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The importance of synchronisation when using PTP and remote production

Rafael Fonseca, VP of Product Management, Artel discusses some of the finer points of syncing using Precision Time Protocol in a remote production workflow

Conventional live production models require the team and equipment to be sent to the venue, and this can be costly in terms of both time and money. Travel is expensive not only because of the need to pay for transportation and lodging, but also because the human and technical resources are tied up for the duration and unavailable for any other production. As a result, you’re limiting the frequency and number of events you can produce.

Remote production solves many of these issues. While you still send a team to the venue, this team can be much smaller, allowing you to keep specialised staff and equipment in a central location, minimising its downtime and making it available to support multiple events throughout the day. In this past year, the emergence of Covid-19 has forced broadcasters to impose distancing measures for the safety of their employees, so the appeal of remote production has become even greater and the number of remote workflows that have been implemented has risen significantly. These circumstances, which have forced the specialised staff to be remote not only from the venue, but from each other, meant remote production models had to evolve quickly to rise to this new challenge.

The rise of IP technologies has made remote production possible, but where do the challenges lie?

IP is definitely a key enabler of remote production models as it supports the transport of both audio and video, as well as the data, communications, and control signals critical in the production environment. One of the major challenges arises when connecting two remote sites, each with its own media-over-IP infrastructure. To do this it is imperative to deploy IP switching technology that allows the Precision Time Protocol (PTP) implementation to preserve the timing and synchronisation across both sites. There are many switches available on the market, but to successfully synchronise your signals, these switches need to be PTP-aware. 

Can you explain a little more about PTP?

PTP specifies a methodology for synchronising devices to a single shared clock across packet-based networks (using SMPTE ST 2110 and AES67), including Ethernet switches and IP routers. PTP creates a common time base for multiple AV sources, and it enables synchronisation of device clocks to within nanoseconds, even across a large network.

How does this work across multiple remote sites?

One key factor to bear in mind is that PTP is sensitive to delay, so the best way to maintain synchronisation across the transport network connecting two sites is to deploy PTP generators at each site. Some facilities do continue to use SDI transport to sidestep this requirement, using IP solely for control, management, and monitoring, though more often this is a transitional phase implemented en route to a full IP solution. 

Each site would typically require a PTP generator, PTP-aware switching, and IP transport, with the resulting signal flow being: PTP Generator 1 — PTP-aware switching — IP transport — fibre — IP transport — PTP-aware switching — PTP Generator 2.

Why is it important that the switches are PTP-aware?

The PTP-aware Ethernet switches connect to the PTP generators and leverage their internal timing circuitry to minimise time drift and maintain highly accurate timing synchronisation. These PTP-aware switches also include integrated support for QoS and traffic management help to ensure signal reliability and integrity.

In that simple signal flow described previously, from PTP Generator 1 to PTP Generator 2, each PTP-aware switch could connect to an SDI-over-IP multifunction gateway, likely autosensing to support 3G, HD, and SD, with an integrated nonblocking Layer 2/3 switch. Ideally the gateway attaches to the IP network without the need for external network elements.

Even though the signal flow in this model is basic and the components install simply, this methodology can be easily expanded to more sophisticated environments. What is crucial is that synchronisation is maintained across multiple sites, ensuring proper handling of audio and video throughout live production. Now production teams can focus their time and energy on other aspects of creating a great show using a collaborative remote workflow without having to worry about technical issues such as synchronisation. The broadcaster and the viewers will benefit from this at-home production model, as it not only increases efficiency, but also frees up the expertise and technical resources so they can be dedicated to multiple live broadcast events.