More explanations about MESH and 802.11n

[cbonnal35]

                   Hello,

I just begin WiFi installations and I have some existential questions.

I have 5 Cisco 1552-E APs. One of them is wired to LAN and act as RAP, the 4 others are MAP.

On each AP, I use 1, 6, 11 channels as 2,4GHz non-overlapping channels.

As I have a 802.11n network, I use 5GHz band with non-overlapping channels too. Because I'm in Europe and outdoor, I want to use 100, 112, 124, 136 and 140 channels.

But all the 5 APs have a MESH backhaul 5GHz link to connect to LAN.

Please clarify my mind, because I don't understand how it is possible for 2 APs, to communicate between themselves on a different 5GHz channel ??

Thank you,

Clement

[Stephen Rodriguez]

They don't.  On the MESH all the 5GHz radios will be on the same channel.  Think repeater

HTH,
Steve

------------------------------------------------------------------------------------------------
Please remember to rate useful posts, and mark questions as answered

[cbonnal35]

I agree.

So what I have to think about these figures ?

http://www.cisco.com/en/US/i/200001-300000/270001-280000/279001-280000/279061.jpg

http://www.cisco.com/image/gif/paws/111902/outdoor-mobi-guide-06.gif

If 5GHz channels are the same to enable AP MESH backhaul, it means that 5GHz 802.11n client's flows are in the same collision domain, even if they are connected to differents APs ?

So as a repeater it reduce dramatically data rates ?

[Scott Fella · Accepted solution]

You are referencing a different mesh ap that has two slots.  The 1550's are different and the backhaul uses the same channels.  This like Steve mentioned is like a repeater and you try not to go more than two hops.

http://www.cisco.com/en/US/docs/wireless/technology/mesh/7.0MR1/design/guide/MeshAP_70MR1.html#wp1219607

Thanks,

Scott

Help out other by using the rating system and marking answered questions as "Answered"

[cbonnal35]

Thank you Scott,

Sales haven't expected directionnals antennas for 5GHz whereas design guide advice to use it.

I have a RAP with 3 MAP hops. All APs are far away from other by 100m (330ft). In these conditions do you think backhaul will be OK with omni antennas ?

A solution might consists to broadcast WiFi over 2.4GHz only (so 802.11b/g), and to use the 5GHz radio only for backhaul to reduce collisions ?

-> In 802.11g, what about the 3rd antenna ?

In a wonderful world, if we want to do 802.11n, MAP may have 3 radios (1x 2.4GHz and 2x 5GHz), and a 5GHz will be dedicated to backhaul ?

[Scott Fella]

Yeah that would be ideal but then the cost would be twice as much:). Here is a good calculator to keep if you have to do a lot of mesh or even a few. It's the range calculator for the 1550's.

http://www.cisco.com/en/US/docs/wireless/access_point/1550/range/calculator/1552_Link_Calculator_V1.xls

Sent from Cisco Technical Support iPhone App

[Scott Fella]

The other thing is that most of my installs I might have 2-5 maps coming back to one RAP. This setup will still use a single backhaul channel. In this case the RAP gets oversubscribed in a way. So you really need to look at what your limits are. Are prefer to only have one hop if possible, but in some cases I can't add another RAP and will have a MAP to MAP link.

Sent from Cisco Technical Support iPhone App

[cbonnal35]

Yes, I've used the Link Calculator, but it gives me 9 APs whereas 4 is very comfortable in Ekahau Pro.

Ok for the tip to place RAP in the middle of the install as a star topology, but it is not possible on all sites !

What can I do if I need a range of 6 MAPs for example ?

Is there an AP which have 3 radios ?

Or :

Place a 1550 with directionnal antenna on 5GHz to get RAP signal, and omnidirectionnal to broadcast 2.4GHz for client + an AP with a single 5GHz radio with directionnal antenna to broadcast MESH for next MAP ?

What are designs with multiple MAPs (like campsites where Internet connection comes only into reception office and must be broadcasted far away) ?

[Scott Fella]

There is a new model which has 3 antenna ports for the 5ghz and 3 antenna ports for the 2.4ghz. This allows you to use one of the Cisco mesh patch antennas for a longer backhaul shoot to the RAP or even a MAP. It's hard to say what you can do but that gives you more options.

Cisco Aironet 1552E/1552EU External Antenna Access Points
The Cisco Aironet 1552E/1552EU Outdoor Access Points are the standard models, dual-radio system with external antenna ports that are compliant with IEEE 802.11b/g/n standards (2.4 GHz) and 802.11a/n (5-GHz). The 1552E has three external antenna connections for dual-band omni or directional antennas. The 1552EU has six external antenna connections, three for 2.4 GHz and three for 5 GHz antennas, that support omni or directional antennas. They have Ethernet and fiber Small Form-Factor Pluggable (SFP) backhaul options, along with the option of a battery backup. These models also have a PoE-out port that can power a video surveillance camera or other devices. Highly flexible models, the Cisco Aironet 1552E/1552EU are well equipped for municipal and campus deployments, video surveillance applications, mining environments, and data offload.

Sent from Cisco Technical Support iPhone App