NETWORKS and NETWORKING ?

A computer network assures: sharing of hardware and software to its computers; lower costs due to collective use of data and peripherals; Shared access to a large number of alternative storage devices; reduction times for obtaining information; emergence and development of a communication environment which is upgraded continuously, etc..

Distributed IT based on computer networks means connecting the computing system resources using the communicating systems at the level of departments, companies, institutions (on a limited area), campuses, towns and even large areas or countries. .

Computer network In terms of the infrastructure: a computer network is a set of computers interconnected through communication media (telephone, cable, etc..) in order to use some common hardware (printer, scanner, copier) and software (operating systems, applications, etc.)… In terms of the resources used: a computer network is a set of physical resources (communications equipment, transmission media), logical (operating systems, applications) and information (bit data) that interact among themselves.

Depending on the covered area, networks can be of different types: Network types   Depending on the covered area, networks can be of different types: Wide Area Network (WAN) over 100 km Metropolitan Area Network (MAN) from 1-100km Local Area Network (LAN) under 1 km.

The component elements of a network are: The PC also named the host ; The transmitter -a device through which information is converted into transmitted signals respecting certain rules called protocols * and using media and information transmission equipment Transmission media * The protocol is a set of conventions and rules by which data transmission is performed;

Communication subsystem The vital role among networks is played by the communication subsystem which assures the communication between the distance parts of the network, using the rules used in the networking protocols and the network ability of transporting information.

Local Area Network (LAN) The LAN components:   Workstations Servers (sometimes named file-servers) Connecting and linking cables Network adapters

LANs elements The working station consists usually in a PC connected to a network using a network board; it is used for executing different tasks and works using application software.  The server is a computer that provides information resource at the demand of the clients. In the case of the LANs, we usually talk about the file server, a computer that is loaded and runs the Net Operating System (NOS). The server supervises the communication among the network and manages the shared resources (the files, the printers, the users, the access rights etc).

Communication equipment From the interconnecting point of view there are several components: -the repeater -the bridge -the router -the gateway

Communication equipment Repeater - allows two or more connecting network segments. A network segment is limited and has a predetermined number of computers depending on the length, the transmission medium is any case that sent a signal strength attenuates with distance once. For example, UTP Cat 5 cable is the maximum permissible distance of 100m, beyond this length no longer guarantee correct operation. To allow the inclusion of computers at longer distances is needed to restore signal device, called repeater device.

Communication equipment The gate (bridge) allows the communications between the networks which have different physic levels and different data linking level. It assures the linking of networks with different transmission environments, for example between fiber and UTP. For instance, using a LAN, a TOKEN RING network can be linked to a ETHERNET network. The router is an element that is used for interconnecting the networks and it assures the right way between different sub-networks.

Communication equipment The Hub is a device level network to have more ports (inputs) necessary for interconnection through UTP cables at least two network computers (hosts); The Switch is a network device, it allows simultaneous communication of several computers at the same time, it filters and sends data packets between different network segments Depending on the physical address (MAC address), Address Resolution Protocol (ARP) is the protocol used to make the correlation between IP and MAC address (physical address of the device's)

Communication equipment The router is a device, or in some cases, the software installed on a computer, which identifies the next network point to which transmit a data packet on its way towards the destination. The router is connected to at least two networks (the point where a network communicate with each other, i.e. the gateway).

Local Area Network topologies   The network topology means the physical plan of connecting the computers in a network (Hubs, commuters, and interconnecting elements like routers, bridges etc).

Network topologies Star Tree Bus Non regular Complete

Star topology In a star topology, each node of network which accepts and delivers information, it is connected to a central node, where all the traffic is directed. The central node must own information that defines the topology of the network. All the other nodes are connected using a distinctive line and the directing table of central node indicates the right line for each destination.

Tree topology In such of network there is only one way between a pair of nodes, but there can exist several ways between non pair nodes. All the information needed for the functioning of the directing algorithm can be contained in the address of destination node.

Bus topology Bus topology means the arranging of the nodes in a linear structure using a unique shared communication line.   The access points are connected using passive joints at the support and the information is sent and received using all the other access points

Ring topology It assures a limited physical connectivity, asymmetrical between the system elements, each element being connected only to the next neighbor using dedicated unidirectional lines. Each node contains a information receiver, so all the access points are active. The cable is the used medium in this type of network.

Non regular topology In this case, the computers are linked in a apparently random way (in fact different rules are being respected considering the criteria asked when designing the network. A combination of topologies is the topology that uses Hubs (a Hub has the role of a repeater and the switch has the role of a central node).

Complete topology This topology assume a total connectivity among the nodes, and it is used when the reliability of the network is asked to be high.

The connection protocol TCP/IP Class Addresses Interval Addresses Network class Hosts/Class A 0.0.0.0-127.255.255.255 128 16.777.214 B 128.0.0.0-191.255.255.255 16.384 65.534 C 192.0.0.0-223.255.255.255 2.097.152 254 D 224.0.0.0-239.255.255.255 268.435.456 E 240.0.0.0-255.255.255.255 undefined Private networks 10.0.0.0-10.255.255.255 - Network class A 172.16.0.0-172.31.255.255-Network class B 192.168.0.0.-192.168.255.255- block Network class C

Domains hierarchy com commercial companies, business edu educational organizations, universities gov governmental organizations int international organizations mil military organizations net portals org non-gov organizations For different countries come from areas namely their short name: ro-Romania, fr-France, etc...

Internet, Intranet Internet is defined as a large collection of networks or as a "network of networks". From a technical standpoint, the Internet is a large network that interconnects autonomous networks. According to Internet World Usage Statistics and News, 31 March 2009, there are 1.596.270.108, Internet users, representing a penetration rate of 23.8% based on estimated world population in 2009. Intranet - a private computer network (LAN or WAN) which allows to a company employees to share and exchange information, email messages or even restricted company files.

World Wide Web URL (Uniform Resource Locators) http://www.ubbcluj.ro HTTP (Hyper Text Transfer Protocol) FTP (File Transfer Protocol) HTML (Hyper Text Mark-up Language) XML (Extensible Markup Language)

Web surfing Browsers Internet Explorer, Netscape Navigator, Opera, Mozilla… Search engines  www.google.com (Language tools, email -gmail) www.yahoo.com (community, email, messenger) www.altavista.com (translate) www.msn.com ( owned by Microsoft). Web editors : Front Page, Publisher, 1rst page, etc.(Word)