I'm wondering how large internet businesses or hosting providers deal with ISPs. Thanks.
2 Answers
"Hosting Providers" is a very broad term. Typical, professional, well established companies that provide web hosting, do so out of a Data Center that has redundant Internet Service Providers, so that if 1 ISP goes down, they still have internet access. Many data centers have several ISPs running through their building.

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Well, it used to be a lot simpler than it is now. Originally, the connection that large companies and ISPs had was generally called a POP (Point of Presence). A POP was connected to to a NAP (Network Access Point), which was run by one of several major companies called NSPs (Network Service Providers). NAPs connected to each other and formed the backbone of the Internet that replaced the original NSFNet, which was a huge part of the original backbone.
Today NAPs are pretty much a thing of the past, being replaced by Internet Exchanges (IX or IXPs). Wikipedia has a decent write up on IXPs.
Depending on the company, they may have connections to one or more ISPs, which also may have connections to other ISPs or to one or more IXPs. Really large companies may actually have direct connections through one or more IXPs, although usually this is brokered through an ISP that happens to have a physical presence in the same location as the IXP.

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