by Alex Goldman
I’ve seen a great deal of discussion on the topic on the WISPA lists. It’s a problem that every ISP faces. When everyone’s using the network at the same time, there may not be enough bandwidth for every application.
Butch Evans, of the eponymous Butch Evans Consulting (a WISPA member), says that people use the internet differently than they did 10 years ago. Then, most activity was bursty and brief, such as checking e-mail and surfing web pages. Now, people download large files (photos, Linux OS images, Microsoft OS updates, game patches). People stream videos and talk over the internet on VoIP. Traffic is heavy and sustained.
In response, some ISPs are trying to identify and throttle bit torrent or other sources of traffic. Some, he says, are even trying to identify and cap Akamai servers (Akamai helps large ISPs by situating servers on the networks of large ISPs but does not do the same for small ISPs).
WISPs tend to pay relatively high rates for bandwidth. While large ISPs can design their networks so that the backhauls terminate in areas where bandwidth is cheap, the same is not true for many ISPs. Some go to extraordinary lengths, building very long links to get to cheaper bandwidth in order to make their business model a success.
However, the 802.11 protocols themselves, and the equipment, create inherent limits in the network (as is the case in wired networks too). The 802.11 protocols, Evans notes, have no provision for packet prioritization or QoS. Of course, equipment makers have been filling this void for years, from Karlnet back in the day to Motorola and many others now. “Ubiquiti has AirMax, Mikrotik has Nstreme,” says Evans.
Within the constraints of the protocols and the equipment, Evans says that smart bandwdith allocation can play a role. He cites Allot for implementing fair allocation rather than throttling, and has, he says, written a fair allocation implementation for Mikrotik hardware and Linux software.
“ISPs should manage bandwidth, not throttle it,” he says.
Those ISPs that have upgraded to WiMAX may have more options, but most need to use the equipment they have, Evans says, and that’s often Wi-Fi and often Mikrotik (or a similar solution such as Imagestream).
The idea is to separate the traffic that is time sensitive from the traffic that is not time sensitive. Evans calls the most time sensitive traffic “interactive” — it’s the traffic that someone’s sitting at a computer and waiting for, second to second, mostly voice and video traffic but also such low bandwidth high importance items as DNS requests and ISP speed tests. The rest of the traffic is Microsoft OS updates, extended downloads, and anything else that goes on in the background that a user expects will take time.
“ISPs are not only managing bandwidth — ISPs are also managing user expectations,” Evans says. This means that ISPs should pay careful attention to speed test results.
Most ISPs, Evans says, buy dedicated rather than burstable bandwidth. So it makes business sense to ensure that customers get access to as much of the ISP’s upstream pipe as is available at any time. When there’s no contention, he recommends allowing customers to use whatever they need.
Of course the tough decisions concern scarcity, not plenty.
WISPs that breach the expected bandwidth limits per AP, or put more than 50 users on one AP, will experience problems than bandwidth management cannot solve.
The problems that bandwidth management can, however, deliver a valuable user experience under certain circumstances. Every network experiences a period of peak usage (business networks during the day, and residential networks during the early evening — and when college kids come home).
Evans says that if you identify the kind of traffic, rather than specifically identifying every packet, you can allocate traffic in a manner than will please users without harming the network. The system does add some latency to the network (as all QoS systems do) but Evans says that for a WISP, the reward is a better experience for customers.
He first wrote his own implementation in November (and announced it on his blog) and says he’s deployed it on about 200 networks by now. Whether you choose to use Evans’ implementation or not, the principles he has elucidated should allow ISPs to allocate bandwidth fairly.
Tags: bandwidth, butch evans consulting, mikrotik, network management
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