7 THINGS
YOU NEED TO KNOW
BEFORE YOU BUY A
TABLE
OF
CONTENTS
0 Introduction ... 2
1 Pick your Technology ... 2
2 Line Of Sight (LoS) ... 3
3 Distance ... 4
4 Speed ... 4
5 Build Quality ... 5
6 Weather and Reliability ... 6
7 Antennas ... 7
I
NTRODUCTION
Before you head out scouring the internet, here is some advice on what every shopper should know before flicking out their plastic to buy a wireless bridge.
Using a wireless bridge is a fast, cost effective and easy way to extend your network. They can produce amazing results, but they can also drive you crazy if you don’t have the right product for your needs.
This guide will help you make sense of all the jargon and have you connected in no time at all!
You will read information that doesn’t line up with other research you have done – that’s because we want to give you an honest expectation of what performance and reliability you will get from your wireless bridge. We’ve been involved in the sales and implementation of thousands of bridges worldwide and our information in this booklet reflects what we have seen over the years.
1
P
ICK YOUR
T
ECHNOLOGY
It is important to choose the right type of technology that will best suit your requirements. There are three main wireless bridge technologies available today;
Wi-Fi bridge aka 2.4 or 5GHz link: This is the most popular technology for small and medium business – fast, simple and robust technology
Millimetre wave aka 60, 70, 80GHz. The highest wireless bridge speeds are achievable through Millimetre wave technology (up to 2.5 gigabits per second!). This is the up and coming band for enterprise and large business customers that want high bandwidth and ease of installation.
Laser link aka FSO (Free Space Optics). Laser links are great for cost effective, high bandwidth applications (up to 1 Gigabit per second). They work especially well over short distances (e.g. sub 1 km). These links work very well in the right setting, but can also not work properly if not installed correctly. Laser links generally need to be installed by professionals given the experience necessary to align and configure them.
There are a few other technologies available, e.g., ultra-low frequency or licenced band, but they are not applicable to 99% of home and small/medium business uses.
A
RE YOU CONFUSED YET?
Well unless you are looking to spend over $5000, Millimetre wave and Laser links are out of the question.
That leaves the most common technology: Wi-Fi Bridges. Fortunately, prices for Wi-Fi Bridges start at a few hundred dollars and are the best place to start when looking for a
2
L
INE
O
F
S
IGHT
(L
O
S)
Line of Sight is one of the critical factors in purchasing a Wireless Bridge. It can mean the difference between a rock solid, fast link; and a problematic, painfully slow connection. The most common objects blocking line of sight are:
Trees. It’s not safe to assume that a small tree or similar is not going to affect your link. The water content in leaves can have a significant impact on your link speed and reliability, especially during or shortly after a rainfall.
Buildings. A building will disrupt nearly any wireless bridge. Find another angle to get line of sight.
Vehicles. Vehicles moving through your link will cause your link to drop in and out. Some applications can handle this, but most cannot. Skype, VoIP, File sharing and Backups will become a nightmare of failed attempts, dropped calls and corrupted backups. If possible, it’s best to go onto the roof.
Hills. Wireless signals won’t bend over hills. You should check the elevation profile between your two end points, especially if you’re looking to set up a wireless bridge over a larger distance (anything over 1 km). There are many great free on-line tools out there to help you, such as Google Earth.
Although there are links that can support non- and near- line-of-Sight applications (NLoS/nLoS), they tend to cost double to triple the cost of a regular wireless bridge and can have far lower speeds. It’s usually cheaper, faster and a better end result if you can find line of sight.
Tips for gaining line of sight:
Masts. A simple mast like the ones used for TV aerials are perfect for Wi-Fi bridges. They are quick and easy to install and have a minimal impact.
Relocate or trim back those trees. If at all possible, we don’t want you to clear a forest - but in some situations, relocating, trimming or removing a tree can be the fastest and easiest way to gain line of sight for your bridge. Be sure to monitor any trees that you trim back – as they can regrow and encroach on your line of sight.
Go up. Many businesses and homes can get access to the roof of their building, which often has superior line-of-sight. Have a chat with your building management and see if they can help. There can be all sorts of regulations and rules that must be followed, so make sure you talk to the right person first.
Add a way-point. If you don’t have a direct line-of-sight, then perhaps add a second link to navigate around the obstacle. For example, if there’s a building in your way, and you have the access and rights to install a mast on that building, you can set up a wireless bridge to that building, and then another one from that building to your far end-point. Navigating around obstacles and hills is a very common approach when setting up wireless bridges.
3
D
ISTANCE
The distance between the points you are connecting is another big factor in choosing the right wireless bridge. Almost any link can work at distances up to 2 km, but greater than that your choices and available speeds begin to decrease. A common feature of wireless bridges is reducing link speed to get additional distance – this is a great feature, but it’s not worth spending thousands of extra dollars for a theoretical maximum speed that you will never achieve.
Distances and speeds can be improved with the right antenna (see the Antennas chapter further on). But generally, some safe assumptions for distances are below:
Wi-Fi Bridge. Ranges up to 20km can be achieved with a Wi-Fi Bridge. Performance will reduce significantly at a few hundred metres with cheaper links, but can be maintained at a high distance with higher grade equipment.
Millimetre Wave aka 60, 70, 80GHz.
o 60GHz max range is around 800m.
o 70, 80GHz max range can be up to 4 or 5km depending on the hardware quality and location.
Laser Link aka FSO (Free Space Optics). Can reliably reach up to 2km.
4
S
PEED
Speed is a tough one for many people to cope with. I recommend you take a minute and think about what your real bandwidth requirements are. If you are creating a wireless bridge to access the internet, there is no point buying a Gigabit link when your internet connection is 1 tenth of that speed.
Although total speed is an important factor, the magic number on the datasheet that will affect the ‘smoothness’ of your Skype and VoIP, as well as provide quality access for many users is - Packets per Second (PPS)
P
ACKETS-P
ER-S
ECOND(PPS)
High grade equipment will have high packets per second and a better user experience. 60,000 PPS and up is a good start for a good quality link. Higher packets-per-second can make users feel like there is more speed than there really is.
5
B
UILD
Q
UALITY
Chances are, your wireless bridge is going to be installed in a location that is completely exposed to the elements and as such are prone to failure due to external events. Common reasons why a wireless bridge will fail are:
Rain. Australia can have some of the harshest rain events in the world. It’s important to choose a wireless bridge that is completely waterproof and does not allow water/dust ingress where your cables connect to each wireless unit. See the section on IP rating below
Wind. Flimsy mounting brackets and poorly installed mounts can be a huge nightmare for wireless links. A strong gust of wind can blow a wireless link completely out of alignment and can result in lost connectivity. This problem gets worse when you have to scale a mast, or pay for a scissor/boom lift to access the wireless unit. Ensure your link has sturdy mounting brackets, if you plan on using it for a long period of time or in a location that is difficult to access.
Lightning. Whilst a direct lightning strike will destroy any wireless bridge, better wireless bridges will have grounding systems available to minimise damage to your network
infrastructure. Cheap bridges will pass a lightning strike through to your network and could damage your IT infrastructure.
The best way to gauge build quality and performance in harsh weather conditions is to check the wireless unit’s ‘IP Rating’ (IP stands for Ingress Protection). Without getting into too much detail on IP rating systems, it’s best to find a link that is at least IP66 rated. A decent wireless link should have at least an IP67 rating. If your product does not mention an IP rating, chances are they will not be very water/dust proof. They could last for a while, but will eventually have problems.
6
W
EATHER AND
R
ELIABILITY
Wireless bridges experience reduced performance during poor weather conditions (rain and fog). Many link calculators give you a reliability number – generally as a percentage. If at all possible, you want to design your link to 99.999% reliability, but depending on your requirements you may be happy to settle with reduced performance/speed for a few minutes of the year.
Fig 1 – Example Link Budget calculation result showing reduced performance/no performance at certain distances
Integrated antenna
External antenna
7
A
NTENNAS
Choosing the right antennas can mean the difference between a fast stable connections and a slow unusable link. Generally speaking, the bigger the antenna, the longer the wireless link will work. There are two different types of antennas that you need to consider:
Integrated (built-in) antennas. These are simplest to install because you don’t need to worry about additional cables and connectors. However, because the antenna is integrated with the wireless unit, it’s vital that the mounting bracket allows for flexible antenna alignment. Cheaper wireless links will restrict your ability to align the antenna in all directions and could prevent the wireless link from working properly
External antennas. External antennas are a bit more complicated to install because they involve RF cables and connectors between the wireless unit and the antenna itself. However, external have a wider range of options for antenna and mounting locations. In 99% of cases, an integrated antenna will do the job and will typically be cheaper when compared to an external antenna option.
A
BOUT
W
IRELESS
G
EAR
There is a lot to know about Wireless Bridges and Wi-Fi technology and the team at WirelessGear are passionate about the technology and are eager to share their knowledge with you.
WirelessGear is a subsidiary of DigitalAir Wireless Pty Ltd, who has been in operation for 10 years, with offices in the UK and Australia. We have installed Wi-Fi and wireless bridges for everyone from government and enterprise, to houses and farms. Our work can be seen throughout Australia, New Zealand, Papua New Guinea and all over Europe.
If you have any questions about Wireless Bridges or need some advice, give us a call on 02 8002 1820 or email us at [email protected]
