Networks and Protocols
The television signal that we can see in our living room, after being generated in a TV studio or in an external shooting site, in order to reach our TV set, makes use of a rather complex and articulated telecommunications network. Broadcasting from the closest TV transmitter represents only the last part of this network.
These transport networks may use a plurality of transmission means (e.g., optical fibers, radio links, satellite links, etc.).
TV contribution is the transport of the high-quality video signal, in point-to-point or point-to-multipoint modality, from the shooting site to the TV studio, where further processing can be made, while TV distribution is the permanent transport of the TV signals towards the end users, from the central head-end (in Rome) to all transmitters located throughout the country, to the satellite uplink station and to the servers for the distribution on the Internet.
Rai uses an extensive nation-wide contribution and distribution network in SDH technology, own and operated by Rai Way, based on radio links and optical fibres. The Research Center has been active for years in close co-operation with Rai Way in the study of the technological developments of this network, such as the NG SDH technology, which allowed to increase its flexibility.
Looking ahead, thanks to the growing availability of IP (Internet Protocol) technology also in the context of video transport, television operators will tend more and more to use IP technologynot only for direct distribution to the end users on the web (in OTT modality), but also on contribution networks, over long distance fiber optic links and on wireless connections (eg. WiFi, WiMAX, 4G/5G), with the advantage of promoting the convergence of all the connectivity needs towards a single network. More recently, IP technology applied to real-time video distribution has begun to find its place also inside the TV studios, where it is likely that it will gradually replace current traditional video switchers.
However, the use of these IP networks, originally designed for transporting data traffic, makes it essential to consider also the aspects relevant to the Quality of Service (QoS) of the transported audio/video streams.
Rai-CRIT actively participates in these activities, in collaboration with ICT and TV Production Departments and with national and international (EBU) working groups, in order to explore opportunities and limitations offered by IP technology. In particular, we should distinguish between “managed” networks, where the network operator takes the responsibility of ensuring the required QoS by implementing specific technologies (e.g., MPLS), and “unmanaged” networks, which can are anyway fit for the distribution to the end user on condition that specific transmission protocols are used.
TV signals on ultra-wideband optical fibre networks
Optical fibres are now increasingly popular in telecommunications, due to their extremely high bandwidth, their very low attenuation, their complete immunity to electromagnetic interference and their reduced diameter and weight.
For these reasons, they are playing an increasing role in trasporting TV content, both for in-building TV signal distribution within the multi-service optical infrastructure, which is mandated in all new buildings (Italian Law 164, 2014) and for TV consumption via broadband networks, which will benefit from ongoing investments in FTTH (Fiber to The Home) architectures, where the fibre is terminated at each building. In Italy, network operators are launching massive optical fiber investment plans over the next five years, not only to cover the most densely populated areas (A and B) but also for less profitable areas (C and D).
New DVB technology to serve satellite customers and to feed terrestrial transmitters
Today, the satellite distribution of DVB-T2 multiplexes to terrestrial transmitters located throughout the territory requires dedicated transponders for the transport of the relevant T2-MI (Modulator Interface) streams, which are not directly accessible also for direct-to-home reception by standard satellite receivers. This causes duplication of the needed satellite bandwidth, with the associated costs. To overcome this problem, DVB (Digital Video Broadcasting) has activated a new ad-hoc group, named TM-T-JSI, with the purpose of defining an optimized way to transport DVB-T/T2 multiplexes from a national head-end to the terrestrial transmitters, while allowing at the same time direct reception via DVB-S/S2 commercial satellite receivers.
TV over the Internet: OTT (Over The Top) distribution of audio/video content
Today, TV content can be distributed via Internet as OTT (Over The Top) delivery, allowing to expand the traditional offer with on-demand services. As the QoS (Quality of Service) cannot be guaranteed on the Internet as on a private IP network, during the years specific network architectures have been designed and developed (CDN: Content Distribution Network) and adaptive streaming protocols (ABR: Adaptive Bit-Rate), in order to optimise the data stream according to the broadband connection and the kind o terminal associated to each user.
ESA SCORSESE Project
Satellite supporting CDNs for the distribution of OTT services
The integration of terrestrial and satellite telecommunication networks will allow the widespread distribution of OTT contents, offloading the CDN backbone during traffic peaks, for the benefit of the effective picture quality perceived by the users.
Experimental activity (completed)
Experimentation of the coexistence of PMSE services and LTE in the 2.3-2.4 GHz band
The growing demand for transmission capacity for mobile access has led in recent years public administrations to consider new ways of spectrum management, which include sharing between different services and operators. At the invitation of the Italian Ministry of Economic Development we have participated and contributed to a field experiment aimed at assessing the problems of interference eventually suffered by PMSE services (wireless cameras for TV production) by LTE services in the 2.3-2.4 GHz band.