Single Channel Architecture VS Multi Channel Architecture

This Blog post is about Fortinet Single Channel Architecture(legacy MERU) and Multi Channel Architecture. This blog is nothing related to the discussion on which will outperform the other.

Since I get chance to work on both SCA and Multi channel architecture, Just thought of sharing some insight about what is all this Single Channel Architecture and how that you can compare with that of traditional MCA from my point of view.


Single Channel Architecture Multi-Channel Architecture


1 Wireless System in control of WLAN network by deciding the Client Association and Roaming Factors Wireless clients do make decisions in your WLAN network for Association and Roaming
2 Wireless clients are connected on single channel called VIRTUAL CELL and their Random back-off algorithm “CWmin – CWmax” for clients  in the same contention space are proposed by Wireless System.

Pros:#No Channel Planning required and easy administration.#Client’s Contention space is decided/Managed by wifi system. So even if there are other client sending/receiving data in same channel the system will calculate, if sending or receiving data from any other client on a calculated RSSI going to cause any impact for others and then decision will be made to give transmit opportunity.

Cons: Design flaws can cause:*high Channel usage*High AP Neighbor count*Management overhead

Wifi clients are allowed to run and select independent BACKOFF value(CWmin-CWmax) for channel access.Note:Since individual clients choose their  own backoff algorithm and no coordination between clients result in retry and Channel access collision mostly in High density environment. So You are forced to create small Cells.Pros:#Effective Spatial reuse(channel planning)and TX power operation is must but once done it works reliably#Can say MCA works parallel to RF physics

Cons: Design flaws can cause:*CCI and ACI*TX power and channel plan*Client contention causing Retries and    Collision when number of client increased.

3 Airtime Fairness is TIME based fairness Even MCA vendors doing Time based Airtime Fairness for long time now.
4 Recommended EIRP 2.4Ghz: 17dbm && 5Ghz: 23dbmNote: Might need to reduce TX power based on Deployments(considering the signal propagation.i.e, More open space env. Recommended EIRP 2.4ghz:10dbm  && 5ghz: 12dbm(+ or – 3dbm).


5 Number of Visible Access point for clients
Data = 2 or 3 APs
Number of Visible Access point for clients
Data = 2 APs
6 VHD=20MHZ, HD=40MHZ,Many SCA Deployments do have channel width of 80MHZ set and works pretty well.  Note sure about field values for 80+80(160)MHZ VHD=20MHZ, HD=20 and/or 40MHZCannot think about 80 MHZ or 80+80(160)MHZ in enterprise network.


7 In High density deployments you might need to check Duty Cycle because management frame and beacons are heard from other APs crowded on Same spacial Diversity(channel), Look for Retry and AP Neighbor counts because that could cause potential issues.Note: Refer High Density Design Guide In High Density Environment you might need to still bring down the TX power/disable low data rates consideration of Antenna Type, ie: Yagi or patch or omni


8 High Density SCA network With More client/bandwidth Requirement  needs Channel Layering or Channel striping and AP poding  and that depends on the Building Structure.  High density/capacity requirement needs you to add more radio and form small micro cells with least CCI by spacial reuse and either disabling radio or reducing AP TX power and more focused coverage pattern and etc.
9 Virtual Cell to Virtual Cell roaming is HARD HANDOFF.Since Microcell is also supported in Fortinet Infrstucture OS, I would like to mention Microcell to microcell is efficient with PMK, 802.11.                                                                Microcell to Microcell roaming is supported efficiently by PMK,OKC,802.11KVR.Note: No virtual cell support.


10 Supports both SCA and MCA with ARRP(Automatic radio resource provisioning. Supports MCA only with (Automatic radio resource provisioning).


My take on SCA over MCA:

SCA “Virtual cell” method take on the traditional “Micro cell” method by negotiation of RF overhead(How well can manage) vs Clients contention based Retry/Collision(How well can manage)

And the System has a central brain call “coordinator” which reads the RF condition based on the interim updates from different supporting worker modules, takes decision in providing better AIRTIME Fairness and user performance for wireless clients.

Test Bed:

If you would like to play around with Fortinet-SCA more just setup your test environment for the following and you can come up with your test cases and values.

A simple example that is easily replicated in the lab is to take five or six access points, all configured for the same channel, and 30 or so wireless clients. Put them all in one room and observe the aggregate throughput.

Then take those same clients and access points and distribute them across the floor of a building and observe the new, increased/decreased aggregate throughput.