1. How Traffic Moves over the Internet
ISP
ISP POP
Access concentrator
PDA

2. ISP
ISP is a company that offers their customers access to the Internet.
The ISP connects to its customers using a data transmission technology
appropriate for delivering Internet Protocol datagrams,
such as dial-up, DSL, cable modem or dedicated high-speed interconnects.

3. ISP POP
POP is an artificial demarcation point or interface point between
communications entities.

4. Access concentrator
A device that connects a number of circuits, which are not all used at once,
to a smaller group of circuits for economy.

5. PDA
personal digital assistant (PDA) is a handheld computer also known
as palmtop computers.
Newer PDAs also have both color screens and audio capabilities,
enabling them to be used as mobile phones, web browsers,
or portable media players.

6. Reference
http://en.wikipedia.org/wiki/