Computer Networking


NETWORKING             INTRODUCTION
A computer network is group of computers that are connected together to share resources, such as hardware, data, and/or Software. It is a data communication system that interconnects computer Systems at different sites. Networking is a collection of individual networks, connected by Intermediate Working devices that function as a single large network. Industries, colleges & many business organizations use internetworking. For many purpose such as fast communications internally, sharing a device for many computers and for many other purposes also. 

HISTORY & CHALLENGES of NETWORKING

The first networks were timesharing networks that use mainframes and
 attached terminals. LAN evolved around PC evaluation. LAN enabled multiple     users in a limited geographical area. Lack of management and duplication of resources resulted in evolution of LAN. Challenges were connecting various systems together having various Technologies. Making standards was again a big challenge. Challenges were face in mostly these areas such as connectivity, reliability, network management & flexibility. The final concern was related to network expansion & new technologies.  

TYPES OF NETWORKS

1.                       LAN (local area network)
2.                       MAN (metropolitan area network)
3.                       WAN (wide area network
LOCAL AREA NETWORK
    INTRODUCTION TO LOCAL AREA NETWORK(LAN)
A local area network is a group of computers and associated devices that share a common Communications line or wireless link and typically share the resources of a single processor or server within a small geographic area. Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users or as many as thousands of users.
A non-public data Communications network Confined to a limited geographic area (usually within a few miles), used to provide communication between computers and peripherals. The area served may consist of a single building, a cluster of buildings, or a campus-type arrangement.
In a typical LAN configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers Connected to the file server are called work stations. The workstations can be less powerful than the file server, and they may have additional software on their hard drives. cables are used to connect the network interface cards in each computer.

OPEN SYSTEM INTERCONNECTION MODEL (OSI)
The International Standards Organization developed a theoretical model of how networks should behave and how they are put together. The ISO's model is used through the industry today to describe various networking issues. This model is called the Open Standards Interconnect Model.
The Open Systems Interconnection reference model for describing network protocols was devised by the Internet Standards Organization. It divides protocols in to seven layers to standardize and simplify definitions.
SEVEN LAYERS OF OSI MODEL
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data-link Layer
Physical Layer
    Layer
                               
                Function
     Protocol
N/W
Device
Application
User     Interface
·                     used for applications specifically written to run over the network
·                     allows access to network services that support applications;
·                     directly represents the services that directly support user applications
·                     handles network access, flow control and error recovery
·                     Example apps are file transfer-mail.
DNS; FTP; TFTP;  TELNET;
NCP;
Gateway
Present-
ation
Translation
Translates from application to network format and vice-versa all different formats from all sources are made into a common uniform format. Responsible for protocol conversion, character conversion, data encryption / decryption, data compression.

Gateway

Session "syncs and sessions"
establishes, maintains and ends sessions across the network provides synchronization services by planning check points in the data stream => if session fails, only data after the most recent checkpoint need be transmitted manages who can transmit data at a certain time and for how long
NetBIOS
RPC
Gateway
Transport packets; flow control & error-handling
·                     divides streams of data into chunks or packets; the transport layer of the receiving computer reassembles the message from packets
·                     provides flow control & error-checking to guarantee error-free data delivery, with on losses or duplications
·                     provides acknowledgment of successful transmissions; requests retransmission if some packets don’t arrive error-free
TCP, ARP, RARP;

Gateway
Brouter
addressing;
routing
·                     translates logical network address and names to their MAC address responsible for addressing, determining routes for sending , managing network problem
·                     If router can’t send data frame as large as the source computer sends, the network layer compensates by breaking the data into smaller units. At the receiving end, the network layer reassembles the data
IP;
ARP;  RARP,
ICMP;
IGMP;
IPX
OSI

Router
ATM Switch
Data Link data frames to bits
·                     Turns packets into raw bits at the receiving end turn bits into packets.
·                     handles data frames between the Network and Physical layers
·                     the receiving end packages raw data from the Physical layer into data frames for delivery to the Network layer
·                     responsible for error-free transfer of frames to other computer via the Physical Layer
·                     This layer defines the methods used to transmit and receive data on the network. It consists of the wiring; the devices use to connect the NIC to the wiring, the signaling involved transmitting / receiving data.
Logical Link Control
error correction and flow control
802.1 OSI Model
802.2 Logical Link Control
bridge
Switch
Hub
NIC
Media Access Control
hardware; raw bit stream
·                     transmits raw bit stream over physical cable
·                     defines cables, cards, and physical aspects
·                     defines NIC attachments to hardware, how cable is attached to NIC
·                     defines techniques to transfer bit stream to cable .
IEEE 802
IEEE 802.2
ISO 2110
ISDN
Repeater
Multiplexer
Hubs
WORKING OF OSI MODEL

Components of LAN
Network Cabling
Network Devices
Network Topology
Protocols

                What is Network Cabling?

Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.
The following sections discuss the types of cables used in networks and other related topics.
·          Unshielded Twisted Pair (UTP) Cable
·          Shielded Twisted Pair (STP) Cable
·          Coaxial Cable
·          Fiber Optic Cable

Unshielded Twisted Pair (UTP) Cable

Twisted pair cabling comes in two varieties: shielded and unshielded. Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks. The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter is the
twisting, the higher is supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated five categories of wire.

Unshielded Twisted Pair Connector  

The standard connector for unshielded twisted pair cabling is an RJ-45 connector. This is a plastic connector that looks like a large telephone-style connector . A slot allows the RJ-45 to be inserted only one way. RJ stands for Registered Jack, implying that the connector follows a standard borrowed from the telephone industry. This standard designates which wire goes with each pin inside the connector

Shielded Twisted Pair (STP) Cable

A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference. Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky. Shielded twisted pair is often used on networks using Token Ring topology.

Coaxial Cable

Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield .The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers
Fiberoptics
          Fiber optics is a system which transmits signals from one location to another through a thin strand of glass which carries light pulses to carry data. This transmission system works on the same principle that copper wires do, but is done in a different way. Data is encoded from electrical signals into optical light pulses, sent through a glass medium and converted back and decoded at the other end. Both copper and optics use electricity at the end of their lines, but optics uses light in between to carry the data.
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