Wednesday, October 26, 2011

Wireless Performance: Gosh Darn Urban Environments!

Over the last couple weeks I've been doing some testing to determine the performance of the baseline hardware config for FF5.  Some things I've been thinking about are directional vs. omni antennas; RTS/CTS vs. not; how fast is 802.11n, really?

The executive summary:
  • Use directional antennas whenever possible
  • Move traffic to 5Ghz links as quickly as possible
  • RTS/CTS provides a noticeable benefit in obstructed PtMP applications
  • Sharing 2.4Ghz radio between access and mesh networks is unlikely to scale.  
Now some details:

Here's the general idea for FF5:


A 5Ghz backbone serving a local 2.4Ghz mesh clouds, which also provide 2.4Ghz access to clients.  The key objective for this design is to make 2.4Ghz (Circle) nodes installable by relatively untrained users, while still allowing the system to perform at broadband speeds.  5Ghz backbone (Triangle) nodes are expected to be installed by more thoroughly trained technicians.  Ideally, this network should provide every user performance equivalent to the broadband connection in a suburban US neighborhood.  In technical terms, this breaks down to the following requirements:
  • Peak Client Speed (link-local): 4Mbps
  • C-Node Aggregate 2.4Ghz Throughput to node with 5Ghz Uplink: 10Mbps
  • C-Node 5Ghz Throughput to T-Node: 10Mbps
  • T-Node Aggregate 5Ghz throughput to child C-Nodes: 30Mbps
In the 5Ghz layer, I was able to achieve the desired T-C speed with a single 20Mhz channel and a single Omni antenna at the T-Node, connecting to C-Nodes with directional links.  This represented the best compromise of simplicity, cost and performance.  Handshaking (RTS/CTS) proved useful with the existence of hidden nodes, and directional links improved throughput.  Interestingly, the 5Ghz layer with directional links achieved roughly 80% of the expected theoretical maximum, even in the nasty RF soup that is my urban residential neighborhood.  Here's our test setup:



At 2.4Ghz, the most surprising result of preliminary tests was the effect of congestion control backoff (presumably) on throughput.  Living in an urban neighborhood, a 2.4Ghz node can easily "see" as many as 50 APs at any given time.  Consequently, it is always sharing airtime...  Inside my plaster and wire-lathe walled apartment, it is possible to find locations where a node will provide 50Mbps of real throughput to a laptop.  Take the same setup outside, and suddenly the performance drops to a little as 15Mbps at close range.  While it's reasonable to expect a much more friendly situation in the developing world, these speeds call the feasibility of a design sharing 2.4Ghz radios between clients and mesh at our desired scale into question (sorry, Amy).  It also highlights the importance of moving traffic off of the 2.4Ghz mesh as quickly as possible.  Here's some graphs of upload and download speeds vs. signal strengths for various configurations.  Larger (more horizontally directional) omni antennas provides marginally better results after normalizing for power:



Click here for  raw Somerville Wireless Test Data

Monday, October 24, 2011

JoinAfrica Progress Report (and so much more)

Looking back at the post history, it's been real long time since we've had an update in fabfi-land. I'd say its entirely my fault, but there are a half-dozen other people who can write to this blog <hands on hips>. At any rate, it's been a long summer for Fabfi, and JoinAfrica, the first African small business venture based on the Fabfi platform. So here's to getting everybody up to date...

As you may remember, I was in Kenya much of summer 2010 working with students from the University of Nairobi to build an all-wireless community ISP with Fabfi. For the last year, the Nairobi team has been building a small business around the pilot project in Mt. View.  Here's their latest update: 


JoinAfrica Kenya
Progress Report, October 2011
Overview
As of October, 2011 the JoinAfrica network in Mt. View / Kangemi is operating with fourteen nodes, providing coverage to approximately eighty residences. After beta testing in the fall of 2010, the network had been in live production since February 2011, beginning with seven nodes and expanding to fourteen over the following months.
Of the eighty residences covered, thirteen have become regular subscribers to the wireless service. Most users pay KES 2000/mo. for a 512kbps peak rate, while a two of the customers pay KES 4000/mo. for a 1Mbps peak rate. In addition to the thirteen existing subscribers, eight additional subscribers are waiting to be upgraded to the paid service. At the time of this writing, the network reliably saturates the available bandwidth of 1.2-1.5Mbps at peak times, requiring that more bandwidth be added for additional users to be served. As a point of perspective, the gross monthly revenue from current user subscriptions is roughly equivalent to the installed cost of one node.
In September, FabCom, LLC was incorporated as a legal entity dedicated to operating the Mt. View network and providing other networking and ISP services on a consulting basis. Additionally, Mr. Nyakundi and Mr. Ochoti have undertaken specialized training in security, routing & switching, virtualization and storage. Mr. Gone has been developing an updated IPv6/802.1x version of the platform used in JoinAfrica with the Fabfi Wireless team. Mr. Gone has also been supporting the fledgling JoinAfrica network in Njabini, Kenya.

Key Challenges
A key concern limiting the expansion of the network is the cost of bandwidth. The current connection has been generously donated by Wananchi Online, but FabCom has been unsuccessful engaging the company in a commercial relationship or negotiating an upgrade of the existing donated bandwidth.
FabCom was quoted retail prices for dedicated bandwidth from other vendors at a rate of KES 21,000/Mbps. At this price it is difficult to provide competitive subscription prices to users. FabCom is actively searching for alternatives to the retail option that can achieve significant savings below the retail price. One potential approach to this problem is acquiring a CCK Network Facilities Provider (tier 3) license. Such licensing would require other ISPs to deal with FabCom at a wholesale level, however the financial barrier to entry for this option is significant (min KES 200,000/yr), and comes with no pricing guarantees. An alternative arrangement would be to enter into a revenue sharing arrangement with an existing ISP, which could easily be sustainable on a revenue sharing model. FabCom is exploring both approaches at this time.

Funding and Future Expansion
Once a suitable bandwidth contract can be secured, FabCom plans to expand the network to serve the eight customers on the waiting list. Increased bandwidth will also enable efforts to increase penetration in areas covered by existing nodes.
A second tier of planned expansion includes jumping across the Wyaki Way highway from Mt. View, and a variety of new sites, including Waterfront Gardens, Highrise, Langata and parts of Westlands. Expansion to these sites will require some outside investment to implement on a short timescale.
A third tier, pending achievement of a CCK license and performance of a small demonstration project, involves the provision of internet to student hostels on UoN campuses.
Fabcom is talking to potential investors (2) to provide funds to enable the first two expansion described above. This capital will in part go into acquiring CCK licence, while the remaining portion will primarily go to hardware and first-month costs for bandwidth.

Additional Opportunities
The expertise FabCom has acquired to in the construction and management of the Mt. View network has placed the company well to act as a contractor for the construction and management of wireless networks for other communities or commercial ISPs.
One specific opportunity for this model is partnership with Orange Telkom, which is in the process of rolling out wireless hotspots in various locations like campuses, airports,shopping malls and other recreation areas. We are actively soliciting them to contract with us to build out these hotspots on a revenue sharing model.

While the ISP project alone is not yet large enough to be sustainable business on its own,  the FabCom team has had success leveraging their experience from operating the network into other business opportunities.  

Perhaps more exciting than the Mt. View pilot itself, is the capacity addition of the Nairobi team has added to the Fabfi ecosystem.  The the FabCom team has begun to support other operators starting Fabfi networks in Kenya and worldwide (Tom from FabCom just hinted at a new network in Madagascar a few days ago).  Tom from FabCom has also been instrumental in the development of our new IPv6 fabfi network (more about that soon).  

Relatedly, the main JoinAfrica website, which we hope will be a digital gateway to more community-scale networks in Africa as they come online, is now live.  (thanks to Plaid Creative for the hot graphic design).  The Kenya team has their own page here. There are plenty of photos from the Kenya project HERE on my website as well.

If you want to keep up to date on the goings-on, be sure to get wired into our social media.  The more of you are listening, the more pressure I get to post useful content :).

Fabfi on Facebook 
Fabfi on Twitter (new!) 
Fabfi Google Group 

JoinAfrica on Facebook
JoinAfrica Google Group 

Mail the Kenya JoinAfrica team directly HERE.