Digital Video Broadcasting and IPTV as alternatives to the OTT media services

Digital Video Broadcasting and IPTV as alternatives to the OTT media services Communication and Broadcast Networks Teachers: Reza Tadayoni Per Lynggaard Written by: Amer Abd Elkawy Andrey Lekov Keshab Raj Adhikari Miguel Portela

Table of Content Introduction... 3 Digital Video Broadcasting... 3 DVB-S2... 4 DVB-C2... 4 DVB-T2... 5 Transmission analysis... 6 Input Interface... 7 Modes... 7 FEC... 7 Modulation... 8 Modulation Schemes... 10 Guard Interval... 10 Interleaving... 11 Internet Television (IPTV)... 11 The Architecture... 11 Infrastructure:... 12 Comparison between IPTV and OTT... 14 IP Multimedia Subsystem (IMS)... 15 References:... 16 2

Introduction This mini project represents a basic attempt to enhance the research and knowledge gained in the semester project regarding the current impact of the OTT media services on the market. By analyzing the main technological aspects differentiating the traditional media entertainment services like DVB family of standards and IPTV, this project work is aiming at building better understanding of how the capabilities of those substitute services can help them compete with the disruptiveness of the new solutions expanding on top of the Internet Hourglass Model.[ 1 ] Furthermore the evolution towards the second generation of DVB family of standards is going to be analyzed as significant part of the customer base, especially amongst the aged user groups are still relying on their ability to provide media entertainment over the existing telecommunication infrastructure. In order to improve the quality of this analysis, the diversity in the use of the different modulation schemes and error correcting codes will be emphasized as well as the difference between other relevant technological properties of the DVB standards. Finally IPTV technology will be examined as an IP-based alternative to the traditional television and predecessor of the Over-The-Top media services. While describing the technologies used for distributing the content, an accent is going to be put on the contrast between transporting it over managed and unmanaged networks. Digital Video Broadcasting DVB is an abbreviation for digital video broadcasting which represents a several international accepted standards concerning the means used in distributing digital TV to TV sets. There are different technological means used by DVB systems to distribute digital video signal. DVB standards describes the technical specifications of the DVB s technologies This part is concerned with the 2nd generation of the most three widely used DVB standards, and they are (DVB-C2, DVB-T2, DVB-S2). 3

DVB-S2 In Satellite communications, the satellite is placed above the equator in an orbit of 36000 km far from the surface of the earth and rotates with the same speed of earth so the transmitted signal can reach the entire continent. DVB-S is the first generation standard for digital video broadcasting for satellite, and developed by DVB project in 2003. DVB-S2 mandated to replace the old generation DVB-S. DVB-S2 was designed to support different applications SDTV, HDTV and interactivity like for example (internet access. DVB-S2 has 30% more efficiency spectrum compared to DVB-S. This significant difference between those two generations came from the modulation schemes and the coding methods used plus the transport streams enabled by both generations. DVB-S based on QPSK and in some cases uses 8PSK for better data rate. DVB-S enable only single Transport stream (MPEG-2-TS) using Reed Solomon FEC reaching a data rate of 50.9 Mbit/s. DVB-S2 has a total different modulation scheme (QPSK, 16ASPK&32ASPK) using a single carrier [ 2 ]. DVB-S2 enables both single transport streams (MPEG-2-TS) and multiple transport streams (MPEG2-TSs) or generic streams (GS) for IP packet data supporting MPEG4 audio video streams. Using single or multiple MPEG-2-TSs or single or multiple generic streams (GS) depends on the application. DVB-C2 DVB-C2 is the 2 nd generation digital video broad casting standard for digital TV over cable networks. It is worth here to mention the first generation DVB-C to know the significant difference between those two generations. DVB-C works on 8MHZ channel with a maximum data rate 38.1 Mbit/s using MPEG2-TS is transmitted using single carrier QAM modulation which need channel coding. In spring of 2009 DVB-C2 was released as draft with a significant difference in terms of spectrum efficiency of 30% greater than DVB-C. The increase of the spectrum efficiency came from the innovative modulation and coding techniques used in the 2 nd generation. Moving to DVB-C2 a 4096 QAM modulation scheme can be used and a bit rate of 81 Mbit/s can be achieved on 8MHZ channel. 4

As mentioned above; this spectrum efficiency is achieved because of new modulation and coding, in DVB-C the modulation scheme is from 16QAM up to 256QAM modulation scheme with maximum bit rate 38 Mbit/s using the 256QAM. In DVB-C2 the modulation scheme is from 16QAM up to 4096QAM [ 3 ]. The modulation it changed from single carrier QAM to COFDM in DVB-C2. In DVB-C a single MPEG2 transport stream (MPEG-2-TS) is used as input signal; in DVB-C2 a multiple (MPEG-2-TS) is used as input signal to its modulator as well as generic stream encapsulation. In DVB-C2 it is possible to combine several 8 or 6 MHZ wide channels to form channel groups; avoiding the gap between channels, increasing by this the effectiveness of the spectrum. DVB-T2 DVB-T2 is the second generation of the digital video-broadcasting standard for terrestrials. DVB-T2 supports HDTV services which have been first lunched in UK; and as the previous two technologies (DVB-C2 & DVB-S2) DVB-T2 provides 30% capacity increase more than DVB-T. The difference between the two technologies is in the modulation and channel coding techniques used in the terrestrials 2 nd generation. Both of terrestrial generations use COFDM (coded orthogonal frequency division multiplexing) modulation. In DVB-S there are two carrier modes (2k and 8k) these numbers is the FFT size used to produce multi carrier signals where both amplitude and phase are modulated by data. The highest modulation scheme available in DVB-T is 64QAM which can carry 6 bits /carrier/symbol (per data cell). In terms of forward error correction DVB-T uses reed Solomon and convolutional coding. In DVB-S2 the carrier modes (FFT sizes) are up to 32K. Where both amplitude and phase of each carrier is modulated by data. DVB-S2 uses higher QAM mode (256QAM) than DVB-T. In 256- QAM which carries 8 bits per data-cell [ 4 ]. The 256QAM constellation are more sensitive to errors produced by noise therefore an enhanced forward error correction is implemented in the terrestrial 2 nd generation to maintain the minimum 30% capacity increase using low density parity check correction codes( LDPC). Input signal is another difference between those terrestrial generations. DVB- T enables single MPEG-TS while in DVB-T2 it enables single, multiple MPEG2-TS or generic streams (GS). 5

Transmission analysis Comparison between the three technologies DVB-S2, DVB-T2, DVB-C2. This 3 technologies have many things in common but they also have some different things because they are simply different as exposed above. One good way to present that similarities but also the differences is with a use of a table. DVB-S2 DVB-T2 DVB-C2 Imput Interface TS and GSE TS and GSE TS and GSE Modes VS & Modulation and AC & Modulation VS & Modulation VS & Modulation and AC & Modulation Foward Correction Error LDPC + BCH LDPC + BCH LDPC + BCH Modulation QPSK OFDM COFDM Modulation Schemes QPSK, 8PSK, 16APSK, 32APSK 16QAM, 256QAM 64QAM, 16- to 4096-QAM 1/4, 19/256, 1/8, Guard Interval none 19/128, 1/16, 1/32, 1/64 or 1/128 1/128 Interleaving Bit-Interleaving Bit- Time- and Frequency- Interleaving Bit- Time- and Frequency- Interleaving Table 1: Compiled by the Authors but inspired in Walter Fischer, Digital Video and Audio Broadcasting and Laurent Roullet, DVB BlueBook A148 6

Input Interface GSE Also known as Generic Stream Encapsulation is the data link layer protocol that DVB uses. GSE is important because allows that packeted oriented protocols like IP to be carried in the network. TS or Transport Stream is a standard transmit audio and video is commonly used in several broadcasting technologies. Like DVB and IPTV. The container used is the MPEG and can be also used for storage. Is very good to do this job because has error correction and stream synchronization features that help in maintaining transmission when the QOS signal is degraded. The input interface are common to the 3 technologies. Modes VC&M also Known as Variable Coding & Modulation like Adaptive Coding & Modulation (AC&M) are techniques that can be associated with DVB standard. VCM provides already different levels of error correction to many components within the DVB service. But ACM goes further and extends VCM does this giving the opportunity to the receiver provide feedback to the transmitter, this feature allows the level of error protection to vary dynamically in accordance with varying propagation conditions [ 5 ]. In the table is also possible to notice that ACM (Adaptive Coding & Modulation) is used in DVB-S2 and also in DVB-C2 but not in DVB -TS and the reason why is that for ACM be possible the end user as to send feedback to the source so the quality of the image can be scaled up or down, but the users that are receiving Terrestrial TV (DVB-TS) through their atenas don t have means to send a feedback so is impossible to apply this mode in DVB-TS. FEC FEC or Forward Error correction is a very important service to archive a good quality of service, especially in noisy channels. It can be done in Upper level (IP and Application) and also in the low Level (Physical level). But in this case we will focus in the low level correction. FEC codes that are adopted in DVB standards are [ 6 ]: Convolutional codes in DVB-T/H. Turbo-codes in DVB-SH. 7

Low-Density-Parity-Check (LDPC) codes in DVB-S2, DVB-T2 and DVB-C2. In the second generation of DVB the LDPC code started to be used to improve the quality of the service. Now quoting the same article [ 7 ]. It should be pointed out that convolutional and LPDC codes are concatenated in the physical layer with an additional (outer) FEC block code with an interleaver in-between. In particular, the convolutional code adopted in DVB-T/H is concatenated with a Reed- Solomon (RS) code to correct physical layer MPEG-2 Transport Stream (TS) packets with only few erroneous bytes, and the LDPC code adopted in DVB-S2/T2 is concatenated with a BCH (Bose- Chaudhuri-Hochquenghem) code to remove the error floor produced by the LDPC at low bit error rates. These codes are not considered as upper layer FEC as they are an integral part of the physical layer FEC. Modulation Modulation is another element that is very relevant when analyzing this three different ways to carry TV to the costumers. In Modulation DVB-S2 uses QPSK or Quadrature Phase Shift Keying, DVB-T2 uses OFDM or Orthogonal Frequency Division Multiplexing, DVB-C2 uses COFDM or Coded Orthogonal Frequency Division Multiplexing. Putting in a nutshell means that QPSK different Phase phases to carry it information same time and OFDM and COFDM use different frequencies. The best way to understand how it works is by visualizing: 8

QPSK Figure 1: Source www.propagation.gatech.edu With this image is very easy to understand how the QPSK is able to carry four different signals same time. Using different phases to do it. OFDM Figure 2: Source http://www.ni.com/white-paper/3740/en/ In this Shows the areas in frequency that carry each signal and in between there is a guard interval to make use the signals don't mix with each other. 9

COFDM *Figure 3: http://www.st-andrews.ac.uk/ Very similar to the one before but uses also code to enhance the quality of the output. Modulation Schemes DVB-S2 uses QPSK, 8PSK, 16APSK, 32APSK and putting in a nutshell means the number of keys that they use to transmit some Information. QPSK would be 4 keys and 32APSK 32 keys. The same thing Happens with the DVB-t2 and DVB-C2. Where the first ranges from 16QAM to 256QAM which in very simple terms means how many symbols it uses to carry/code Information, In DVB-C2 works the same way but it can range until 4096QAM. Guard Interval Is used in DVB-T2 and DVB-C2 in between the signals and the reason behind it is that makes the signals more reliable because it creates a buffer zone between them. Can be seen in figure 2. 10

Interleaving Interleaving is a method used to improve the experience of the users that have slow connections or are experience that temporarily. So the user in the worst case scenario will receive a degraded version of the picture that is better than no image. Interleaving is used with forward error correction to improve its performance. What interleaving does is shuffling the source message across several words and by doing that creating a uniform distribution of the error between all of them In DVB-S2 is used bit interleaving which means that grabs some bits shuffle them and send them in the other side they are reconstructed. In DVB-T2 and DVB-C2 when shuffling is not only a stream of bits that is shuffled it also takes in account Time and frequency. To give an example in the first one would start let s say with 100 bits and send all odds then all pairs. With time and frequency would send for example 1 Bit 10 in 10 from different frequencies and then all odds and all pairs. Internet Television (IPTV) Internet Protocol Television (IPTV) is a digital television delivered on the television set throughout the Internet connection. The delivery of content required high speed internet connection (broadband). Normally the delivery channels are encoded in IP format and deliver to the TV through a set top box. Live television, video on demand (VOD) and interactive TV (itv) are the services also included in IP television. The IP TV services are delivered across and access agnostic, packet switched network that employs the IP protocol to transport the audio, video and control signals. The Architecture IPTV architecture have many different types, a high-level architecture where they comprise four key blocks, each one with particular functions and interdependencies. Content providers form the first blocks of figure. These could be number of sources depend on context. IPTV service provider forms the second block. These are responsible for sourcing content. The network providers are responsible for delivering configuration, status, update and control information from IPTV. The subscriber are the last element of the infortune, they have special equipment configured to received, interpret and display the content send by IPTV service providers [ 8 ]. 11

Service types: The most commonly offered service in IPTV is inclusion of content broadcast and VoD or perhaps games for new generation. VoD and PPV (Pay-perview) are the premium content sent directly by IPTV to end-users [ 9 ]. * Figure 4:High-Level IPTV Architecture (white paper, cisco.com) Functional Architecture for IPTV The environment of IPTV can be divided by basic elements. This provides a functional architectures view that allows segregation of duties and specialization. Content provision, content delivery, IPTV control, IPTV transport, Subscriber and Security functions are the main attributes. * Figure 5: book by Ramirez, David, IPTV security, 2008 Infrastructure: A simple IPTV consist of three major building blocks;! Content acquisition! Content distribution! Content consumption 12

Constructed in a hierarchy of nation, regional, local coverage to consumer premises. Each part is implemented with different elements and must be able to expand when needed. *Figure 6: A simple IPTV system (Source: Heather Yu, Huawei technologies) Acquisition server (A-Server) which encode video and add DRM or metadata; Distribution Servers (D-server) handle caching and QoS ; Video-on-Demand (VoD) creators and servers which retain a library of encoded VoD movies to provide Video-on-Demand services; IP routers which route IP packets and provide fast reroute for failover; Residential gateways (GG); IP routers for bundled service at home and set-top boxes (STP), which receive video for TV. IPTV- Protocols Inter protocol Television includes the live TV as well as stored video service (VoD but these services require a broadband or wireless IP network connected to device to playback the request. The idea of IPTV is not yet standardized to insert video and audio streams into and MPEG-2 transport stream as said in MPEG-2 and MPEG-4 standards, and then transport that to transport stream in UDP and IP packets. 13

*Figure 7: IPTV protocols (sources: book DV&ABT) In the method specified as part of DVD-IP in ETS 102034 standard, the RTP (real time transport protocol) is additionally inserted between the transport stream and UDP layer. Comparison between IPTV and OTT Over The Top technology (OTT) and Internet Television (IP) both uses the Internet to deliver the content to end-users. Hence OTT use unmanaged Internet to reach the end users whereas IPTV uses a dedicated and managed network to reach their end-users. Dispute the same method of content delivery, OTT has been spread vey wisely and gaining the market in past couple of years with their relatively low cost services like Netflix, Hulu many mores. The best part of OTT is, the content delivery provide more freedom, convenience and empowerment for users in terms of direct relationship with viewers. Few key comparison of OTT and IPTV: Particulars OTT IPTV Network Topology Unicast (HTTP) Multicast and Unicast Quality of Service Works on Best-effort delivery Having control over quality of delivery Protocol HTTP, HLS (Apple), HDS (Adobe) Transport Steam, USP, connectionless protocol Key challenges Key benefits Non premium content, need to work on QoS, NO live events low-cost, Flexibility of content consumption and very portable Expensive, competing with cable, bandwidth and infrastructure Quality of Service and Quality of e Experience 14

IP Multimedia Subsystem (IMS) The IMS is an architectural framework for delivering IP multimedia services. The IP Multimedia subsystem was initially defined by 3GPP and 3GPP2 wireless working bodies [ 10 ]. The main aim of IMS is to provide new network architecture to enable the convergence of voice, data and multimedia service over an IP based network infrastructure. Multimedia services include real-time communication like speech, audio, video and text applications. The service is currently provided as best effort networks. In order for the IMS to support the sophisticated demand of the services there has to be some key mechanisms to be followed. The mechanism includes session negotiation and management, QoS and mobility management [ 11 ]. The main attribute of MIS are as listed below. Signaling in IP networks Layered Architectures of IMS Access Layer Transport Layer Session Control Layer Application Layer The Simple architecture of IMS *Figure 8: Source : Nashologu, Mlindi, Performance Optimization of IP multimedia Subsystem, 2010) 15

References: 1 Markus Hofmann and Leland Beaumont, Content Networking, 2005 2 Walter Fischer Digital Media and Broadcasting Technologies 2010 3 Walter Fischer Digital Media and Broadcasting Technologies 2010 4 Walter Fischer Digital Media and Broadcasting Technologies 2010 5 http://www.buydvb.net/blog/variable-coding-and-modulation-vcm-and-adaptive-coding-andmodulation-acm.html 6 Laurent Roullet, DVB BlueBook A148, 2010 7 Laurent Roullet, DVB BlueBook A148, 2010 8 Ramirez, David, IPTV security, 2008 9 Ramirez, David, IPTV security, 2008 10 Nashologu, Mlindi, Performance Optimization of IP multimedia Subsystem, 2010 11 Nashologu, Mlindi, Performance Optimization of IP multimedia Subsystem, 2010 16