NNSquad - Network Neutrality Squad
[ NNSquad ] Re: define: "service providers have to manage their networks somehow, especially during peak times."
Nick, et al,
http://www.nyquistcapital.com/2007/09/10/the-bandwidth-explosion-myth/
Month/year Upload Gbps Download Gbps Dec-04 276 323 Jun-05 320 425 Dec-05 349 468 Jun-06 412 524 Dec-06 463 637 Jun-07 517 722
Regards, andy
During times of congestion, "best effort" fails to provide a notion of fairness that USERS would find equitable.
Firstly, TCP congestion control is NOT about "keeping an ailing network working", its about providing a balance between flows when the desired use by all parties exceeds the available bandwidth of the network. Thus the obsession with "TCP Friendly", you want to as-fairly-as-possible share a constrained resource.
The core is overprovisioned, because bandwidth in the core is cheap (its lighting more fiber). But bandwidth to the PoP, and bandwidth between the PoP and end user, is not, and short of replacing the last mile infrastructre (eg, FIOS, at what Verizon claims is $10k/customer, and even at $2k/customer would be a lot of cash), will not be overprovisioned. (And even replacing the network may not be sufficient: usage grows to absorb available bandwidth seems to be a rule of thumb.)
So, yes, in an ideal world, you would overprovision your network. But that is notgonnahappen.com when users pay flat-rate and look at the "Speed" as what the provider claims (which is at 4am, or to the whitelisted bandwidth-test site) rather than real-world throughput, so they can't even know the difference.
And there is nothing fundamentally wrong with underprovisioned networks, as long as the resources are allocated fairly and the network is still usable. Remember, the Internet was suable for the most part from 28.8kbps modems. The iPhone, with the pathetically slow EDGE network (~50 kbps) is still usable (not great, mind you, I'm waiting for the 3G myself, but usable nonetheless).
So giving, say 1000 users a link which at idle time works at 8 Mbps, but at peak works at 1 Mbps, is still sensible (and 8x cheaper on the bandwidth costs). So IF you can fairly allocate an underprovisioned network, MOST of the users are still happy, it costs less money, and all is right and good.
The problem however, is, TCP's notion of "Fair" does not match what people would call "fair". Which forces the network owner to do something, because end hosts are effectively adversarial:
User A has 5 torrents downloading, each with 4 connections open. This is 20 TCP flows, all at high volume. Or is using another method (e.g. Joost) which violates the conventions of congestion control completely.
User B is watching a YouTube video of a baby dancing. This is one TCP flow, but still fairly high volume. [1]
User C is doing some websurfing, generally a few small TCP flows.
User D is trying to call a friend using Skype.
All are experiencing congestion, (and in reality, for every A you have 10 B/C/D)
What will happen is that unless A's congestion is due to behavior on the other side, for every byte B or C is able to receive, A receives 20.
At the same time, D will be experiencing a boatload of jitter (and perhaps drops), and his call will be effectively unusable.
Hardly seems fair, does it? Yet from the TCP best-effort model, this is perfectly fair.
Traffic management would be traffic shaping designed to maintain some notion of user fairness, rather than flow fairness, so that for every packet A gets, B and C get a packet. And during peak congestion, when even that isn't sufficient, observe that over the past two hours, A got 100x the data B did, so its OK to reduce A still further, to say 1/2 or 1/4 of what B and C are getting. [2]
And unless and until the Bs and Cs are so numerous, and/or the network is so underprovisioned, cutting back A to the level of B and C is a huge win for the Bs and Cs, who grossly outnumber the As yet are paying the same. So A gets hurt, Bs and Cs win. Since they are paying the same, why shouldn't this be good for B and C?
Likewise, detecting that D is doing a low-latency realtime application, and then prioritizing the traffic for D, improves D's user experience without affected A, B, and C much (Ds are low bandwidth). Yes, end to end QoS would do the job better, but again, thats notgonnahappen.com. Thus D's experience is greatly benefited if the ISP is able to automatically classify the protocol accurately and prioritize it.
Additionally, overprovisioning is not a fair solution to B, C, and D in the flat rate pricing world. If you overprovision to the point where you stop getting congestion, A is going to benefit hugely (the As, generally, will take all the bandwidth they can get), B a bit (youtube is starting to be limited by realtime behavior, not congestion for many users), and C and D hardly at all. Yet A, B, C, and D will all have to pay the costs equally.
So if you want an overprovisioned network, pay for it! Vote with your pocketbook! There are plenty of business-grade providers who will happily sell you a network with a Service Level Agreement. (As a bonus, you are likely to get a provider who will know what a "trouble ticket" is.), and even some consumer networks (eg, Lariat) that will guarentee you an allocation.
Likewise, if you have demand-based billing, an overprovisioned network makes sense. Those who us it pay for it. If I'm an ISP with demand billing, I'm going to be properly/over provisioned, because I want to extract every dime from the As.
But if you want Cheap, (reasonably) fast, flat-rate, and usable, you need traffic shaping and management to keep the A's from outcompeting everyone else.
Because otherwise A will be happy (his downloads are still fast, even at 7pm), but B, C, and D will all be miserable, and shift to a provider which does favor them.
[1] THe reason B is not using a boatload of flows is twofold. First there is a convention that the web browser should only have 4 TCP flows transmitting at a time. But moreso, the webservers themselves have incentive to enforce this, because they don't want one user taking up too much of their bandwidth to the detriment of other users.
[2] Additionally, heavily shaping the asymmetric leeches/seeds doesn't generally hurt A at all (it hurts the OTHER bittorrent users, but not A), but can be a huge benefit for B, C, and D if the uplink is experiencing congestion.