||5/22/2012 9:54:00 PM|
Real-World Testing of Wi-Fi Hotspots
It’s not uncommon for today’s consumer to rank the cost and quality of Wi-Fi Internet as one of the main reasons for selecting between hotels. Everyone knows seasoned travelers that route their airline flights based on the speed of a connecting airport’s Wi-Fi system, or that switch their coffee drinking habits to be at a shop with better Wi-Fi. But what are some of the features today’s general public think about when evaluate Wi-Fi Hotspots? And, as an organization offering hotspot connectivity, what should you be testing for to ensure a positive experience?
Let’s first look at some of the common hotspot features in-depth and how they are facilitated: Wi-Fi Hotspots have existed for years in coffee shops, airports and hotels. But now they are popping up everywhere, from local corner pubs to retailers – even in fast food restaurants and car dealerships.
Ease of Use
Hotspots use the 802.11 Open authentication method, meaning no authentication process at Layer 2 – at all. The customer’s client device (laptop, iPad, smartphone, etc.) joins the Hotspot’s SSID, and is forwarded to the DHCP service, and the client device receives an IP Address, Default Gateway and DNS.
At this point the client is now ready to access the Internet. One option is to just allow direct access. This is the easiest of all systems. It causes no difficulty with devices, because there is no user interaction.
Most hotspot providers opt for a Captive Portal solution – whereby any attempt by the client device to either load a browser-based Internet session, check e-mail, etc., will all be redirected to an HTTP web page. By capturing all possible outbound ports, the customer’s experience is changed from what they would get at home.
On this Captive Portal page the customer can then choose to accept the terms of service, and/or pay for Internet usage. The use of a Captive Portal makes accessing the Internet via a hotspot quite difficult for devices that do not have native web browsing capabilities.
The more hoops you make the customers go through, however, the lower their valuation of the Hotspot service.
The next feature that is on the top of customer’s mind is the actual throughput. If Internet access is slow or inconsistent, customer complaints rise. With the advent of streaming audio and video services, users expectations of throughput have increased faster than most Hotspot providers have increased bandwidth.
A business can have the best Wi-Fi system available, with data-rates going over the Radio Frequency (RF) medium, but without an adequately sized backhaul – end users will still complain.
Many customers are getting increasingly more sophisticated in their IT skills and use of technologies like Public IP addresses, VPN support, and even higher in-bound needs. Many of the smaller hotspots won’t need to address these more advanced features – but in airports, conference centers and hotels, the ability to offer access to these features will be paramount to those users who need them.
Measuring and Analyzing Hotspots
There are two parts to every Wi-Fi Hotspot service. The most obvious is the Wi-Fi component – the ability to use RF to transmit packets from the client devices to the Internet. The second, and just as important, is the backhaul to the Internet.
Many of the earlier pioneers of Wi-Fi systems mistakenly thought the main goal of designing Wi-Fi was all about the RF coverage, specifically the measure of Received Signal Strength Indicator (RSSI). This measurement is usually captured in Decibels (dBm.) compared to one thousandth of a watt. Client devices have a calibrated receive sensitivity at different data rates, and need a certain amount of RF signal above the ambient RF noise floor in order to operate.
Though measuring the RSSI in any given target area is certainly important and necessary, simply focusing on this alone is not sufficient. In order to capture, analyze and report the performance of any given hotspot, it’s necessary to measure the actual throughput of data, not merely the RF energy. To do this, we need tools that can consistently replicate and collect data in a known method and repeatable format.
The first way to evaluate a hotspot is to use a tool like Fluke Networks’ AirMagnet Survey PRO to capture active Wi-Fi signals throughout the facility’s footprint to verify adequate RF coverage. This is a minimum – RF coverage is a critical requirement. Professional tools will also give you helpful, visually appealing heat maps and full reporting capabilities.
Testing and Measuring Layers 1-3: RF, 802.11, and IP Connectivity
After you’ve verified RF coverage, the next process is to use tools to test and measure performance of the hotspot. Many hotspots these days measure the throughput of the Wi-Fi network and then visualize the “performance weather-map” in the AirMagnet Survey application. Below are a few of the metrics we’ll want to look for in our performance analysis:
RSSI – Received Signal Strength Indicator – the amount of RF energy received at any given location and time.
Noise – this can be captured with a Wi-Fi NIC to show packets flowing via RF in the area, and augmented by a Spectrum Analyzer to see non-modulated RF from other potentially interfering devices.
SNR – the difference between the RSSI and the Noise floor. The more SNR the better. Higher SNR values are indicative of potentially higher data rates. The quicker each client gets on and off the wireless medium, the more clients can share the frequency in the same space without causing interference to each other.
802.11 Association - This 802.11 Association is to Wi-Fi what a ‘Link Light’ is to an Ethernet connection. It is the minimum requirement that shows connectivity between the device and the rest of the local area network. In Wi-Fi connections we need the BSSID – or the MAC Address of the Access Point we are connected to. This BSSID will be used to help move packets to and from the Wireless network.
DHCP – in order for any device to transmit packets to the Internet – it requires IP address information for the specific subnet it is connected to. Quick, repeatable DHCP responses, with complete answers, including Default Gateway, DNS and Subnet Mask information is a hard requirement.
At this point we have Layer 1 – RF, Layer 2 – 802.11, and Layer 3 – IP connectivity. This is the minimum in order to connect via the Hotspot to the Internet. These together mean our client device is connected to the AP as well as through the AP back to at least the DHCP server.
At this point we also need to test and measure the connection from the default gateway on to the Internet itself.
Testing and Measuring Default Gateway Connectivity to the Internet
We’ll now be using different tools and metrics – these are just as important and the first set of tools, just focusing on a different part of how hotspots work.
To test off-site connectivity we can use a couple of standard Internetworking tools, PING and TraceRoute. These two will give us metrics of how long and how many hops it takes to get to a site on the Internet. The lower th