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Introduction to Data Communications
5. Why Telecommunications? (cont'd)
5b. Data Channels (cont'd)
Data Channels are special communications channels provided by the "common carriers" such as
Telus, Sprint, Bell Canada, AT&T, etc.. for transferring digital data. Data Channels are also called
"Leased Lines". They are "directly" connected and you don't have to dial a connection number. The connections are up and running 24 hours per day. They appear as if there were a wire running directly between the source and destination. Typical transfer rates for data communication are: 56 k, 128k, 1.544 M, 2.08 M, 45M and 155 Mbps.
Common carriers charge for data connections by
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the amount of data transferred (megabytes per month)
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the transfer rate (bits per second)
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the amount of use (time per month)
What is a Network? This is a difficult question to answer. A network can consist of two computers
connected together on a desk or it can consist of many Local Area Networks (LANs) connected
together to form a Wide Area Network (WAN) across a continent.
The key is that 2 or more computers are connected together by a medium and they are sharing resources. The resources can be files, printers, harddrives or cpu number crunching power.
Many individuals have asked to see The Big Picture of networking: "where does everything fit in?". Where does Microsoft NT fit in with routers and the OSI layers? What about UNIX, Linux and Novell? The following page has a graphic showing The Big Picture. It attempts to show all areas of networking and how they tie into each other. The following key describes the graphical symbols used:
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Circles Network Operating Systems
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Squares Communication & cabling protocols (OSI Transport to Physical Layer)
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Storm Clouds Telecommunications media or Information providers that connect to the Internet
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Machine symbol Network "linker" can be a Bridge, Router, Brouter or Gateway
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The Internet jagged haphazard dotted line
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