A Guide to Testing IPTV: Technologies and Challenges Part 3


Before we can go on to look at testing IPTV systems, it would be useful to provide an overview of the technologies involved.
Network Architectures
Figure 3 shows an example of a typical IP network structure. Content is first delivered into the video headend; this can be done in a variety of formats over a number of different delivery mechanisms (e.g. satellite and terrestrial). From here, the data are encoded, packetised, and multiplexed appropriately for receipt by the consumer premises equipment (normally in the form of an MPEG Transport Stream) and are then sent to the Core Network which is used for the transmission of services at a national (or even global) level. The system services (voice, video and data) are then passed to the Access Network for distribution over the “last mile” to the consumer.
A variety of access network technologies (such as xDSL, HFC and FTTx) can be used to reach the subscriber; the type of technology used will depend on what sort of connectivity is required at the subscriber site. All of these additional technologies add complexity to the distribution models, and bandwidth may need to be carefully managed to ensure good QoS and QoE for the subscribers.
Video Compression Technologies
Earlier in the series we explained that insufficient bandwidth over an IPTV network can lead to “bursty” video delivery. One way to alleviate bandwidth restrictions is to use video compression technologies.
MPEG-2 encoding, H.264/AVC and VC-1
MPEG-2 encoding compresses the video frames into three different types of frames: I-frames, B-frames, and P-frames. An I-frame contains all the information in one frame of the video stream such that an MPEG decoder can recreate the original frame using only the information from the I-frame. To achieve the required video compression, special spatial and temporal encoding techniques are used to create B- and P-frames that contain partial information associated with the I-frame. The picture is recreated using the I-frame and the compressed information in the B and P-frames
These I-, B- and P-frames are carried across the network in 188 byte MPEG Transport Stream (TS) packets which are encapsulated in IP packets (a single IP packet contains approximately seven TS packets). Dropping any packet (particularly those containing I-frames) can lead to serious QoE issues.
The use of new compression technologies such as H.264/AVC or VC-1 can further reduce bandwidth usage; H.264, for example, can offer up to a 50% reduction in bandwidth utilisation for the same picture quality compared to existing MPEG-2 compression. These new technologies can, however, render video streams more susceptible to dropped packets (as each packet effectively contains more information). Clearly this will have a greater impact on the viewing experience.
Transmission across an IP Network
There are many different protocols used in modern IPTV systems to govern the transmission of voice, video and data services across the network. In this article we will consider four:
  • UDP and RTP (IP transmission protocols)
  • RTSP and IGMP (signalling protocols)
First, however, we should look at the basic structure of an IP packet.
IP Packets / Datagrams: Structure
The term ‘datagram’ or ‘packet’ is used to describe a chunk of IP data. Each IP datagram contains a specific set of fields in a specific order so that any receiver knows how to decode the data stream. Many protocols can be encapsulated within the IP packet.
Network Protocols
UDP (User Datagram Protocol)
UDP is one of the core protocols of the IP protocol suite. The datagram headers contain:
- 16 bit source port address.
- 16 bit destination port address.
- 16 bit length field.
- 16 bit checksum.
UDP requires a relatively small overhead compared with the amount of data in the payload. This simplicity is one of the main advantages of UDP, however it can also cause difficulties. For example its stateless form means there is no way to know whether a sent datagram ever arrives, and there are no reliability or flow control guarantees which can identify lost packets and re-send them as necessary.
UDP has been described as a ‘fire and forget’ protocol because it is difficult to discover if a packet has been lost before the subscriber does. In an IPTV environment, where it is essential that the video data is delivered reliably and in the correct sequence, the use of UDP can be precarious.
RTP (Real Time Protocol)
RTP describes a packet-based format for the delivery of audio and video data. RTP actually consists of two closely linked parts:
  • Real Time Protocol provides time stamping, sequence numbering, and other mechanisms to take care of timing issues. Through these mechanisms, RTP provides end-to-end transport for real-time data over a network. Use of sequence numbering also enables lost or out of order packets to be identified.
  • Real Time Control Protocol is used to get end-to-end monitoring data, delivery information, and QoS.
It should be noted however that while RTP allows lost packets to be identified, it does not define any mechanisms for recovering from such packet loss.
RTSP (Real Time Streaming Protocol)
RTSP describes a set of VCR-like controls for streaming media. Typically, RTSP messages are sent from client to server, although some exceptions exist where the server will send to the client.
In IPTV systems, RTSP is used in VoD applications for the consumer to access and control content stored at the VoD servers. VoD is essentially a one-to-one communication established using unicast.
IGMP (Internet Group Management Protocol)
IP multicasting involves the simultaneous delivery of an IP datagram to a set of subscribers who wish to receive a particular program (a “host group”).
IGMP is the protocol used to handle channel changes in an IPTV system. In response to remote control commands, a series of IGMP commands to leave the current multicast and join a different service are issued. The time that it takes to execute these commands has a direct impact on channel change times.
Multicasting, using IGMP, allows control of which content goes to which users and therefore controls the amount of data being sent across the network at any one time.
***
This article gives only a brief overview of some of the technologies involved in the delivery of IPTV services; however even this “bird’s-eye view” plainly demonstrates the degree of complexity inherent in IPTV systems. Clearly, this complexity will present many technical challenges for service providers when trying to meet the stringent QoS and QoE requirements needed for successful IPTV delivery.
In the next part, we will begin to discuss how we can test IPTV systems.

Tags: tektronix | iss033 | iptv | test and measurement | network architecture | video compression | mpeg-2 encoding | h.264 | avc | vc-1 | ip network | transmission | rtp | N/A
Contributing Author N/A

Article Copyright tv-bay limited. All trademarks recognised.
Reproduction of the content strictly prohibited without written consent.

Related Interviews
  • Tektronix at IBC2011

    Tektronix at IBC2011

  • Tektronix at IBC 2016

    Tektronix at IBC 2016

  • Tektronix at IBC 2015

    Tektronix at IBC 2015

  • Tektronix at IBC 2014

    Tektronix at IBC 2014

  • Tektronix at IBC 2013

    Tektronix at IBC 2013

  • IPTV Digital Signage from VITEC at NAB 2017

    IPTV Digital Signage from VITEC at NAB 2017

  • Elemental Technologies news at IBC 2015

    Elemental Technologies news at IBC 2015

  • Thomson Video Networks at IBC 2014

    Thomson Video Networks at IBC 2014

  • BBright at IBC 2014

    BBright at IBC 2014

  • Viaccess-Orca at IBC 2014

    Viaccess-Orca at IBC 2014

  • Perception at NAB 2014

    Perception at NAB 2014

  • Elemental Technologies Software-Defined Video at NAB 2014

    Elemental Technologies Software-Defined Video at NAB 2014

  • Elemental Technologies HEVC solutions at NAB 2014

    Elemental Technologies HEVC solutions at NAB 2014

  • Elemental Technologies Multiscreen Solutions at NAB 2014

    Elemental Technologies Multiscreen Solutions at NAB 2014

  • Haivision on BroadcastShow LIVE at IBC 2013

    Haivision on BroadcastShow LIVE at IBC 2013

  • Albis Technologies celebrating ten years at IBC 2013

    Albis Technologies celebrating ten years at IBC 2013

  • Bridge Technologies QoE Monitoring with Mobile Videowall Display at IBC 2013

    Bridge Technologies QoE Monitoring with Mobile Videowall Display at IBC 2013

  • Visionary Solutions at NAB 2013

    Visionary Solutions at NAB 2013

  • Telestream Vantage v5 at NAB 2013

    Telestream Vantage v5 at NAB 2013

  • Visionary Solutions at NAB 2012

    Visionary Solutions at NAB 2012

  • Phabrix RX2000 at NAB 2013

    Phabrix RX2000 at NAB 2013

  • Phabrix at BVE 2012

    Phabrix at BVE 2012

  • Sencore at IBC2011

    Sencore at IBC2011

  • Leader at IBC2011

    Leader at IBC2011

  • Murraypro at IBC2011

    Murraypro at IBC2011

  • Hamlet at IBC2011

    Hamlet at IBC2011

  • Phabrix at IBC2011

    Phabrix at IBC2011

  • Thomson Video Networks at IBC 2015

    Thomson Video Networks at IBC 2015

  • ATEME at NAB 2014

    ATEME at NAB 2014

  • ATEME at IBC 2013

    ATEME at IBC 2013

  • Video Devices PIX-E at IBC 2016

    Video Devices PIX-E at IBC 2016

  • Sound Devices Wingman app at IBC 2016

    Sound Devices Wingman app at IBC 2016

  • Matrox at IBC 2015

    Matrox at IBC 2015

  • JVC GY-HM850 and GY-HM650 at NAB 2014

    JVC GY-HM850 and GY-HM650 at NAB 2014

  • Telestream at NAB 2012

    Telestream at NAB 2012

  • JVC at BVE 2012

    JVC at BVE 2012

  • Hireacamera at ProVideo2011

    Hireacamera at ProVideo2011

  • Boxx TV Wireless Transmission with Meridian, Atom and Zenith on show at IBC 2017

    Boxx TV Wireless Transmission with Meridian, Atom and Zenith on show at IBC 2017

  • Facility Management Software from Xytech at NAB 2017

    Facility Management Software from Xytech at NAB 2017

  • Dejero at IBC 2016

    Dejero at IBC 2016

  • Guntermann and Drunck at IBC 2015

    Guntermann and Drunck at IBC 2015

  • PacTV Truck at NAB 2014

    PacTV Truck at NAB 2014

  • Thomson Broadcast at NAB 2014

    Thomson Broadcast at NAB 2014

  • Dejero on BroadcastShow LIVE at IBC 2013

    Dejero on BroadcastShow LIVE at IBC 2013

  • SIS LIVEs Martyn Hopkins on BroadcastShow LIVE at IBC 2013

    SIS LIVEs Martyn Hopkins on BroadcastShow LIVE at IBC 2013

  • Cobham on BroadcastShow LIVE at IBC 2013

    Cobham on BroadcastShow LIVE at IBC 2013

  • Guntermann and Drunck CrossDisplay switching and CCD at IBC 2013

    Guntermann and Drunck CrossDisplay switching and CCD at IBC 2013

  • SIS Live at IBC 2012 Part Two

    SIS Live at IBC 2012 Part Two

  • SIS Live at IBC 2012 Part One

    SIS Live at IBC 2012 Part One

  • Thomson Broadcast at IBC2011

    Thomson Broadcast at IBC2011


Related Shows
  • Content you want, when you want it: Recommendation Engines

    Content you want, when you want it: Recommendation Engines


Articles
The Biggest Toy Shop in the World
Emma Morrison When Nigel Woodford started his career at BBC Wood Norton in 1962, television was black and white and BBC Two had not yet been launched. In 2018 Nigel will retire, and Richmond Film Services, the pro-audio equipment rental company set up by Nigel in 1973, can count numerous contributions to iconic moments in British cultural, sporting and film history over this time.
Tags: iss133 | richmond film services | audio rental | auction | liquidity | go-dove | Emma Morrison
Contributing Author Emma Morrison Click to read or download PDF
Ride along on the Tour de Tech at IBC
Lorna Garrett Finding your way through the halls and aisles of the massive IBC can feel a bit like attempting to complete all 21 stages of the Tour de France — but in far fewer days. But have no fear; your team at Garland is all geared up and ready to show you the best on show at this year's exhibition.
Tags: iss133 | garland | liveu | lu600 | media excel | teracue | wisi | broadcast wireless systems | bws | artel | ibc | Lorna Garrett
Contributing Author Lorna Garrett Click to read or download PDF
Creating Authentic Content That Counts
Frank le Mair We’re deep into the 2010’s and the way in which we consume content has changed forever. Broadcasters and content owners are fighting for eyeballs in a saturated market where consumers are watching their favourite shows on different devices across a number of platforms. To target millennials and younger generations, who generally consume short bursts of video on YouTube and social media - particularly Snapchat, Instagram and now IGTV - media companies are creating more and more authentic stories and are using platforms that are compelling for this demographic. Unlike generations before them, they have totally new video viewing patterns and ideals.
Tags: iss133 | insight tv | monster energy | amazon | millennial | Frank le Mair
Contributing Author Frank le Mair Click to read or download PDF
Peli Air 1507 Review
Phil Vinter Originally named after a bird that carries its precious cargo through the skies, it was, perhaps, only a matter of time before Peli released its Air range.
Tags: iss133 | peli | peli air 1507 | trekpak | Phil Vinter
Contributing Author Phil Vinter Click to read or download PDF
The Pace of Change
Dick Hobbs - new

The youngest human to stand on the moon (so far) was Charles Moss, the lunar module pilot of Apollo 16. Charlie had a wonderful claim: his father witnessed the Wright Brothers’ first flight at Kitty Hawk, and lived to see his son on the moon.

Does anything capture the speed of technological advance better than that? The whole of the history of powered flight in one lifetime.

Tags: iss133 | state of the nation | st2110 | st2110-10 | Dick Hobbs - new
Contributing Author Dick Hobbs - new Click to read or download PDF