It represents all the electrical and physical specifications for devices.
Layer 2: Data link layer
It provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the Physical layer.
Layer 3: Network layer
The Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks.
Layer 4: Transport layer
It provides transparent transfer of data between end users.
Layer 5: Session layer
It controls the sessions between computers. It connects, manages and terminates the connections between the local and remote application.
Layer 6: Presentation layer
It transforms data to provide a standard interface for the Application layer.
Layer 7: Application layer
It provides a means for the user to access information on the network through an application.
Types of Networks:
LAN Local Area Network connects a group of nodes covering a small physical area. LANs are most commonly seen in offices, building etc. LANs enable higher transfer rate of data, smaller coverage of area and hence less wiring.
WAN Wide Area Network connects a group of nodes covering a wide area. WAN typically connects and allow communication between regions or national boundaries. The most common example of WAN is internet.
VPN Virtual Private Network connects or links nodes in some larger area by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. It is used for secure communication through the public internet. VPN alone may not support explicit security features, such as authentication or content encryption.
Intranet It is a set of networks under the control of a single administrative person. It can be considered as an internal network of an organization. If it is large, web servers are used to provide information to the users.
Extranet It is a network that restricts itself within a single organization. It can be categorized as WAN, MAN etc. however; it cannot have a single LAN. It must have a connection (at least one) with external network.
* All nodes connected with another in a loop.
* Each device is connected to one or more another device on either side.
* All nodes connected to a central and a common cable called as a back bone.
* In bus topology, the server is at one end and the clients are connected at different positions across the network.
* Easy to manage and install.
* If the backbone fails, the entire communication fails.
* All nodes connected to a central hub.
* The communication between the nodes is through the hub.
* Relative requires more cables as compared to BUS. However if any node fails, it wont affect the entire LAN.
IP Internet protocol is used for transmission of data over the internet. IP uses IP addresses to identity each machine uniquely. Message is sent using small packets. The packet contains both the sender and receivers address. IP does not guarantee the delivery in the same order as sent. This is because the packets are sent via different routes. It is a connectionless communication protocol at the third level (network) of the OSI model.
UDP User Data Protocol is a communication protocol. It is normally used as an alternative for TCP/IP. However there are a number of differences between them. UDP does not divide data into packets. Also, UDP does not send data packets in sequence. Hence, the application program must ensure the sequencing. UDP uses port numbers to distinguish user requests. It also has a checksum capability to verify the data.