WLAN - Voice & Data Design

[Roble Mumin]

Today we discussed a good design for a voice and data wlan network for approx. 500-800 user and about 500 access points.

So far i came up with two different approaches. One using a rather large /16 network and handle the roaming only on l2 or on the other hand take advantage of mobile ip and let the clients additionally roam on l3.

I made some visio drawings to visualize my ideas which might help discuss this issue better. You can access them on following URI.

http://www.f-consulting.de/design/WLAN_Design.html

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If i would head for a design similiar to drawing #1 do i have to expect excessive broadcast alltough i use high dhcp lease times (1 week)?

Also is there any possibilty to filterunwanted broadcast(storm control) on the AP dot11 interface?

If u had to use a design with "mobile ip" is a configuration like in drawing #2 sufficient, so that the ap's can actually handle the assignement and negotiation or do i in any case need another l3 device to act as a mobile ip FA like in design #3?

If case #2 would be sufficient, is it possible with this design to avoid use of third party software for laptops or do you still need to have software running on the regarding machines?

Are Cisco wlan phones able to act as mobile node (MN) for mobile ip networks?

If anyone has a better idea or a "best practice" approach i would appreciate any hint.

Thanks for reading and greetings from Germany

Roble Mumin

[michaelgillespie]

Probably what wold be recommended for a deployment of this size is to utilize WLSM, where APs can communicate via GRE tunnel. APs could be in different native VLANs, but voice would be the same VLAN/SSID. Want to ensure to use only non-overlapping channels (i.e. 1,6,11) and there is sufficiet overlap of cells. Refer to http://www.cisco.com/en/US/products/hw/phones/ps379/products_white_paper0900aecd800f6d97.shtml for more info on deploying VoWLAN.

[Roble Mumin]

Thanks for the reply. I just read this document and it is very usefull for site surveys regarding RF limitations and placement of APs. I am also aware of the different channel issue but my main problem still is that i need a good IP design for the roaming 7920 phones.

After reading the wireless ipt guide for 7920 i found out that layer 3 roaming based on mobile ip is not supported for the 7920 and proxy mobile ip is not supported for voice on the cisco APs.

Guide can be found here ->

http://www.cisco.com/en/US/products/hw/phones/ps379/products_white_paper09186a00801ca827.shtml#understanding_roaming

So i am stuck with layer 2 roaming based on the design in drawing #1.

But the question still is how much broadcast can i expect in a flat campuswide vlan in conjunction with 7920 phones.

This vlan will probably be trunked to any l2 device that is available so this might be an issue with large networks.

Regarding the WLSM which starts shipping June/July 2004 i am still missing some information on how this module and the management of the AP's is supposed to work. So far i read about limitations of 300 max per module. But found nothing in detail which explains how it works.

[michaelgillespie]

Yes, so the phone can only roam seamlessly within the same L2 network. Can roam to a different network off call though. Not sure if you can break up your network where maybe some bldgs are not close by, where you could use the same SSID, but different L2 network. Only L3 roaming supported w/ 7920 would be using WLSM, but SSID 7920 uses is still the same VLAN only native VLAN would possibly be different VLAN. The WLSM is a blade that fits in the Cat 6K chassis and requires the Sup 7920. WLSM also serves as a WDS server providing CCKM support for fast secure roaming for LEAP. Yes there is a limitation of 300 APs per WLSM blade. Below is the link to the product data sheet.

http://www.cisco.com/en/US/products/hw/switches/ps708/products_data_sheet09186a00802252b7.html

[Roble Mumin]

Thanks for the info, guess i am on the right track.

At the end it narrows down to less expensive solution with L2 Roaming and possible broadcast issues. And an expensive L3 Solution with Sup720 and the WLSM Module.

[srahn]

I just went through a depployment of about 700 AP's with around 1000+ 7920/350/pda clients. This was spread out through 7 different sites, but the design model might help. Mike actually helped us at the first hospital with ensuring the survey was good for the 7920's. Our model was to utilze multiple SSID's, each assigned to it's own respective vlan (l2 domain). Putting the phones on one, laptops on another and pda's on yet another, we were able to limit the number of actual clients per Ip subnet. We used a separate l2 mgmt domain for certain areas up to 60 Ap's per. With the 7920's, it's very unlikely that you would have so many active phone calls at one time that number of clients would be an issue. If you put them on their own SSID/VLAN and implement Qos throughout, you'd be good. Even if you have a 23 bit subnet, it's extremely unlikely you'd have 500 active phone calls at a time.

[jmagnusson]

FYI-

To design your network with a voice and data vlan - it requires alot of trunking on the wired side.

We have 350+ APs and it was alot of work to create that design.

We have WLSM in-house now and have tested it in one building for a month now - no hiccups.

So we do have multiple layer 3 management networks..

If you have a 6500 - the wireless implemention with the WLSM is 100X's easier plus you have one place to configure acls ..also all WDS info is in one place.

If you have more than 300's - you can get two blades.. the issue with the number of AP's it supports and the number of roams per second (app.20)

I vote for WLSM - much better design and offers you data clients L3 roaming which is well worth the cost.