WiFi Salon has been asked often “What is the capacity of your network?” “How many simultaneous users can you have at any one Hot Spot?” Currently, WiFi Salon has 3 Mbps DSL lines to all its locations, with Columbus Circle and Sheep Meadow upgraded to 8 Mbps with Covad’s new ADSL2+ lines, and with Washington Square, Union Square, Summerstage, and The Delacorte/Great Lawn getting the same upgrade.
What does what we have now deployed, 3 Mbps, get us? If this DSL line was say serving a small office and several people at the same time were trying to download something, performance would suffer unless of course there was some kind of bandwidth throttling.
By bandwidth throttling, we mean apportioning to each user a certain amount of the pipe when they download — for us it is now 200 kbps. As a Youtube video only requires 55 kbps, we consider this a sufficient amount.
In this scenario, if say 15 people were downloading a video four times as bandwidth intensive ( better resolution, larger size ) as the standard Youtube video at the same time, that 3 Mbps pipe would accommodate only 15 users.
Real world, user behavior is quite different. Culling from years of data analysis in administration of the Bryant Park Wireless Network, Marcos
Lara, my CTO, and network architect found that the most congested his
network ever got was ~75 users on about 2.4 Mbps of the available 3.0 Mbps.
Bryant Park has, to be sure 2 T-1s, which are dedicated, versus our one DSL at each location, which is “best effort.” Shouldn’t 2 T-1’s then outperform? Not necessarily, so we manage the network, allocating bandwidth per user, shaping traffic.WiFi Salon believes that we will witness the same performance on its network. 3 Mbps well managed will support around 70 users, that we will see the same performance on the parkwifi network that Marcos was able to achieve at Bryant Park.
At ~$900 a month for two T-1’s it would not be financially possible to
install T-1’s at all 17 of our locations. Byrank Park has the luxury of
being a location that is at one physical address, we do not. This leaves us
with DSL as our only consistently reliable solution.
So the question is can we provide a similar experience to Bryant Park’s dedicated two T-1s (1.5 Mbps each), versus our single DSL lines at each location.
The answer is yes, thru traffic shaping. Each of our DSL location employs network traffic shaping to ensure each user gets a quality experience similar to that Marcos was able to achieve at Bryant Park.
For example, in Washington Square recently, we had 23 simultaneous users consuming just 688 kbps of bandwidth, or less than 25% of the 3 Mbps capacity. This is due to the nature of web surfing and Internet usage.
The truth is that web surfing behavior in the real world consists of people mostly reading and writing documents, which uses up no bandwidthand the time a user is actually transferring data is quite small. this is not the case with VOIP and Video, but those still represents a small but growing amount of Internet traffic at this time.
Over the next several weeks we will be nearly tripling our capacity with the new ADSL2+ lines in Washington Square and at five other key locations. this will further increase each users experience. however there are still other factors involved in how many simultaneous users can we support.
If more than 70 users were all trying to transfer data with the same wireless access point at the same time any wireless network would start to experience wireless network congestion that limits the all the connected clients ability to communicate effectively.
This “crosstalk” — too many trying to be communicate on the same wireless frequency can only be addressed thru the addition of more wireless access points to share the user load.
WiFi Salon would start to worry about crosstalk when usage reaches around 70 simultaneous users. Such as if there was an event we were hosting that might attract a larger number of users for an extended period of time. in those cases we bring out our big guns, very special wireless hardware, that can really handle a heavy load. it is expensive
but well worth the cost if you’re hosting a special event.
One such piece of equipment is a world class radio manufactured by Altai. For distance, performance, quality of service, and we have seen nothing better.
Combine Altais with ADSL2+ in a commercial district, you really would have something. It works really as best as WiFi can within very noisy urban and congested environments.
WiFi Salon would start to worry about the crosstalk problem at around 70 users. If there was an event we were hosting that might attract larger numbers, we’d bring out our very favorite piece of hardware, the Altai.
This is a world class radio — for distance, performance, quality of service, we have seen nothing better. Combine Altais with ADSL2+ in a commercial district, you really would have something. It works really as best as WiFi can within very noisy urban and congested environments.
As it is, when we look at historical data on usage, we note at no more than 1% of park goers will log on a park’s WiFi network on a given day. In other words, 7,000 people would have to be on the Sheep Meadow at the same time for us to be concerned we were hitting capacity, at least in terms of crosstalk. Crosstalk, and not bandwidth, would be the first problem — and now especially at Sheep Meadow after its upgrade to ADSL2+.
So if crosstalk appears to be the limiting factor, and not bandwidth, why are we adding the ADSL2+ lines? What if we were able to give each user a larger ‘pipe’ than is otherwise available in public WiFi Hot Spots? How much better can we make the user’s experience? How much more in the way of multimedia could we support?
We want the very best speeds available, and we want to support as many users as possible. We believe that WiFi’s true strength lies in its ability to deliver rich local multimedia content, services and experiences, and local high speed wireless connectivity.
WiFi, a low power piece of open spectrum as regulated by the FCC, has many inherent real world limitations. The WiFi industry, born by accident and incredible resourcefulness, is engineering feat by engineering feat, eke-ing out further performance enhancements within the very restrictive parameters that constitute its regulation.
WiFi Salon’s mission is work with companies that are seeking to push the technology as far as it can go, where let’s say for now 70 people at a WiFi Hot Spot can all have a rich media experience. With the parkwifi network, we are providing park goers in New York with a free amenity that we will continue to scale as needs evolve.
