LAYER 7 : APPLICATION LAYER
In this layer, the interfaces work directly with the application and offer standard web application capabilities. It then makes a request to send anything to the presentation layer. The uppermost layer of open systems is the application layer, which directly supports the application process. This layer's functions include access to files, mail services, remote log-in, and WWW access. Examples of protocols at this layer include Domain Name System (DNS), Simple Mail Transfer Protocol (SMTP), Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), and others.
LAYER 6 : PRESENTATION LAYER
The presentation layer is responsible for syntax and semantics of the information exchanged between two systems.
LAYER 5 : SESSION LAYER
The construction of connections, the maintenance of sessions, authentication, and security are all handled by this layer.
The session layer's functions are:
Session establishment, maintenance, and termination : The layer permits connection establishment, use, and termination between the two processes.
Synchronization : Through the use of this layer, a process is able to include checkpoints, which are synchronization points for the data. These synchronisation sites help in error detection to prevent improper data resynchronization, premature message termination, and data loss.
Dialog Controller : The session layer enables the beginning of half-duplex or full-duplex communication between two systems.
LAYER 4 : TRANSPORT LAYER
The transport layer transfers services from the network layer to the application layer.All the data in the transport layer is based on the Segments. It is responsible for the End to End Delivery of the complete message. Additionally, the transport layer offers confirmation of a successful data transmission and re-transmits the data if an error is discovered.
Usually, either manually or by default, this destination port number is specified. For example, when a web application makes a request to a web server, it typically uses port number 80, because web apps are assigned to this port by default.Many applications have default ports assigned.
LAYER 3 : NETWORK LAYER
Ø The
network layer is responsible for the delivery of packets from the original source
to the final destination.
Ø Duties: - Logical Addressing
- Routing
>
The main functions of the network layer are as
follows −
·
It is responsible for routing packets from the source host to the
destination host. The routes can be based upon static tables that are rarely
changed, or they can be automatically updated depending upon network
conditions.
·
The data link layer assigns the physical address locally. When the data
packets are routed to remote locations, a logical addressing scheme is required
to differentiate between the source system and the destination system. This is
provided by the network layer.
·
This layer also provides mechanisms for congestion control.
· The network layer tackles issues like transmission delays, transmission time, etc.
SOURCE- TO-DESTINATION
DELIVERY
LAYER 2 : DATA LINK LAYER
The Data Link layer is the second layer of the seven layers in the OSI model. This layer is the protocol layer that transfer data between nodes on a network segment across the physical layer. The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer. Data Link layer host will always by using its MAC address.
There are two sublayers for Data Link:
1. Logical Link Control (LLC)
2. Media Access Control (MAC)
There are 5 functions of the Data Link layer:
1. Framing: Framing is a function of the data link layer that’s provides a way for a sender to transmit a set of bits that are meaningful to the receiver.
2. Physical addressing: After creating frames the Data link layer will be added physical addresses (MAC address) of the sender or receiver in the header of each frame.
3. Error control: The Data link layer will detect and retransmits damaged or lost frames.
4. Flow Control: The date rate must be constant on both sides else the data may get corrupted. With the flow control they will coordinates the amount of data that can be sent before receiving acknowledgement.
5. Access control: When a single communication channel is shared by multiple devices, the MAC sub-layer of the data link layer helps to determine which device has control over the channel at a given time.
LAYER 1: PHYSICAL LAYER
The physical layer is the first and lowest layer of the Open System Interconnection Model (OSI Model.) The physical layer defines the means of transmitting a stream of raw bits over a physical data link connecting network nodes. The bitstream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a transmission medium.
This layer plays with most of the network’s physical connections such as wireless transmission, cabling, cabling standards and types, connectors and types, network interface cards, and more —as per network requirements. The physical layer does not deal with the actual physical medium (like copper, fiber, etc.)
Physical topologies:
Topology is the physical or logical arrangement of links in a network
1. Bus topology
- One long cable (the backbone) link all the device in the network- multipoint
- Advantages: easy installation and use less cabling than mesh, star or tree
- Disadvantages: difficult reconfiguration and fault isolation (a fault or break in the bus cable stops all transmission)
2. Star topology
- Each device has a dedicated point-to-point link only to a central controller ( or hub)
- Advantages: only one link and one I/O port are required per device, less expensive than mesh topology, if one link fails only that link is affected.
- Disadvantages: if the hub fails, the network is down and requires more cabling than tree, ring, and bus topology
3. Ring topology
- Each device is linked only to its immediate neighbors
- Advantages: each device incorporates a repeater and is easy to install and reconfigure
- Disadvantages: in unidirectional traffic, a break in the ring can disable the entire network
4. Mesh topology
- Each node has a dedicated point-to-point link to every other node
- Advantages: each connection can carry its own data load, if one link becomes unusable, it does not incapacitate the entire system
- Disadvantages: the amount of cabling and number of I/O ports are required and expensive
Modes of transmission medium:
1. Simplex mode
2. Half-Duplex Mode
3. Full-Duplex Mode
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