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I've always been wondering how do ISPs increase their users bandwidth. Do they actually change the client's modem configuration? or do they change an specific router conf? I got an email from them saying that I only needed to restart the modem to get the new speed. Any ideas?

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They have bandwidth throttling hardware sitting outside you default gateway. So, traffic for 5MB account goes through one gateway and the accounts 10MB pipe goes through another. So, when they asked you to restart your modem, the DHCP server assigned a different gateway to your modem. This is how they also limit ssl-based and torrent traffic. For that they monitor tcp packets as it flows through their network. I'm sure there are other ways but this is what I know most companies do. –  Nikolas Sakic Jun 20 '10 at 18:09
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3 Answers

In most cases it's a configuration change at the Demarc. A Demarc is the point where the customer's network meets the ISPs network. For consumer grade equipment it's usually called a Modem regardless of how it functions (Cable Modem, DSL Modem, Wireless Modem, etc). For business grade equipment, it's usually called a router (T1 Router, GEPON Router, etc).

There are cases where the physical medium limits the speed of the connection, as is the case with a T1; but these usually only apply in older business-class connections. Almost everything new has rate limiting in the Demarc equipment.

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If you're talking about DSL, then it's mostly done on the ISP's side. DSL connections can reach speeds of 24Mbps but are usually bandwidth capped. In such cases, the ISP just needs to raise the bandwidth cap to increase your bandwidth.

In certain cases, such as upgrading from ADSL to ADSL2+, there may be a need to upgrade the client's modem to support the higher speeds. This is often done by simply replacing the modem, but sometimes it can be accomplished by upgrading the firmware—which can often be done by the ISP over the network. That may or may not be what your ISP did.

Edit:

Some cable modems do store bandwidth limits in their configuration files. These files are automatically re-downloaded from the ISP each time the modem is rebooted. So this is another possibility if you have cable broadband.

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I'd say the question is entirely subjective to the type of connection you have from your service provider. For example, at my office, we have an AT&T Opt-E-Man connection, which is fiber to the premises, and an Ethernet connection to your equipment (they provide a fiber switch). We pay for 10mbps, but can go all the way to 1gbps, and it's just a case of a configuration change.

However if you have a T1 service to your office, then increasing bandwidth will require a new connection to be installed, as a T1 is limited to 1.54mbps, so if you need more, you need a new connection (either bonded, or an upgrade to a different class).

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