Introduction To Networks

In today’s world, we use shared Client-Server and peer-to-peer topologies. Although there are many protocols used to connect the nodes together, and hence many network types – there are three defined sizes of Networks namely LAN, MAN, and WAN.

• LAN (Local Area Network) – a computer network confined to a relatively small area, such as a single building or a group of adjacent buildings. A LAN can cover an entire campus, so long as the buildings are directly connected. The nodes (computers, printers, servers, etc. ) are connected via bridges and routers. Devices can be connected by a twisted-pair wire, coaxial cables, or fiber optic cables.
• MAN (Metropolitan Area Network) – a data network designed for a town or city. MANs are larger than local-area networks (LANs) in terms of geographic breadth but smaller than wide-area networks (WANs). Some MAN networks do without connecting media altogether, communicating instead via radio waves, using dish antennas on rooftops.
• WAN (Wide Area Network) – a computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet.

The definitions can blur a bit.

• A LAN becomes a MAN if there are connections between separate LANs across a town or city – typically via a LEC (Local Exchange Carrier), such as Bell South or Verizon.
• A MAN becomes a WAN if there are connections between separate LAN’s across the country – typically via an IXC (InterExchange Carrier) such as AT&T, Sprint, or MCI.
• For example, if a company had two sister sites in Philadelphia and New York each with their own LAN, and they decided to connect them together by purchasing a T1 (a 1.544 Mbps data connection) from MCI – then each city still has its own LAN, but the two LAN’s connected together is WAN.

Point A to Point B. Data = Information. Well, OK, but right away we have two problems. ..what to use to connect the computer together (cables – the medium), and what type of interface to use (sockets, jacks, etc. – the connectors).

We have to define these cables and connectors in both electrical and physical terms. Thankfully, that has already been done for us, and a huge set of standards are in place. We need only select which standard to use.

The data can be analog or digital. There are no more pure analog networks anymore. Residential voice and dial IP does traverse an analog medium, but only for a short distance – it is quickly converted to digital at the first remote facility it encounters.

Usually before it even reaches the central office of the local exchange telephone company. Many Engineers and Technicians concentrate their learning 100% on digital Data. For the most part, that is fine – few work with analog communications these days.

But to be a true professional, you should at least be familiar with the basics of the PSTN (Public Switched Telephone Network) and telephones themselves, so take some time, and read that awfully dry section on Telephones (Telecom 101 ).

NOTE: one crucial point, that for some odd reason is never discussed, ANYWHERE – but you should keep in mind that virtually all networks communicate bi-directionally. They don’t tell you whether a defined speed for a circuit is shared between the two directions. Fortunately, it is not.

For example, a T1 is 1.544 Mbps – both ways !! This means you can be sending 1.544 Mbps, and at the same time, receiving 1.544 Mbps. So, functionally, a T1 can transmit twice that, or 3.088 Mbs. It’s a wonder that advertisers never picked up on this and began touting their wares at the full, additive, bi-directional speed.

Also, circuits can be symmetrical, as is the case with a T1, or asymmetrical, as is the case with ADSL (Asymmetric DSL) and dial IP (56 kbps in and 33.3 kbps out).

That will give you a good foundation, and you can now chat with the old vets before they retire. Then mosey on over to the Electricity , Standards , and CPE (Customer Premises Equipment) pages – and finish up by reading the Voice (Switched Networks) , IP , Frame Relay , and ATM sections.

Protocols are defined as a “set of rules“. They are the details of how the data is formed, transmitted, and received. They also include error checking, flow control, and numerous interfaces.

Instead of just creating hundreds of protocols and listing them in standards manuals separately, it was decided that some type of layered structure was needed for digital, packet-based communications.

A packet is nothing more than a set of bits (1’s and 0’s) contained as a single unit of data. The whole concept of managing bits as packets revolutionized data communications.