FAQs

Email Ed Suor for answers to your wireless questions

The frequencies you are considering deploying (2.4 GH & 5 GHz) are non-ionizing (do not produce cell mutation). The FCC has a good website on this topic, and so I urge you and you team to become familiar it: http://www.fcc.gov/oet/rfsafety/rf-faqs.html.

Additionally, the FCC requires that any mobile device that will be touching (or coming within close contact of) a user's skin be tested for its 'Specific Absorption Rate' (SAR). More information of that can be found here: http://www.fcc.gov/oet/rfsafety/Welcome.html.

Q: We have rolled out 15 wireless carts to our five schools. Login times are too long (5-20 minutes). We have tried allowing three or four students at a time to login and that has not improved the situation.

We have no more than 15 laptops associated with an AP. What can we do to improve this unacceptable performance?

A. A good place to start is looking at your channel assignments. I see from the details in your email that you have a fair number of APs that are configured to use the least busy channel. This is almost never a good idea. The sole exception would be a single AP in a hot spot area where the owner has no control over radio traffic around them.

However, in your case you should settle on a single channel assignment paradigm. I see at one of your schools you're using channels 1,4,8 and 11 and also 1,6 and 11. You need to decide which of these paradigms you are going to follow. If you are using channels 4 and 8, by using channel 6 you raise the co-channel interference significantly. This can result in a heavy level of retries which will have a marked impact on performance.

Another area to examine is your wired network hierarchy. For example, is your network, when examined critically, just one flat network, or is it a hierarchically routed network? Do you have equipment at the edge that is capable of Layer 3 routing and Layer 4 Quality of Service. Have you implemented those functional capabilities?

See my following answer to another customer's question regarding the use of VLANs in a wireless environment.

Why install more than a single VLAN for your wireless network?

Multiple VLANS reduce the amount of broadcast traffic on the wireless side for a cleaner WiFi environment. Installing multiple VLANs at the beginning of a wireless rollout saves money and effort as wireless use expands within the organization. The work required to implement multiple VLANs at the beginning of a wireless project is far more efficient than migrating to new VLANs as demand increases.

Another advantage to early deployment of VLANS is the extra layer of security they add. For example, in a school setting, a staff VLAN and a separate student VLAN, with two VLANS reserved for future allocations (e.g. streaming video or voice) makes it very easy and secure to block or permit access to resources.

Q. What are rogue access points?

Rogue access points can be everything from hackers and outside intruders hanging out in the parking lot to your own employees who don't even know they are violating company wireless security policies.

The larger the organization the more likely that users who love to be mobile have set up their own access points and in the process have created security holes where malicious intruders can easily get at your corporate data.

The Gartner Group estimates that one in five companies has a WLAN (created when an employee unplugs his laptop from the Ethernet jack and plugs it into an unsanctioned access point) the CIO doesn't know exists.

Steps to take:

• Investigate automated rogue access point products. (WiMetrics-identifies the switch port that the rogue access point is plugged into.)
• Publicize a new acceptable use policy addressing wireless access devices.
• Routinely cruise the perimeter of your network with the AirMagnet product-preferably the distributed product, but at least the handheld or laptop.
• With a CISCO network, install WLSE (Wireless LAN Solution Engine-management platform for CISCO SWAN-Structured Wireless Aware Networks.