Computer Networks
CSci232:
Introduction
1
Introduction to Networking
•What is a (computer/data) network?
•Statistical multiplexing–Packet switching•OSI Model and Internet Architecture•Introduction to theInternet
•
Readings
–
Chapter 1

Computer Networks
CSci232:
Introduction
2
What is a Network?
Therearemany types of networks!
Transportation Networks
Transport goods using trucks, ships, airplanes, …
Postal Services
Delivering letters, parcels, etc.
Broadcast and cable TV networks
Telephone networks
Internet
“Social/Human networks”
…

Computer Networks
CSci232:
Introduction
3
Key Features of Networks
Providing certain services
transport goods, mail, information or data
Shared resources
used by many users, often concurrently
Basic building blocks
nodes (active entities): process and transfer goods/data
links (passive medium): passive “carrier” of goods/data
Typically “multi-hop”
two “end points” cannot directly reach each other
need other nodes/entities to relay

Computer Networks
CSci232:
Introduction
4
Data/Computer Networks
Delivery of information (“data”) among
computers of all kinds
servers, desktops, laptop, PDAs, cell phones,
......
General-Purpose
Not
for specific types of data or groups of nodes, or using
specific technologies
Utilizing a variety of technologies
“physical/link layer” technologies for connecting nodes
copper wires, optical links, wireless radio, satellite
or even “non-electronic” means: e.g., cars, postal services, humans -- e.g., recent
“delay-tolerant networks” efforts for 3
rd
world countries

Computer Networks
CSci232:
Introduction
5
How to Build Data/Computer Networks
Two possibilities
infrastructure-less (ad hoc, peer-to-peer)
(end) nodes also help other (end) nodes, i.e., peers, to relay data
infrastructure-based
use special nodes
(switches, routers, gateways)
to help relay data

Computer Networks
CSci232:
Introduction
6
Connectivity and Inter-networking
•
Point-to-point vs.
•
broadcast links/
wireless media
•
switched networks
•
connecting “clouds”
(existing physical networks)
–
inter-networking using gateways, virtual tunnels, overlays
(a)
(b)
base
station

Computer Networks
CSci232:
Introduction
7
Resource Sharing in Switched Networks
Multiplexing
Strategies
•
Circuit Switching
–
set up a dedicated route (“circuit”) first
–
carry all bits of a “conversation” on onecircuit
•
original telephone network
•
Analogy: railroads and trains
•
Packet Switching
–
divideinformation into small chunks (“packets”)
–
each packet delivered independently
–
“store-and-forward” packets
•
Internet
(also Postal Service, but they don’t tear your mail into pieces first!)
•
Analogy: highways and cars

Computer Networks
CSci232:
Introduction
8
Common Circuit Switching Methods
Sharing of network resources among multiple users
•
Common multiplexing strategies for circuit switching
•
Time Division Multiplexing Access (TDMA)
•
Frequency Division Multiplexing Access (FDMA)
•
Code Division Multiplexing Access (CDMA)
•
What happens if running out of circuits?


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