Reaching the World Through One Connection to the Internet

Reaching the World Through One Connection to the Internet

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In the figure, ISP represents the term Internet service provider. An ISP creates a network over which IP packets can be forwarded, similar to the way a telco creates a network over which bits (for WAN links) and Frame Relay frames (for Frame Relay) can be forwarded. In fact, some ISPs are also telcos.

As you see in Figure 16-1, Fredsco's headquarters is now connected to the Internet. To connect to ISP1, Fredsco uses a point-to-point WAN link. In Chapter 14, the WAN links connect routers inside the Fredsco internal network. Now, a WAN link connects a FredsCo router to a router at ISP1.

IP routing is the key to appreciating what the Internet provides to Fredsco. Because Fredsco's router connects to a router in ISP1, it can forward packets to and from that router. And because the rest of the Internet is connected out there, somehow, someway, IP hosts in Fredsco's network can send and receive data to and from the rest of the IP hosts in the Internet. For instance, in Figure 16-1, Fredsco could exchange data with his supplier, GeorgeCo, who's connected to ISP2 over a Frame Relay permanent virtual circuit (PVC). Also, customers can connect to their local ISPs using the technologies you'll learn about in the rest of this chapter. Then, customers can order things from Fredsco from Fredsco's website, send e-mails to Fredsco's customer service department, and so on.

Notice that the actual connectivity between Fredsco and ISP1 and between GeorgeCo and ISP2 are familiar services from the telco (WAN link and Frame Relay, respectively). Because I've already covered those, the rest of this chapter focuses on some other WAN technologies, mainly ones that are used to access the Internet from home. Table 16-1 summarizes the three options for WAN connectivity that you've learned about in this part of the book, with a few comments.