Cellular Bonding & Streaming Video
This week, and at NAB2017, JVC Professional will be releasing the latest development in their continued focus on live acquisition streaming. The PB-CELL200 is a portable version of the ‘Bridge’ cellular bonding up-link products that have previously been announced for vehicle use. It works by combining multiple 3G/4G, WiFi and wired network signals, combining bandwidth, delivering improved resilience in case of failure and VPN security. It then makes this fast, reliable and safe link available to devices (ie. all your JVC Professional cameras) via a dual band WiFi hotspot, allowing you to deliver multiple video streams from the field to your BPL-380 Router and BR-D800 ProHD Broadcaster back at base.
Now, cellular bonding technology is by no means new, neither is it actually JVC’s – It is, as they state quite clearly, built around Peplink’s SpeedFusion – as are their other Bridge products and the BPL-380 Router above. It is also not likely to appear outside the US if history is any example. In and of itself, it isn’t all that exciting, particularly for those of us in Australia. What it does however, is segue nicely into a discussion on the technology in general.
Technologies like SpeedFusion (Viprinet is another that springs to mind) come at the cellular bonding world from the IT networking perspective. VPN’s for security, zero packet loss error correction, redundant link fail-over more so than aggregation of performance. As a result, latency tends NOT to be a major concern and if it takes a bit of time to get all of the data sent and put back together again, it is worth it to deliver data integrity. This is why, in live production, you will tend to see these products being targeted at ‘as live’ situations where back and forth discussion are not required. While these tools are great for streaming to a CDN, Facebook or Youtube, where 10sec is neither here nor there, a few second latency is just unacceptable in a live cross in a news broadcast.
Here, latency is king. In a live news interview, the video ideally needs to be back to the studio in fractions of second, so that the round trip discussion is not stuttering and to reduce interruptions. To do this, not only does the encoder and decoder need to be extremely efficient (potentially sacrificing quality over speed), the transport protocols need to be able to overcome some pretty big limitations in the transport mediums – those mediums being 3G/4G mobile broadband and WiFi.
These networks are notoriously unreliable. You just need to go for a walk with your mobile phone and see how dramatically your signal strength fluctuates to understand how susceptible link performance is to interference. Not only that, but they also have ZERO quality of service (QoS). This means that contention caused by over-subscription and population density around cell towers results in a huge amount of the sent data just getting ignored. Other than the receiving server eventually getting bored and asking for the data again, there is no way to know if and when the data has arrived. These ‘dropped packets’ don’t impact heavily on the average mobile phone user – odds are you can just refresh and all of a sudden things are fine again. In a live video stream however, it can mean the audio and video dropping out during vital breaking news reports.
This is where now familiar technologies such as TVU Networks (and Teradek Bond, LiveU, Dejero etc) step up. Using advanced forward error correction technologies, dynamic variable bit-rate encoding and clever link analysis, they are able to overcome this packet loss and performance fluctuation. In the case of TVU at least, they do not even technically use ‘bonding’, rather aggregating bandwidth by leveraging each connection independently, but still simultaneously. The technologies implemented in the background vary considerably and are quite complex, with the results in terms of comparative performance being open to debate. On the surface, however they are similar in a lot of ways.
Forward Error Correction (FEC), simply put, doesn’t wait to hear back from the receiver before re-sending packets that may have been dropped. Instead, it uses the the bandwidth and latency buffer available to keep sending packets repeatedly in the hope that one will make it. The receiver can then keep what it needs to to put the stream back together. The result (hopefully) being more of the stream getting through at the cost of using significantly more data – in some cases 2-3 times more (ie. a 10Mb/s stream would use 20-30Mb/s of data). Again, simply put.
Dynamic variable bit rate encoding in this sense is different to the ‘VBR’ encoding that you are possibly familiar with, which adapts bit rate to the complexity of the video being encoded. Working in conjunction with the link analysis, this dynamic variable encoding allows the encoder in the field to quickly adapt to situations where the performance of the networks is inadequate or fluctuating dramatically – whether through link failure or contention. If the links simply cannot sustain a 10Mb/s stream, the encoder will, in fractions of a second, dynamically change the bit rate of the encoder up and down as the performance dictates. This is important when it comes to quality. If you are encoding a 10Mb/s stream and half of it doesn’t make it, you end up with lost image and audio information that can render the stream unintelligible. However, if you change to a 5Mb/s stream on the fly, the image quality may soften, but it will not break up or drop out. This is a far better result in a live television or web stream situation.
To do all this, as well as encode and decode the video, with latency as low as 0.5sec is pretty impressive and the reason why these technologies are preferred in the news-gathering world.
That said, there are times and places for different approaches to data connectivity. The Peplink IT solution is likely to be more cost effective than the TVUPack solution. It is also likely to deliver data integrity monitoring and privacy/user management features that are required by your IT department. If what you need is an Internet connection in the field that is robust and secure, you will not be disappointed in a cellular/wireless bonding router like this. Configured correctly and used appropriately, they even make perfectly capable video streaming solutions, as seen in the JVC implementation. If, however, for you latency is king, they are not likely to deliver to the level that a specialised live video solution does.
There are a rapidly growing number of cellular bonding solutions and as wireless network technologies evolve to deliver better performance and reliability, so to do the technologies that rely on them. At NAB2017, we have already seen a number of new announcements, like HEVC/H.265 support across the board (more to come on that later), so if you’re confused by any of it, please do get in touch and have a chat!
Follow Broadcast Bruce
...on LinkedIn, Facebook, Twitter or wherever works to keep updated on industry announcements!
I am always looking to connect with industry professionals with a passion for the technologies and processes of video creation. If you are keen for a coffee and a chat about what you are seeing going on around you – some new technology or policy; its impact and implications – please feel free to reach out and connect. More ways to Contact Broadcast Bruce…