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Network Architecture
Network Architecture is the design of communication network. It is a framework for the specification of a network’s physical components and their functional organization and configuration, and its operational principles and procedures, and also data formats used in its operation.
In the telecommunication, the specification of the network architecture can also include the detailed description of the products and services that are delivered through a communication network, and also the detailed rate and billing structures under which the services are compensated.
Rather than using a specific model for interconnecting the networks or nodes in a network, or by the usage of specific types of hardware links, the network architecture of the internet can be expressed by the use of Internet Protocol Suite.
Types of Network Architectures:
Network architectures are sometimes classified into two types. They are:
Client-server architectures
Peer-to-peer architectures
Client-Server Architecture: In the client-server architecture model, a system is decomposed into server and client processors or processes, where server provides services (or computational resources) to one or many clients. Clients consumes the services that are provided by the server. Hence there is generally a 1:M relationship between the server and clients and also sometimes it may have between a client and its servers. This model will support the separation of functionality based on the service concept.
The client-server architectures are commonly divided into layers which are called as “Tiers”.
Tiered Architectures:
Two-tier architecture: In this architecture, it consists of two tiers which are data server layer which associates with data access computation and the client application layer which is the user interface. The client sometimes can be referred as a “fat client”, if most of the application logic is associated with client application logic and sometimes referred as “thin client”, if it is associated with the data access server.
Three-Tier Architecture: In this architecture, it consists of a data server layer, a client application layer and an application server layer which facilitates the separation of application logic from presentation, and promotes the distributed processing.
Multi-Tier Architecture: This architecture is a superset of a three-tier architecture, and includes additional layers for data and application servers.
Peer-To-Peer Architecture: In contrast to the client-server architectural model, where the client and server nodes are divided into server and client roles, this model consists of a system which is decomposed into computational nodes that have equivalent capabilities and responsibilities.
The example of a peer-to-peer architecture is a system of intelligent agents that will collaborate to collect, correlate and filter the information. Sometimes peer-to-peer and layered architecture are combined, where the nodes in some particular layers are in peer-to-peer relationships.
OSI Network Model:
The Open Systems Interconnection Model (OSI Model) is a product of the Open Systems Interconnection effort at the International Standard Organization (ISO) which says that it is the sub-division of a communications system into smaller parts called layers. A layer is a collection of similar functions which provides services to the above layer and receives services from the below layer. On each and every layer, an instance will provide the services to the instances that are in above layer and requests the services from the below layer.
Study Material for Network Architecture
Physical Layer:
In this layer, it defines the electrical and physical specifications for the devices and also it defines the relation between the device and transmission medium like copper or optical cable, which transmits a stream of bits. It includes the layout of pins, repeaters, hubs, cable specifications, host bus adapters etc.
Data-Link Layer:
In this layer, it provides the procedural and functional means to transfer the data between network entities and to detect and correct the errors that may occur in the physical layer. Originally, this layer was for the point-to-point and point-to-multipoint media, characteristic of wide area media in the telephone system. In this layer, the input data will be broken into frames.
Network Layer:
In this layer, it provides the functional and procedural means for transferring the variable length data sequences from a source on one network to the destination on a different network by maintaining the quality of the service that is requested by the transport layer. It performs network routing functions, fragmentation and reassembling, and also reports the delivery errors. For sending data throughout the extended network and to make internet possible, routers will be operated at this layer. The addressing scheme is not hierarchical and it is a logical addressing scheme where values are chosen by the network engineer. It controls the operation of subnet and determines the routing strategies between Interface Message Processor and insures that all the packs are received correctly in proper order at the destination.
Transport Layer:
In this layer, it provides transparent transfer of data between the end users and provides the reliable data transfer services to the upper layer. This layer controls reliability of a given link through flow control, segmentation and desegmentation, and error control. Some protocols are state and connection oriented which means that it can keep the track of segments and will retransmits if any of them are failed and also provide the acknowledgement on successful transmission of data. Some protocols like TCP supports virtual circuits which provide the connection-oriented communication over an underlying packet-oriented datagram network which assures the correct order delivery of the packets and that are free of errors. The packets are delivered randomly and will be broadcasted to multiple nodes by the datagram transportation.
Session Layer:
In this layer, it provides a user interface to the network where the user negotiates to establish a connection and for contacting, the user must provide the remote address. The operation of setting up a session between two processes is known as “binding”, which is merged with transport layer in some protocols. Its main work is to transfer the data from other application to this application, so that this application will be mainly used for transferred layer.
Presentation Layer:
In this layer, it establishes context between entities on the application layer, in which the higher-layer entities may use the different syntax and semantics if the presentation service provides a mapping between them. The presentation service data units are encapsulated into session protocol data units, and are passed down to the stack, if a mapping is available. This layer will provide the independence from data representation by translating between the application and network formats and transforms the data into the form that is accepted by the application. And this layer will format and encrypts the data that is to be sent across a network and it sometimes called as syntax layer.
Application Layer:
The application layer is the closest layer to the end user, which means that both OSI application layer and the user can interact directly with the software application that implements a communicating component. Such application programs will fall outside the scope of the OSI model. This layer functions are identifying communication partners which determines the identity and availability of communication partners for an application with data to transmit, synchronizing communication and determining resource availability.