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2007 protocol (IPTV): The Killer application for the next-generation internet Yang Xiao

Xiaojiang

Jingyuan Zhang

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Recommended Citation IEEE Communications Magazine, November 2007

This Article is brought to you for and open access by RIT Scholar Works. It has been accepted for inclusion in Articles by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. XIAO LAYOUT 10/18/07 2:37 PM Page 126

TOPICS IN INTERNET TECHNOLOGY Television (IPTV): The Killer Application for the Next-Generation Internet

Yang Xiao, University of Alabama Xiaojiang Du, North Dakota State University Jingyuan Zhang, University of Alabama Fei Hu, Rochester Institute of Technology Sghaier Guizani, University of — Trois Rivières

ABSTRACT able on the Internet and can be accessed freely with Internet-connected computers, iPods, and Internet Protocol Television (IPTV) will be cellular phones. The current quality of IPTV in the killer application for the next-generation the United States does not yet approach that of Internet and will provide exciting new revenue cable TV services, but the gap will shrink as opportunities for service providers. However, to increases and codecs improve deploy IPTV services with a full quality of ser- [2]. In 2005, there about four million homes vice (QoS) guarantee, many underlying tech- in the that already had IPTV. Minerva has nologies must be further studied. This article about 50 IPTV deployments that cover 150,000 serves as a survey of IPTV services and the users with VCR quality services [2]. Asia has underlying technologies. Technical challenges been at the forefront of IPTV services, launch- also are identified. ing IPTV service tests in eight out of thirteen economies in the Asia-Pacific region [2]. It is an INTRODUCTION appealing consumer application that can use the 20-Mb/s promise of asymmetric digital subscriber Internet Protocol television (IPTV) provides dig- line 2+ (ADSL2+), the 50-Mb/s capability of ital television services over Internet Protocol very high (VDSL2), and (IP) for residential and business users at a lower the 100-Mb/s potential of (FTTx) cost. These IPTV services include commercial- [2]. Microsoft TV IPTV Edition is a software grade multicasting TV, (VoD), platform to develop TV services over triple play, voice over IP (VoIP), and Web/email networks including features such as instant chan- access, well beyond traditional nel change (ICC) and multiple picture-in-picture services. IPTV is a convergence of communica- (PIP), VoD, and recorder (DVR). tion, computing, and content [1], as well as an BellSouth, a service provider, integration of and telecommunica- recently performed trials of Microsoft IPVT [3]. tion. IPTV has a different infrastructure from AT&T and Verizon recently announced signifi- TV services, which use a push metaphor in which cant investments in adopting fiber optic cables to all the content is pushed to the users [1]. IP deliver IPTV channels to residential customers. infrastructure is based on personal choices, com- The challenges of IPTV include integration bining push and pull, depending on people’s of different operators with different infrastruc- needs and interests [1]. Therefore, IPTV has tures and back-office systems, stability of long two-way interactive communications between term, (QoS) matching cable operators and users, for example, streaming con- providers, and so on [3]. The current systems trol functions such as pause, forward, rewind, won’t be able to keep up with the changes in the and so on, which traditional cable television ser- video distribution model for IPTV [2]. The vices lack. Triple play is a service operator’s Video Networks Ltd. (VNL) rollouts of its package including voice, video, and data. Video HomeChoice video, triple play service over DSL adopting either MPEG-2 or MPEG-4 format is use a Cisco Internet Protocol next-generation delivered via IP . network (IP NGN) solution in the United King- The IPTV service first started in Japan in dom (UK) [4]. HomeChoice offers up to 4 Mb/s 2002, then became available in Korea [2]. IPTV , IPTV with over 70 channels, and is a convergence of broadcasting and telecom- thousands of movies, , and hit TV pro- munication. Many free IPTV services are avail- grams on-demand with up to 10 Gb/s per slot for

126 0163-6804/07/$20.00 © 2007 IEEE IEEE Communications Magazine • November 2007 XIAO LAYOUT 10/18/07 2:37 PM Page 127

next-generation IP multiprotocol label switching (MPLS) [4]. A chicken and egg situation exists: The indus- FTTx try needs IPTV to justify the investment in IPTV broadband, but there is no good IPTV without IPTV content devices broadband [2]. However, the investment is a way delivery services CORE networks to survive for some telecommunication compa- (sources, (IP/GMPLS/MPLS and xDSL nies [2]. IPTV is a convergence of IP-based com- database, multicast) programs IPTV munication and broadcasting. devices It is claimed that IPTV is the killer applica- Carrier tion for the next-generation Internet (NGI). In this article, we provide a survey of IPTV, as well IPTV as a description of its technical support. Some devices technical challenges and research issues also are 802.11n identified. WLAN IPTV The rest of this article is organized as follows. devices We first introduce IPTV and then present access networks and core networks for IPTV. Then, I Figure 1. mobile TV and peer-to-peer (P2P) IPTV are IPTV services. introduced. Finally, we present technical chal- lenges. Successful deployment of IPTV services requires excellent QoS for video, voice, and data. IPTV QoS metrics for video include jitter, number of To bring IPTV to reality requires changes in out-of-sequence packets, packet-loss probability, physical infrastructure. IPTV uses IP protocol to network fault probability, multicast join time, deliver multicasting TV, VoD, triple play, VoIP, delay, and so on. QoS metrics for voice include and so on, to consumers via broadband connec- mean opinion score (MOS), jitter, delay, voice tions, with a QoS guarantee. IPTV has unique packet loss rate, and so on. QoS metrics for features in addition to simply broadcasting ordi- IPTV services include channel availability, chan- nary TV programs over the Internet. IPTV can nel start time, channel change time, channel be incorporated with high- DSL access change failure rate, and so on. Before system technologies, such as ADSL2, ADSL2+, and deployment, accurate testing should be per- VDSL, as well as high-speed carrier-grade Eth- formed to test high-quality IPTV services for TV ernet and the emerging high throughput IEEE service, video, voice, as well as interactive service. 802.11n LAN. MPEG-2 and MPEG-4-Part 10 /H.264 are IPTV is an integration of voice, video, and typically used for encoding video with a large data services using high bandwidth and high range of compression rates, allowing a trade-off speed Internet access. IPTV includes several between quality and bandwidth with either a components as shown in Fig. 1: constant bit rate or a variable bit rate [6]. Much • IPTV sources including VoD database and of the compression comes from inter-frame dif- other programs ference encoding instead of intra-frame coding, • High-speed Internet with functions of multi- particularly when there is relatively little change casting, QoS guarantee, and so on, includ- in each scene [6]. For an I frame, with intra- ing an optical backbone network to serve as frame encoding, its image frame consists of an IP multicast core network blocks converted to a set of coefficients using • High-speed access networks such as ADSL, discrete cosine transform (DCT). A group of ADSL2+, VDSL, a combination of fiber- blocks forms a slice carried within one packet. If to-the curb (FTTC) and DSL, fiber-to-the- the first block is damaged, the whole group may home (FTTH) access, carrier-grade be lost, which creates a strip in the image [6]. Ethernet, and the emerging IEEE 802.11n wireless LAN ACCESS NETWORKS • IPTV user devices such as digital In this section, we introduce access networks including high definition televisions such as DSL technologies, carrier-grade Ether- (HDTVs) , high-speed 802.11n wireless LAN, fiber-to- IPTV features [5] include: the-home (FTTH), and fiber-to-the curb • Selection (users are able to select their TV (FTTC). All these networks can contribute to programs with fast channel selection and the IPTV service deployment. short channel changing time) • Storage (TV programs are stored in local DSL TECHNOLOGIES storage devices so that users can watch DSL technologies, shown in Fig. 2, provide high- them anytime; furthermore, service pro- speed digital data transmissions over a viders should store at least 100 hours of TV from users to end offices. Downlink programs and videos) speed of a typical DSL is about 128 kb/s ~ • QoS (QoS must be guaranteed; a standard 24Mb/s, depending on the service providers. definition TV and a high definition TV ADSL standards can deliver 8 Mb/s over about 2 need bandwidth of 1~4 Mb/s and 4~12 km, and ADSL2+ can deliver up to 24 Mb/s, Mb/s, respectively) depending on the distance between a user and • Low cost (cost to the user must be low; this the nearby end office. ADSL is the most widely is the key to success) deployed DSL technology.

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The high-speed IEEE 802.11n wireless Voice LAN can be one of switch Ethernet/USB the underlying xDSL infrastructures to assist IPTV service as Codec the access network Splitter with better QoS via Splitter high data access I D rates. We call it DSLAM ISP wireless IPTV.

Telephone

End office End office

I Figure 2. DSL.

DSL improves dial-up phone service via the networks across the country, enabling same local loop of the fixed phone system. The customers to view on Wi-Fi- phone system normally filters about 4-MHz enabled devices on 15 channels of news, sports, voice traffic at end offices to save bandwidth and entertainment, and full-length music videos, to let a voice be intelligible. End offices can available May 2006 to 7,000 hotspots nationwide beyond the 4-MHz limit over a phone line to for a monthly fee of $11.99. provide higher bandwidth using DSL. A DSL The high-speed IEEE 802.11n wireless LAN modem can connect multiple computers via Eth- can be one of the underlying infrastructures to ernet, HomePlug, or the IEEE 802.11 wireless assist IPTV service as the access network with (WLAN). better QoS via high data access rates. We call it VDSL (very high bit-rate DSL) has a theoret- wireless IPTV. ical limit of 52 Mb/s downstream and 12 Mb/s The IEEE 802.11 Task Group (TGn) was upstream, using up to two bands for announced in January 2004 to improve through- upstream and two frequency bands for down- put of the IEEE 802.11 WLAN to 100Mp/s ~ stream, with quadrature amplitude 600 Mb/s, as well as offering a better operating (QAM) or discrete multitone (DMT) modula- range than current networks [7]. There were two tion techniques. competing PHY proposals for the IEEE 802.11n VDSL2 (very-high-bit-rate digital subscriber standard: line 2, ITU-T G.993.2 Standard) provides full- • World-Wide Spectrum Efficiency (WWiSE) duplex aggregate data rates up to 200 Mb/s using supported by Broadcom, Texas Instruments, a bandwidth up to 30 MHz. and others DSL techniques are the first choice for access • TGn Sync supported by Intel, Philips, and networks in IPTV. others Both proposals adopt multiple-input multiple- CARRIER-GRADE ETHERNET output (MIMO), using multiple and Ethernet has been the dominant technology in receiver antennas for better throughput with LAN for a long time and still is. spatial and spatial diversity to Carrier-grade Ethernet can provide up to 10 increase range. The two proposals are different Gb/s access speed, eight classes of service (CS) in terms of how to use MIMO: TGn Sync adopts and /multicast/broadcast modes via a vir- 40-MHz mandatory channel width with a mini- tual local area network (VLAN) technique [1]. mum of two antennas; whereas WWiSE adopts In IEEE 802.3ae, 10 Gb/s Ethernet with full the mandatory channel width with four antennas. duplex has been standardized for optical single- In January 2006, the IEEE 802.11n Task Group mode interfaces, maintaining the IEEE 802.3 approved a joint proposal specification based on frame and format size. an enhanced wireless consortium (EWC) specifi- Carrier-grade Ethernet can be one of the cation. The 802.11n Draft was sent for letter bal- candidates for the access networks for IPTV ser- lot at the March 2006 meeting but did not pass a vices. With its high data access rate, it provides a majority vote in the May 2006 meeting. Howev- better QoS guarantee. er, it was scheduled to complete the 802.11n standard in the middle of 2007 [7]. HIGH THROUGHPUT IEEE 802.11N In [7], the author presented a potential IEEE WIRELESS LAN 802.11n medium access control (MAC) via aggregation techniques and classified frame Recently, AT&T announced that it is working aggregation mechanisms into many different and with MobiTV to deliver live TV to its Wi-Fi orthogonal aspects, such as distributed versus

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centrally controlled, ad hoc versus infrastructure, uplink versus downlink, single-destination versus multidestination, physical (PHY)-level versus MAC-level, single-rate versus multirate, immedi- 6 ate acknowledgment (ACK) versus delayed ACK, and no spacing versus short interframe 5 spaces (SIFS) spacing. 4 FTTH FTTH and fiber to the premises (FTTP) use fiber-optic cables for IPTV services to businesses 3 and homes. They will be ideal choices for access networks as fiber deployment cost decreases. FTTP includes active FTTP and passive FTTP IP multicast 2 architectures. In the active FTTP architecture, an equipment cabinet is built for every 400–500 users, performing layer 2–3 functions. The IEEE 1 802.3ah standard provides full-duplex 100 Mb/s to the premises. The passive FTTP architecture I Figure 3. IP multicast. avoids building equipment cabinets by using pas- sive splitters to optically split fibers into multiple (e.g., 64) fibers to different users’ homes, and manipulating optical network resources, with a layer 2–3 functions are performed at the carri- separation of media data plane and control er’s central offices instead of at equipment cabi- plane [2–4]. nets in the active FTTP. MULTICAST FTTC Multicast delivers information to a group of des- To reduce cost, FTTC is used to install fiber to tination stations. IP multicast, shown in Fig. 3, within 1000 feet of a home or business, and then sends voice, video, and data to multiple receivers cable or carrier-grade Ethernet can be used to using RTP/TCP/IP protocols, with a multicast further connect to home or business. address. Currently, IP multicast has a scalability prob- ORE ETWORKS lem when there are a large number of users and C N groups. Furthermore, there is not a fully In this section, we briefly introduce deployed multicast application in the commer- GMPLS/MPLS and IP multicast as the core net- cial Internet, with the exception of some applica- work technologies. tions limited in location, such as multicast backbone () and private IP networks. GMPLS/MPLS There are three kinds of multicast delivery: MPLS provides better IP traffic . dense multicast, sparse multicast, and source- Connectionless IP behaves more like connec- specific multicast. tion-oriented so that a path between a source • Dense multicast is to construct a tree for and a destination is pre-determined and sending packets to the multicast users. A labeled. This looks similar to ATM protocols. source broadcasts to all routers and The labels are used to establish end-to-end all nodes, which in turn send pruned pack- paths that are called label switched paths ets if they do not want the multicast so (LSPs). MPLS is a switching protocol between that the routers do not send correspond- layer 2 and layer 3, adding labels in MPLS ing packets to these nodes or routers. packet headers and forwarding labeled packets Reverse-path forwarding is used for pre- in corresponding paths using switching instead venting loops. of . However, an MPLS header does not • Sparse multicast does not depend on any identify the type of data carried in the path particular unicast and is to such that Internet service providers (ISPs) construct a tree for sending packets to the could manage different kinds of data streams multicast users. If a node wants to based on priority and service. Major applica- join/prune a multicast group, it sends a tions of MPLS are traffic engineering and the join/prune message via Internet Group virtual private network (VPN). MPLS is similar Management Protocol (IGMP) to a , to differentiated services (DiffServ) in marking which forwards data packets to the multi- traffic at ingress boundaries and unmarking at cast group. Join/prune messages are sent egress points. periodically to a group-specific rendezvous Generalized MPLS (GMPLS) extends MPLS point (RP) by a designated router (DR) for to add a signaling and routing control plane for each active group. A term route entry is the devices in packet domain, time domain, wave- state maintained in a router to represent length domain, and fiber domain, providing end- the distribution tree including source to-end provisioning of connections, resources, address, group address, timers, and so on. and QoS. This state creates a distribution tree that GMPLS is a better protocol for broadband reaches all group members. Routers also and IPTV services, controlling all the layers, use reverse-path forwarding to ensure that including packet layer, time division multiplexing there are no loops for layer, lambda layer, and fiber layer; effectively among routers.

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• Source-specific multicast delivers multicast them into a local media player using two buffers The QoS guarantee packets originating in a specific source (to smooth video variation and to efficiently dis- address to those that request them. tribute video content among peers), uploads the and traffic IP multicast is an approach for sending a cached video chunks to other peers, and launch- management are message simultaneously to multiple nodes es a media player when the streaming file length challenging for core instead of one. Multicast group addresses range reaches a predefined threshold. from 224.x.x.x to 239.x.x.x. networks and access IP multicast is required to provide IPTV ser- TECHNICAL CHALLENGES networks, in vices, and it saves bandwidth in both core net- works and access networks because there is a In this section, we first describe the QoS guaran- particular for IPTV high probability that more than one user watches tee and traffic management for IPTV services. services. For the same program, and both core networks and Since admission control mechanisms are essen- downstream traffic, access networks are capable of multicasting. tial for IPTV services, we then present multicast Both IGMP and real time streaming protocol admission control, admission controls for Ether- differentiated (RTSP) are required. Both multicast and unicast net, congestion control, WLAN (wireless IPTV), services are used for are useful for IPTV. and DSL. Finally, we briefly mention security and standardization aspects, as well as communi- different users with OBILE cations among admission control schemes. different schedulers. M TV Current video services over cellular networks are QOS GUARANTEE AND TRAFFIC MANAGEMENT either downloadable video (i.e., the download The QoS guarantee and traffic management are time exceeds the video’s playing time) or still challenging for core networks and access net- images with real-time voice (e.g., Sprint PCS works, in particular for IPTV services. For down- brings real-time television content to mobile stream traffic, differentiated services are used phones at a rate of one or two frames per sec- for different users with different schedulers. For ond). upstream, user traffic is monitored. Each user In the near future, (mobile class requires a separate scheduler to prevent TV) will combine IP and digital video broadcast the starvation of lower classes. Admission con- (DVB) to broadcast TV content over cellular trols are required for a QoS guarantee. networks. DVB is a suite of standards of the In normal TV services, multiple program European Standards Insti- channels to users are achieved by sending all the tute (ETSI), defining the PHY layer and data programs and filtering out the unsubscribed link layer of a distribution system and MPEG-2 channels. A channel changing program is to transport streams as the format of video content. select one channel and filter the rest of channels. Mobile TV services can be treated as an exten- The mechanism is not suitable for IPTV services sion of IPTV services. due to bandwidth limitation. IP multimedia subsystem (IMS) is for next-gen- In IPTV services, a user requests channel eration networking (NGN) architecture to provide changing by sending a request for a video chan- mobile and fixed multimedia services. IMS may be nel. After the request is accepted by admission a good candidate for future mobile TV. control, a multicast tree is built to send video and voice of the requested channel with QoS guarantees. The procedure causes a channel P2P IPTV changing delay. If the IPTV sets in a household A new kind of IPTV, different from the infra- are off, the available bandwidth can be used for structure-based scheme introduced previously, is Internet access and other uses. P2P IPTV, in which each IPTV user is potential- The goal of traffic management is to effi- ly a server, multicasting received content to ciently support QoS requirements for diverse other IPTV users [8]. In a P2P IPTV system, services, including policing, scheduling, con- users serve as peers and participate in video data trol, multicasting, traffic differentiation, admis- sharing. A popular P2P IPTV system such as sion control, and so on. It is implemented via PPLive supports 100,000 users simultaneously either a centralized manner or a distributed with proprietary signaling and video delivery manner. The latter approach is more scalable protocols [8]. PPLive has more than 400 chan- and flexible. Policing ensures that traffic con- nels with an average channel data rate of 325 forms to a service level agreement (SLA). kb/s. PPLive does not own video content but Scheduling ensures the handling of voice, video, limited information about its video content dis- and data traffic to meet QoS requirements such tribution mechanism, and is mostly fed from TV as delay, its variation, and so on, as well as effi- channels in Mandarin, encoded with windows cient utilization of bandwidth. Flow control is to media video (WMV) or real video (RMVB) [8]. control traffic flow to avoid or reduce temporary A user must download and install the PPLive congestion. Multicasting is used both in down- software to use PPLive P2P IPTV. When the stream and upstream to efficiently utilize band- PPLive software is running, the user becomes a width. Traffic differentiation gives higher priority PPLive peer node, sending out a query message traffic such as voice, audio, and video a higher to a PPLive channel server for an updated chan- priority to be transmitted and gives data a lower nel list. When the user selects one channel, the priority. This should be done in both the core software requests an online peer list (including network and the access network. Admission con- IP addresses and port numbers) for this channel trol decides to accept or reject upstream and and sends probes to peers to find active peers downstream bandwidth requests, ensuring an that may provide more peers. The software accepted flow of bandwidth that satisfies the downloads video chunks from peers, streams QoS requirement.

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Service providers must indicate the level of ADMISSION CONTROL FOR ETHERNET the QoS that is guaranteed in an SLA, which Since DiffServ may cause communication costs for the service Carrier-grade Ethernet is no longer a con- providers. tention-based Ethernet, but an aggregation and resources are Detailed QoS guarantee mechanisms and switching technology. A carrier-grade Ethernet consumed based on traffic management for IPTV services require should provide QoS guarantees on throughput pre-negotiated SLA, further investigation and research. and delay for leased-line and real-time services [11]. For carrier-grade Ethernet, distributed IP multicast in MULTICAST ADMISSION CONTROL admission control can be implemented using an DiffServ may cause Large scale IP-multicast deployment has not in-band signaling protocol to reserve bandwidth been seen at ISPs. However, IPTV services will in each network node, and centralized admission the actual consumed be one of the main drivers for upcoming IP-mul- control can be implemented by using a central resources to exceed ticast deployments. This means the capability of controller to allow polices at the edge to track the pre-negotiated end-to-end QoS, accounting, and service avail- load on each network link [11]. ability, as well as supporting multicast layer 3 Designing efficient and distributed admission SLA because a VPNs and multicast MPLS. control for carrier-grade Ethernet requires fur- multicast tree can Differentiated service (DiffServ) is for unicast ther investigation and research. QoS in IP networks. For IPTV services, multicast branch at any node is another way to provide better QoS, but there ADMISSION CONTROL FOR so that outgoing are three problems for multicast as follows [9]: IEEE 802.11N WLANS traffic may exceed • Multicast trees should have different QoS levels on different branches for the cus- Although contention-based MAC protocols are incoming traffic. tomers demanding different levels of quali- very successful commercially and are robust for ty. best effort traffic, they are unsuitable for multi- • DiffServ is scalable with stateless routers, media applications with QoS requirements [15]. whereas IP multicast is not scalable with On the other hand, centrally controlled MAC group information and router forwarding protocols and reservation-based protocols man- states; therefore, IP multicast running over age QoS more easily but are rarely implemented DiffServ should be more scalable. in today’s products due to several reasons, such • The neglected reserved subtree (NRS) prob- as high complexity, inefficiency, lack of robust- lem exists because one flow can be replicat- ness, global synchronization, and so on. Without ed into many egress nodes. QoS support at the MAC layer, it is impossible Since DiffServ resources are consumed based to provide a QoS guarantee solely from higher on pre-negotiated SLA, IP multicast in DiffServ layers. may cause the actual consumed resources to IEEE 802.11 WLANs have achieved tremen- exceed the pre-negotiated SLA because a multi- dous success in terms of deployment and usage. cast tree can branch at any node so that outgo- The popularity of the IEEE 802.11 WLAN is ing traffic may exceed incoming traffic [10]. This due mainly to the contention-based MAC dis- is called the NRS problem. tributed coordination function (DCF), whereas Admission control in IP multicast over Diff- the optional point coordination function (PCF) Serv is difficult because policing is not intelligent is barely implemented in today’s products due enough. Resources must be checked whenever a to its complexity and inefficiency for normal new user joins a group [9]. A bandwidth broker data transmissions. However, the current con- can be a centralized solution, but it is not scal- tention-based MAC is unsuitable for multime- able due to its huge database [9]. A scalable dia applications with QoS requirements. To approach should be a distributed method, in support the MAC-level QoS, the IEEE 802.11 which edge routers make decisions locally based Working Group published the IEEE 802.11e on measurement-based algorithms [9]. specification, providing QoS features and multi- DSMCast [11] solves the problem of hetero- media support to existing 802.11a/b/g WLANs, geneous trees and scalability and gives a compe- while maintaining full backward compatibility tent framework for solving the NRS problem. with these legacy standards. The IEEE 802.11e In [9], a distributed admission control, an MAC employs a channel access function, the extension of DSMCast at edge nodes, is present- hybrid coordination function (HCF), which ed to solve the NRS problem, based on filtering includes both contention-based and centrally join requests: controlled channel access mechanisms. The • A join request is accepted if an edge router contention-based channel access mechanism is receiving the request is already forwarding also referred to as the enhanced distributed the particular group. channel access (EDCA). The EDCA provides a • Otherwise, the process inspects paths (with priority scheme by differentiating the inter- increased utilization) between egress edge frame space, as well as the initial and maximum node and branching node if there is enough contention window sizes for back-off proce- capacity on the links for the new request. dures. IEEE 802.11e cannot provide guaran- • Measurements are conducted first on sever- teed QoS, and multimedia traffic cannot be al obtained packets by temporary accep- protected. In [15], distributed QoS admission tance to see whether measurements are control mechanisms and data control mecha- beyond the history limits. nisms are proposed to provide a QoS guarantee Designing more comprehensive, distributed, and provisioning at the contention-based wire- efficient, and scalable multicast admission con- less MAC layer, which can be coupled with the trol mechanisms requires further investigation emerging IEEE 802.11n high throughput and research. WLANs to support IPTV services.

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Designing efficient contention-based admis- flows, they may be differentiated with regular A flow is TCP-friendly sion control and bandwidth allocation requires voice/video and premium voice/video. further investigation and research. Single packets such as changing a channel of if, and only if, in a IPTV services should have the highest priority steady state, it uses ADMISSION CONTROL FOR DSL and can be sent via SIP. in the long term no One challenge for DSL networks is that the broadband and voice services are separated at IPTV CONGESTION CONTROL more bandwidth the physical layer so that they lack resource Congestion control is critical when many IPTV than a conforming sharing. Therefore, IP-based QoS support for flows are transmitted simultaneously. The con- access network is required. gestion control is an end-to-end protocol, that is, TCP flow that would Voice, video, and data packets are carried it is implemented in either the side (i.e., be used under over IP from customer premises equipment IPTV video sources) or the receiver side (i.e., comparable (CPE) to a DSL access multiplexer (DSLAM), customers’ machines). The typical approach to which then routes or switches them toward the congestion control is to adjust the sending rates conditions. Among core network. Voice packets are encapsulated by of different IPTV sources (i.e., TV channels) the principal Real Time Protocol (RTP) and User such that the IPTV traffic does not overwhelm Protocol (UDP) before being sent to the IP the Internet routers. representatives of layer. At the CPE, multiple sources such as two Although the congestion control algorithm in the TCP-friendly con- IPTV video and audio channels, voice over IP TCP is efficient for bulk data transfers, applying gestion control (VoIP) phone, and Internet access (via fixed PC a typical multiplicative decrease to the data rate or WLANs) are aggregated together via DSL available to a real-time video stream can severe- algorithms is the services. Therefore, without admission control at ly affect the video quality perceived by the end TCP-friendly rate DSL, the QoS of video and voice traffic can not user. Thus new congestion control algorithms, be guaranteed if either there are too many tailored to the rate acceleration and variability control algorithm. video/voice flows, or there is too much Internet requirements of IPTV applications, should be access traffic (e.g., downloading large files such developed. Because of the coexistence of video as movies). An admission control is required at traffic with normal TCP traffic, some TCP-com- the CPE to guarantee QoS of IPTV services patible congestion control algorithms have been such as video/voice delay, and so on. proposed for audio/video-streaming applications Furthermore, normally DSL providers offer [13]). To compete with TCP flows in a fair man- users with rates of upstream and downstream ner, these algorithms have two important charac- and the SLA is defined by transport parameters, teristics in common: but IPTV services are defined by application • Slow responsiveness in order to smooth experience, such as the number of channels pro- data throughput vided, quality of video, functionality, and so on, • TCP friendliness and they are so-called quality of experience A flow is TCP-friendly if, and only if, in a steady (QoE) [12]. It is difficult to translate between state, it uses in the long term no more band- QoE and QoS. Admission control is important width than a conforming TCP flow that would be to avoid oversubscription with degraded QoE used under comparable conditions. Among the and QoS. principal representatives of the TCP-friendly Per-flow admission control for DSL QoS is congestion control algorithms is the TCP-friend- required to provide bandwidth on demand, and ly rate control (TFRC) algorithm [13]. application-level admission control also can be Shortcomings of current congestion control applied in addition to network-based admission schemes when implemented in IPTV are stated control. Usage of IPTV services depends on as follows. Although these schemes can ensure time of day, location, and so on. Some services that the video streams do not overload or under- have higher priorities than others. Therefore, utilize the available network bandwidth, they can different admission control thresholds are not simultaneously maximize the perceived required for different applications. It also can IPTV video quality. For instance, in the slow- limit the number of channels simultaneously sent start phase, they just start from one packet per to the DSLAM. round-trip-time (RTT) and slowly approach the There are typically two kinds of admission maximum available rate, which can greatly harm control methods: end-point admission control the QoS of video traffic in the entire slow-start and network admission control. In end-point duration. Even though TFRC [13] tries to admission control, end-hosts send probe packets smooth out rate variability, it does not take the to networks to measure the QoS to make admis- properties of the overlying media application sion decisions, while network admission control into consideration when protecting media flows makes decisions based on end-hosts’ request via from short-term congestion. a signaling mechanism such as Session Initiation Protocol (SIP). COMPATIBILITY OF COMMUNICATION AND For either a voice flow or a video flow, admis- BROADCASTING sion control should track its activities such that The following are compatibility issues between in case there is no activity for a maximum peri- communication and broadcasting: od, the resource should be recollected. For voice • Harmonization between ubiquitous traffic flows, admission control should consider whether and multicast traffic silence suppression is used or not. For video • Harmonization between telecommunication flows, both constant bit rate (CBR) video and signaling and multicast signaling variable bit rate (VBR) video should be consid- • Separation of media transport network and ered. signaling network [14] Furthermore, for either voice flows or video Ubiquitous traffic is defined as data traffic from

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communication networks, normally has narrower many users within a cell with downlinks only. bandwidth, and is non-real-time, whereas multi- Both broadcasting uplinks and downlinks should For purposes of cast traffic is one-to-many real-time video; har- be used with a high capacity . monization between telecommunication signaling Due to limited bandwidth, mobile TV service robustness, mobile and multicast signaling should be further investi- may degrade performance and capacity of cell TV is normally gated because multicast signaling, having differ- sites, and it is difficult to provide personalized distributed from two ent signaling mechanisms for core networks and interactive services. The most challenging issue access networks, is quite different from telecom- of mobile TV is, of course, the bandwidth issue. or more video munication signaling, which has an end-to-end Wireless multicast plays an important part for content sources to signaling mechanism; separation of media trans- mobile TV. For purposes of robustness, mobile port network and signaling network may be TV is normally distributed from two or more multiple destinations. required due to a congestion consideration video content sources to multiple destinations. Most of the research caused by the conflict of multicasting and priori- Most of the research about multicast does not about multicast does ty of real-time traffic. address the problem of multiple sources and multiple destinations. not address the SECURITY AND PRIVACY Wireless multicast is similar to wired multi- problem of multiple There are possible attacks and network outage cast in concept. However, minimizing energy failures for IPTV services. Rapid recovery after consumption of mobile devices should always be sources and multiple attacks/failures is important to minimize nega- considered for wireless multicast. Computing an destinations. tive impact. IPTV services should provide user optimal-energy-consumption multicast tree is security and privacy with confidential delivery of nondeterministic polynomial time (NP)-hard. data such as program channels and content, pre- There is still some work required for IMS to vention of attacks from malicious users/software, provide IPTV services. and denial of service (DoS). Designing secure and anonymous IPTV ser- CHALLENGES OF P2P IPTV vices requires further investigation and research. Challenges of P2P IPTV services include provid- Especially, the following issues must be solved: ing QoS, which is difficult because the services distributed digital rights management (DRM) to are provided via the public Internet so that the protect the copyright of video contents, the video quality is subject to network traffic condi- authentication of clients to verify their access tions. privileges, and the prevention of traffic flooding / bandwidth over-consumption attacks. CONCLUSIONS STANDARDIZATION OF IPTV This article presents an overview of IPTV ser- Standardization of IPTV is important and diffi- vices and its key technologies in terms of access cult; however, it is mandatory for successful networks, core networks, mobile TV, P2P IPTV, deployment. There are no established standards and challenging issues including QoS guarantee, at this stage. Lack of standardized technologies traffic management, congestion control, multi- causes unnecessary investments and unavailable cast admission control, Ethernet/WLAN/DSL new services, and therefore it is feared that some admission control, standardization, communica- businesses may be forced to use proprietary tions among admission controls, and security and solutions [14]. Standardization of NGN has pro- privacy issues. gressed in the International Telecommunication Union — Telecommunication Standardization Sector (ITU-T) that includes IPTV services [14]. REFERENCES [1] . Jain, “I Want My IPTV,” IEEE Multimedia, vol. 12, no. COMMUNICATIONS AMONG 3, July–Sept. 2005, pp. 95–96. [2] C. Wales et al., “IPTV — The Revolution Is Here,” white ADMISSION CONTROLS paper. [3] B. Alfonsi, “I Want My IPTV: Internet Protocol Television Further studies are required to learn how differ- Predicted a ‘Winner,’” IEEE Distrib. Sys. Online, IEEE ent admission control schemes become consis- Comp. Soc. 1541-4922, vol. 6, no. 2, Feb. 2005. [4] “Video Networks Extends Reach of HomeChoice ‘Triple tent and communicate well, for example, Play’ Services to 10 Million UK Homes with Cisco and between multicast admission control and xDSL Telindus,” http://www.cisco.com/global/UK/news/pdfs/ admission control, between multicast admission 2005/20050706.pdf control and carrier-grade Ethernet, between car- [5] S. Kim and D. Kataria, “Delivering the Next Big Motion Picture: IPTV,” Nov. 2005. rier-grade Ethernet and carrier-grade Ethernet, [6] “IPTV Performance Management,” white paper, Telche- between multicast admission control and 802.11 my App. Note, Sept. 2005, http://www.telchemy.com admission control, and so on. For example, [7] Y. Xiao, “IEEE 802.11n: Enhancements for Higher changing a channel in IPTV services may require Throughput in Wireless LANs,” IEEE Wireless Commun., vol. 12, no. 6, Dec. 2005, pp. 82–91. of DSL admission control only a small action, [8] X. Hei et al., “Insight into PPLive: Measurement Study such as changing parameters, but multicast of A Large Scale P2P IPTV System,” WWW ’06. admission control may involve join and leave [9] O. Alanen et al., “Multicast Admission Control in Diff- operations at a multicast tree so that DSL admis- Serv Networks,” Proc. ICON ’04, vol. 2, pp. 804–08. [10] B. Yang and P. Mohapatra, “Multicasting in Differenti- sion control should communicate with multicast ated Service Domains,” Proc. IEEE GLOBECOM ’02. admission control to work together. [11] I. Voorde et al., “Carrier-Grade Ethernet: Extending Ethernet into Next Generation Metro Networks,” white CHALLENGES FOR MOBILE TV paper, Alcatel. [12] “Integrated Video Admission Control for the Delivery of a Current cellular networks cannot support high Quality Video Experience,” white paper, Cisco, 2006. bandwidth, real-time applications such as video, [13] S. Floyd et al., “Equation-Based Congestion Control for whereas mobile broadcast networks support Unicast Applications,” ACM SIGCOMM, 2000.

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[14] I. Kase, “TSB Director’s Consultation Meeting on IPTV works, security, wireless networks, and computer networks. Standardization,” Doc. 20-E, Geneva, Switzerland, 4–5 He is an Associate Editor of Wiley’s Wireless Communica- Apr., 2006. tion and Mobile Computing. He is (was) Chair of the Com- [15] Y. Xiao, “QoS Guarantee and Provisioning at the Con- puter and Network Security Symposium of IEEE/ACM tention-Based Wireless MAC Layer in the IEEE 802.11e Wire- International Wireless Communication and Mobile Comput- less LANs,” IEEE Wireless Commun., Feb. 2006, pp. 14–21. ing Conference 2007 (2006).

JINGYUAN ZHANG [M] ([email protected]) received his Ph.D. BIOGRAPHIES degree in computer from Old Dominion University YANG XIAO [SM] ([email protected]) is currently with the in 1992. He is currently an associate professor with the Department of Computer Science at the University of Department of Computer Science at the University of Alabama. His research areas are security, telemedicine, sen- Alabama. His current research interests include wireless sor networks, and wireless networks. He is a member of networks, mobile computing, and collaborative software. the American Telemedicine Association. He currently serves Prior to joining the University of Alabama, he was a princi- as Editor-in-Chief for the International Journal of Security computer scientist with ECI Systems and Engineering, and Networks, International Journal of Sensor Networks, an assistant professor at Elizabeth City State University, and International Journal of Telemedicine and Applications. and an instructor at Ningbo University. He serves as a referee/reviewer for many funding agencie as well as a panelist for the U.S. National Science Founda- FEI HU [M] ([email protected]) received his B.S. and M.S. tion (NSF), and is a member of the Telecommunications degrees from Shanghai Tongji University, China in 1993 expert committee of the Canada Foundation for and 1996, respectively. He received his first Ph.D. degree in (CFI). He has served on the Technical Program Committees the field of telecommunications engineering from Shanghai for more than 90 conferences such as INFOCOM, ICDCS, Tongji University in 1999 and received his second Ph.D. MOBIHOC, ICC, GLOBECOM, and WCNC. He serves as an from the Department of Electrical and Computer Engineer- Associate Editor or on editorial boards for several journals ing at Clarkson University in 2002. He is currently an assis- (IEEE Transactions on Vehicular Technology, etc.). He has tant professor in the Computer Engineering Department at published more than 200 papers in major journals (more Rensselaer Institute of Technology, New York. His research than 50 in various IEEE journals/magazines), book chapters interests are in cognitive , ad hoc sensor networks, related to his research areas, and refereed conference pro- 3G wireless and mobile networks, and network security. ceedings. He was a voting member of the IEEE 802.11 Working Group from 2001 to 2004. His research has been SGHAIER GUIZANI ([email protected]) received a supported by the NSF. B.Sc. from the State University of New York at Binghamton in 1990, an M.A.Sc. degree in electrical engineering from XIAOJIANG (JAMES) DU [M] ([email protected]) received his B.E. North Carolina A&T State University in 1992, and a Ph.D. in degree from Tsinghua University, China in 1996, and his telecommunication from the University of Quebec, Trois M.S. and Ph.D. degrees from the University of Maryland, Rivières, Canada. He is currently working as an assistant College Park in 2002 and 2003, respectively, all in electrical professor at Qatar University in the Mathematics and Com- engineering. He is an assistant professor in the Department puter Department. His research interest are in the areas of of Computer Science, North Dakota State University. His communication systems, over fiber, wire- research interests are heterogeneous wireless sensor net- less networks architecture, and wireless communication.

134 IEEE Communications Magazine • November 2007