WLAN Questions

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Hello to anyone who may know! I have 2 questions on WLAN technology either with reference to Cisco or other vendors.

The Cisco documentation essentially states ‘In a multi-story building WLAN with different subnets per floor, a client attempting to roam to a different AP on the same floor might acquire an AP from an adjacent floor, which is not a desired behavior. Switching APs in a multi-subnet environment changes the roaming activity from a seamless Layer 2 roam to a Layer 3 roam, which in turn might disrupt sessions and require user intervention.’

1. My question on the above is: In practical application, how is the scenario best managed?

2. Is there a rule of thumb for provisioning WLAN APs per number of estimated data only users and HOW and WHY would this change for other devices such as VOIP or wireless video devices?

Thank you for any insights or refences you can share!

My answer is only for Question 1.

In my company, all floors AP's ssid are hidden. The admin will configured the client device according to his privileged. And this type of scenario prevent the client to acquired or seen another AP's ssid and also each floor's users know only his AP. Concerning security, people outside the company, can't break easily into the company network using the WLAN.

@FLM,

@Karramutally-Yousha's company is a good way to do it without involving other measure that can get tricking and complicated very quickly. If using enterprise wireless you may want to do a site survey choose more directional antennae. You can even control some of the channels and coverage by adjusting the APs themselves.

There is a guidance out there. But it boils down to total throughput needed. You can create a simple one on paper. Ask what amount of bandwidth do each of the application used over wireless for a single user. You also take into consideration the number of devices and types of devices connecting as well and their wireless requirements. These can all be estimated from the application and device throughput requirements. Then get the total number in Mbps.
Then you multiply the number of users you expect to be on your wireless. This will give you a rough estimate of the total throughput in Mbps.

Thank you both for the very helpful details!

For question 1, we already have devices grouped according to specific SSIDs. The problem I am experiencing is how some of the mobile industrial devices will become "sticky" to the APs on the adjacent floor it may have been used on previously. How does the Cisco wireless system mitigate this issue?

For question 2, I have heard that there is almost like an approximate 3/1 ratio. That is, 3 data devices to 1 VoiP or Video device. Any thoughts on this?

A follow up question I have is: What is Cisco talking about how the "Switching APs in a multi-subnet environment changes the roaming activity from a seamless Layer 2 roam to a Layer 3 roam," ? If you can please, I would like a deeper explanation of this.

Thank you and anyone else who wants to jump on the discussion for the advice!

@FLM said in WLAN Questions:

Thank you both for the very helpful details!

For question 1, we already have devices grouped according to specific SSIDs. The problem I am experiencing is how some of the mobile industrial devices will become "sticky" to the APs on the adjacent floor it may have been used on previously. How does the Cisco wireless system mitigate this issue?

There may not be an "easy button" the information may be cached on individual devices. You may have to clear caches of the individual devices by getting endpoint devices to forget those mac addresses of the APs they connect to.

For question 2, I have heard that there is almost like an approximate 3/1 ratio. That is, 3 data devices to 1 VoiP or Video device. Any thoughts on this?

Every AP coverage and capacity will be different. You'll have to look up the model and instead of making a generalized ratio, unless you know. The safe bet would be how I described in the earlier approach.

A follow up question I have is: What is Cisco talking about how the "Switching APs in a multi-subnet environment changes the roaming activity from a seamless Layer 2 roam to a Layer 3 roam," ? If you can please, I would like a deeper explanation of this.

A "multi-subnet" environment means that you have different subnets. As you move your wireless devices from one AP to another AP, all supporting multiple subnets. Applications that require persistence do not need Layer 2 when roaming across multiple access points but Layer 3. So as you move from an access point on floor to another floor, this allow for applications to maintain their connections, this is part of Mobile IP networks.

Hi Mr. Wong, Thank you for spending the time to elaborate on the questions, I sincerely appreciate it!

If I may let you know the challenge I am facing. The devices I am supporting are medical patient monitors, the device's cashe cannot be cleared by the nurse since she would need to enter the service mode to warm boot the device or unplug it and physically remove the battery (both options would be a violation of policy). The vendor does not currently have a solution since their firmware updates are regulated by the FDA and can take several months to be approved for release. Being that this "sticky" AP issue is almost a daily occurrence since these devices are transported up and down the hospital floors, it would be much better to find out if Cisco has any possible work-around to help minimize this issue.

Thank you for giving me the opportunity to trouble you with this. Respectfully FLM

@FLM,

If you have Cisco Equipment, you have Cisco TAC support for that. I would send a support in to them and see if they can help you with your specific questions. This will be more direct.

Unfortunately the network admin is unresponsive to our requests to escallate this. I guess we'll just have to wait for it to hit the fan. :(

Healthy competition in the wireless vendor area pays off. Pulling in the Aruba engineers to consult on a redundant solution was the way to get some traction on resolving this issue with Cisco. Very funny indeed!