The baseband paradox
The logic of leveraging networking hardware to distribute signals around a facility is becoming clearer. Network bandwidths now exceed those of baseband video, and the price point is hard to resist.
Signals over network hardware could ultimately replace all circuit switching electronics, disposing of a myriad of connecters and chipset standards.
Every year this tantalising thought is presented to us, but seems strangely out of reach. Baseband, in all its forms, has yet to be sent into the history books.
Baseband is simple and flexible
Part of the reluctance is that baseband maybe old, but inherently flexible and understandable. If networked signals are to succeed in entirely replacing baseband within a facility, they must at least emulate the essential functionality that baseband has now.
In baseband, signal delineation is simple. At different points, different versions of the signal are produced. Clean feeds would contain just the origin’s video signal. Other versions might contain graphics, digital video effects, subtitles etc., all created at separate stages.
Bypassing faulty equipment
Also signals over baseband can be easily traced and verified. A router, or baseband switch, allows bypassing of faulty equipment easily.
Low latency and timing
Of course, the major ability of baseband is to seamlessly switch predictable, very low latency signals frame accurately.
But surely the broadcast industry is utilising network technology for signal distribution today? At IBC this year there will be hundreds of stands promoting IP based solutions. SMPTE have created standards for this, SMPTE 2022 allows encapsulation of video over standard IP networks.
SMPTE 2022-6 and 7
Later extensions to the standard seem to have solved some of the remaining hurdles. SMPTE 2022-6, removes the impediment of MPEG compression and opens up uncompressed distribution.
SMPTE 2022-7 adds ‘Seamless Protection Switching’. This defines a way to send two identical streams over separate paths between sender and receiver, and switch seamlessly between them, ideal for path failure.
Inside the broadcast facility
SMPTE-2022 is perfect for video contribution, allowing multiple signals from a remote site to be sent to a broadcast facility for example. But is it the perfect solution for distribution inside a facility?
Bound to IP
Although there is nothing to stop SMPTE 2022 from being used within a facility per se. SMPTE 2022 is bound to IP, designed for IP based networks.
To open up the full potential of network hardware to replace baseband, we should look beyond IP.
‘IP’ might be the problem
In our industry, I often hear the word ‘IP’ used as a ‘catch-all’ term for anything which utilises network hardware. But there is a fundamental separation between the protocols on the network, and the network hardware itself. Networks are as flexible as the protocols that run upon them.
IP quick history
Networking was created by DARPA (Defense Advanced Research Projects Agency) an agency of the DoD (US Department of Defense) in the 1970’s. DARPA’s desire was to make better use of communication equipment. To this end, they created packet-switching technology. This broke messages into small datagrams and independently sent them over the new communication structure, called a network. This optimised the structure for multiple senders and receivers.
Get the Message
DARPA’s other priorities were scalability and pristine message reliably. A suite of protocols (software components that ran on the structure) were created to address this. This new protocol suite was named TCP/IP, after its two most famous components. IP, the addressing protocol, allowed nodes on the network to have a unique scalable identity. TCP, the transport protocol, ensured error free delivery.
So TCP/IP was created for a very particular purpose by DARPA.
AVB (Audio Video Bridging)
AVB (Audio Video Bridging) is an entirely new suite of protocols created by the IEEE for Ethernet hardware only.
The principles of packet-switching hardware have not really changed since the 1970s. The standards war however appears to have been won by Ethernet. This is fortunate for us, because we now have very fast and cheap hardware we can exploit.
AVB’s agenda is entirely different from TCP/IP’s. AVB has been designed purely to utilise Ethernet hardware to provide time sensitive, low latency, messages over the network.
AVB allows signal streams and control data to be delivered to multiple pre-defined timing planes on the switched network reliably. It can handle timing down to μs accuracy, traffic shaping (to avoid jitter) and admission control to ensure reserved and consistent bandwidth.
Currently, AVB is restricted to Ethernet switches and so cannot travel over IP routers. This effectively restricts it to a LAN (Local Area Network), but this is fine for replacing baseband within a broadcast facility.
Circuit switched emulation
AVB may now give us the chance to emulate the functionality of circuit switched hardware. Ethernet switches can act like baseband switching devices. Accurate timing can be achieved between different sources without the need for separate timing signal cables. Existing control systems could even switch AVB streams.
We can also make use of the inherent advantages of packet-switching, over and above the baseband emulation. For example, if a signal is present on a given Ethernet switch, it could be duplicated at that point and sent anywhere, avoiding the need to return to a central source like a router.
All over a single structure
In short we can use Ethernet hardware to replace all baseband hardware. Even computer processing nodes could be added to the LAN, mimicking baseband inserters and graphics devices.
A little bit of TCP/IP
AVB has nothing to do with TCP/IP. But networks are heterogeneous structures, which mean they are capable of handling different traffic with entirely different criteria.
In an AVB network the majority of the bandwidth is used for AVB data. But a portion of the bandwidth can be used for TCP/IP. The TCP/IP traffic does not impinge on the AVB bandwidth due to the design of AVB’s protocols.
Now a single structure can be used for signals and control, plus any extra IP data we might need.
In reality, networks are incredibly flexible. Some of the bad stories we hear about this technology are often down to the choice of protocols used.
The only time we need IP, is over an IP network. Within the boundaries of a building of facility, other protocol suites might be more suitable.
AVB is designed by the IEEE to deal with time specific messaging. If signals need to exit the facility, for content delivery for example, they can simply be converted to SMPTE 2022 using a computer processing node.