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Comment: Re:Almost all router bandwidth management is shit. (Score 1) 88

by tlambert (#46786077) Attached to: Ask Slashdot: Which Router Firmware For Bandwidth Management?

OK, as someone who has been trying different methods of QoS over the past years, with varying levels of success, mainly to have my VoIP phone rock solid over DSL, I'm very interested in what you're saying.

Is there a reason this approach hasn't been implemented yet? Does it break something? If my router is lying to one my upstream router about its TCP window size, wouldn't that impact both the FTP and video stream?

You lie about the window size on a per connection basis, so no, since it's not a global policy, it's a resource policy by application, and potentially by port/IP tuple, so it's not a problem. The point is to keep the upstream router packet buffers relatively empty so that the packets you want don't have to be RED-queued. Nothing breaks because of it.

It generally won't work, unless everyone "plays fair", and the port overcommit ratio for upstream vs. downstream bandwidth is relatively low. As the downstream data rate increases to approach the upstream data rate, the technique loses value, unless you get rid of overcommit, or do it on a per-customer "flow" basis (as opposed to a per virtual circuit "flow" basis) within the upstream router itself, or move to a "resource container" or similar approach for buffer ratio allocation in the upstream router.

So in theory, Comcast (as an example) could do it if they made everyone use the router they supplied, and their routers all participates in limiting upstream buffer impact.

Maybe the next time they replace everyone's cable modems, they'll bother to do it?

Without the deployed infrastructure, it's easier to RED-queue and just intentionally drop packets, forcing a client to request a retransmit as a means of source-quenching traffic. This wastes a lot of buffers, but they probabilistically get through, and for streaming video, that's good enough if there's a lot of client overbuffering going on before playback starts (JWZPlayer, for example, is a common player used for pirated content that will habitually under-buffer so intentional drops tend to make it choppy).

For VOIP, unfortunately, forced retransmit causes things to just typically suck, unless you use a sideband protocol instead, where the router at the one hop upstream peer agrees to reserve buffers for specifically that traffic. This is why Skype is terrible, but your phone calls over your wall jacks which are actually wired to the same packet interface instead of a POTS line are practically as good as a land line or cell phone.

Google hangouts tend to get away with it because they are predominantly broadcast, and are either "gossip"-based CSMA/CD (ALOHA style) networks between participants (i.e. people talk over each other, or wait until the other end is done before talking themselves). It means they tolerate large latencies in which 1:1 VOIP/Skype connections won't. They can be a bit of a PITA for conference calls because of that (Google uses it internally, and gets away with it, but mostly because Google has its own, parallel Internet, including transoceanic fibers), but if Google employees never see the problem, they never fix the problem. Same way any company that assumes local-equivalent bandwidth works as well for their customers as it does for them (free hint to Microsoft inre: Office 386 there).

Comment: Almost all router bandwidth management is shit. (Score 5, Interesting) 88

by tlambert (#46784685) Attached to: Ask Slashdot: Which Router Firmware For Bandwidth Management?

Almost all router bandwidth management is shit.

Bandwidth management schemes currently used by everything you mention are all base on rate limiting packet delivery based on some mythical QoS value, and they ignore the actual problem that the people who are using these things are attempting (and failing) to address.

The problem is that the point of a border routers is to hook a slower border uplink to a faster interior connection; on the other end of the slower uplink, you have a faster ISP data rate. In other words, you have a gigabit network in your house, and the ISP has a gigabit network at their DSLAM, but your DSL line sure as hell is *NOT* a gigabit link.

What that means is that software that attempts to "shape" packets ignores an upstream-downloads or a downstream-uploads ability to overwhelm the available packet buffers on the high speed side of the link when communicating to the low speed side of the link.

So you can start streaming a video down, and then start an FTP transfer, and your upstream router at the ISP is going to have its buffers full of untransmitted FTP download packets worth of data, instead of your streaming video data, and it doesn't matter how bitchy you are about letting those upstream FTP packets through your router on your downstream side of the link, it's not going to matter to the video stream, since all of the upstream router buffers that you want used for your video are already full of FTP data that you don't want to receive yet.

The correct thing to do is to have your border router lie about available TCP window size to the router on the other end, so that all intermediate routers between that router and the system transmitting the FTP packets in the first place also lie about how full the window is, and the intermediate routers don't end up with full input packet buffers with nowhere to send them in the first place.

Does your border router do this? No? Then your QoS software and AltQ and other "packet shaping" software is shit. Your upstream routers high speed input buffers are going to end up packed full of packets you want less, and you will be receiver live-locked and the packets that you *do* want won't get through to you because of that.

You can either believe this, or you can get a shitty router and not get the performance you expect as the QoS software fails to work.

Then you can read the Jeffrey Mogul paper from DEC Western Research Labs from 1997 here: ...after which, you should probably ask yourselves why CS students don't read research papers, and are still trying to solve problems which were understood 27 years ago, and more or less solved 17 years ago, but still have yet to make their way into a commercial operating system.

BTW: I also highly recommend the Peter Druschel/Guarav Banga paper from Rice University in 1996 on Lazy Receiver Processing, since most servers are still screwed by data buss bandwidth when it comes to getting more packets than they can deal with, either as a DOS technique against the server, or because they are simply overloaded. Most ethernet firmware is also shit unless it's been written to not transfer data unless you tell it it's OK, separately from the actual interrupt acknowledgement. If you're interested, that paper's here: and I expect that we will be discussing that problem in 2024 when someone decides it's actually a problem for them.

Comment: Re:Over 18 (Score 1) 629

by tlambert (#46777399) Attached to: IRS Can Now Seize Your Tax Refund To Pay a Relative's Debt

Nothing you say says that Mr Saverin has gotten away from his US tax liability. Only by renouncing citizenship can one end the tax liability, and even that continues for some years (10 I think) after the renouncement.

He did renounce it. And he renounced it before the IPO. So his liability is for what he owed before he renounced it, which is ... not the $1.1B.

Comment: I think there's a more important question... (Score 1) 316

How many homeless volunteers took off with the camera and sold it to buy booze?

I think there's a more important question... how many mountain lions, gazelles, and other animals took off with the Harmless Radio Collars(tm) that Marlon Perkins had Jim Fowler attach to them while filming Mutual of Omaha's "Wild Kingdom"?

Comment: Re:City within a Building (Score 4, Interesting) 98

by tlambert (#46765347) Attached to: Google Looked Into Space Elevator, Hoverboards, and Teleportation

Once thing they should look at is a city within a single mega-structure.

Why should they build an Arcology, when there are already two in progress:

Masdar City in Abu Dhabi:

Arcosanti North of Phoenix Arizona:

Comment: Re:The real deal (Score 1) 352

by tlambert (#46764179) Attached to: San Francisco's Housing Crisis Explained

If those San Francisco residents who are "entrenched" had to pay for their taxes like new residents do, they would be paying 1.25% per year property taxes on the current value rather than the basis of when they bought the property.

That's a great reason to do what rental property owners do, and own a company that owns the property, instead of owning it themselves. Then if they ever want to sell it, they can sell if for a heck of a lot more money by selling the company, rather than selling the property, so the taxes don't go up any more than if you'd bought under prop 13 and never sold.

That's the McDonald's model (McDonald's happily admits to being a real estate company that happens to sell burgers and rents out properties their franchisees). It's also the same model that the Kaiser Family Trust uses.

Comment: Re:Simple problem, simple solution (Score 1) 352

by tlambert (#46764157) Attached to: San Francisco's Housing Crisis Explained

The only way to fix the Bay Area housing crisis is to build more fucking housing.

One of the things that isn't talked about is the amount of empty office and residential apartments in the Bay Area. It's actually worth more money to price them out of the range that people are willing to pay, and then take the "market rent you are not getting", and use it as a tax write-off. It's a common practice in China (Google "ghost cities"), and it's becoming more common in the Bay Area.

If you want to take a little trip on 101 between SF and SJ, it's easy to see a lot of empty buildings, and it's easy to see some of the mega-complexes that are going in in Redwood City and elsewhere, which are probably going to remain mostly empty as a tax write-off to balance out other income.

Comment: Re:BS (Score 1) 352

by tlambert (#46764067) Attached to: San Francisco's Housing Crisis Explained

They Bay Area is one of the few economically active places in the USA, that's why housing is expensive there.

If you want cheap housing, go to an economically dying area, like Detroit; or a place with no regulations such that chemicals leak into your house or explode in your face, like Texas.

Surely San Bruno would be more to one's liking...

Stated like someone who has never lived under an airport noise footprint. There's a reason that you see all the boarded up houses right under the flight path in all the movies... no one actually wants to live there.

Comment: Re:Changing IMEI is NOT illegal (Score 2) 109

by tlambert (#46754705) Attached to: Inside the Stolen Smartphone Black Market In London

Under a 2002 law it was made illegal to change the IMEI unless you're the manufacturer.

It's a Chuck Schumer bill that he introduces every couple of years, it gets thrown to the Judiciary committee, and then it dies in committee. Like clockwork. Here's the text of the current bill, which is presently dying in the Judiciary committee right now:

The people who care about this are the people who traffic in stolen phones, and the people who want to buy a handset and use the same SIM in a different GSM phone, or who want to change the MEID on a new phone so that they don't have to re-up their Verizon contract once they are paying month-to-month for their CDMA phone. And the phone companies, that want you to have to re-up your contract to get a new phone. It's the same reason there's about zero incentive to update the OS in Android phones, since if they never update the OS, in order to get the new +0.0.1 version number bump, you have to get a new phone, and the manufacturer gets to sell another phone, and the phone company gets to lock you into a new 2 year contract every 18 months when the new shiny object becomes available.

Since it's a PITA to get a phone unlocked for international roaming, since it has to be listed by ID with the cell network in the country you are traveling to, and it can take many weeks to get them to actually unlock the thing, and do the registration, most times it's just easier to clone the IMEI to your old phone, and then either destroy the old phone, or do an IMEI swap. This is a common "repair/refurbish" technique, and you'll notice that it's allowed under the Schumer bill.

You might also see both NASDAQ OMX Group and TeleCommunication Systems Inc. campaign contributions, and you'll notice contributions from Facebook in 2012, the year the bill was introduced, when Facebook was going big into the mobile market.

Little bit of vested interest there.

Comment: Re:Not getting funded. (Score 1) 157

by tlambert (#46754531) Attached to: Will This Flying Car Get Crowdfunded?

Flying cars are technically possible.

Flying cars however are not desirable for everyday drivers: they have a hard enough time managing 2 dimensions, we don't need them to occupy a third. So unless they're fully automatic in flight mode (with manual control disabled), flying cars can only be flown by trained pilot.

Rename them "manned drones" and outsource the piloting to third world countries. Problem solved, since the FAA is OK with drones in U.S. airspace.

Comment: Re:Over 18 (Score 1) 629

by tlambert (#46754397) Attached to: IRS Can Now Seize Your Tax Refund To Pay a Relative's Debt

The only way for U.S. citizens to avoid this would be to go through a process to renounce their U.S. citizenship, which is not practical or desirable for most people.

Except for Eduardo Luiz Saverin, the Facebook co-founder who was basically paid by California and the federal government about $1.1B to move to Singapore. For him, it's was a pretty desirable and practical decision, given that the bite for short term capitol gains is treated as ordinary income by California for taxation purposes.

Who would have thought someone with a degree in economics from Harvard knew how to do money math? Uh... everybody? Hello?

Someone is unenthusiastic about your work.