802.11n + wireless IP phone

[wim_depauw]

Hi,

We are considering to implement 1250 AP with 802.11N standard and use wireless IP phones.

I'm not a voice expert but I can't find a cisco phone which supports the 802.11n ( draft ) standard.

Is there a phone which supports this and if not when will there be one ?

The ap1250 are supporting a/b/g/n band so it could be that the wireless phone is supported on 802.11a .

If I have a laptop which uses 802.11N and I have a phone with 802.11a on the same AP will the speed of the laptop drop also to 54 Mbps/s ?

or

Can I configure the AP to use 802.11a and 802.11n at the same time ?

gr

wim

[Rob Huffman]

Hi Wim,

Excellent questions!

1. Correct, no Wireless 802.11n phones yet

2. The Cisco 7921 will work with the 1252.

3. The 7921 is supported on the 802.11a band

4. No

5. Yes

Q. Will the Cisco Aironet 1250 Series support the Cisco Unified Wireless IP Phone 7921?

A. Yes. The Cisco Unified Wireless IP Phone 7921 is Wi-Fi-compliant and will interoperate with any Wi-Fi-compliant access point, including the Cisco Aironet 1250 Series. The 802.11n standard ensures backwards compatibility for 802.11a/b/g devices.

From this good Q&A doc;

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps6973/ps8382/prod_qas0900aecd806b7c82.html

Hope this helps!

Rob

[jeromehenry_2]

Thanks Rob for this very concise answer (and 4 for you!).

- To add to it, the difficulty for an 802.11n phone is to stick enough antennae in the (small) body of the phone, knowing that the antennae are supposed to be a certain distance apart from each other, which is a bit incompatible with the idea of keeping the phone small... but I am sure that engineers at Cisco and elsewhere will solve this difficult equation someday. There already are some "802.11n" phones on the market, but I am not too sure on how "802.11n" their performances are, or if they are just compatible, like the 7921 is.

- When in a mixed environment, 802.11n devices with non 802.11n devices, the performances of the 802.11n devices will degrade, in the sense that they would not be as high as if no non 802.11n would be in the cell. They will still be higher than pure 802.11a, to take this spectrum as an example. So if you get 150 Mbps throughput, you may degrade down to 72 Mbps when a non 802.11n is around (don't take these number as absolute references, they are just example). Note that your non 802.11n devices will also benefit from the fact that the 1252 AP is 802.11n, not as far as speed is concerned, but as far as link quality vs distance, basically getting a better link at a farther distance...

Sorry, many more words that the excellent Rob!

:-)

[Rob Huffman]

Hi Jerome,

Very nice buddy :) +5 for this excellent info. Never too many words when the info is this good!

Take care,

Rob

[migilles]

802.11n is backwards compatible with 802.11a/b/g. The Cisco 7921G phone is 802.11a/b/g.

[wim_depauw]

Hey,

Would the performance degrade even if my phone would be working in the 802.11g ? We would use the 5 GhZ band for 802.11n because we will have more channels available.

So actually phone and data would be working in another frequency band ...

I talked to a guy who's doing site surveys and he thought the performance wouldn't degrade but it can't hurt to get a second opinion.

Thx for the great answers until now !!!

[jeromehenry_2 · Accepted solution]

Hey Wim,

The phone would work just fine in the 802.11g band.

The only differences I would see:

- the cells are slightly larger (in 802.11g) at same speed

- there are only 3 non overlapping channels, so design has to be done carefully, especially in a multi-story environment

- beware of the other 802.11g (and mainly 802.11b) devices probing around. They can seriously degrade the performances of your network

- there is a larger part of 2.4Ghz band that is ISM, which means that many other devices might use this band as well (analog wireless cameras, DECT phones, microwave ovens and so on).

So be careful in your site survey, but there is no problem with the phone itself.

Hope it helps

Jerome

[migilles]

So over the air, depends on the enabled data rates. Think of 802.11b as the tortoise and 802.11a/g as the hare. The tortoise has to get out of the way before the hare can show its speed. So basically wouldn't advise to enable all data rates, but only the rates, where you would the system to perform at a miminum (i.e. 12 mbps).