Calling the Internet Calling the Internet

Calling the Internet! Calling the Internet!

Let's face it: Practically everyone on the planet knows about the Internet. But we all probably have our own opinions about what the Internet is and is not. One definition of the Internet is that it is an IP packet forwarding service. The Internet is a bunch of networking devices, cables, and software, which collectively try to forward IP packets to their correct destination IP host.

As mentioned earlier, the Internet includes Enterprise networks, home users, ISPs and their networks, as well as all the connections between them. If you think of the Internet as an IP packet forwarding service, each Enterprise will want to have at least one router that can route packets to and from an ISP router. For instance, by using a point-to-point WAN link between a router in an Enterprise network and a router in an ISP network, the two routers can route IP packets back and forth.

Ultimately, the WAN link just lets the routers forward packets. And as long as each Enterprise network has some form of WAN link between itself and an ISP, the Enterprise can communicate with the Internet.

The rest of this chapter focuses on ways you can connect to the Internet from home. After you're connected, all your PC needs to do is send and receive IP packets so that your applications will work. Essentially, once your PC can send and receive IP packets with an ISP, it has become a part of the global Internet.

Now That I Know How to Talk, Whom Should I Call?

These days, you can pick up your home phone and call almost anywhere on the planet. Although the cost for long-distance calls has fallen a lot over the past 10 years or so, it still costs a little money to call someone far away. However, most local telcos let you make local phone callsat least calls that they define as "local"without charging extra cash for making the call.

Many ISPs allow you to connect to their networks using modems, but the trick is to keep the cost down. To keep the costs down, ISPs try to make sure that as many people as possible can make a local free phone call to one of their routers. ISPs strategically locate routers in various parts of the world so that you can make a local call from your house to a phone number of a phone line that runs into the building where the ISP puts its gear. That type of building, and the gear inside it, is called a point of presence (POP), as shown in Figure 16-5.

Figure 16-5. Calling the ISP Local POP

As you can see, Fred can make a local call to the POP in Atlanta, and Barney can make a local call to the POP in Cincinnati. Both calls are free because the ISP thought ahead and located a POP in the local calling areas near Fred and Barney. All Fred and Barney need to make the call is a local telephone line. The ISP also charges a small fee for the service, which in most markets in the United States today costs $10 to $20 per month.

Now That I Know Whom to Call, What Do I Say?

So far, you've learned a few of the concepts behind how two modems, on either end of a telephone circuit, can transmit and receive data. Those details mostly relate to OSI Layer 1, the physical layer.

Like all good networking devices, when a PC makes a phone call to an ISP, the PC typically needs to send and receive IP packets to and from the Internet. In most cases today, the PC and router use PPP as the data link protocol. (PPP was covered in Chapter 14.) PPP lets Fred send and receive packets over the dialed phone circuit.

For instance, in Figure 16-5, imagine that Fred hits the www.bowling.com website to check out the latest in bowling news. You know from Chapter 13 that Fred will need to send an IP packet to the DNS server to resolve the name www.bowling.com to an IP address. Then, he will need to send some IP packets to the web server, just to set up the TCP connection. After that, Fred can send a packet to the server asking for the home page of www.bowling.com. Routing takes place, just like it always did. Between the ISP router and Fred's PC, PPP is used to send and receive frames over the dialed circuit.