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1. Networks
2.
3 types of networks. Elements of a local area network
4. Network topology
5. Client / server protocol
6. Transmission media (communication lines)
NETWORKS:
set of techniques, physical connections and software used to connect two or more computers or computers. The network users can share files, printers and other resources, send emails and run programs on other computers.
A network has three levels of components: application software, network software and network hardware. Application software consists by computer programs that communicate with users on the network and to share information (such as database files, documents, graphics or video) and resources (such as printers and disk drives). One type of application software is called client-server. Client computers send requests for information or use of resources to other computers, called servers, which control the data flow and execution of applications across the network. Another type of software application is known as "peer to peer (peer to peer). In one such network, computers send each other messages and requests directly without using a server as intermediary. These networks are more restricted in their security capabilities, audit and control, and are typically used in work areas with few computers and that does not require a strict control of application usage and privileges for accessing and modifying data , are used, for example, home networks or workgroups within a larger corporate network.
Network software consists of computer programs that establish protocols and standards for computers to communicate. These protocols are implemented by sending and receiving formatted data groups called packets. The protocols indicate how to make logical connections between applications network, directing the movement of packets across the physical network and minimize the chances of collision between packets sent simultaneously.
The network hardware consists of the hardware components that connect computers. Two important components are the transmission media that carry signals from the computer (typically standard cables or fiber optics, but there are wireless networks that perform transmission infrared or RF) and network adapter, which allows access to material medium that connects computers to receive software packages from the network and to transmit instructions and requests to other computers. The information is transferred as binary digits, or bits (ones and zeros) that can be processed by electronic circuitry of computers.
TYPES OF NETWORKS:
LOCAL AREA NETWORK (LAN)
One of the most critical events for networking is the emergence and rapid spread of local area network (LAN) as a way to standardize the connections between machines that are used as office systems. As its name suggests, is a way of connecting a series of computers. At its most basic level, a LAN is simply a shared medium (such as a coaxial cable that connects all computers and printers) together with a set of rules governing access to such means. The most widespread LAN, Ethernet, uses a mechanism known as CSMA / CD. This means that each connected device can use the cable only when no other team is using. If there is any conflict, the team that is trying to connect the void and makes a new attempt later. Ethernet transfers data at 10 Mbits / s, fast enough to make negligible the distance between the various teams and give the impression that they are connected directly to its destination.
There are many different types (bus, star, ring) and different access protocols. Despite this diversity, all LAN share the characteristic of having a limited range (usually span a building) and having a sufficiently high speed connection to the network invisible to the used equipment.
addition to providing shared access, modern LANs also provide users with many advanced features. There are software packages to control the configuration management of computers in the LAN, the user management and control of network resources. A widely used structure consists of several servers available to different users. The servers, which are often more powerful machines, provide services to users, usually personal computers, and control of printing, file sharing and email.
ELEMENTS OF A LOCAL AREA NETWORK A LAN
there hardware and software elements among which are the following:
• Server: the main processing element contains the network operating system and is responsible for managing all processes within it, also controls access to shared resources such as printers and storage drives.
• Workstations: sometimes called nodes, can be personal computers or any terminal connected to the network. In this way works with its own programs or take advantage of existing applications on the server.
• The network operating system-the program (software) that allows control of the network and reside on the server. Examples are network operating systems: NetWare, LAN Manager, OS / 2, LANtastic and Appletalk.
• Communication protocols: they are a set of rules governing the transmission and reception of data over the network.
• The network interface card, provides connectivity to the terminal or user of the physical network, as it handles the communication protocols of each topology specified.
Wide Area Networks (WAN)
When it reaches a certain point, ceases to be impractical to continue to expand a LAN. Sometimes this is imposed by physical limitations, although there is usually more appropriate or economic ways to expand a network of computers. Two important components of any network is the telephone network and data. They are links to great distances that extend the LAN to turn it into a wide area network (WAN). Almost all the national network operators (such as DBP in Germany, British Telecom in England or Telefonica in Spain) offer services to interconnect computer networks, ranging from simple data links and low speed running based on the public telephony to complex high-speed services (such as frame relay and SMDS-Synchronous Multimegabit Data Service) adequate for LAN interconnection. These data services are often called high-speed broadband connections. Is expected to provide the necessary links between LAN to make possible what has been called the information superhighway.
NETWORK TOPOLOGY:
refers to as distributed, organize and connect all computers or devices within a network, ie how interconnected the different nodes that form.
CRITERIA WHEN CHOOSING A NETWORK TOPOLOGY:
• Seek to minimize routing costs (need to choose the easiest route between the node and others)
• Fault tolerance and ease of location to them.
• Ease of installation and reconfiguration of the network.
types of topologies: Star Topology
:
is characterized by all nodes connected to a central controller. All transactions pass through the central node being the manager to manage and control all communications. The central controller is usually the network server, but can be a special connecting device commonly called hub or hub.
Advantages:
• It has good flexibility to increase the number of computers on the network.
• If one computer fails the network behavior continues without problems, however, if The problem arises in the central controller will affect the entire network.
• Diagnosis of problems is simple, because all computers are connected to a central controller.
Disadvantages:
• Not suitable for large installations due to the amount of cable which should be grouped in the central controller.
• This configuration is quick for communications between stations or nodes, and the driver, but communications between stations is slow.
Ring topology:
All stations or nodes are interconnected in a ring, forming a closed one-way road that connects all nodes. Data travels the ring along a single direction, ie, the information passes through the stations that are on the way to reach the destination station, each station gets the information that goes out to her and relayed to the next node have a different address .
Advantages:
• This topology can increase or decrease the number of stations without difficulty.
• The speed depends on the flow of information, many more stations try to use the slower network information flow.
Disadvantages:
• A failure of any party fails blocked the whole network.
bus topology or channel:
nodes forming a path connecting vi directional communication with well-defined termination points.
When a station transmits, the signal is propagated on both sides of the issuer did all the stations connected to the bus, up to the terms.
So when a station transmits a message reaches all the stations, so the bus is called a broadcast channel.
Advantages: • Allows
easily increase or decrease the number of stations.
• The failure of any node does not prevent the network continues to function normally, which can add or remove nodes without disrupting its operation.
Disadvantages:
• Any break in the bus prevents the normal operation of the network and the fault is very difficult to detect.
• Control the flow of information has drawbacks because several stations try to transmit at a time and there is a single bus, so it only achieved the transfer station.
client / server protocol
Instead of building monolithic systems like elements, there is general agreement to build as client / server systems. The client (a PC user) requests a service (such as printing) that a server provides (A processor connected to the LAN). This common approach to the structure of computer systems leads to a separation of the functions previously form a whole. The details of the performance range from simple approaches to the real possibility to manage all computers in a uniform manner.
transmission medium (communication line)
is the physical facility used to interconnect computers or devices to create a network that carries data between users. TWISTED PAIR CABLE
:
is the most ancient in the market and some types of applications is the most common.
consists of two copper wires or aluminum often isolated and a thickness of 1 millimeter.
The wires are twisted in order to reduce electrical interference from nearby peers.
twisted pairs are grouped under a cover co'mun of PVC (polyvinyl chloride) in multi-pair twisted pair cables (2, 4, 8 to 300 pairs)
An example is the twisted pair telephone system now have become a standard in the field of local, standard colors for this purpose are:
• Orange / White - Orange
• Green / White - Green
• White / Blue - Blue
• White / Brown - Brown
TYPES OF TWISTED PAIR CABLES:
• Shielded Twisted Pair Cable (STP) is generally used in data processing facilities for their ability and good characteristics of electromagnetic radiation, but the downside is that cable is a robust, expensive and difficult to install.
• Cable unshielded twisted pair (UTP) is the best that has been accepted by its cost, accessibility and ease of installation. The UTP cable is the most widely used in telephony. There are currently 8 categories of UTP cable. Each category has the following electrical characteristics:
attenuation. Ability
line Impedance.
or Category 1: This cable is specially designed for telephone networks, cable is typically used for mobile phone companies. Reach a maximum speed of up to 4 Mbps
or Category 2: cable properties identical to category 1.
or Category 3: It is used in computer networks of up to 16 Mbps speed and with a bandwidth of up to 16 Mhz.
or Category 4: This is defined for computer networks such as Token Ring ring with a bandwidth of up to 20 Mhz and with a speed of 20 Mbps
or Category 5: A communications standard in LANs. Is able to support communications up to 100 Mbps with a bandwidth of 100 MHz. This type is 8-wire cable, which is four twisted pairs. Cable attenuation in this category is given by the table referring to a standard distance of 100 meters:
or Category 5e: This is a Category 5 enhanced. Minimizes attenuation and interference. This category has no standardized rules even if differentiated by the different agencies.
or Category 6: It is not standardized but is already being used. Defining its characteristics to a bandwidth of 250 MHz.
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