ASK THE EXPERTS - WI-FI NETWORKS

[ciscomoderator]

Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity to get an update on different aspects of wireless network design and installation with Fred Niehaus.  Fred is a Technical Marketing Engineer for the Wireless Networking Business Unit at Cisco, where he is responsible for developing and marketing enterprise wireless solutions using Cisco Aironet and Airespace wireless LAN products. In addition to his participation in major deployments, Niehaus has served as technical editor for several Cisco Press books including the "Cisco 802.11 Wireless Networking Reference Guide" and "The Business Case for Enterprise-Class Wireless LANs." Prior to joining Cisco with the acquisition of Aironet, Niehaus was a support engineer for Telxon Corporation, supporting some of the very first wireless implementations for major corporate customers. Fred has been in the data communications and networking industry for more than 20 years and holds a Radio Amateur (Ham) License "N8CPI."

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Fred might not be able to answer each question due to the volume expected during this event. Our moderators will post many of the unanswered questions in other discussion forums shortly after the event. This event lasts through July 16, 2010. Visit this forum often to view responses to your questions and the questions of other community members.

[Leo Laohoo]

I have never tried using 802.11n on a point-to-point bridge.  I don't know if this is recommendable because 802.11a has some limitations particularly distance and penetration power.

[Scott Pickles]

Jerco -

It is not possible to achieve the 300 Mbps across a bridge link.  This is a limitation of both the 802.11n specification and the hardware itself.  In order to achieve 300 Mbps rates, there are 9 or 10 settings that must be configured, a few of which include:

1.  5 GHz greenfield

2.  400ns guard interval

3.  Minimum of 2 transmitting antennas, but I think it's actually all 3 that are required

4.  Channel bonding

5.  WMM - if you turn off WMM, the Modulation Coding Scheme which compresses the data to achieve high data rates is actually disabled

6.  WPA2 encryption

Some of these I believe are Cisco specific, such as WMM and WPA2 as Cisco is trying to let everyone know that using those features is a really good idea and Cisco is a large part of the body that developed the 802.11n specification (among others).  The hardware limitation is the number of antennas.  We don't use diversity on point to point links for bridging.  Also, I'd be concerned about the 400ns guard interval over long distances.

Cisco has some good guides on 802.11n here:

http://www.cisco.com/en/US/partner/prod/collateral/wireless/ps5678/ps6973/ps8382/prod_white_paper0900aecd806b8ce7_ns767_Networking_Solutions_White_Paper.html

http://www.cisco.com/en/US/partner/solutions/collateral/ns340/ns394/ns348/ns767/white_paper_80211n_design_and_deployment_guidelines.html

Hope that helps.

Regards,
Scott

[rudydekeninck]

Hello,

I am wondering whether having a 3500 series AP deployed “in overlay” to other APs would influence the RRM channel assignment of other APs as well? Will the controller for example change the channel on neighboring APs because the 3502 is reporting an interferer or not at all? From a presentation at Cisco I recall a discussion from which I understood that having the spectrum analyzer in the AP would result in immediate channel changes, whereas the information collected by the spectrum analyzer would influence RRM for any AP with the next recalculation. Is that correct?

Furthermore I am wondering where I could find an overview of what is and is not possible with or without an MSE in the system. Is MSE for example required to have interferers and channel changes reported in WCS, or is this done at the controller level? I don't see any channel changes reported on WCS for example, whereas the controller shows they are actually taking place....


Thanks in advance and best regards

Rudy