The ISP is housed in a building called a data centre, which contains all of the computing and networking computer that runs the ISP. However, the equipment inside the data centre uses up a lot of power as well as generates a lot of heat. If the power from the local utility goes down, the customers will be offline. If there is too much heat generated, equipment may become damaged and stop working permanently. Power from the local utility is supplemented with a backup UPS and diesel power generator system that kicks in automatically when the utility power drops. To deal with the heat generated by the equipment inside the ISP's building, HVAC units are installed which vent cold air evenly around the room to keep a constant temperature and humidity. As equipment gets added, power and HVAC requirements also change which requires the ISP data centre manager to order extra power and cooling whenever new networking or computing equipment is added.
The ISP uses data centre grade networking and computing equipment. The equipment handles many more simultaneous connections than what is possible from equipment bought by consumers from electronic retailers such as Best Buy. Even though wireless networks are common in the home and office, ISPs do not use wireless for customer traffic. Fibre and copper cables transmit much more data than wireless radio. The computer servers bought by the ISP need to have many CPUs with as many cores as possible per CPU. This allows the ISP to buy fewer computers while servicing many more customers on a single computer server. The multi-core computers also help save the ISP power and cooling costs. In today's ISPs, VPS (virtual private server) offerings are very popular. They allow the customer to run their own operating system instance on a multi-core computer that's shared by many other customers. If the ISP provides connectivity to the home user, there will be a wired connection (either cable or telephone wire) from the home to the neighbourhood's central office which aggregates all customer traffic in the area. The ISP then carries the data the rest of the way on the ISP's private network to the data centre, which will pass the traffic on to the Internet.
Making the Connection To The Internet
The ISP purchases telecommunication lines from the local telecommunications utility to carry traffic to other ISPs. In most cases, the telecommunication lines far exceed the capacity of the fastest wireless or wired connection available to consumers. Peering arrangements are signed with other ISPs so that traffic can get to the rest of the Internet. Usually, a peering agreement is signed with at least two major Tier-1 or Tier-2 ISPs in case one of them goes down. All ISPs use the same TCP/IP protocol to manage traffic from and to the rest of the Internet. Once all of this is working, the traffic from the data centre can travel to one of the ISP's peers on the way to its final destination on the Internet.