A classification for networks:

1. Peer-to-peer networks;

2. Server-based networks.

At least two computers form a peer-to-peer network. In a peer-to-peer network there are no dedicated servers, and the there is no hierarchy between computers - all the computers are equal. That's why its name is peer-to-peer network.

Every computer in this network is a client and a server in the same time. It is obvious that in this type of networks you won't find an administrator. Every user must take care of his/her computer - he/she is user and administrator for his/her machine.

This kind of network is cheaper than the server based network. You realized you don't have to buy a system and make it a server in this network. Maybe you need to know what a server is. A server is a dedicated machine, that isn't used like a client and that responds to clients requests. A server-based network is more secure than peer-to-peer, that's why if security is an important factor, you'll have to implement a server-based network.

Topology

This term is referring to spatial disposal of the computers in a network. Later on, I'll explain only the most important topologies and their characteristics, without giving details and explanations about the transfer of data in a network.

If your network computers are tied one after another and they are connected to one single cable, this topology is BUS. This is the simplest method of connecting computers to a network.

Another topology is STAR. In this example, all the computers in the network are connected to a central device, named HUB. A characteristic to this topology, which I have to mention, is that one of the network computers crashes, the other systems aren't affected, and the network is still employable. The HUB status must be ok, because the network performance depends on it.

RING topology is that where the computers are connected to a cable that forms a closed loop. This example doesn't have free terminals, and all the systems are regenerating the signal. The signal goes trough all the computers in this loop that's why when one of the systems breaks down the network doesn't work. There are combined topologies used now, like: BUS-STAR, RING-STAR.

Cable types You'll definitely need a cable, so the most used cables are:
- Coaxial cables;
- Twisted cables;
- Optic fiber cables.

Thin coaxial cable (10Base2)
This is the cable used for TV's. Everybody must know which is that, so the details are useless.

The signals goes approximately 180 meters trough this cable. They usually use it for the BUS networks. It has a thickness for about 6mm and it is a cheap cable.

Thick coaxial cable (10Base5)

The difference between thick and thin coaxial cable is obvious the diameter. In the thin coaxial cable case we can see the thickness is no more than 6mm. The thick one is approximately 12mm. It can be used for bigger networks, so it can connect computers that are at an approximately 500 meters distance in between. This kind of cable is usually used as the main cable for a BUS network.

The connectors for coaxial cables are BNC (British Naval Connectors). There are 3 types of BNC that are used to build a network with coaxial cable. The needs for a functioning BUS network are: a BNC, a BNC T (it connects the network device to the coaxial cable) and a terminator to indicate an extremity to the network.

Twisted cables (UTP or STP) (10BaseT)

You don't know which is the unshielded twisted cable? Then you must look at the cable that connects your phone to your modem, if you have something like this. The connector for this cable is RJ-11 and it is used to four wires twisted cables. In a network the RJ-45 is used. This connector contains connections for 8 wires. There are two types of twisted cables:

• Unshielded Twisted Pair - UTP (unshielded twisted cable)
• Shielded Twisted Pair - STP (shielded twisted cable)
The UTP cable is cheaper than STP cable, which has a protective shield that protects the transmitted data by eventually interferences.

Optic fiber cable
The last important cable type is optic fiber cable, which is the most expensive. Why is it expensive? The answer is obvious after you'll see its properties. Optic fiber cable can be used on 2000 meters distances without the need of a repertory. This cable isn't affected by interferences and it can send the data with greater than 100Mbps, or even 1Gbps speeds. A core, glass reinforcement and a protective shell make the optic fiber cable. Just one fiber can't assure a double senses transmission, that's why an optic fiber cable is formed by two fibers.

What about the network architectures?

Two of the most important architectures for a network are Ethernet and Token Ring. Ethernet is without a question the most popular network architecture at this moment. This architecture uses the BUS topology and can be used to transmit data at 10Mbps and 100Mbps, because of the 100 BaseXEthernet (or, usually named Fast Ethernet). In this architecture the most often used topology is the BUS, but we can use the BUS-STAR topology. This architecture uses coaxial cables and UTP cables.

The transfer speeds of data are grouped in four standards created by IEEE (stands for Institute of Electrical and Electronics Engineers) for greater than 10Mbps speeds and two standards for 100Mbps.
• 10Base2 refers to an Ethernet network that uses the thin coaxial cable.
• 10Base5 refers to an Ethernet network that uses the thick coaxial cable.
• 10BaseT refers to an Ethernet network that uses UTP cables to connect the computers.
• 10BaseFL refers to an Ethernet network that uses optic fiber cable.
• 100Base VG - Any LAN Ethernet.
• 100BaseX Ethernet Another architecture may be Token Ring architecture. It can reach a transfer rate of data for about 16 Mbps. This architecture is not so frequent like the Ethernet architecture. Some of its characteristics are: RING-STAR topology, STP or UTP cables and 4 to 16 Mbps transfer rates.