LOCAL NETWORKS

LOCAL NETWORKS

1. COMPUTER NETWORK

   • A computer network is a set of computers and devices connected to each other for the purpose of sharing information and resources.
     • Network allow information, hardware and software to be shared between the computers that compose it. In any type of network we will find:
       • transmitter
       • receiver
       • channel
       • encoding
       • decoding
       • protocol

2. SIZE OF THE NETWORKS

   • There are three types of computer networks depending on the distance between the computers that compose it
     • LAN: Local Area Networks
       • the computers are very close to each other, they are into the same building
     • MAN: Metropolitan Area Networks
       • they are made up of computers distributed throughout a city
     • WAN: Wide Area Networks
       • they are made up of computers spread throughout a country, a continent or the entire world

3. WHOSE NETWORKS ARE THEY?

   • depending on their level of access or privacy
     • Public networks
     • Private networks
     • Virtual Private Networks
       • they are a type of networks resulting from the interconnection of several private networks with each other

4. PEER-TO-PEER NETWORKS AND CLIENT-SERVER NETWORKS

   • Networks can be organized according to two types of functional approaches:
     • CLIENT-SERVER NETWORKS
       • A server is a computer in charge of centralizing a certain necessary function within a network. The rest of the computers on the network are called clients or terminal and are the stations from which users communicate with the central computer
     • POINT-TO-POINT NETWORKS
       • They are also called peer-to-peer networks. In this type of network, all nodes or workstations behave simultaneously as clients and servers. These networks are usually valid models in small and simple networks, with little data, few resources to share and few users.

5. THE TOPOLOGIES

   • The topology is the way in which we can connect
     • Bus topology
       • It consists of a single cable that sequentially connects all the equipment on the network. The ends of the bus are closed with a terminator
     • Ring topology
       • It is a closed network in which the equipment is located in a similar way to that of the bus, but in this case forming a completely closed ring, so the cable doesn't have terminators
     • Star topology
       • In this type of network, all computers are connected to a specific device that is responsible for transmitting information. This device is usually a hub or, more often, a switch

6. THE ETHERNET STANDARD

   • Depending on the physical medium used to interconnect the different elements of a network, it receives a certein name following international standards specified by the Institute of Electrical and Electronics Engineers (IEEE)
   • Ethernet networks have been presenting different adaptations throughout their little history. Today, most LANs that use copper cable are Ethernet 100 Base-T, depending on the data transmission speed. On the other hand, the networks that use fibre optic cable are Ethernet 1000 Base-LX/SX
   • There are also other standards such as IEEE 802.11, which defines the characteristics of Wi-Fi networks, that is, networks without cables or wireless

7. WIRED NETWORKS

   • In this type of network, the information travels in the form of waves encapsulated within a cable. Said cable can be twisted pair, fiber optic or coaxial
     • The twisted pair cable (UTP and STP)
       • UTP cable consists of copper or aluminum wires interwoven in pairs in order to maintain stable electrical properties and avoid interference with nearby pairs of wires. Depending on the number of pairs of wires used and the length of each twist, different transmission speed are obtained, which the industry has called categories (CAT)
       • STP cable is a variant of UTP that is even more secure in transmission. It increases the amount of insulation around the cable, that increases its immunity to noise, it's more expensive than UTP. It's normally used for industrial installations and those where the signal is subject to a high level of interference
     • Fibre optics
       • Is a transmission medium that is increasingly used in data and telecommunications networks. A fibre optic is made up of a group of optical fibres, each of which is a very fine thread of transparent material through which light pulses are sent that represent the data to be transmitted. The light source can be a laser or an LED.
         • Its bandwidth is very large. In addtition, it is quite safe, since it is totally immune to electromagnetic interference
         • The disadvantages are mainly in the cost, because it uses receivers and transmitter that are more expensive and complex to repair
         • The fibers most used in LAN networks are the so-called multimode. When large distances are to cover, fibre is used single-mode, which allows reaching long distances and transmitting high information rates

8. WIRELESS NETWORKS

   • They are also called WLANs, provide a very flexible communication system by completely eliminating the use of cables. This has meant that in recent years they have had a great acceptance. Even so, WLANs aren't intended to completely replace wired LANs. but rather serve as a complement to these, mainly due to the fact that their transimission speed is lower for now, and they are subject to greater interference
     • Wi-Fi technology
       • Wi-Fi is a system for sending data over computer networks that uses radio waves. There several devices that interconnect elements Wi-Fi
         • Wi-Fi routers
           • They are receiving signal line offered by the telephone operator. 
         • Access points
           • They work as a remote sender, in places where the Wi-Fi signal of the router doesn't have enough radio. 
         • The reception devices can be of three types: Wi-Fi cards integrated into the motherboards of computer, PCI network cards and USB cards
     • Bluetooth technology
       • Bluetooth defines a global standard for wireless communication over a radio frequency link. The devices that normally use this technology are included in the personal computing sector, such as PDAs, mobile phones, laptops, etc
     • Other wireless media
       • Infrared using a transmission technique based on the light rays moving in the infrared spectrum. Supports a wide range of electrical, computing and communications devices. On the other hand, there is also microwave transmission

9. DEVICES ON A LAN NETWORK

   • The network card
     • Network cards are the devices that connect computers to the network. Each network card has a unique identifier called MAC
   • The switch
     • It is a device that centralizes the wiring of a star network and thus constitutes its central node. A switch can also act as a LAN
   • The router
     • It is an interconnection device for computer networks. Its function is to interconnect network segments or entire networks

10. THE TPC/IP COMMUNICATION PROTOCOL

    • Computers must speak the same language (communication protocol) in order to share information and resources on a network
      • TCP/IP
        • It has become a fundamental element of the structure of today's operating systems
        • It's formed by the union of two protocols
      • Classes of IP adress
        • The Internet community has defined classes of IP addresses to accommodate networks of various sizes 
        • There are three classes of IP address: Class A, Class B and Class C
      • Routing or gateway
        • This role of routing addresses outside the network is perfomed by a router
        • The router communicates with the rest of the computers on the LAN
      • IP address
        • Each node or element of a network must be identified by a unique IP address
        • The IP number is made up of a set of four one-byte decimal digits

11. TCP/IP SERVICES

    • The DNS is a system similar to the phone book, Instead of remembering complicated IP adresses, we can connect to a host using its DNS name, more easily. DNS service is provided by a DNS server. Normally the Internet provider must be the DNS server at the same time and has to interpret the names we type by translating them into IP addresses.
      • The DHCP service
        • It's a network protocol that allows nodes in a networkobtain its IP configuration parametres automatically
      • Fixed port services: HTTP, FTP, POP3...
        • Many programs on a network use TCP to create connections between them, nd these programs usually run simultaneously. The TCP protocol allows the connections of these programs between the different hosts by means of a mechanism called port

12. DOMAIN WORKGROUPS AND NETWORKS

    • Local networks can be classified from the point of view of their operation in peer-to-peer networks (workgroups) and client-server networks (domain networks).
      • In a peer-to-peer network, users must be created or defined on all computers that share resources such as folders, pinters, etc.
      • In domain networks, there is a team in charge of defining which users can access the network and with what permissions