question about how broadband usage meters work

Forums › New Zealand Broadband › question about how broadband usage meters work

ta77

2 posts

Wannabe Geek

#77727 21-Feb-2011 18:22

I don't know much about the technical details, but this thought occured to me the other day and i don't know any other 'techie' people to ask.

Imagine two computers on the internet, computer A and computer B. My crude understanding is that if A wants to download something from B, A first sends some kind of 'request' to B. B then sends the data and addresses it to A. The ISP then forwards this data to A and logs it as "download usage".

So my question is this: what happens if B sends data addressed to A without A requesting it first?

Does the ISP still forward this data to A, only for A to discard it because it wasn't expecting it? If so, does the ISP have some way of checking that A really did request the data, or does this data get recorded as download usage by the ISP regardless?

richms

28173 posts

Uber Geek

Trusted

Lifetime subscriber

#442046 21-Feb-2011 18:32

That is basically flooding A's connection, and yes it does count. There is no required proof of accuracy or standards for ISP bandwidth recording so noone really knows what the hell they are counting to come up with the numbers that they give you.

For it to not count, the ISP would have to run a stateful firewall outside of the traffic counters, and really, what benefit do they have to do that when all it would do is decrease what they end up charging people?

If IP address's do start to really run out, we might see some budget internet plans going behind ISP side NAT which would achieve this outcome. That will bring some other hassles tho like who do you blame when someone does piracy on that IP etc.

Richard rich.ms

snnet

1410 posts

Uber Geek

#442056 21-Feb-2011 19:01

Often this type of traffic, in a sense, is called "overhead" traffic, when it is not requested and not "sent" as such on purpose (on purpose meaning by a human being) - it is a normal byproduct of the Internet (excluding of course things like botnets running denial of service attacks etc)

michaeln

238 posts

Master Geek

Trusted

#442075 21-Feb-2011 19:26

Complexity,

costs money

is slow

usually both.

Normally, every byte that goes through a connection (as opposed to low level overhead chatter between the ISP and the customer) is simply counted. In both directions.

The IP protocol in general does not have a concept of "request", "connection" or "session". There are such things, layered onto the IP protocol, but they are, so to speak, extra. (layers 4-6 of the OSI model). Most accounting happens at layer 3 (but not, generally, at layer 2. If it did, then overhead such as ARP would also count and it usually doesn't).

If you wanted to pay less in order to pay only for traffic you originated, or requested, then the ISP would need to put in place (very expensive) equipment to track that usage. The net result would most likely be that it would cost more to send you a bill, which is probably not what you wanted. (Actually, some ISPs do offer a 'clean Internet' service where you get only what you asked for. This service is generally remarkably expensive, for the reasons I've just described).

If you send a simple UDP message to a server, there is no real way for the ISP to determine whether this was a request for the contents of the Library of Congress, or an inflammatory poke at 4chan, without looking deeply at the packet---potentially having some intelligent entity read the contents of the packet. The somewhat uncomfortable result is that several terabytes of data is heading your way in either case. If that is indeed what you want, you might want to spend some time thinking carefully about the implications. For example, since the ISP has no way to determine if a stream of UDP packets is actually accepted by the host computer or simply discarded, if the ISP did not charge for 'unsolicited' incoming traffic, then it would be all of several femtoseconds before someone created a service where a 'completely unrelated' message sent to one IP address resulted in scads of 'unrequested' (cue Tui billboard) data appearing at the customer address.

ta77

2 posts

Wannabe Geek

#442105 21-Feb-2011 20:50

thanks for all the replies.

I wasn't thinking so much about being charged for overhead traffic (I accept this is simply part of using the internet) but rather the possibility of someone getting nasty and flooding a connection for the purpose of running up large overage bills on the target account.