Why low cost wireless bridges can be false economy

On the face of it, 2 products can look very similar and when shopping around it is easy to just look at throughput and the maximum link distance when comparing 2 products

The reality is that this can be misleading, and the age old saying of "you get what you pay for" comes into play. I'm basing this on RRP and typical sell prices but of course this doesn't always ring true when paying for an installed link where the hardware information is vague… In short I've seen people quoting the installation of a consumer grade product for twice the price of its enterprise equivalent so ensure you know exactly what is being installed when considering a link. Insist on seeing some datasheets for the products!

When comparing consumer grade and enterprise grade links, some of the key differences that may not be spotted at first glance are;

  • Build quality
  • link availability
  • ethernet port speed
  • mean time between failure (mtbf)
  • realistic link distances

Build Quality: Often this is very difficult to establish unless you physically get hands on with the kit. If this is not possible then look at the materials the product is made of and the weight. Also any close up images you can see of the product. Are joined properly sealed, connections properly grommeted, brackets made of metal with good adjustment options. Does the hardware have a high IP rating to ensure that it is weather proof?

Link Availability: this is expressed in nines and refers to the expected uptime of the link. For example "3 nines" equals 99.9%, uptime and "5 nines" equals 99.999% uptime. This may not seem like a huge difference but it is. The table below shows the differences in expected downtime. As you can see, a link that offers "2 nines" can suffer almost 4 days of downtime a year whereas a link of "5 nines" will suffer only a maximum of 5.26 minutes. If a link doesn\'t quote a value (which most consumer grade kit doesn't) then the amount of possible downtime is any ones guess!

Availability % Downtime per year Downtime per month* Downtime per week
90% ("one nine") 36.5 days 72 hours 16.8 hours
95% 18.25 days 36 hours 8.4 hours
97% 10.96 days 21.6 hours 5.04 hours
98% 7.30 days 14.4 hours 3.36 hours
99% ("two nines") 3.65 days 7.20 hours 1.68 hours
99.5% 1.83 days 3.60 hours 50.4 minutes
99.8% 17.52 hours 86.23 minutes 20.16 minutes
99.9% ("three nines") 8.76 hours; 43.8 minutes 10.1 minutes
99.95% 4.38 hours 21.56 minutes 5.04 minutes
99.99%("four nines") 52.56 minutes 4.32 minutes 1.01 minutes
99.999% ("five nines") 5.26 minutes 25.9 seconds; 6.05 seconds
99.9999% ("six nines") 31.5 seconds 2.59 seconds 0.605 seconds
99.99999% ("seven nines") 3.15 seconds 0.259 seconds 0.0605 seconds

Ethernet port speed: cheaper kit may be limited by 100mbps ports giving you a bottleneck where more expensive kit will usually have 1gbps ports. For a lot of links, data flow is heavily weighted in 1 direction. If your link offers 200Mbps then it is a big bottleneck to limit this to 100Mbps as you are halving your potential throughput in that direction.

Mean Time Between Failure: If a manufacturer is confident in their product and has invested in the development, they will quote a mean time between failure which on the higher end kit will usually be 25 years or more. This is based on the expected lifetime of the components and various other factors but is a good indication that the product is sound.

The above hopefully gives you a little insight into why there is a justified price difference between consumer grade and enterprise grade hardware. Now to give you a scenario that should further strengthen the case for enterprise hardware, consider the following:

Company XYZ has 2 buildings which are joined by a wireless bridge. The servers and internet connectivity are only in building 1. In building 2 are 20 workers who all rely on access to the internet and server to carry out their jobs. The workers are paid £100/day each and generate the company on average £1,000 of revenue per day each. If the wireless link was to fail they could not do their job which would mean that for every day of downtime the company would be paying out £2,000 to workers who are not able to work and would be losing £20,000 of revenue. Now if the link being used is offering only "2 nines" then this is almost 4 days of potential downtime or £8,000 paid out to workers who cant work and £80,000 of lost revenue. When you consider that the initial investment to install enterprise kit over consumer kit may have been as little as £1,000 extra, it's a no brainer! Now the downtime quoted above is more likely to be small periods spread out over the year (e.g a few minutes here and there) but it still has the same accumulative effect of lost productivity.