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Monday, August 5, 2013



DCCN Presentation Transcript: 
1.Introduction DCCN

What is a network?
Digital transmission
Components of a network
Network hardware
Network software
Network standards

3.What is a network?
“an interconnected collection of autonomous computers”
    interconnected = able to exchange information
“a set of nodes connected by media links”
    node = any device capable of sending / receiving data to/from other nodes in the network
“a connected collection of hardware and software that permits information exchange and resource sharing”
    information = data, text, audio, video, images, …
    resources = printers, memory, link bandwidth, ...

4.Networks vary in:
type: Ethernet, Cable TV, telephone network, Internet, cellular…
size: from a few computers close together, to a world-wide network of networks containing millions of computers
technology: copper wire, coaxial cable, wireless, fibre optics…
technical issues: services offered, rules for inter-computer communications, how users are charged for network use...

5.Why all these variations?
historical reasons
different operating environments
lack of (sensible) standards
difficult problems ?no optimal solutions
different target applications

6.Uses of Computer Networks
Companies and Organizations
Private Individuals

7.Companies and Organizations
resource sharing: programs, equipment, data…
high reliability: multiple processors/links/file copies/...
scalability: gradually improve system performance
rapid communications & remote cooperation saving money

8.Client Server Model

9. Private Individuals
Person-to-person communication

10.Digital transmission
all information represented by bits(only values are 0 and 1).
more resistant to noise, which unpredictably changes transmitted values.
basic idea: transmit two very different signals for 0 and 1.
even if these signals are corrupted during transmission, they should still be distinguishable–and as long as the destination can distinguish 0 and 1.
in addition, extra bits (not part of the information to be transmitted) can be added in order to reduce noise effects
    e.g. automatically correct bit errors.
may require analog-to-digital / digital-to-analog conversions (e.g. if input/output information is in analog form).

11.Components of a network
Components of a network
•message: information to be communicated
•sender: device that sends the message
•receiver: device that receives the message
•medium: physical path from sender to receiver
•protocol: set of rules that govern data communications

12.Network hardware
Transmission technology
•broadcast networks: single communication channel shared by all network nodes
can send to: one node, all nodes, (maybe) group of nodes
•point-to-point networks: many possible connection paths between any pair of nodes
message may have to pass through intermediate nodes on the way from sender to receiver
usually, need a routing algorithm to decide if a path exists from sender to receiver, and --if multiple such paths exist --which one(s)to use

13.Network Scale

14.Local Area Networks (LANs)
restricted size
low propagation delay(e.g. small fractions of a second)
high speed(e.g. 10 Mbps up to 1 Gbps and beyond)
low error rate

15.Metropolitan Area Networks (MANs)
bigger version of wired broadcast LANs
may be a means of connecting multiple LANs 

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