Networks and Internetworks
We already know the social, political and economic impact
of computer networking. We already know it's popular.
We care about technical details!
Terminology
A network: A group of devices that can
communicate with each other. Each device is called a host.
Each host has a unique address.
An internet: A network of networks. Some reserve
the term for an association of networks that communicate
with each other with IP. On an internet, each host has an
address of the form n/h where n is the network number and
h is the number of the host on network n.
As long as all of the networks in the internet have unique
network numbers, combining the network number and host number
will give unique global names. Therefore from the
outside an internet looks like a single network!
- A router: A device that appears simultaneously
on two networks. (Usually this is a computer or device with two
"network interface cards", or NICs.)
- The Internet: The biggest internet around.
"You know it when you see it." The Internet is useful not only
because it is so large,
but because so many zillions of useful services are
available on it.
Advantages of Internets
Heterogeneity
Networks that appear on an internet do not have
to have the same type. It is fine to connect a token-ring
based network to an Ethernet based one, or an FDDI to a X.25, etc.
Internets aren't about physical media -- they are more abstract.
Sotware known as a protocol suite (e.g. TCP/IP) is required to
give the illusion of a single, universal network.
Performance
"Segmenting" a network into an internet using routers
can increase performance in many cases because many networks
(such as Ethernet) work by broadcasting frames to every
other device on the network. Isolating a particularly
busy segment reduces the traffic the rest of the devices
have to put up with.
Security
Routers can be programmed to let only certain packets through
to particular segments.
Scale
Some networking techologies (such as Ethernet) can only work
over short distances. Adding such a network to an internet
allows communication over a much wider area.
Areas of Study
Networking Technology can be studied by looking at
four areas:
| Area |
Topics |
| Data Transmission |
hardware, physical media (wire, satellite, infrared),
carrier signals, modems, ... |
| Packet Switching |
packets, network topologies, LANs and WANs |
| Internetworking |
combining networks into multiple networks, routing
between networks, "universal service" |
| Network Applications |
Email, DNS, FTP, Web, Simple client-server programs,
Middleware, Security and Performance, ... |