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

  • VITEC IPTV Digital Wall and Digital Signage Platform at ISE 2019

    VITEC IPTV Digital Wall and Digital Signage Platform at ISE 2019

  • VITEC EZ TV IPTV and Digital Signage Platform at NAB 2019

    VITEC EZ TV IPTV and Digital Signage Platform at NAB 2019

  • 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

  • Ki Pro GO - Multi-Channel H.264 Recorder from AJA at NAB 2019

    Ki Pro GO - Multi-Channel H.264 Recorder from AJA at NAB 2019

  • 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

  • Sony HXR-MC88 palm-sized camcorder shown plus UWP series wireless transmission at NAB 2019

    Sony HXR-MC88 palm-sized camcorder shown plus UWP series wireless transmission at NAB 2019

  • Wireless 4k transmission from BOXX TV at NAB 2019

    Wireless 4k transmission from BOXX TV at NAB 2019

  • 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
Original KVM or KVM over IP
Jochen Bauer Will the technology used in broadcasting solely consist of IP devices? For years, IP has been entering all areas of life. Especially control room applications as they are typically deployed in broadcasting benefit from the IP revolution in many ways. But an “IP-only broadcast world” is not yet here. Nevertheless, the trend clearly moves towards IP transmission, even though a large part of content production still uses traditional transmission paths. And therefore we continue to live in a hybrid world, using both original and IP-based technology. KVM experts Guntermann und Drunck still rely on both original KVM and KVM-over-IP™ to be able to offer their customers the best of both worlds.
Tags: iss139 | kvm | gdsys | guntermann and drunck | kvm-over-ip | Jochen Bauer
Contributing Author Jochen Bauer Click to read or download PDF
Keeping the Show on the Road
Andy McKenzie There is long-established saying in the media business that, if something goes wrong, at least nobody dies. It is almost true unless you happen to be a TV producer suffering a cardiac arrest because your primary video feed has gone blank during a high-budget programme.
Tags: iss139 | service | support | finepoint | maintenance | Andy McKenzie
Contributing Author Andy McKenzie Click to read or download PDF
Why MADI is Still Relevant
Stephen Brownsill While the original idea for MADI was to cater to a very narrow recording studio application, the standard remains a viable go-to multichannel audio technology. Beginning as a standard in 1991, MADI was first introduced to the world as digital production was beginning to come of age. MADI was put together in 1988 by Solid State Logic, AMS-Neve, Sony (DASH) and Mitsubishi (ProDigi) as a way to transport up to 56 channels of digital audio between large-format audio consoles of the day and digital multi-channel tape machines via 75-Ohm coaxial cables. Both tape-based machines have long since disappeared from the equipment landscape.
Tags: iss139 | madi | tsl products | aes10 | aes | dolby atmos | st-2110 | sam-q | Stephen Brownsill
Contributing Author Stephen Brownsill Click to read or download PDF
The Future of Broadcast Connectivity
Jamie Adkin The use of KVM equipment has been essential to meet the evolving needs of the broadcast industry for many years. Over that time, many in the industry have recognised the importance of using IP-enabled KVM to break down technological barriers and enable real-time access to visuals wherever and whenever they’re needed. These components are vital parts in live production environments in particular.
Tags: iss139 | adder | kvm | ip kvm | Jamie Adkin
Contributing Author Jamie Adkin Click to read or download PDF
Keeping Pace with the Content Revolution
Kevin Fitzgerald These are uniquely challenging times for broadcasters and their technical teams. Not only are they having to negotiate the move to IP-based infrastructures and the introduction of new formats and techniques such as 4K and HDR, they are also having to generate more content than ever before to support OTT and web services as well as traditional linear broadcast.
Tags: iss139 | streamstar | streaming | case 800 | ipx | ipx-3g | Kevin Fitzgerald
Contributing Author Kevin Fitzgerald Click to read or download PDF