1. Introduction to Local Area Networks

2. What is a Local Area Network?
A local area network is a network whose size is not large. For example, the size may be a room, a department, a company, a campus, etc.
A network that covers a place that is city-wide is called a “metropolitan network.”
A network that spans states or countries is called a “wide area network.”

4. Why We Study Local Area Networks?
You are using local area networks (e.g., Ethernets, wireless LANs, NFS, MW’s neighborhood, etc.) everyday and everywhere.
You better know them well.
This course is aimed to be self-contained. If you have taken “計網概” course, that is good. If not, that is still OK. We will spend the first four weeks on the basics that are covered in “計網概”.
After taking this course, you will have hand-on experiences of using and configuring a switch.

5. How Is a Local Area Network Implemented?

6. A computer network physically is composed
of end hosts, intermediate routers/switches, and
transmission links. (like nodes and edges in a graph)
End host (PC)
Router/Switch
Link

7. A computer network is used to transfer a piece of
data from one node (traffic source) to any other
node (traffic destination).
destination
source
data

8. A computer network also needs protocols so that
different nodes can talk to and work with each other
to finish a job.
Error control protocols
Hey, your 3rd data is lost.
destination
source
data
Hey, you send
too fast!
Congestion control protocols

9. Computer Networks Protocols Are Very Complex
For examples:
Framing (PPP, SLIP)
Medium access control (Ethernet 802.3, WLAN )
Addressing (IP, Appletalk)
Routing (RIP, OSPF)
Error control (ARQ) and congestion control (TCP)
Quality of service (RSVP, Diffserv, IntServ)
Security (IPsec)
WWW (HTTP), FTP, Telnet, Bit-torrents (P2P)

10. Protocol Layering Is Used To Manage Complex Protocols
The ISO OSI seven-layer reference model

13. The Internet TCP/IP Protocol Stack
application
transport
network
physical

14. Why You Study Computer Networks As A Student?
Learn how computer networks work today
As numerous protocols are emerging and fading out rapidly, understanding protocol principles is far more important than knowing protocol details.
E.g., instead of memorizing how frequently routers exchange their “hello” messages and when to declare a router is dead in RIP, it is more important to understand why doing this protocol allows a router to detect that its neighboring router is dead.

15. Why You Study Computer Networks As A Student (cont’d)?
Learn the real reasons behind the designs of today’s computer networks
Once you know the reasons, you can apply them to other places.
E.g., Knowing why Ethernet uses Manchester encoding is more important than knowing that Ethernet uses Manchester encoding to encode signals.

16. Why We Study Computer Networks As An Engineer?
Try to achieve the following ideal goals:
A user’s data can be transferred from one node to any other node reliably, in-sequence, and spontaneously.
A network’s resources (e.g., bandwidth) can be efficiently and fully utilized to reduce the operation costs.
However, sometimes these goals are conflicting,
which makes achieving these goals at the same time
very hard!

17. Welcome to the Internet!
Internet’s topology