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The Basic Network | Ethernet | ATM | SDH | Glossary of Network Terms
A network is simply a collection of "nodes" connected together in some manner by wires (or possibly fibre optics or wireless links) and some electronic circuits, AND THAT IS ALL THERE IS TO IT. The network only becomes useful when everyone on the network speaks the same language. The installation, maintenance, upgrading, and management of the network is quite complex; but these are all things for the network managers to worry about, and not the users. (It is a bit like a postal network. Letters are easy to address, obeying an agreed convention, and easy to put in a letter box. How they get from sender to receiver can remain a mystery!)
I use the term "node" to mean a piece of equipment fitted with the appropriate interface for the network. This piece of equipment could be, a UNIX workstation, a PC, a printer or some other electronic device. Data goes into and out of the network at the node and is passed by the network from node to node without being stored or processed.
Of course, like a computer, the network is not much use without any software tools to ease its use. The software needs to be set-up correctly which can often be quite time consuming! It is the combination of complex computer hardware and software that causes most of the problems with "networks", and not the network itself.
When dealing with networks it is important to understand the difference between software used for communication (for example ssh, software for simply communicating with a remote computer); and applications (for example mail, an application that runs on a UNIX host).
We only really use one type of network here at Essex. This is Ethernet, which comes in four speeds: 10Mbps, 100Mbps, 1000Mbps (or 1Gbps) and 10Gbps, and three forms: twisted-pair; fibre; and wireless there are a couple of other types of network worth mentioning: ATM, and SDH.
The higher level protocol (language) that we use on our Ethernet network is IP (the Internet Protocol).
This is a "Local Area Network" (LAN). All this means is there is a physical limit on the size of the network (in this case about 1.5km radius, or conveniently, about the size of the University!). Recent developments have extended the range of Ethernet, so it can now be considered a "Metropolitan Area Network" (MAN) too.
The Ethernet specifications define the lowest level of communication protocol (language). There are several higher levels of protocol used on Ethernet, but only applications that use the same protocol can talk to each other.
This is a network that can run as a LAN, a MAN, or as a WAN (Wide Area Network). ATM (Asynchronous Transfer Mode) was heralded as the network to end all networks because it is flexible enough to be used as a LAN, a MAN, or as a WAN, and (in theory) scalable in speed without limit. In practice it turned out to be too complex, and therefore too expensive to be of great practical value.
This is another WAN. SDH (Synchronous Digital Hierarchy) is a fast network based on glass fibre optics, usually leased from a telecomms company (as it's main use is to carry telephony traffic). Although it's low-level protocols are different from those of Ethernet, it can transparently carry IP traffic. We only use SDH for some of the WAN links to the other campuses.