Deploy Multimedia-on-Demand Services over ADSL s Chih-Cheng Lo and Wen-Shyen E. Chen Institute of Computer Science National Chung-Hsing University Taichung, Taiwan 40227 {loremi, echen}@cs.nchu.edu.tw Abstract. As the broadband information highway being constructed, many multimedia applications will be realized. Nowadays, customers desired not only purely high-speed Internet access, but also versatile interactive multimedia applications. This article illustrates a multimedia-on-demand (MOD) system that can be provided by incumbent telcos. It provides both multicast and unicast streaming services, including True VOD, Near VOD, Live TV, KaraOK-ondemand (KOD), High-speed Internet access applications, and POTS services. In this paper, we give an overview of broadband access technologies, including HFC, ADSL, FTTx, MMDS/LMDS, and Satellite access networks, to support a MOD system. We also depict the components of deploying a large-scale MOD system from end to end, from customer premises equipment, video servers, storage system, network system, service management system, DBMS system, to content sources. Finally, we give a complete example to describe the signal flows among the components of the system. As we shall see, deregulation will accelerate the convergence of the telecommunications, cable TV, entertainment, and e-commerce while ADSL is the mainstream technology of access network today and provides a viable solution to the Multimedia-on-Demand services. 1 Introduction As the Internet revolution progresses, the number of households getting on the Internet has increased exponentially. The activity in the field of broadband services such as VOD, NVOD, Interactive TV, Video conferencing, Datacasting, E-Commerce and Games, etc., have been expanding at a rapid rate. Multimedia-on-demand (MOD), including most of the above services, is emerging to be one of the killer applications in recent broadband services. The market has also expected to capture a significant share of the huge potential revenues contributed by business and residential market [1]. Services of the MOD system include True Video-on-demand, Near Video-ondemand, Live TV, KaraOk-on-demand, and High-speed Internet access services, etc. MOD can deploy on various network architectures. For incumbent Telcos, use of the ADSL for broadband access is the most popular and rapid solution to promote existing twisted-pair telephone lines toward broadband services to the residential and small businesses. Although in the next few years, we shall see that the increased presence and closer setup of optical fibers in the access network to the customers, ADSL technologies remain to be a viable solution since the connection is readily available [2,3]. A large-scale MOD system comprised many elements that are necessary for the provision of a complete service, including set-top unit, video servers, storage system, Y.-C. Chen, L.-W. Chang, and C.-T. Hsu (Eds.): PCM 2002, LNCS 2532, pp. 295-302, 2002. Springer-Verlag Berlin Heidelberg 2002
296 C.-C. Lo and W.-S.E. Chen network system, service management system, and content sources, etc. [4,5]. We will discuss those components in more detail in Section 3. This paper is organized as follows: Section 2 presents the deployment environment. Section 3 presents the system architecture and its components. Section 4 describes signal workflow of the system. Finally, the conclusions are given in Section 5. 2 Services Deployment and Broadband Services Currently, there are various technologies to deliver multimedia services from a video repository to the customers premise network, such as Hybrid Fiber/Coax (HFC) networks, xdsl, FTTx, MMDS/LMDS, and Satellite access networks [2-4,6,7]. One of the most active debates that are widely discussed in residential broadband deployment is the choice of access network architectures. Nowadays, it is observably, the mainstream access architectures in Taiwan are HFC and ADSL networks, especially the later. There are almost 1,178,000 households ADSL customers versus 235,000 cable modem households as of March 2002. We represent the different access technologies as follows. l HFC (Hybrid Fiber/Coax) networks A feasible commercialized deployment providing VOD services can be based on a CATV network. Fig. 1 shows the architecture of the HFC networks. Even it had been provision in many countries such as USA, but it is still a challenge in Taiwan. Since most of CATV networks in Taiwan are still one-way architecture that cannot support interactive application, and the service can only be realized in the future twoway transmission infrastructure. Upgrading the CATV network infrastructure into a two-way HFC (Hybrid Fiber/Coax) network has just started and initially the provider will focus on downtown area for cost consideration. Internet Contents Regional Headend Distribution HUB High speed backbone Distribution HUB Distribution HUB 500-2000 homes Fiber node Tap 125-500 homes Coax Bi-directional amplifier Tap Fig. 1. Architecture of the HFC networks. l ADSL (Asymmetric Digital Subscriber Loop) networks Most of the Telcos prefer to capitalize on their existing twisted-pair telephone lines by pushing the evolution of a new technology called digital subscriber line (DSL). xdsl is a generic abbreviation for various flavors of DSL technologies, and ADSL, as shown in Fig. 2, is one of the xdsl families. It is developed by telephone
Deploy Multimedia-on-Demand Services over ADSL s 297 companies to provide the next generation high bandwidth services to the homes and businesses using the existing telephone cabling infrastructure [8]. Typically, ADSL provides a data rate from 1.544 Mbps to 8 Mbps downstream and from 16 Kbps to 640 Kbps upstream, depending upon line length and condition. Service Provider Regional Broadband Access Customer Premise Content Provider Internet Home ISP Regional Broadband CO ATM Access Switch Local loop ADSL modem PC Clients ROC (ATM core network) Access node *This may or may not be located in the CO PC-based Remote Access SOHO Server Corporate network Fig. 2. The end-to-end ADSL-based network architecture. l Fiber to the Building (FTTB) Fiber access networks, namely Fiber to the Building (FTTB), Fiber to the Curb (FTTC), Fiber to the Home (FTTH), etc., are referred to the FTTx family. Basically, FTTx is a star-connected network that connects the access networks and customer premises networks directly with optical fibers. It provides interfaces for user terminals as output from optical network unit (ONU) installed at customer premises. Current deployments are trial systems and are at a very early rollout stage. But it will be seen as an emerging technology in the very near future. l Satellite access networks The satellite access system such as direct broadcast system (DBS) uses geosynchronous satellites operating in the Ku band. It is downstream with QPSK modulation using satellite transmission in the 10-15 GHz or 2-6 GHz bandwidths with digital television broadcasting. Since it is a one-way service, the return-path network could be telephone line, xdsl, or other wireless services. l MMDS/LMDS access networks The Multichannel Multipoint Distribution System (MMDS) and Local Multipoint Distribution System (LMDS) belong to the wireless local loop architecture. It realizes asymmetric wireless network as an alternative to HFC. MMDS occupies 198 MHz of bandwidth in the 2.5 GHz range. The frequency permits long distance distribution to about 50 miles. LMDS occupies up to 1.15 MHz of bandwidth in the 28 GHz range, it is a two-way, high bit rate services. LMDS is a small cell technology, with each cell about 3 to 6 Km in radius.
298 C.-C. Lo and W.-S.E. Chen 3 System Architecture The system we propose [9] can be a commercialized system to serve at least 20,000 customers in the first phase, and will be able to scale up to serve more customers (up to one hundred thousand customers) in the succeeding deployments. Many papers have discussed about deploying VOD systems [2,6,10,11]. Generally speaking, they can be divided into centralized and distributed architectures. The topics of interests include economics, performance, reliability, and management. As compared to a number of VOD operations, such as request batching and multicasting, unicasting, etc., it has been shown that distributed servers architecture has a much lower system cost to offer on-demand video services [12]. This MOD system is deployed with such considerations. An example of the system architecture is illustrated in Fig. 3. We will describe the functions of each component briefly in the following: l Set-top Box (STB) or Set-top Unit: The STB is a device installed in customer premises to interconnect legacy A/V equipment to the broadband network. STB accepts MPEG packets from the access network and translates the packets for presentation on an analog TV set or PC monitor. DAVIC [13] specifies this as the A0 interface. Since the operations are designed to be very user friendly, users can browse all services on the screen through an IR (infrared) remote control or remote keyboard with fully VCR-like functionality. The major functions of STU includes receiving the incoming video streams; demodulating, demultiplexing, and decoding the signals; performing the necessary signal conversion, such as D/A transformation for playback on the TV monitor; and sending outgoing control messages [6]. The others configurations are similar to below MOD networks Internet GSRs BB-RAS HPER PC ATU-R DSLAM STB TV Jukebox Media servers Ma Management servers Disk Array GSMS, LSMS Fig. 3. An example of MOD system architecture. l Set-top Box Server/User Database: The STB Server is located in the central office to receive the requests from STB in every household, and each one server should serve at least 15,000 customers. The main functions of STB Server are authorization and account management. When a user logs in this system, the system executes the primary account check. If it is a legal user, then the system redirects this session to LSMS (Local System Management Server) or Video Server Gateway (VSG) depends on system configuration.
Deploy Multimedia-on-Demand Services over ADSL s 299 The user database stores the customer s information for STB server to retrieve, such as customer ID, account information, service class, bandwidth reservation, locality and CPE ID, etc. Each user database can serve more then one STB Server and should adapt the fault-tolerance architecture to make sure the absolute safety of customers data. l Access /Core : The broadband access network is an ADSL- based network architecture. It comprises a Digital Subscriber Line Access Multiplexer (DSLAM), a number of ATU-Rs, and the POTS splitters to construct a broadband access network between central office (CO) and customer premises network. The network uses ATM over ADSL technology to provide the broadband data communication services. The DSLAM uses ATM technology to statistically multiplex the subscriber interface signals into its network interface. The core network system comprises Gigabit Switch Routers (GSRs) and High Performance Edge Routers (HPERs). The former is constructed by GSRs that transport packets between video servers in the center offices (COs) in a huge bandwidth form STM-1 up to STM-64. The HPER performs as an edge switch to connect the core and the access network. It also performs many complex functions, such as rich routing protocols, data forwarding or duplication to the customer premises network (CPN), and QoS. It should have high efficiency to handle video stream to prevent locking effect, frame freezing, and frame skipping. The system should support at least 10 Gigabit per second of aggregate switching capacity. l Video Servers: The video server consists of massive storage and media controllers to store the video (or other services) source in specific compressed format in order to can be requested and accessed by the customers efficiently. In general, there are stored in two formats: MPEG-1 or MPEG-2. For example, a 90 minutes program, using MPEG-1 compression, requires about 1 Gbytes of storage. The video server is different from a traditional database server in several ways. It performs some basic functions, such as request handling, random access, and user interactions, in addition to admission control, QoS guarantees, and VCR-like functions, including play, pause, resume, fast forward, and rewind. Since the transmission of video data is stream oriented, it needs to be well constructed and offers precise tuning such that programs can be delivered to the end users without any glitches, such as blocked effect, and freeze frame. l Video Server Gateway/Video Server Database: the video server gateway is one of the most important components in a video system. It performs as a portal of multimedia services. While video server database is cooperating with video server gateway to record the needed information of this system, it adopts an Oracle database to store the massive customers profile and accounting information. The main functions of a video server gateway are shown in the following: l Detect the state of STB l Provide main menu and send it to the STB for customer to select. l Notify local system management system to reserve or release the bandwidth for program streams. l Dynamically report the bandwidth, video servers loading, massive storage and resources utilization message and status to local system management system.
300 C.-C. Lo and W.-S.E. Chen l Create accounting records, including customer ID, service ID, program ID, starting time, and finish time, etc. The information will be sent to the video server database for billing purpose. l High-speed Internet access Management System: It consists of the Broadband Remote Access Server (BB-RAS), Remote Authentication Dial In User Services (RADIUS), and routers. When users login in this system for Internet access. The primary functions of BB-RAS are Authentication, Authorization, and Accounting (AAA), Internet roaming, user management, virtual router, etc. The RADIUS server is a database that keeps the detailed profiles and accounting information of the customers. It provides a mechanism of recognizing a user who has registered its rights to access the network source of a service provider and logging the billing record. l Video Service System: the video service system comprises four components as shown in the following: l Video input component: The functions of this unit are to digitalize the input analog signal source and encoding to MPEG format to store in the system. l Video output component: As the services divide into two different types, multicast and unicast. The video output component should provide a mechanism to handle each delivery scheme. Both of them support MPEG-1 and MPEG-2 formats. l Media storage component: This component consists of massive disk arrays to store at least 500 MPEG-2 movies. l Media management component: The main functions of this unit are managing all of those medias on-line, off-line, update, storage control, and monitoring those operations. It also schedules the interval of NVOD services. In addition, it reports the status to the service management system. l Service Management System: the service management system (SMS) includes three main components: l Media Management Database Server: The main functions of it are to manage and coordinate each video server database distributed in different central offices. l Global Service Management System (GSMS): There are only one GSMS in a MOD system, but may be lots of LSMSs located in central offices. The GSMS is responsible to interconnect with legacy systems, e.g., customer ordering system, billing system, and CDRS (Call Detail Record System). l Local Service Management System (LSMS): The main functions of this component are bandwidth management, supervisory the status of multicast and unicast streaming services, and reply messages to the video server gateway about the status of every local video servers operations. 4 Signaling Control In addition to construct of each component, there should be the interfaces, signaling flow, and procedures to coordinate the system s operation [14]. The video services will be provided in basic units of streams. The original benefit of streaming media was developed so that viewers do not have to wait a long period of time to download large files. Streaming video is essentially video or image that has been digitized and compressed in standardized formats. Streams can originate from a content provider,
Deploy Multimedia-on-Demand Services over ADSL s 301 live source, or an audio feed from a radio station. In either case, a customer needs not to download the file when viewing the stream of a movie. The data is simply being displayed as it arrives by the player and no copy remains on the viewer s hard disk. Users can now view and listen to a streaming video while a media player simultaneously requests packets of information from the host media server and caches these packets of information in the media player s memory buffer. Today s streaming media solutions do not utilize TCP in which web content is delivered, but instead UDP that has been specifically designed for the transmission of multimedia applications. STB 5 4 LSMS 3 7 10 STB Server 2 User DB 1 9 6 8 11 Billing system Customers Multimedia Servers Media Management DB Video Server GW Video Server DB Fig. 4. An example of signaling control flow of the MOD system. Fig. 4 depicts an example of signaling control flow of this MOD system. Customers are allowed to select programs from a remote control or keyboard. We explain the control flows step by step as follows: 1. When customer wants to enter the MOD system, he/she should enter his/her username and password to initial a request. The STB will pass this request to the STB server. 2. The STB server will make security check according to the information stored in the user database, including customer ID, username, password, privacy information, etc. 3. After the checking phase, if it passes authorization checking, the request flow will be passed to the LSMS; otherwise, the request will be rejected and the customer is notified. 4. The LSMS will reply with a main menu to the STB and it will be displayed on the screen for customer to select the service what he/she wants. 5. The STB get the information from customer and the LSMS will redirect this request flow to the Video server gateway. 6. The video server gateway sends the available programs (movies or other multimedia programs) listing to be shown on the screen for customer to select. 7. After the customer makes a choice, the video server gateway then sends a message to LSMS for requesting a bandwidth and some other resources to delivery that program. 8. If the bandwidth and resources are available, then the video server gateway will notify the STB the location of the video server and where to access this program.
302 C.-C. Lo and W.-S.E. Chen Otherwise, it will reject this request and prompt a notification to the customer to wait a moment or select other services, for example, NVOD instead of TVOD. 9. The STB connects to the video server to receive the video stream. 10. After finishing delivering the program, the stream will be terminated. The video server gateway will notify the LSMS to release the bandwidth and related resources. 11. The video server gateway sends accounting information to the billing system and update the data records in the video server database. 5 Conclusions Today, as the rapid deployment of high-speed Internet infrastructure, interactive multimedia applications are becoming emerging killer applications of the broadband services. This paper gives an overview of the multimedia-on-demand system, including many visible access technologies, the main components of this large-scale commercial system, and the signal flows of system operation. As we shall see, deregulation will accelerate the convergence of the telecommunications, cable TV, entertainment, and e-commerce while ADSL is the mainstream technology of access network today and provides a viable solution to the Multimedia-on-Demand services. References [1] T-H. Wu and B-C. Cheng, Distributed Interactive Video system Design and Analysis, IEEE Commun. Mag., pp. 100-108, Mar. 1997 [2] K. Asatani and Y. Maeda, Access Architectural Issues for Future Telecommunication s, IEEE Commun. Mag., pp. 110-114, Aug. 1998 [3] Y. Maeda and R. Feigel, A Standardization Plan for Broadband Access Transport, IEEE Commun. Mag., pp. 166-172, Jul. 2001 [4] V. O. K. Li and W. Liao, Distributed Multimedia Systems, Proceedings of the IEEE, Vol. 85, No. 7, pp. 1063-1108, Jul. 1997 [5] Chunghwa Telecom, Telecommunications Technical Specification Multimedia On Demand System, Jan. 2000. [6] Y-H Chang, D. Coggins, D. Pitt, D. Skellern, M. Thapar, and C. Venkatraman, An Open- Systems Approach to Video-on-demand, IEEE Commun. Mag., pp. 68-80, May. 1994 [7] Gorge Abe, Residential Broadband, Second Edition, Cisco Press, 2000. [8] C-C Lo andw-s E. Chen, Toward Broadband Services on Telecommunication Access, Proceedings of Taiwan Area Conference 2000 (TANET 2000), pp. 134-140, Oct. 2000 [9] HwaCom Systems Inc. BM-plaza Introduction, Jun. 2001. [10] D. Deloddere, W. Verbiest, and H. Verhille, Interactive Video-on-demand, IEEE Commun. Mag., pp. 82-88, May. 1994 [11] S-H Gray Chen, and F. Tobagi, Distributed Servers Architecture for ed Video Services, IEEE/ACM Trans. on networking, Vol. 9, No.2, pp. 125-136, Apr. 2001 [12] C-W Lin, J. Youn, J-Zhou, M-T Sun, and S. Iraj, MPEG video streaming with VCR functionality, Multimedia Software Engineering, 2000. Proceedings. International Symp. 2000. pp. 146-153 [13] Digital Audio-Visual Council, DAVIC Specifications 1.4.1, Geneva, Switzer- land, 1998 [14] Thomas D.C. Little, and D. Venkatesh, Prospects for Interactive Video- on- Demand, IEEE Multimedia Mag., pp. 14-24, 1994