Contention/Oversubscription maths

Jared Mauch jared at puck.nether.net
Fri May 27 07:45:36 CDT 2011


On May 27, 2011, at 8:14 AM, Adam Armstrong wrote:

> No SLA, residential customers.

I would watch out for the 'abusers' in this case, and have the capability to rate-limit the ports if necessary.  Some hardware doesn't deal well with 'small' buckets of rate-limiting, eg: taking a 1G port to 1M.

I'm interested in your operational results, as i've had a few general ASSumptions i've offered in this space:

- Most people are going to be limited by their wireless gear (few people care to run wired very far)
- Most servers on the far-end aren't going to be fast enough to cope
- Most people aren't going to spend time debugging network problems
- Some percentage of users are going to run a torrent or something else and flatline their port.  You need to be able to police them at a reasonable bandwidth cap, eg: 10M if they have 1G, but that's 1% and many dumber switches won't go under 10%.

The other solution is to just throw more bandwidth at the problem.  Make sure your switches can easily take a 10G or n*10G uplink.

I'd expect that the single bursty user is going to drown out the rest of them into the noise, as they will likely plug in directly and have no wireless hops that limit their speeds.

One of my friends operates a WISP in this area and has periodic issues with the heavy usage users and wonders what they're doing with that 150GB of data they "download" in a month.

- Jared



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