ASK THE EXPERT - MOBILE PERFORMANCE WITH 802.11n

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Feb 8th, 2008

Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity to ask questions on how next generation wireless with 802.11n can enhance mobile performance while decreasing operational costs with Cisco expert Chris Kozup. Chris is a Senior Manager within the Mobility Solutions team with Cisco, responsible for market development and strategy for Cisco's portfolio of enterprise wireless networking products and solutions. Chris has a specific focus on articulating the business case for a unified wired and wireless approach to enterprise-wide mobility. He is responsible for the strategy and marketing of next-generation wireless technologies including IEEE 802.11n, enterprise wireless mesh, and secure wireless solutions. And he helps ensure the success of Cisco's wireless team within specific industry markets through relevant collateral, including cost/benefit models and business cases.

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reginald-pugh Sun, 02/10/2008 - 05:29

Hi Chris,

Thanks for taking on this new venture with 802.11n.

As you are well aware, there is some reluctance to deploy Draft 2.0 for the IEEE not having a ratified standard. But as I have seen on your Mobility TV discussions, Maximum Ration Combining--- MRC does provide benefits to the legacy clients using B/G and A single radios with more predictable coverage and reliable throughput enhancements.

Q's

1. Will Cisco be swapping out the radios out to support a newer Marvel chip set that provides the theoretical 450Mbps throughput enhancement opposed to the current 300Mbps 1250 radio?

http://www.marvell.com/products/wireless/wi-fi_450mbps_802.11n/release/972/

I have a 1250 up and running as a test in IOS mode and will be converting it to LWAPP shortly;

2. Noticed significant range improvements as well as higher data rates ...but the only thing is with the extended range getting a DHCP address is somewhat of a challenge. I can see the AP with full strength almost 1000 feet away but can not connect. As soon as I get closer within 300 feet I can? Perhaps this is the noise is too high (City Environment)

3. Also is there any way you can suggest that the Ethernet and console port be moved so that it is easier to insert the CAT5?

Thanks for the support and taking on this forum.

Reggie

reginald-pugh Sun, 02/10/2008 - 06:19

2. Noticed significant range improvements as well as higher data rates ...but the only thing is with the extended range getting a DHCP address is somewhat of a challenge. I can see the AP with full strength almost 1000 feet away but can not connect. As soon as I get closer within 300 feet I can? Perhaps this is the noise is too high (City Environment)

I think I have answered my own question. This may be my legacy client card can receive well at that distance, but not transmit to the AP to get the request to the AP 1000 feet away. I need to use a draft 2.0 PC card in the laptop to get the true range benefits?

chkozup Thu, 02/14/2008 - 17:18

Hi Reggie,

Yes, see my other response. I believe this is the reason you are experiencing this problem. Have you tested with one of the Intel Centrino vPro clients (with support for draft 2.0 11n)? Cisco has conducted extensive testing with Intel to ensure compatibility. I would recommend either Dell or Lenovo.

Regards,

Chris Kozup

chkozup Thu, 02/14/2008 - 17:15

Hi Reggie,

Thanks for joining us on the chat and thanks for tuning in to Mobility TV. Here are the questions to your answers:

1. Cisco typically does not comment on components. We currently support 300Mbps per radio module on the Aironet 1250 Series access point.

2. Without further information, we can only speculate. But remember that there are two sides to a wireless connection: the AP and the client. Most likely, this is because the client can see the AP's signal quite well but the AP cannot see (or hear) the client at an acceptable SNR (Signal to Noise Ratio). This is analogous to a large audience with a speaker wearing a microphone; the entire audience can hear the speaker very well, but what happens when someone tries to ask a question from way in the back of the room? The AP1250 is like the speaker with the microphone. Your client is like the person asking the question.

Again, this is purely speculative given the information we have. A high noise floor could also be a problem given the urban environment.

3. Thanks for the feedback. I have passed this on to the folks in our engineering team that focus on the mechanical aspects of the Access Point.

Many regards,

Chris Kozup

Chris,

With the increased range provided by MIMO technology, how does the 5GHz 802.11n survey change from an 802.11a survey? How much range does MRC and TBF add to legacy .11a clients? Does legacy mode allow for 40MHz wide channels, and if so to which channel does it switch to support legacy diversity clients?

Thanks Chris,

chkozup Sun, 02/17/2008 - 12:54

Hello.

Thanks for your question. Range gains with 802.11n are minimal, when looking to deploy for application performance. The coverage pattern in 5GHz is almost identical on the Aironet 1250 as compared to the Aironet 1240 (about a 5-15% increase for the Aironet 1250, depending on environmental variables).

Existing 11a clients cannot make use of MRC, though the benefit of TBF does extend to existing 802.11a/b/g clients. Existing 802.11a/b/g clients will experience increased data rates at any given distance from the access point.

I'm not sure what you mean by 'legacy mode allow for 40MHz wide channels', but you can support existing 11a clients when using 40MHz operations - these clients simply use the 'primary' 20MHz channel, while 11n clients that support 40MHz operation (Wi-Fi certification requires devices support this in 5GHz) will make use of the combined 20MHz primary and 20MHz secondary channels.

Hope this is helpful.

Regards,

Chris Kozup

chkozup Mon, 02/18/2008 - 21:06

Hi Bruce,

Happy to help. If you are deploying access points in an environment where there is greater multipath, you will see greater performance enhancements thanks to the elements of MIMO than you would if deploying without much multipath. In other words, if you were to deploy an 11n access point in an open field, without any multipath, you wouldn't see the same performance improvements as you would in an indoor environment with multipath.

While we're generally seeing a 1 for 1 placement of APs from existing 11g/a APs to 11n APs, it's always best to conduct a site survey.

Hope this helps.

Regards,

Chris Kozup

rduke Mon, 02/11/2008 - 07:51

Chris,

I have a number of locations where the RF enviroment is very challenging. These are metal airplane hangars with 60 ft ceilings. That coupled with the fact that airplanes are also very reflective does not help matters. We were placing access points on the ceiling; however, we can not work on them without moving the airplanes - very inconvenient. Because of that we have been installing patch antennas at the building perimeter at about 16 to 20 ft high. This seems to be working better in all repects.

I have been interested in testing the 1250; however, I don't know what do do about mounting them against a metal hangar walls. Right now we use patch antennas and none are available for the 1250. (We only use the 5GHz "A" radios on 1230/1240 APs at present)

My questions:

1. Are there going to be any patch type antennas for the 1250 ?

2. Do I even need patch antennas ? Since the wall is metal and the 1250 is supposed to make use of reflected signals, perhaps mounting omni antennas next to a metal wall is OK ?

3. Does is make sense to replace my A radio's with N, and would I need fewer APs. My largest building is 300 by 700 ft of open space.

Thanks,

Randy

chkozup Thu, 02/14/2008 - 17:06

Hi Randy,

Thank you for logging in. Here are the answers to your questions:

1. Yes, any of our current patch antennas will work fine with the Aironet 1250 Series.

You will want to use at least two antennas, three if you plan to use 802.11n rates due to the 2 x 3 nature of the standard.

Cisco may investigate whether or not it makes sense to have three patch antennas in a single housing depending on the market demand.

To find a complete listing of which antennas can be used with the Aironet 1250 Series, please see Figure 6 in the Aironet 1250 Series deployment guide which you can find here: http://www.cisco.com/en/US/solutions/collateral/ns340/ns394/ns348/ns767/white_paper_80211n_design_and_deployment_guidelines.html

2. Patch antennas are designed to radiate forward and typically a patch antenna has a metal backing so installing it against a metal wall doesn't effect it like it would effect an omni-directional antenna. If you use an omni-directional antenna, you will want to space it a few feet away from the wall.

3. Areas that have high multi-path such as your environment would benefit from 802.11n which can use multi-path to an advantage.

Since most clients (today) are not 802.11n there is a fair chance your AP density should remain the same. We typically advise that customers deploy for performance as opposed to deploying for coverage.

Hope this helps.

Regards,

Chris Kozup

aemberson Thu, 02/14/2008 - 01:13

We have some PDA's and blackberry phones but we cannot seem to connect any of them to our cisco 4402 to get our internet. It is open, so no wep key needed, but they don't seem to authenticate with the wifi at all. I can see them as clients and can ping them.

chkozup Thu, 02/14/2008 - 17:24

Hello,

It is moderately difficult to diagnose the problem you're experiencing. Cisco works with most of the leading Wi-Fi silicon manufacturers with the Cisco Compatible Extensions program to ensure that Wi-Fi enabled devices, like laptops and PDAs are able to establish a simple and secure connection to the infrastructure. This is the first step towards helping to ensure you don't run into connection problems. You may want to check the compatibility of your devices - of course, provided they are Wi-Fi certified, they shouldn't experience problems in connecting.

Within the WLAN management solution, Cisco WCS, Cisco has also provided some client troubleshooting tools that help to diagnose the reason why devices are not connecting. In general, we find that it is a device problem, rather than a missconfiguration in the infrastructure.

If you experience continued problems, contact your Cisco services and support organization.

Regards,

Chris Kozup

chkozup Thu, 02/14/2008 - 18:18

Hello,

Thanks for your question. It is true that existing 802.11ABG client will experience improved performance based on the effects of MIMO. In addition to this, the benefits of 5GHz are even more noticeable since you now have access to up to 23 non-overlapping 20MHz channels and up to 11 non-overlapping 40MHz channels. This means the likelihood of encountering co-channel interference is greatly reduced. While there is no direct relationship between co-channel interference and MIMO, the benefits of 11n with MIMO and the greater number of available channels in 5GHz will improve performance for 802.11a devices.

Many thanks,

Chris Kozup

skint Sat, 02/16/2008 - 12:28

Hello Chris,

We are running a 1250 in autonomous mode and are in the process of installing WLC with 4 1250's. I realize that Cisco recommends against 40 Mhz channel widths in the 2.4 range like a lot of SOHO devices are pushing right now. The 4965 card in my Lenovo also does not permit (by default) joining 2.4 radios in dual mode. However, this is not our issue.

Using the 5 Ghz model, the command sequence for the autonomous mode AP is something along

in rad 1

channel width 40_above

least-congested (doesn't seem to be a supported command under the most release)

Once I enter this command, my connection will no longer establish. It was my understanding that the Intel Centrino with the 4965 was used as the test bed for this project. Am I missing something in the configuration or is there possibly a client setting that needs to be enabled? Under the 20 mhz channels, I connect at 144 mpbs (client reading) using the zero config (built in MS client) with the WPA2 supplicant KB917021.

Thanks,

-ryan

chkozup Mon, 02/18/2008 - 21:01

Hi Ryan,

Thanks for your question.

In Autonomous mode it's very easy, simply browse into the AP and select 40 MHz mode (that's it).

From the CLI you can as you stated select upper or lower 40 (all this is doing is choosing which channel to bond with).

From the CLI it should look something similar to this..

c1250(config-if)#channel width 40?

40-above 40-below

c1250(config-if)#ch wi 40-a

From the controller side of things (if unified) then you can verify here.

WLC commands

Show 802.11a

Show ap config general

Show running-config

From a client perspective, check the client (device manager) properties,

Verify you have auto set and that you do **NOT** have the client hard set to a 20 MHz mode.

Also verify you didn't enable any legacy encryption like WEP.

If still a problem, do a Show ap config 802.11a and verify it is in 40 MHz mode.

If you still have an issue, verify you have the latest code on both the AP, controller and the very latest Intel client code.

We have no outstanding issues with the Intel card in 40 MHz mode, perhaps reach out to Cisco TAC if these suggestions fail to resolve it.

Hope this helps.

Regards,

Chris Kozup

k.khawaja Tue, 02/19/2008 - 08:47

Hi Chris,

I have a question regarding the power injectors for 1250 series APs. Does the power injector require 110 v power source or will it work on either 220 v and 110 v?

jbligh Fri, 02/22/2008 - 12:26

Hi Kaleem,

The Aironet 1250 Series access point supports both 110 and 220 volts for the local power supplies. The access point ships with the appropriate voltage based on the country and regulatory domain. For more information please review the product data sheet at www.cisco.com/go/nextgen-wireless.

Regards,

Chris Kozup (jb)

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