Internet Architecture- Lecture 6

Internet Architecture
Lecture 6: How Routers Work & Connecting to the Internet

How Routers Work:
A router has input ports for receiving IP packets and output ports for sending those packets toward their destinations. When a packet comes to an input port, the router examines the packet header and checks the destination in it against a routing table a database that tells the router how to send packets to various destinations.

Connecting to the Internet:
You can connect to the Internet in many ways and many more ways pop up practically every day. They range from simple telephone dial-in connections to high-speed cable and digital subscriber lines (DSL) to satellite connections, TV connections, wireless connections, connections at work and home via local area networks (LANs), and even connections via cellular telephones.
One general rule is true about Internet connections: the faster, the better. People want the fastest connection possible because many pictures, sounds, and videos are available on the Internet. Today, the three most common ways you can connect to the Internet are through a corporate or university LAN, at home via a cable modem or DSL modem, or over telephone lines. Increasingly important, though, are wireless connections via the WiFi networking standard. Direct connections over LANs are generally the fastest connection, cable modems and DSL modems are the second fastest, and telephone-line connections the slowest. Cable modems, DSL modems, and LAN connections are all very high-speed connections, and are known as broadband connections.

At one time, most people connected to the Internet via dial-up modem. Typically, when you use your modem to connect to the Internet, you dial in to an Internet service provider (ISP). When you dial in to and connect to your ISP, you re in fact connecting to a modem attached to a more powerful computer called a server. ISPs typically have banks of hundreds or thousands of modems that accept dial-ins from subscribers trying to connect. Modems are controlled by your computer and communications software by a set of commands called the AT command set (also known as the Hayes command set, named after one of the original modem manufacturers, Hayes). It s a language that instructs the modem on what to do at various points during a communications session, such as opening up a line and sending out tones that the telephone system can understand.
But there s a major problem with connecting this way it s too slow to be of much use. Websites use many graphics and multimedia features, and dial-up connections are so slow that the Web can seem unusable.