How to Maximize the Reliability of a Cellular Bonding Solution
VSAT, WI-FI, OR CELLULAR?
In terms of reliability, VSAT has to be the leader because the operator will license a committed information rate segment to you. This is as good as having a private network link from you back to the target. VSAT will connect through the RJ45 to most cellmux. As soon as your location becomes mobile you either have to factor in a high-spec gimbal for your VSAT dish or you need to give up on VSAT and go cellular. In a few circumstances, Wi-Fi might be your best option, but there are many variables: competition for the upstream link, distance from the Wi-Fi antenna, and any variable interference such as a kitchen with a microwave or a neighbor downloading movies on a shared DSL link. Personally, I would never use Wi-Fi for a commercial uplink, even though it is the cheapest option. With VSAT you commit the money and you get the link you want, although you lack mobility and portability. With cellular you get mobility, you generally have more than enough capacity (or this sector would never have emerged) even though that capacity cannot be guaranteed, and with the multiple SIMs/cellular routes you effectively always have route diversity, which in turn gives you much better overall uptime -- something you don’t have with Wi-Fi (unless you pass it though a link-aggregation process).
LINE OF SIGHT
Obviously, in radio frequency models, the line of sight from the source to the destination is critical. While propagation means that radio can appear to pass through even solid walls, the reality is that at all times when operating cellmux you want to try to maintain a clear line of sight to the mast, tower, or satellite you are using to ensure maximum signal gain and thus maximum potential throughput. Large objects can cause shadows, but can also refract radio. Dense fog can be transparent to a radio link, and then within a few moments its temperature and density can change and it can suddenly appear as a solid wall to the radio link.
Antenna systems vary tremendously. Here the Mobile Viewpoint extender is being deployed—it provides significant height clearance, making it optimal for use in crowds.
This is something that often gets forgotten at live events: The presence of a crowd dramatically changes the radio frequency conditions of an event. People, who are largely made up of water, absorb a huge amount of radio signal, so sitting in a product booth in the middle of a crowded amphitheater you will probably find your signal when the stadium is full is considerably lower than when it was tested 2 hours before the doors opened. This is not the only problem that a crowd will cause. Crowds are increasingly heavy consumers of mobile data. Many check-ins on Facebook, accompanied with selfies, will flood over the local cellular networks throughout the event. As this reaches a peak, people will even start encoding their own video clips and uploading those too, and this puts the entire crowd in direct competition to the cellmux for available bandwidth. Today it is not broadly possible to buy guaranteed bandwidth over cellular networks. While the operators would probably love to sell it, it is a relatively marginal service compared to the cost of installing and leaving latent surplus capacity for the one day a year that a cellmux user wants to film a live event at that location.
Several cellmux vendors provide separate antenna systems that can be detached from the core unit and connected with a cable run. This can be useful -- for example, when you want to use the cellmux in a basement or inside a corporate building with a signal-blocking Faraday cage, since you can run the cable out to the antenna on the roof or other outdoor location. One vendor has a telescopic mount on its backpack unit that was initially designed to accommodate concerns by the operators that they had multiple microwave data services very close to their head. It turned out that by addressing this concern the vendor noted that in crowds the extra altitude of the antenna was giving significant signal gains, and so the model stuck.
Backhaul Data Signal Path
There is one final part to the story that needs to be examined carefully to understand all the different aspects of reliability for cellmux-based backhaul.
When you connect your smartphone to a data network, several layers of connection are enabled. Initially your carrier allows you to send and receive radio signals between the RF kit in the tower and your phone. Once you are authenticated at RF level to the mast network, your data service layer will authenticate with the operator’s access point name (APN). The APN is the equivalent to the dial up number you used to dial to get online years ago. The APN is where the operator authorizes you to connect the IP services on your phone to their IP network, and their IP network is then connected to the internet.
Obviously a large network operator will have hundreds of thousands of active sessions on an APN at any one time, and the traffic for these sessions is then connected through the operator’s peering to the rest of the internet. These routes will be busy, and they have a single common class of service. If a herd of users suddenly demands something, there is nothing to prevent the peering points from becoming congested, and so at best a cellmux will get a best effort signal and at worst it can simply time out. While these circumstances are rare, they are a risk -- the cycling final of the 2012 Olympics was hit with an outage that was largely blamed on users tweeting photos of the finish, but was in fact much more likely to be the local saturation of the networks by probably 20 or 30 cellmux operators.
The network location of the demuxer is as critical as the field kit. Here’s the AVIWEST DMNG 1RU Demux in action.
The best way to operate your cellmux is to connect it to the internet using an alternative APN provider. These operators allow you to authorize on their APN, and since these providers offer a boutique service to broadcasters, their APNs are often directly peered to the target broadcaster’s network, or at least their ISP, and have limits on the number of users. While this doesn’t help the issue of backhaul contention between the cellmux and the operator (via the tower and its fiber back to the network core) this capacity is often quite abundant. The bigger issue is the connection from the operator to the internet, and an alternative APN provider can really help you address this issue. Also, because the alternative APN is an internet service, this means you can centralize your data path billing with them, while leaving the carrier activation to your locally purchased SIM cards.
As you can see, there are many variables to tune in the cellmux game, and it goes much deeper than it might first appear. It is impossible to guarantee service over cellular or Wi-Fi, but since these devices work well with VSAT systems, that option should be your first port of call when you are looking for reliability. Once you move to cellular, explore alternative APNs; make sure you know your location, weather, and crowd dynamics; and test the workflow as hard and in as many ways as you can before you go to shoot.
And when you can, get that antenna up as high as possible.
This article appears in the September 2014 issue of Streaming Media as "How to Maximize the Reliability of Your Cellular Bonding Solution."
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