Telephone Company Wide Area Network (WAN) Technologies
You implement Wide Area Network (WAN) links using whatever technologies your telephone company supports. You should be able to choose from many technologies. Although use of high-speed Internet connections and site-to-site VPN solutions is becoming popular, there are still many places outside major metropolitan areas where your choices will be quite limited.
Consider, for example, a connection between offices in New York to an office in Toronto: The traffic leaves the serial or WAN port on your router in Toronto and enters your service provider's network. The traffic then traverses your service provider's network — and possibly several service providers — until it arrives at the serial or WAN port on the New York router.
When the traffic is on the service provider’s network, your traffic is isolated from other users' traffic, whereas your Internet traffic is mixed together with everyone else's traffic. Depending on the service provider, you can choose from various options or types of services.
Here are the three main options for connections offered by telephone companies:
Circuit switching: A system that establishes a connection each time it has data to send, such as using a telephone.
Leased lines: A system on which a connection that is always connected.
Packet switching: A system on which the data on the service provider network may not always take the same path.