context-awareagent determines the most suitable elect server, thatis, the elect server which can provide the requiredcontents has the best network/system performance.

(iii) When a client changes his service requirement, e.g.,the visiting location and device capability, and trans-mits the context-aware request to the agent, the agentdetermines the new elect server.

(iv) The client establishes a connection, and downloadscontent from the new elect server.

3.3. The semi-heterogeneous candidate architecture

Fig. 6 depicts the semi-heterogeneous candidate archi-tecture, which consists of one server and multiple proxies.In this architecture, the server stores the full media con-tents, and different proxy servers store their own parts ofthe contents. The processing server loads are distributedon the proxies. This architecture has the best system perfor-mance, and works well under high network traffic loads.Fig. 7 shows the control procedure of the semi-heteroge-neous candidate architecture. The control procedure is asfollows.

(i) When the client transmits a request message to thecontext-aware agent, the agent transmits detectionmessages to all proxies.

(ii) The proxies suitable for the request message transmitresponses to the agent.

(iii) The agent determines the most suitable elect proxyaccording to the evaluation criteria.

(iv) When a client changes its service, and transmits thecontext-aware request to the agent, the agent deter-mines the new elect proxy. The new elect server thenobtains the remaining media contents from the mainserver, and transmits media contents to the client.

Fig. 6. System architecture of the semi-h

(v) If none of the proxies can satisfy the client’s request,then the agent determines a suitable proxy to estab-lish a connection with the main content server forthe client.

4. System performance definition and comparison

This section defines the performance cost function forthe proposed context-aware anycast architectures. Table 1shows the related messages adopted in performance evalua-tion. Table 2 shows the related performance evaluationparameters. The evaluation cost function is the total trans-mission time for a client to obtain the completed mediacontents from the elect servers and/or the elect proxies.

4.1. Identical candidate architecture

Fig. 8 depicts the transmission time diagram in the iden-tical candidate architecture. A client obtains media con-tents from the elect server previously determined by thecontext-aware agent. The transmission operations are asfollows.

(i) The agent determines the most suitable elect serverMA and notifies the client (T A

search).(ii) The client transmits the request message to the desig-

nated elect server MA and obtains the response(DA

RTT).(iii) The MA transmits the first medium frame to the client

(DAtrans).

(iv) The total number of media frames is n, and the nom-inal transmission time of each frame is h. The averageirregular transmission jitter of a medium fame is q.

(v) Under this architecture, the cost function of obtain-ing the completed media contents for a client is givenby:

xtotal time ¼ T Asearch þ DA

RTT þ DAtrans þ ðhþ �qÞ � n� �q ð1Þ

eterogeneous candidate architecture.

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Client Agent Proxies

4. Assign_Elect_Proxy

1. Request_Elect_Proxy (Anycast)

5. Request_Connection (Unicast)

6. ACK_Connected

MainServer

7. Request_Related_Contents

22. Request_Disconnected_ Message

23. ACK_Disconnected_Message

Candidate Proxies Elect Proxy A2. Detect_Message (contents, server load , network load)3. ACK_Detect_ Message

17. Request_Connect

18. ACK_Connected

19. Request_Continued_Contents

24. Request_Disconnected_ Message

25. ACK_Disconnected_Message

Elect Proxy B

14. ACK_Connected

12.Request_ Connection

13. ACK_ Connected

16. Request_ Continued_ Contents

8. Request_Context_Aware_ Service

11. Request_Connection (Unicast)

15. Assign_Mirror_Proxy

20. Request_ Disconnected_ Message

21. ACK_ Disconnected_ Message

(To transmit contents form the Elect Proxy B)...

Contents

9. Detect_Message (contents, server load , network load)

10. ACK_Detect_ Message

(To transmit contents form the Elect Proxy A)...

Contents

Contents

Fig. 7. Control procedure of the semi-heterogeneous candidate architecture.

Table 1Performance evaluation messages

Parameters/messages Meaning

Sending_Request The client transmits a request message to the elect serverRequest_Arrive The elect server/proxy receives the request from the clientRequest_ACK Delay time of the server/agent replying to the request messagedetect The agent identifies network traffic and the server processing loadsassign The agent assigns a suitable elect server to the clientContext-Aware_Request Client transmits a context-aware service request to the elect server/agentContent_Request Agent transmits a content request message to the elect proxy. The elect proxy retrieves

the requested contents from the main serverProxy_Request The elect proxy obtains the requested contents from the main serverMA, B Elect servers A and B

H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301 293

4.2. Heterogeneous candidate architecture

All servers in this architecture have different contents.The heterogeneous candidate architecture has better ser-vice diversity and stores fewer media frames than theidentical candidate architecture. Under the same filmprovision, the space costs of the heterogeneous candidate

architecture is F Xi , and the space cost of the identical

candidate architecture is n� F Xi , where n is the number

of servers. However, all clients may request the samecontent from the same server for the most popular mov-ie, increasing the processing loads of the server and sig-nificantly degrading the content service. Fig. 9 depictsthe transmission time diagram in the heterogeneous

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Table 2Performance evaluation parameters

Parameters/messages Meaning

xtotal_time Total time to transmit the complete media content to a client

F Xi Medium frame i of content X

T Ssearch Time for agent to discover the server/proxy S

DSRTT Round-trip delay of the sending request between the client and the server/proxy S

DStrans Transmission delay time of the first medium frame from the server S to the client/proxy

h Nominal transmission time of a medium frame�q Average irregular transmission jitter of a medium fameTdata_trans Total time of retrieving contents from the content serverTqc The quality control time of changing content-aware serviceC(t) The overlapping time of frame F X

i to frame F X 0i0 at the buffer of the client

Fig. 8. Transmission time diagram in the identical candidate architecture.

Fig. 9. Transmission time diagram in the heterogeneous architecture.

294 H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301

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H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301 295

candidate architecture. The transmission operations areas follows.

(i) The client obtains the contents from the designatedelect servers MA and MB from the agent. Therequired time costs include T A

search, T Bsearch, DA

RTT,DB

RTT, DAtrans and DB

trans.(ii) The client first obtains parts of contents from with n1

frames of the elect server MA. The time cost is givenby ðhþ �qÞ � n1.

(iii) The client changes his service request (Tqc) and thenobtains the new contents from n2 frames of the electserver MB.

The time cost is ðhþ �qÞ � n2. Some frames overlap in thetransmission of frames n1 and n2. The overlapping time isC(t). Since the time of Tqc, T B

search, DBRTT, and DB

trans is includ-ed in the time of transmitting MA’s frames, the cost func-tion of obtaining the completed media contents for aclient is given by:

xtotal time ¼ T Asearch þ DA

RTT þ DAtrans þ ðhþ �qÞ � n1

þ ðhþ �qÞ � n2 � 2�q� CðtÞ ð2Þ

4.3. Semi-heterogeneous candidate architecture

The semi-heterogeneous architecture combines theadvantages of the identical and heterogeneous candidate

Fig. 10. Transmission time diagram in t

architectures. All proxies store portions of contents. Themost suitable elect proxy provides the client with therequest contents to reduce the loads of the main server.Fig. 10 shows the transmission time diagram in the semi-heterogeneous candidate architecture. The transmissionoperations are as follows.

(i) The client obtains the contents from the designatedelect proxy MA with the determination of the agent.The required time costs include T A

search, DARTT, and

DAtrans.

(ii) The client first obtains j content frames from the electproxy MA. The time cost is ðhþ �qÞ � j.

(iii) The client changes its service request and transmitsthe context-aware request to the agent. The agentdetermines the elect proxy MB, which obtains theremaining frames from the main server. The initialtime includes Tqc, T B

search, DBRTT, and DB

trans.(iv) Meanwhile, the client transmits the content request to

the elect proxy MB, and then obtains the remaining(n � j) frame of contents from the elect server MB.

The time costs are DCRTT, DC

trans and ðhþ �qÞ � ðn� jÞ.Some frames overlap between the frames (j + 1) and n.The overlapping time is C(t). Since the time of Tqc,T B

search, DBRTT, DB

trans, DCRTT, and DC

trans is included in the timeof transmitting MB’s frames, the cost function for obtain-ing the completed media contents for a client is given by:

he semi-heterogeneous architecture.

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Low Threshold High Threshold

Bouncing Region(1) (2) (3)

(4)(5)(6)

Display

Buffer size

Buffering

Exhaust

Fig. 11. Buffer control procedure.

1 Control_Scheme_BEGIN

2 if (buffer_allocation Low_threshold) then

3 Request contents from related proxies/servers,

4 if (Low_Threshold< buffer_allocation < High_Threshold) then

5 Client could request new contents or handoff to another proxy/server,

6 if (HighThreshold<buffe_allocation) then

7 Display related contents where buffering in client’s buffer,

8 Control_Sheme_END.

Fig. 12. Buffer control algorithm.

296 H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301

xtotal time ¼ T Asearch þ DA

RTT þ DAtrans þ ðhþ �qÞ � j

þ ðhþ �qÞ � ðn� jÞ � CðtÞ ð3Þ

4.4. Buffer control scheme

The proposed buffer control scheme for the handoff andchanging contents is depicted in Fig. 11. As depicted inFig. 11, two thresholds are defined: the low threshold andthe high threshold. In buffer region (1), the client requeststhe related contents from proxies or servers. In bufferregion (2), the client buffers the related and enough con-tents and prepares to display all contents. When bufferingthe contents over the high threshold in region (3), the clientstarts displaying the related contents. When the volume ofbuffer is within the buffer region (2), i.e., the bouncingregion, or over the high threshold, the client could requestthe handoff operation and change the different contents.Fig. 12 depicts the buffer control algorithm.

5. Simulation results

This section discusses the system evaluation based onthe diversity degree of service requests and the networktraffic loads, and compares the performance of the pro-posed anycast and non-anycast (unicast) architectures.Fig. 13 depicts the simulation environment of the identicalarchitecture. The bandwidth is 5 Mbps between clients androuters. The bandwidth is 2 Mbps between routers andservers. The bandwidth is 1 Mbps between routers. Allmedium files are the same in all servers.

Fig. 14 depicts the simulation environment of the hetero-geneous architecture. The simulation bandwidth is the sameas the identical architecture. All medium files are differentand are distributed in all servers. Fig. 15 depicts the simula-tion environment of the semi-heterogeneous architecture.The bandwidth is 5 Mbps between clients and proxies. Thebandwidth is 2 Mbps between proxies and routers. Thebandwidth is 2 Mbps between routers and the main server.The bandwidth is 3 Mbps between proxies. The bandwidthis 1 Mbps between routers. The main server stores all mediafiles, which are distributed to all proxies.

5.1. The diversity degree of service requests

The diversity degree of service requests is the degree ofsimilarity of the content requests of the clients, e.g.,requested movies. A low-diversity degree means that manyclients request the same contents, e.g., a popular movie anda high diversity degree means that many clients request dif-ferent contents. Figs. 16 and 17 depict the simulationresults of different diversity degrees.

Under both low- and high-diversity degrees, the semi-heterogeneous (heterogeneous) candidate architecture hadthe best (worst) throughput. In particular, the throughputunder the low-diversity degree was similar to the through-put under the high-diversity degree in semi-heterogeneouscandidate architectures, revealing that the proxy and any-cast-based architecture is appropriate for popular contentretrieval environments.

The heterogeneous candidate architecture had the worstperformance under the low-diversity degree, because manyclients requested the same movie, turning popular electservers into bottlenecks. However, the heterogeneous can-didate architecture performed better with a high-diversitydegree than with a low-diversity degree, revealing that mul-tiple content servers are appropriate for cases with highhabit diversity under anycast-based transmission.

5.2. The network traffic loads

Figs. 18 and 19 depict the conditions of low and highnetwork traffic loads, respectively. The semi-heterogeneousarchitecture had the best and stable throughput, especially

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Router 3

Client 1

Client 2

Client 3

Server 1

Server 2

Server 3

Router 1

Router 2

1Mbps

1Mbps

2Mbps

2Mbps

2Mbps

5Mbps

5Mbps

5Mbps

File3File2File1

File6File5File4

File3File2File1

File6File5File4

File3File2File1

File6File5File4

Fig. 13. Simulation environment for the identical architecture.

Router 3

Client 1

Client 2

Client 3

Server 1

Server 2

Server 3

Router 1

Router 2

1Mbps

1Mbps

2Mbps

2Mbps

2Mbps

5Mbps

5Mbps

5Mbps

File1File2

File4File3

File5File6

Fig. 14. Simulation environment for the heterogeneous architecture.

H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301 297

under high traffic loads, because it benefited from proxyand anycast functionality. The heterogeneous architecturehad the worst throughput, since a specific elect server couldeasily become the bottleneck, especially under high net-work traffic loads.

5.3. Throughput comparison between the context-aware

anycast and non-anycast (unicast) architectures

Fig. 20 depicts the average throughputs under the iden-tical, the semi-heterogeneous, heterogeneous, and unicast

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Router 3

Client 1

Client 2

Client 3

Main Server

Router 1

Router 2

3Mbps

3Mbps

2Mbps

2Mbps

2Mbps

5Mbps

5Mbps

5Mbps

File3File2File1

Elect Proxy 2

Elect Proxy 1

Elect Proxy 3

1Mbps

1Mbps

2Mbps

2Mbps

2Mbps

File6File5File4

Fig. 15. Simulation environment for the semi-heterogeneous architecture.

Fig. 16. Conditions of low-diversity degree.

Fig. 17. Conditions of high-diversity degree.

Fig. 18. Condition of low network traffic loads.

Fig. 19. Condition of the high network traffic loads.

298 H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301

architectures. The simulation environment is in the hightraffic status and high diversity. In this simulation, the cli-ents request popular media films over the environments.Fig. 20 depicts that the throughput of the semi-heteroge-neous candidate architecture and identical candidate archi-tecture are stable. However, the throughput of theheterogeneous candidate architecture is unstable because

media frames are distributed from different servers and tomake the traffic diversity worse. When the client requeststhe different film frames from the other server, the through-put is decreased. However, the proposed architectures wereall better than the unicast architecture. Experimentalresults indicate the benefits of adopting context-awareand anycast functions.

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Fig. 20. Throughput comparison between the proposed context-awareanycast and non-anycast (unicast) architecture.

Fig. 21. Total transmission time comparison between the proposedcontext-aware anycast and non-anycast (unicast) architecture.

H.-Y. Kung et al. / Computer Communications 30 (2007) 288–301 299

5.4. Total transmission comparison time between thecontext-aware anycast and non-anycast (unicast)

architectures

Fig. 21 depicts total transmission time (xtotal_time),which is derived from the cost functions (1)–(3), based on

Table 3Comparison the proposed context-aware anycast architectures

Architecture Comparisons

Identical candidate Advantages (1) High reliability(2) Load balance/load sharing(3) Low network load(4) Low time cost

Disadvantages (1) High hard-disk space cost

Heterogeneouscandidate

Advantages (1) Low hard-disk space cost(2) Middle time cost

Disadvantages (1) Low reliability(2) High server load(3) High network load

Semi-heterogeneouscandidate

Advantages (1) Middle hard-disk space cost(2) Middle reliability

Disadvantages (1) Middle server load(2) Middle network load(3) High time cost

the identical, the semi-heterogeneous, heterogeneous, andunicast architectures. As depicted in Fig. 21, the totaltransmission time of identical candidate architecture andsemi-heterogeneous candidate architecture is less than theheterogeneous candidate architecture when different mediaframes are requested and transmitted from the differentserver. Especially in high density environment, the timecost of the heterogeneous candidate architecture is worsethan unicast architecture. Table 3 depicts the performancecomparisons among the proposed distributionarchitectures.

6. Conclusions

This study proposed three anycast-based multimediadistribution architectures, namely the identical, the hetero-geneous, and the semi-heterogeneous candidate architec-tures, to identify the most suitable media server selectionfor different application domains. The designed context-aware agent detects the network traffic loads and the diver-sity degree of requested contents, i.e., the server loads,based on the IPv6 anycast transmission, to determine themost suitable server/proxy. The performance cost functionand the characteristics comparison for the proposed archi-tectures were also determined to indicate the most appro-priate application domain for various context-aware andanycast-based architectures.

Evaluation results indicate that the semi-heterogeneouscandidate architecture has the best throughput underlow- and high-diversity degrees. Furthermore, the identicalcandidate architecture is also more appropriate than theheterogeneous architecture under the content distributionenvironment. For the semi-heterogeneous candidate archi-tecture, the throughput under a low-diversity degree is sim-ilar to that under a high diversity degree revealing that theproxy and anycast-based architecture is also suitable forpopular media contents retrieval environments. Moreover,the semi-heterogeneous architecture has the best and stablethroughput, especially under the high traffic loads, reveal-ing that the proxy and anycast-based architecture is aneffective solution for congested networks. Comparisonresults indicate that the system performance of theproposed context-aware anycast architectures is better thanthe system performance of the traditional unicastarchitecture.

Acknowledgement

The authors thank the National Science Council ofRepublic of China, Taiwan, for financially supporting thisresearch under Contract No. NSC-95-2221-E-020-034-MY2.

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Hsu-Yang Kung received his B.S. degree fromTatung University, M.S. degree from NationalTsing-Hwa University, Ph.D. degree fromNational Cheng-Kung University, Taiwan, all incomputer science and information engineering.He is currently an associate professor at theDepartment of Management Information Sys-tems, National Pingtung University of Scienceand Technology, Taiwan. His research interestsinclude distributed multimedia systems, wirelessand mobile communications, and the embeddedmultimedia applications.

Chung-Ming Huang received the B.S. degree inelectrical engineering from National TaiwanUniversity, and the M.S. and Ph.D. degrees incomputer and information science from The OhioState University. He is a Distinguished Professorand Chairman of Deptartment of ComputerScience and Information Engineering, NationalCheng Kung University, Taiwan. Dr. Huang alsois the director of The Promotion Center forNetwork Applications and Services Education,

National Innovative Communication Education Program, Ministry of

Education, Taiwan. He has published more than 100 referred journal andconference papers in wireless and mobile interactive multimedia systems, audio and video streaming, and formal modeling of communicationprotocols. His research interests include media streaming protocols andapplications, wireless and mobile interactive multimedia systems, wirelessand mobile communication protocols and software, and broadband/mo-bile Internet applications and service systems.

Hao-Hsiang Ku received the B.S. degree in thedepartment of Management Information Systemsfrom Chung-Hua University on 2001/6, and theM.S. degree in the department of ManagementInformation Systems from National PingtungUniversity of Science and Technology on 2003/6,Taiwan. He is currently working for his Ph.D.degree in the Department of Computer Scienceand Information Engineering, National ChengKung University. His research interests are sen-sor networks, pervasive computing and embed-ded multimedia applications.

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Ching-Yu Lin is currently a master student inDepartment of Management Information Sys-tems of National Pingtung University of Scienceand Technology majoring, Taiwan. His currentresearches are context-aware systems and multi-media streaming control.