Network Architecture- ​Basics of Computers for Bank Exams

NETWORK  ARCHITECHURE:

Network architecture refers to how computers are organized in a system and how tasks are allocated between these computers.

Two of the most widely used types of network architecture:

Peet to Peer:   Tasks are allocated among all the members of the network.

Client Server:    Network clients or workstations request resources or services from the network. Client/server architecture is also called ‘tiered’ because it uses multiple levels.

Client-Server vs. Peer-to-Peer and Other Models

The client-server model of networking was originally developed to share access to database applications among larger numbers of users. Compared to the mainframe model, client-server networking gives better flexibility as connections can be made on-demand as needed rather than being fixed. The client-server model also supports modular applications that can make the job of creating software easier. In so-called two tier and three tier types of client-server systems, software applications are separated into modular components, and each components is installed on clients or servers specialized for that subsystem.

Client-server is just one approach to managing network applications. The primary alternative to client-server, peer-to-peer networking, treats all devices as having equivalent capability rather than specialized client or server roles. Compared to client-server, peer to peer networks offer some advantages such as better flexibility in expanding the network to handle large number of clients. Client-server networks generally offer advantages over peer-to-peer as well, such as the ability to manage applications and data in one centralized location.

• A printer is connected to the network – to print a document, the client sends a print request to the server.
• All the e-mail messages are stored on the server – the client is used to view and manage the messages but does not store the actual files.
• Very large databases are stored on the server – the client accesses these without copying them onto the local hard drive.

Switches:

 It is used to connect multiple devices on the same network within a building or campus.

Example:

A switch can connect your computers, printers and servers, creating a network of shared resources.

 

Routers:

The second valuable component of your networking basics, are used to tie multiple networks together. The router will act as a dispatcher.

Example:

you would use a router to connect your networked computers to the Internet and thereby share an Internet connection among many users.

 

OSI MODEL:

The OSI model defines internetworking in terms of a vertical stack of seven layers. Upper layers of the OSI model represent software that implements network services like encryption and connection management. Lower layers of the OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control.

Data communication in the OSI model starts with the top layer of the stack at the sending side, travels down the stack to the sender’s lowest (bottom) layer, then traverses the physical network connection to the bottom layer on the receiving side, and up its OSI model stack.

The OSI Model Stack

The OSI model divides the complex task of computer-to-computer communications, traditionally called internetworking, into a series of stages known as layers. Layers in the OSI model are ordered from ​the lowest level to highest. Together, these layers comprise the OSI stack. The stack contains seven layers in two groups:

Upper layers:

7. application
8. presentation
9. session

Lower layers:

4. transport
5. network
6. data link
7. physical

Upper Layers of the OSI Model:

OSI designates the application, presentation, and session stages of the stack as the upper layers. Generally speaking, software in these layers performs application-specific functions like data formatting, encryption, and connection management.

Examples of upper layer technologies in the OSI model are HTTP, SSL, and NFS.

Lower Layers of the OSI Model:

The remaining lower layers of the OSI model provide more primitive network-specific functions like routing, addressing, and flow control.

Examples of lower layer technologies in the OSI model are TCP, IP, and Ethernet.

Benefits of the OSI Model:

By separating the network communications into logical smaller pieces, the OSI model simplifies how network protocols are designed. The OSI model was designed to ensure different types of equipment (such as network adapters, hubs, and routers) would all be compatible even if built by different manufacturers.

A product from one network equipment vendor that implements OSI Layer 2 functionality, for example, will be much more likely to interoperate with another vendor’s OSI Layer 3 product because both vendors are following the same model.

The OSI model also makes network designs more extensible as new protocols and other network services are generally easier to add to a layered architecture than to a monolithic one.

1)Physical Layer

At Layer 1, the Physical layer of the OSI model is responsible for ultimate transmission of digital data bits from the Physical layer of the sending (source) device over network communications media to the Physical layer of the receiving (destination) device. Examples of Layer 1 technologies include Ethernet cables and Token Ring networks. Additionally, hubs and other repeaters are standard network devices that function at the Physical layer, as are cable connectors.

At the Physical layer, data are transmitted using the type of signaling supported by the physical medium: electric voltages, radio frequencies, or pulses of infrared or ordinary light.

2)Data Link Layer

When obtaining data from the Physical layer, the Data Link layer checks for physical transmission errors and packages bits into data “frames”. The Data Link layer also manages physical addressing schemes such as MACaddresses for Ethernet networks, controlling access of any various network devices to the physical medium. Because the Data Link layer is the single most complex layer in the OSI model, it is often divided into two parts, the “Media Access Control” sublayer and the “Logical Link Control” sublayer.

3)Network Layer

The Network layer adds the concept of routing above the Data Link layer. When data arrives at the Network layer, the source and destination addresses contained inside each frame are examined to determine if the data has reached its final destination. If the data has reached the final destination, this Layer 3 formats the data into packets delivered up to the Transport layer. Otherwise, the Network layer updates the destination address and pushes the frame back down to the lower layers.

To support routing, the Network layer maintains logical addresses such as IP addresses for devices on the network. The Network layer also manages the mapping between these logical addresses and physical addresses. In IP networking, this mapping is accomplished through the Address Resolution Protocol (ARP).

4)Transport Layer

The Transport Layer delivers data across network connections. TCP is the most common example of a Transport Layer 4 network protocol. Different transport protocols may support a range of optional capabilities including error recovery, flow control, and support for re-transmission.

5)Session Layer

The Session Layer manages the sequence and flow of events that initiate and tear down network connections. At Layer 5, it is built to support multiple types of connections that can be created dynamically and run over individual networks.

6)Presentation Layer

The Presentation layer is the simplest in function of any piece of the OSI model. At Layer 6, it handles syntax processing of message data such as format conversions and encryption / decryption needed to support the Application layer above it.

7)Application Layer

The Application layer supplies network services to end-user applications. Network services are typically protocols that work with user’s data. For example, in a Web browser application, the Application layer protocol HTTP packages the data needed to send and receive Web page content. This Layer 7 provides data to (and obtains data from) the Presentation layer.

Computer Network Topology:

A computer network topology is the physical communication scheme used by connected devices. These pages illustrate the common computer network topology types including bus, ring, and star. More complex networks can be built as hybrids of two or more of these basic topologies.​

Bus Network Topology

This diagram illustrates the bus network topology. A bus topology such as 10Base-2 or 10Base-5 Ethernet uses a single communication backbone for all devices.

Ring Network Topology

This diagram illustrates the ring network topology. A ring topology such as FDDI or SONET sends messages clockwise or counterclockwise through the shared link.

 

Star Network Topology

This diagram illustrates the star network topology. A star topology typically uses a network hub or switch and is common in home networks.

Mesh Network Topology

This diagram illustrates the mesh network topology. A mesh topology provides redundant communication paths between some or all devices (partial or full mesh).

Tree Network Topology

This diagram illustrates the tree network topology. A tree topology integrates the star and bus topologies in a hybrid approach to improve network scalability.

 

 

 

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