A network diagram depicts the nodes and connections amongst nodes in a computer network or, more generally, any telecommunications network
Symbolization
Readily identifiable icons are used to depict common network appliances e.g. Router, and the style of lines between them indicate the type of connection. Clouds are used to represent networks external to the one pictured for the purposes of depicting connections between internal and external devices, without indicating the specifics of the outside network. For example, in the hypothetical local area network pictured to the right, three personal computers and a server are connected to a switch; the server is further connected to a printer and a gateway router, which is connected via a WAN link to the Internet.

OSI LAYER 1: THE PHYSICAL LAYER

The first and foundational layer of a network is the Physical Layer. The Physical Layer is literally what it’s name implies: the physical infrastructure of a network. This includes the cabling or other transmission medium and the network interface hardware placed inside of computers and other devices which enable them to connect to the transmission medium. The purpose of the Physical Layer is to take binary1 information from higher layers, translate it into a transmission signal or frequency, transmit the information across the transmission medium, receive this information at the destination, and finally translate it back into binary before passing it up to higher layers. Transmission signals or frequencies vary between network standards and can be as simple as pulses of electricity over copper wiring or as complex as flickers of light on optical lines or amplified radio frequency transmissions. The information that enters and exits the Physical Layer must be bits; either 0s or 1s in binary. The higher layers are responsible for providing the Physical Layer with binary information. Since nearly all information inside of a computer is already digital2, this is not difficult to achieve. The Physical Layer does not examine the binary information nor does it validate it or make changes to it. The Physical Layer is simply intended to transport the binary information between higher layers located at points A and B.

OSI LAYER 2: The DATA LINK LAYER
The second layer in the OSI Model is the Data Link Layer. The primary focus of the Data Link Layer is revealed in its common nickname, The Physical Address Layer. The only layer in the OSI Model that specifically addresses both hardware and software, the Data Link Layer receives information on its software side from higher layers, places this information inside of “frames”, and finally gives this frame to the Physical Layer, Layer 1, for transmission as pure binary. A frame essentially takes the information passed down from a higher layer and surrounds it with Physical Addressing information. This information is important to the Data Link Layer on the receiving end of the transmission. When the frame, in binary form, arrives at the destination node3, it is passed from the transmission medium to the Data Link Layer (Layer 2) by the Physical Layer (Layer 1). The Data Link Layer on the receiving node then checks the frame surrounding the information received to see if it’s Physical Address matches that of its own. If the Physical Address does not match, the frame and its encapsulated data is discarded. If the Physical Address is a match, then the information is removed from the frame and passed up to the next highest layer in the OSI Model. The Physical Address check is Obviously not of much use if there are only two nodes on a network, but suddenly becomes extremely valuable when three or more nodes exist. The Physical Addressing system allows multiple nodes to be on the same network medium, but retain the ability to address only a specific node with a transmission. On the simplest networks, all nodes receive every frame transmitted on the network, but discard frames not specifically addressed to them.

The Physical Address used in the Data Link Layer’s Physical Addressing system is known as a MAC address and is embedded physically into the node’s Network Interface Card during manufacturing. Every NIC’s MAC address is unique in order to prevent addressing conflicts. It is this relationship that causes the Data Link Layer to be known as the only layer that addresses both hardware and software. This layer is where the information on the network makes the move from the physical infrastructure of the network into the software realm. The remainder of the OSI Reference Model’s layers are entirely software.

OSI LAYER 3: THE NETWORK LAYER
OSI Layer 3 is known as the Network Layer. The first layer to deal entirely in software, the purpose of the Network Layer is to direct network traffic to a destination node who’s Physical Address is not known. This is achieved through a system known as Logical Addressing. Logical Addresses are software addresses assigned to a node at Layer 3 of the OSI Model. Since these addresses are able to be defined by software rather than being random and permanent like Physical Addresses, Logical Addresses are able to be hierarchical. This allows extremely large networks to be possible. Up until this point, only small networks would be possible since all traffic was addressed to all nodes. This works fine until more than one person attempts to utilize the network at once, at which point a data “collision” occurs. While OSI Layer 4 protocols may attempt to compensate for this collision by retransmitting packets until they have reached the destination node without issue, this degrades network performance exponentially as the number of nodes on a network grows. The larger the network is the greater this issue becomes. OSI Layer 3 takes on this problem by its Logical Addressing system and a concept known as routing.
The Oxford American Dictionary defines routing as “Sending or directing along a specified course”. Layer 3 routing on a network takes this foundational definition and puts it to use to enable millions of computers, rather than just a handful, to communicate at once without interference. This is achieved by having a smart device working at Layer 3 that handles network signals from each node directly rather than nodes just blindly repeating packets at Layer 1 until they happen to reach their destination. Such a device is known as a network router. A network router sits in the center of a network with all nodes having a direct link to it rather than being linked to each other. This strategic position allows the router to intercept and direct all traffic on the network. A routed network can be illustrated by a star formation, as shown in Diagram 1. On a routed network, Layer 3 packets are no longer broadcasted to all nodes, but rather received by the router and passed on only to the appropriate node. This is a valuable concept because it allows for the collision free-transport of packets across a network.

As well as being linked directly to all nodes in a local network, a router can be linked directly to other routers. This allows groups of nodes separated by distance to communicate with each other in a practical way. It would not be practical to have nodes separated by a great distance all connect to a single router. The amount of cabling required would be immense, and depending on the number of nodes involved, the router may not posses the required number of physical connections. Placing a router at each group of nodes and running a single line from router to router, however, is quite practical. Routers can be chained in a line, or as shown in Diagram 2, can be connected by a central router. This concept is virtually infinitely scalable and is very efficient.

When a node starts a transmission, the OSI Layer 3 protocol takes the information passed down from higher layers and encapsulates it with the logical address of the destination node in a unit called a packet. This packet, then passing through the remaining lower layer protocols, is transmitted over the network medium from the node to the router. This router reads the logical address that the packet contains and compares it to a list of physical addresses of nodes directly connected to it. If the packet’s destination address matches an entry in this list, the packet is transmitted directly on the line that leads straight to the destination node. If the router does not know of a direct connection to the destination node, the packet is transmitted on a line leading directly to another router. This router then treats the packet much like the first router did upon receipt. The packet’s logical address is checked for matches against the list of logical addresses belonging to nodes directly connected to the router. If the packet reaches a router with connections only to other routers, as shown in Diagram 2, the router uses the logical address’ orderly numbering scheme to try and determine the closest router to the destination node and then transmits the packet to that router.

IP, undoubtedly the world’s most used Layer 3 Protocol, provides an excellent example of how this system works. In IP, logical addresses look like four sets of up to three numbers.5 Diagram 3 shows an example of an IP address. IP addresses are orderly on four levels, from left to right. The first section of the IP address refers to a top level router, or a router that is at the highest level of this particular branch of the network. In Diagram 3, the first number is 66. Therefore all IP addresses between 66.0.0.1 and 66.255.255.255 are managed by this router. Only one router is required in a routed network, but more may exist. A router may have a maximum of 255 nodes, which may be either ordinary nodes or other routers. This effectively means that each branch of a network, a group of nodes that have the first set of numbers in their IP address in common, could theoretically have over sixteen million end nodes and still operate with near peak efficiency6.

As we can now see, the OSI Reference Model Layer 3 is one of the most complex, but most functionally important, parts of the modern day network. The Layer 3 protocol IP stands for Internet Protocol and is the protocol handling virtually all traffic on the internet today. The fashion in which Layer 3 protocols connect computers in a star-shaped, extensible network is much of the reason the internet is commonly called the “web”.

OSI LAYER 4: THE TRANSPORT LAYER
OSI Layer 4 is known as the Transport Layer. Since we are now above Layer 3, all information transfered is assumed to be at the correct destination node and is being passed up to Layer 4. The Transport Layer is responsible for the reliability of the link between two end users and for dividing the data that is being transmitted by assigning port numbers to its Layer 4 packages, known as segments. Ports can be thought of as virtual destination mailboxes or outlets. When information reaches a Layer 4 protocol, the segment is examined to determine the destination port of the data it contains. Once the port is determined, just as all of the past layers have done, the wrapper is discarded and the payload data passed up to the next layer’s protocol.
Ports allow more than one set of Layer 5-7 protocols to exist on a single node. This is important if the node has more than one purpose. Modern home computers utilize many ports during everyday use, because the modern computer user demands that a computer serve many purposes at once. Higher layer protocols that provide services such as email, web browsing, text chat, file transfer and more each operate on their own unique Layer 4 port, allowing all of these protocols to be operated at once without interference.

On the reliability front, Transport Layer protocols can be capable of running a checksum7 on the payload data they carry. This allows the protocol to determine the integrity of incoming payload data. If this data has been corrupted or its integrity compromised, the Layer 4 protocol will request the segment be retransmitted.

OSI LAYER 5: THE SESSION LAYER
While being an optional layer in most protocol packages today, OSI Layer 5, known as the Session Layer, still serves a purpose in the OSI Reference Model. The Session Layer draws the outline for protocols that manage the combination and synchronization of data from two separate higher layers. Layer 5 protocols are responsible for ensuring that the data is synced and consistent before transmitted. A good example situation is the streaming of live multimedia audio and video, where near perfect synchronization between video and audio is desired.

OSI LAYERS 6 & 7: THE PRESENTATION AND APPLICATION LAYERS
The sixth and seventh layers in the OSI Reference Model are the Presentation Layer and the Application Layer. The primary purpose of these layers is to facilitate the movement of formatted information between applications interacting with end users on nodes by way of the lower layer protocols. Commonly used top layer protocols are HTTPS (for the secure transfer of web page related files), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP, used for the sending of email messages), and SSH (Secure Shell, used for secure remote shell8 access to a computer operating system).

Nokia release mobile web server / How to start a blog /Free language transulation tool /Amazing America blog/Ten tips to get start a blog / World Fastest Supercomputers / Generation of computers / Hisiory And types of mouse / Memory Stick / DDR, SD, Dr, Rd RAM /Cartridge tape/ Plotter printer / Floppy Disk Drive System /Browsing settings in google/Different Types Of Networking,P2P,clint server /Network Diagram & OSI Reference Model

source:wikipedia ,compnetworking , networking.ittoolbox ,networkcomputing, computerworld, networking ibm

Network Topology is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes.

A local area network (LAN) is one example of a network that exhibits both a physical and a logical topology. Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network. Likewise, the mapping of the flow of data between the nodes in the network determines the logical topology of the network. It is important to note that the physical and logical topologies might be identical in any particular network but they also may be different.

Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes – Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identica.

Basic Types of Topologies

The arrangement or mapping of the elements of a network gives rise to certain basic topologies which may then be combined to form more complex topologies (hybrid topologies). The most common of these basic types of topologies are (refer to the illustration at the top right of this page):
• Bus (Linear, Linear Bus)
• Star
• Ring
• Mesh
partially connected mesh (or simply ‘mesh’)
fully connected mesh (or simply fully connected)
• Tree

Classification of Network Topologies
There are also three basic categories of network topologies:
• physical topologies
• signal topologies
• logical topologies
The terms signal topology and logical topology are often used interchangeably even though there is a subtle difference between the two and the distinction is not often made between the two.

Physical Topologies

The mapping of the nodes of a network and the physical connections between them – i.e., the layout of wiring, cables, the locations of nodes, and the interconnections between the nodes and the cabling or wiring system

Classification of Physical Topologies:

Bus:
Linear Bus:
The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly two endpoints (this is the ‘bus’, which is also commonly referred to as the backbone, or trunk) – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network virtually simultaneously (disregarding propagation delays)

Distributed Bus:
The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium – the physical distributed bus topology functions in exactly the same fashion as the physical linear bus topology (i.e., all nodes share a common transmission medium).

Star:
The type of network topology in which each of the nodes of the network is connected to a central node with a point-to-point link in a ‘hub’ and ‘spoke’ fashion, the central node being the ‘hub’ and the nodes that are attached to the central node being the ‘spokes’ (e.g., a collection of point-to-point links from the peripheral nodes that converge at a central node) – all data that is transmitted between nodes in the network is transmitted to this central node, which is usually some type of device that then retransmits the data to some or all of the other nodes in the network, although the central node may also be a simple common connection point (such as a ‘punch-down’ block) without any active device to repeat the signals.

Ring:
The type of network topology in which each of the nodes of the network is connected to two other nodes in the network and with the first and last nodes being connected to each other, forming a ring – all data that is transmitted between nodes in the network travels from one node to the next node in a circular manner and the data generally flows in a single direction only.
Mesh:
Full:
Fully Connected:
The type of network topology in which each of the nodes of the network is connected to each of the other nodes in the network with a point-to-point link – this makes it possible for data to be simultaneously transmitted from any single node to all of the other nodes.

Tree (also known as Hierarchical):
The type of network topology in which a central ‘root’ node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central ‘root’ node, while each of the second level nodes that are connected to the top level central ‘root’ node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central ‘root’ node being the only node that has no other node above it in the hierarchy – the hierarchy of the tree is symmetrical, each node in the network having a specific fixed number, f, of nodes connected to it at the next lower level in the hierarchy, the number, f, being referred to as the ‘branching factor’ of the hierarchical tree.

Signal Topology
The mapping of the actual connections between the nodes of a network, as evidenced by the path that the signals take when propagating between the nodes.

Note: The term ‘signal topology’ is often used synonymously with the term ‘logical topology’, however, some confusion may result from this practice in certain situations since, by definition, the term ‘logical topology’ refers to the apparent path that the data takes between nodes in a network while the term ‘signal topology’ generally refers to the actual path that the signals (e.g., optical, electrical, electromagnetic, etc.) take when propagating between nodes.
Example:

Logical Topology

The mapping of the apparent connections between the nodes of a network, as evidenced by the path that data appears to take when traveling between the nodes.

Classification of Logical Topologies
The logical classification of network topologies generally follows the same classifications as those in the physical classifications of network topologies, the path that the data takes between nodes being used to determine the topology as opposed to the actual physical connections being used to determine the topology.

Notes:
1.) Logical topologies are often closely associated with media access control (MAC) methods and protocols.
2.) The logical topologies are generally determined by network protocols as opposed to being determined by the physical layout of cables, wires, and network devices or by the flow of the electrical signals, although in many cases the paths that the electrical signals take between nodes may closely match the logical flow of data, hence the convention of using the terms ‘logical topology’ and ‘signal topology’ interchangeably.
3.) Logical topologies are able to be dynamically reconfigured by special types of equipment such as routers and switches.

Network Topology ,types, design / Different Types Of Networking,P2P,clint server /Network Diagram & OSI Reference Model /Keyboard Shotcuts /Nokia release mobile web server / / How to start a blog /Free language transulation tool /Amazing America blog/Ten tips to get start a blog / World Fastest Supercomputers / Generation of computers / Hisiory And types of mouse / Memory Stick / DDR, SD, Dr, Rd RAM /Cartridge tape/ Plotter printer / Floppy Disk Drive System /Browsing settings in google/Different Types Of Networking,P2P,clint server /Network Diagram & OSI Reference Model /mobile nikia 6600 software/

source:wikipedia ,compnetworking , networking.ittoolbox ,networkcomputing, computerworld, networking ibm

There are three types of relationships ;

• One-to -One
• One-to-many(or many -to-One)
• Many-to-many

Consider the example of a university .For a particularDEPARTMENT (like the department of social sciences) ther can be only one DEPARTMENT HEAD .This is an example of a one-to -one relationship.

A STUDENT can MAJOR in only one course , but many STUDENTs would have riegistered for agiven MAJOR course . This is an example of many-to-onerelationship.

A STUDENT can take many COURSE and many STUDENTs can register for a given COURSE. This is an example of many- to-many relationship.

The types of relationships between two entities are represented in E/R diagrams by certian symbols .An entity may be associated with one , none,or occurrences of another entity.

Attributes

An attribute is a property of a given entity, for example , ROLL NO is a property of entity STUDENT.An attribute instance is a particular property of an individual entity instance. For example ,Peter is the instance of STUDENT entity and the roll number 101 is the instance of a attributes ROLL NO and also the property of the entity instance peter.Anattribute types is a property of the entity type.For example ,”male” is an attribute instance, while ”gender” is an attribute type .Attributes are depicted as ellipses ,labeled with the name of the property .Thekey properties are underlined. A key property uniquely identofies an entity instance .In the example below , a perticular student can be uniquely identified from the roll number rather tan the name. It is possible for more than one student to have the same number ,but a rollnuber is never duplicated . Arelationship can also have attributes.

DBMS model conversion / SQL server / Entity Relationship

Chen defined an entity as “a thing , which can be easily identified ” An entity is any object , place , person, or activity about which data is recorded, Some examples of entity are Student, course and Grade. In the diagramming technique, entities are named and represented inside a box.

Relationships

chen defined a relationship as ” an assocition among entities “. for example , there is a relation on ship between students and instructors . This relationship represents the fact that an instructor teachesteaches several students and a student s taught by several instructors . This relationship chould be named TEACH. As with entities ,it is necessary to distinguish between relationship types and insancs.

DBMS model conversion / SQL server / Attribute Relationship

Entity Relationship Diagrams are a major data modelling tool and will help organize the data in your project into entities and define the relationships between the entities. This process has proved to enable the analyst to produce a good database structure so that the data can be stored and retrieved in a most efficient manner.

The Entity-Relationship Model

The entity -relationship model is based on a real-eorld preception that comprises a collection of objects or entities and the relationship among these.chen introduced not ony the E/R model , but also a correspondig diagraming technique.

DBMS model conversion / SQL server / Attribute Relationship

Developer: Microsoft

Latest release:2005 / November 7, 2005

OS:Microsoft Windows

Use:RDBMS

License: Microsoft EULA

Features of M S sql server: Microsoft Sql Server provides various feautres to manage data.some of the features offerd by Microsoft SQL Server are:

• Fully Web-enabled:SQL server provides various features to facilliate easy and secure accessto data via the web.you can http to find querys to the server.

• Highly Scalable and releable: inthis case the load of the SQL server incrases,it can use the scale up and and scale out features to meet the requirement.

• Fastest Tlme To-to-Market: SQl Server provides features that reduse the time taken to develop an application from its design to a complete product.

Structed query language: The Language to access data objects from the SqL Server is known as the Structed query language(SQL). SQL has reduced the need for lenthy programing to acess data.

What is SQL?

SQL stands for Structured Query Language
SQL allows you to access a database
SQL is an ANSI standard computer language
SQL can execute queries against a database
SQL can retrieve data from a database
SQL can insert new records in a database
SQL can delete records from a database
SQL can update records in a database
SQL is easy to learn
SQL is a standard computer language for accessing and manipulating databases.

SQL is a Standard – BUT….

SQL is an ANSI (American National Standards Institute) standard computer language for accessing and manipulating database systems. SQL statements are used to retrieve and update data in a database. SQL works with database programs like MS Access, DB2, Informix, MS SQL Server, Oracle, Sybase, etc.

Unfortunately, there are many different versions of the SQL language, but to be in compliance with the ANSI standard, they must support the same major keywords in a similar manner (such as SELECT, UPDATE, DELETE, INSERT, WHERE, and others).

SQL Data Manipulation Language (DML)

SQL (Structured Query Language) is a syntax for executing queries. But the SQL language also includes a syntax to update, insert, and delete records.

These query and update commands together form the Data Manipulation Language (DML) part of SQL:

*SELECT – extracts data from a database table

*DELETE – deletes data from a database table

*INSERT INTO – inserts new data into a database table

SQL Data Definition Language (DDL)

The Data Definition Language (DDL) part of SQL permits database tables to be created or deleted. We can also define indexes (keys), specify links between tables, and impose constraints between database tables.

The most important DDL statements in SQL are:

*CREATE TABLE – creates a new database table

*ALTER TABLE – alters (changes) a database table

*DROP TABLE – deletes a database table

*CREATE INDEX – creates an index (search key)

*DROP INDEX – deletes an index

Displaying specific attiributes from a table

selecting columns:the SELECT statement is usd to retrive specific columns(s).from a table by specifying the column name from the table. the column names specified in the SELECT statement are separated by a comm(,).

syntax

SELECT column_name {,column_name2, …..}
FROM table_name

Example

SELECT pub_Id, Pub_name
FROM Publishers

DBMS model conversion / Entity Relationship /Attribute Relationship

Manage of data involves:

• Defining structers for data storage
• Providing mechanisms for data manipulation such as adding ,editing , and deleting data.
• Providing Data Security Against unauthorized access.

The main objectives of any DBMS are to:

• Provide an efficent and convenient that is used to store data i , and retrive dat from a database
• Manage information about Users who interct with the DBMS and the activities that these users can perform on data.

Data Modeles:

A data model is a description of the organization of data in a database . Data models can broadly be classified in two categories:

• Obeject-based logical model-focuses on describing the data , the relation among the data ,and any constraints defined.
• Record-based logical model-focuses ondescribing the data structures and the access techniques in a database managment system.

SQL server / Entity Relationship /Attribute Relationship/How to start a blog /Free language transulation tool /Amazing America blog/Ten tips to get start a blog / World Fastest Supercomputers / Generation of computers / Hisiory And types of mouse / Memory Stick / DDR, SD, Dr, Rd RAM /Cartridge tape/ Plotter printer / Floppy Disk Drive System /Browsing settings in google/Web hosting service