In the late 1970s, the Open Systems Interconnection (OSI) Reference Model was created by the International Organization for Standards (ISO). Way for the data transfer between disparate hosts running different operating System.
The OSI model was meant to help vendors create interoperable network devices and software in the form of protocols so that different vendor networks could work in peaceable accord with each other.
A reference model is a conceptual blueprint of how communications should take place it addresses all the processes required for effective communication and divide them into logical grouping called layers. When a communication system is designed in this manner it's known as a hierarchal or layered architecture.
List of some more important benefits of OSI layered Model:
It divides network communication process into smaller and simpler components, vacillating component development, design and troubleshooting.
It allows multiple vendor development through the standardization of network components.
Encourage industry standardization by clearly defining what functions occur at each layer of the model.
It allows various types of network hardware and software to communicate.
It prevent the changes in one layer from affecting other layers to expedite development.
it also provides a framework for creating and implementing networking standards, devices and internetworking schemes.
Way for the data transfer between these separate running different operating systems like Unix host, windows machines, Mac, smartphone and so on.
The OSI has seven different layers divided in two sub layers i.e., Upper Layers and Lower Layers
Upper Layers -
Lower Layers -
The following networks devices can operate on all seven layers of OSI Model:
Network Management Stations (NMSs)
Web and Application servers
Gateways (not default gateways)
Servers
Network Hosts
OSI Layer Functions -
Application Layer
The Application Layer is working as the interface between the actual location program and the next laid down by providing ways for the application to send information down through the protocol stack. It worked with those applications which use Network. Good examples of these kinds of events:
Web Browsing
File Transfer
Email
Enabling remote access
Network management activities
Client/Server processes
Information location
Presentation Layer
The Presentation layer present data to the application layer and it still is responsible for data transformation and code formatting would include protocols that define how standard data should be formatted. Data compression, decompression, encryption and decryption are also associated with this layer some presentation layer standards are involved with multimedia operations as well.
Session Layer
The Session layer is responsible for setting of managing and dismantling stations between the presentation layer entities and keeping user data separate.
Various application the session layer as from client to server is coordinated and organized by three different modes - Simplex, Half Duplex and Full Duplex.
Simplex
Simplex is a simple one way communication kind of like saying something and not getting a reply example radio. For Example: Radio Broadcast or TV Broadcast, Keyboard, Mouse.
Half Duplex
and where have two places actual two way communication but it can take this in one direction at a time.
Full Duplex
Full duplex is exactly like a real conversation with devices and transmitter receiver at the same time.
Transport Layer
The Transport layer segments and reassemble data and single data stream services located this layer take all the various data received from the upper layer applications then combined into the same concise data stream. To transport the data this layer use either TCP or UDP. TCP is reliable where UDP is non-reliable. Most of the services use TCP. The term Reliable Networking can be used at the transport layer reliable networking request that Acknowledgement, Sequencing and Flow Control will be used.
Connection Oriented Communication :
Establish connection oriented communication session with the remote device it's their system known as a call set up for the Three Way Handshake. Once this process complete the data transfer occurs and when it's finished up call read termination takes place to tear down the virtual circuit.
Connection oriented sessions that Three Way Handshake is occur in the following manner -
The first "connection agreement" segment is a request for synchronization (SYN).
The next segments acknowledge (ACK) the request and establish connection parameters - the rules - between hosts. These segment request that the receiver sequencing is synchronized here as well, so that bidirectional connection can be formed.
The final segment is also an acknowledgement, which notifies the destination host that the connection agreement has been accepted and that the actual connection has been established. Data transfer can now begin.
Sometimes during a transfer, congestion can occur because a high speed computer is generating data transfer a lot faster than the network itself can process.
When a machine receives a flood datagram too quickly for it to process? It store them in a memory section called buffer. This buffering action can solve the problem only if the datagrams are part of a small burst. If the datagram deluge continues, eventually exhausting the device's memory, its flood capacity will be exceeded and it will dump any and all additional datagrams it receives like an overflowing bucket!
Flow Control :
Its job is to ensure data integrity at the transport layer allowing applications to request reliable data transport between systems.
The protocols involved ensure that the following will be achieved:
The segments delivered are acknowledged back to the sender upon their reception.
Any segments not acknowledged are retransmitted.
Segments are sequenced back into their proper order upon arrival at their destination.
A manageable data flow is maintained in order to avoid congestion, overloading or worse, data loss.
The purpose of flow control is to provide a way for the receiving device to control the amount of data sent by the sender.
Notes: The types of flow control are buffering, windowing and congestion avoidance. A service is considered connection-oriented if it has the following characteristics.
A virtual circuit, or three-way handshake" is set up.
It uses sequencing
It uses acknowledgment
It uses flow control
Windowing :
Windows are used to control the amount of outstanding, unacknowledged data segments. The size of windows control how much information is transferred from one end to the other before an acknowledgement is required. While some protocols quantify information depending on the number of packets. TCP/IP measure it by counting the numbers of bytes.
In reality, the transmission isn't based on simple numbers but on the amount of bytes that can be sent.
Note: If a receiving host fails to receive all the bytes that it should acknowledge, the host can improve the communication sessions by decreasing the window size.
Acknowledgments :
Reliable data delivery ensures the integrity of a stream of data sent from one machine to the other through a fully functional data link. It guarantees that the data won't be duplicated or lost. This is achieved through something called positive acknowledgment with retransmission - a technique that requires a receiving machine to communicate with the transmitting source, by sending an acknowledge .
A technique that is used to send the when sender receive the data. The transport layer, working in tandem with the Session Layer, also separate the data from different applications, an activity known as session multiplexing.
Network Layer
The Network layer or Layer 3 manages devices addressing, tracks the location of devices on the network, and determines the best way to move data. Routers which are layer 3 devices are specified at this layer and provide the routing services within an internetwork. Data and Route Packets are the two types of packets used at the network layer:
Data Packets:
These are used to transport user data through the internetwork. Protocols used to support data traffic are called routed protocols. IPv4 and IPv6 are examples of Data Packets.
Route Update Packet:
These packets are used to update neighboring routers about the network connected to all routers within the internetwork. Protocol that send the route routing update are called routing protocols. Route Update packets are used to update and maintain the routing tables. The routing table each router keep and refer to include the following information:
Network Addresses:
Protocol specific network addresses. A router must maintain a routing table for individual routing protocols because each routed protocol keep track of a network with a different addressing scheme.
Interface:
The exit interface a packet will take when destined for a specific network.
Metric:
The distance to the remote network is called metric.
Routers break up broadcast domains, which means that by default, broadcasts aren't forwarded through a router. Each interface in a router represents a separate network, it must be assigned unique network identification numbers, and each host on the network connected to the router must use the same network number. Here are some router characteristics that you should never forget:
Routers, by default, will not forwarded any broadcast or multicast packets.
Routers use the logical address in a Network layer header to determine the next hop router to forward the packet to.
Routers can use access list, created by an administrator, to control security based on the types of packet allowed to enter or exit an interface.
Routers can provide layer 2 bridging functions if needed and can simultaneously route through the same interface interface.
Layer 3 device - in this case, routers - provide connection between virtual LANs (VLANs)
Routers can provide quality of service (QoS) for specific types of network traffic.
Data Link Layer
The Data Link layer provide for the physical transmission of data and handles error notification network topology and flow control this means that the data link layer will ensure that the message are delivered to the proper device on the LAN using hardware address and will translate message from the network layer into bits for the physical layer to transmit. The data link layer format the message is called a data frame and adds a customize header containing the hardware destination and source addresses. For host to send packets to individual host on the local Network as well as transmit packets between routers the data link layer uses hardware addressing. The IEEE itna Data Link Layer has two sublayers:
Media Access Control (MAC):
Defines how packets are placed on the media contention for media access is first come or first serve access where everyone shares the same bandwidth.
Link Layer Control:
Responsible for identifying network layer protocols and then encapsulating them an LLC header tells the data link layer what to do with the packet once a frame is receive. It work like this - A host receives a frame and looks in the LLC header to find out where the packet is destined - for instance the IP protocol at the network layer. The LLC can also provide flow control and sequencing of control bits. Layer 2 switching is considered hardware based bridging because it uses specialized hardware called application specific integrated circuit (ASIC). Note: Latency is time measured from when a frame enters a port to when it exits a port.
Physical Layer
At this layer the frames are converted into the bits and it is sent out from the NIC in the form of electric signals. It is transported from using wireless or through wired in the form of digital signals. Changes in the voltage from high to low and low to high - specific protocols are needed for each type of media to describe the proper bit patterns to be used.
Hubs at the Physical Layer:
A hub is really a multiple-port repeater. A repeater receives a digital signal, reamplifies or regenerates that signal, then forwards the signal out the other port without looking at any data. A hub does the same thing across all active ports: any digital signal received from a segment on a hub port is regenerated or reamplified and transmitted out all other ports on the hub. This means all devices plugged into a hub are in the same collision domain as well as in the same broadcast domain. Hubs and repeaters can be used to enlarge area covered by a single LAN segment.