02. What is a Network? | Free CCNA RS training 200-125 CCNA v3.0 | Networking

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By definition a network is a group of two or more computer systems linked together.

To be blunt a network is a bunch of devices interconnected, some devices are requiring information, others are providing the information and others are carrying the information.
In CCNA you’ll learn how that information is carried. And the carriers are the network devices.
But the most important components are the hosts (PCs, phones, smartphones, tablets, etc.) now a days as hosts, we also have fridges, washing machines, surveillance cameras, vacuum cleaners and so on believe it or not.
On the left you can see how they look in a logical diagram and on the right it’s the real world.
Than you have the network devices that gives you access to a network (switches, bridges, wireless access points, hubs), after you pass those you will hit the infrastructure devices which are Firewalls, Routers. Well talk about more about these devices in the next videos, and for the next video we’ll talk more about hubs, bridges and switches.
Now all of these types of devices they connect to each other via a medium of transmission, that consists in thin air (like when you connect to a wi-fi network), cables (co-axial, Twisted Pair for LAN, for WAN serial cables, fiber optic)

Twisted pair cables. The first question you may ask might be: “why are they twisted?”. Well they are twisted so the electricity flow is much better and to have less interference.

Fiber optic cables people. Now these are fast, instead of electrical signal they are using light, for sort distances most of them are using Lightning Emitting Diode and longer distances like hundreds of miles they use Laser, ain’t that cool?
MMF vs SMF
Multimode fiber offers high bandwidth at high speeds over short and medium distances. Light beams are sent in different modes as they travel through the cable's core. The drawback for long cables, greater than 914.4 meters or 3000 feet, multiple paths of light can cause signal distortion at the receiving end, which gives an unclear and incomplete data transmission.
Single mode fiber offers a higher transmission rate, up to 50 times more distance than multimode, but it also costs more. Single-mode fiber has a much smaller core than multimode. The small core and single light beam will almost eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fiber cable type.
are hot-swappable input/output device plugs into a Gigabit Ethernet port or slot.