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The Seven Layer Osi Model

Seven-layer OSI model is a reasonable layer and produced by the ISO international standardization organization. The purpose of this layer is to comprehend the transmitting of data moves from source to vacation spot and also to identify problems during data transmitting. The seven layers include Application, Display, Session, Transportation, Network, Data website link and Physical layer. The sequence of layer titles to be kept in mind by this term "All people appear to need data processing". The following is a general description of each layer. OSI research model is now being regarded as the main model for the internetworking and inter processing. The seven levels divide the task of data transmitting in sub responsibilities and then complete the data transmission cycle.


In the 1980s, the European-dominated International Specifications Organization (ISO) began to develop its Open up Systems Interconnection (OSI) networking suite. OSI has two major components: an abstract style of networking (the essential Reference Model, or seven-layer model), and a couple of concrete protocols.

Briefly explain each one of the seven OSI layer included their function and utilization in data communication and networking.

OSI Reference Model

OSI research model (Start Systems Interconnection) illustrates how information from a software program over a computer moves via a network medium to a software application on another computer. OSI guide model is conceptually split into 7 tiers where each layer has a particular network function, as defined by physique 1. 1 (with no physical mass media). This model was created based on a proposal created by the International Benchmarks Business (ISO) as a first step toward international standardization of protocols used at various layers. ЇїЅThis model is named ISO OSI (Start Systems Interconnection) Research Model because this model is supposed for sharing open up systemЇїЅ. [1] Open up Systems can be interpreted as an wide open system to communicate with other systems. For his brief, we will call this model as the OSI model only.

Figure 1. 1. OSI Reference point Model

OSI model has seven layers. The principles used for the seven levels are:

1. A layer must be produced when needed different degrees of abstraction.

2. Each layer shall have certain functions.

3. The function of each layer should be chosen carefully relative to the provisions of international protocol standards.

4. Layer boundaries labored to reduce the flow of information through the software.

5. The amount of tiers must be quite a bit, so that different functions do not need to be united in a single layer outside needs. However, the number of layers must also be cultivated less than possible so that the network architecture does not become difficult to use.

Below discuss about each layer of the OSI model sequentially, beginning with underneath layer. It ought to be known that the OSI model itself is not network architecture, because this model will not explain the exact services and protocols to be utilized on any layer. OSI model only points out about what should be achieved by way of a layer. However, ISO has also established standards for all those layers, although these expectations do not constitute a reference model itself. Each layer has been declared as another international standard.

Characteristics of the OSI Layers

To seven layers of OSI reference model can be divided into two categories, particularly higher and lower tiers. The very best layer of the OSI model deals with software issues and generally put in place only in software. The best layer (program layer) is the cover prior to the individual (users), both users and application layer processes interact with software applications which contain a communication part. The term higher layer may also be used to make reference to some of the top layer of another coating layer in the OSI model. Underneath layer of the OSI model to control data carry issues. Physical layer and data web page link layer integrated in hardware and software. The levels below others are usually only implemented in software. ЇїЅThe least expensive layer, the physical layer is a layer of cover for the physical network medium (cable connection networks), as responsible for the placement of home elevators the network pressЇїЅ. [2] The following stand shows the parting of both layers in the layers of the OSI model.

Application Program Overlay



Transport Data Transfer Undercoat


Data Link


Table 1. 2 Separation of top layer and bottom layer of the OSI model


OSI model provides a conceptual platform for communication between computer systems, but this model is not a approach to communication. In fact communication can occur due to utilize of communication protocols. Within the context of data systems, a protocol is a formal rules and contracts that determine how pcs exchange information on the network medium. A protocol implements a number of of the levels of the OSI. A wide variation of the communication protocol, but all retains the flow in a single group: the LAN protocols, WAN protocols, network protocols, and routing protocols. LAN protocols operate at the physical and data web page link layer of the OSI model and define communication over various LAN advertising. WAN protocols operate at the third lowest layer of the OSI model and define communication over various WAN. Routing protocol is a network layer protocol that is accountable for determining the street and traffic plans. Finally, the network protocol differs from top of the layer protocols which exist in some protocols.

Layers of the OSI Model

Physical Layer

Physical Layer functions in the delivery of raw bits in to the route of communication. Design issues that must be considered here's to ensure that whenever one side directs data 1 bit, the info must be accepted by the other part as a little too, and not 0 little bit. The question that arises in cases like this is: how many volts should be used to declare a value of just one 1? And how many volts is also necessary for the number 0?. It takes a bit how microsecond will be tired? Is the transmitting can be refined simultaneously in both guidelines? Just how many pins are owned by the network and what's the use of each pin? Generally, design problems are found here related to the mechanical, electric powered and procedural interfaces, and physical multimedia which is under the physical layer.

Data Hyperlink Layer

The main job of the info link layer is as raw data transmitting facility and transforms the data to a channel that is clear of transmission errors. Before forwarded who work layer, data web page link layer perform this task by allowing the sender meme cage breaking suggestions data into a number of data frames (usually numbering in the hundreds or thousands of bytes). Then the data hyperlink layer transmits these frames in collection, and process the acknowledgment frames sent back by the recipient. As the physical layer receive and send little bit stream without regard to the meaning or architectural body, then with respect to the data hyperlink layer was to create and identify frame boundaries it. This is done by affixing a particular bit to the start and end of the body. If incidental little patterns can be found in the data, it's important to pay special attention to ensure that the routine is not incorrectly regarded as the boundaries of the body.

The incident of noise in the route may damage the frame. In this case, the data link layer software on the foundation machine to send back the cracked frame. However, transmitting of the same frame over and over again can cause duplication of frames. Duplicate frames have to be directed if an acknowledgment framework from the receiver who went back to the sender has been lost. ЇїЅDepending on the layer is to defeat the problems that brought on the destruction, loss and duplication of frames. The info website link layer provides some service classes for the network layer. This service class can be distinguished in conditions of quality and priceЇїЅ. [4]

Other problems that arise in the info link layer (and also almost all of the tiers above it) are seeking the smooth process of data transmitting from the sender to the recipient a slow-moving speed. Mechanism of legislation of traffic data should allow the sender to know the amount of buffer space owned or operated by the recipient at a certain moment in time. Often setting movement and error handling is done in an included manner. Route that can send data in both guidelines can also be problematic. So therefore need to be considered for the info web page link layer software. Problems that can arise here's that the frames acknowledgement moving from A to B compete with each other ahead of the flow from B to A. Settlement of the best (piggy support) might have been used, then we will discuss it in depth. Broadcast systems have an additional problem in the info link layer. The problem is in conditions of controlling access to a shared route. To repair this you may use a particular sub layer of data link layer, called the medium access sub layer.

Network Layer

Network layer serves to control operation of the subnet. Important design problem is how to determine the route packets from source to vacation spot. Route can be predicated on static furniture are "associated with" network. Route can be determined at the start of a dialog like a terminal treatment. Finally, the route can even be very dynamic; it could be different for every package deal. Therefore, the delivery course of the packet depends on network load at that time. If at the same time in a subnet there are too many packets, then there is the likelihood of the deals arrive at once. This may lead to bottlenecks. Congestion control as it is also the duty of the network layer. Because the sub net operators expect the good fortune of his job duties. There may be often some accounting function built at the network layer. To create billing information, at least the program should calculate the amount of packets or heroes or bits that are directed by each customer. Accounting becomes more difficult, when a packet crosses a country which has a different rate.

The move packets in one network to another can also cause issues that are not small. Addressing setting used by a network can be different from the techniques utilized by other network. A network may struggle to receive the deal at all because the packet size is too large. Protocol was vary, as well as others. Network layer has been given the duty to solve all these problems, allowing different systems interconnected to one another.

Transport Layer

The basic function is the carry layer receives data from the period layer, split the info into bits smaller if required, forwards the info to the network layer, and ensure that all pieces of data can arrive at the other area correctly. Moreover, all of this must be achieved efficiently, and aspires to protect top of the layers of the changes in hardware technology that can not be averted. Under normal circumstances, the transfer layer makes the network interconnection is different for every transport connection which is necessary by the program layer. Once the transport connection takes a high throughput, then the move layer can make a great deal of network contacts. Transport layer separate sending data to a number of sites to increase throughput. On the other hand, if the make or maintenance of the network interconnection is very costly, carry layer can incorporate multiple transport contacts to the same network connection. That is done to get this to merger is not seen by the program layer.

Transport layer also determines the sort of service for the procedure layer, and in turn the sort of service for users of the network. Kind of the most popular transport layer is a channel error-free indicate point that forward information or bytes relative to the order delivery. However, there's also other types of travel services. The assistance are travel isolated messages that not promise order of delivery, and broadcast messages to lots of purposes. Kind of service determined when the connection starts.

Transport layer is a layer end to get rid of in reality, from source to destination. Quite simply, a program on the foundation machine to bring the chat with the same program on the mark machine. In the low layers, there are protocols between your two machines and other machines that are close by. Protocol is not found in the outer or the source machine's outer purpose machine, which may be separated by a router. The distinctions between layers 1 to 3 are intertwined and layer 4 to 7 are end to get rid of. This is explained as shown in Physique 1-1.

In addition to merging multiple channels of announcements into a single channel, transportation layer must be cautious in defining and deciding on the network connection. This process requires a naming device, so a process on the machine has ways to describe with whom the device wants to speak. Also there should be a mechanism to regulate the stream of information, so that the circulation of information from a fast host does not overwhelm a slow-moving host. Such system is called circulation control and takes on an important role in the transport layer (also in other layers). Flow control between hosts with different hosts by handling the stream of the router with the router. We'll find out later that the same guidelines used for both types of the control.

Session Layer

Session layer allows users to establish trainings with other users. A time in addition allows common data transport, as does the carry layer, also provides special services for specific applications. A treatment is used to permit one end user logs into a remote control timesharing system or even to move files from one machine to some other to machine. A session layer service is to use the dialogue control. Sessions makes it possible for traffic to go in two guidelines at one time or only in one direction only. If at one time in traffic only in a single course only analogous to a single railway series, the time layer helps to determine who's eligible for use the channel's switch at an instant.

Service trainings are described as token management. For some protocols, it is important to ensure that both parties worried do not perform surgery at exactly the same time. To modify this activity, the treatment layer provides tokens that can turn. Only a party that contains the token is allowed performs critical functions.

Another program is a synchronization service. Take for example that can occur when endeavoring to transfer data files that lasted 2 hours in one machine to some other machine with the opportunity of having an interval of 1 1 hour between your two crashes that may appear. After each copy is canceled, the copy may need to be repeated again from scrape, and could experience another inability. To reduce the likelihood of the problem, the time layer can put a specific signal to the stream of data. Therefore, in case a crash, only the data that is after the sign is usually to be transferred back.

Presentation Layer

Presentation layer does certain functions that must ensure the discovery of the common solution for certain problems. Presentation Layer does not allow users to resolve their own problems. Unlike the layers underneath are only moving the bits from one location to another place, presentation layer focus on syntax and semantics of information transmitted. One example is the encoding of data display service. Most users do not move a arbitrary string of binary bits. The users exchange data just as the name, date, amount of money, and bills. The items are expressed in the form of a string of character types, integer amounts, floating point volumes, a data framework developed from some simpler items. There's a difference between one computer to some other computer in confirmed code to declare a string of character types (for example, ASCII and Unicode), integer (for example, match and go with one two), etc. To allow both computers that contain different demonstration to connect, data buildings to be exchanged can be indicated by means of abstract, relative to standard encoding to be utilized "on line". Display layer-data set in place and convert this abstract framework of representation that is utilized on a computer into a network standard representation, and vice versa.

Application Layer

Application layer contains a number of protocols. For example there are a huge selection of incompatible terminal types in the whole world. Take the problem where full-screen editor is likely to work on a network with a number of terminals, which each have different screen layouts, have a way different series of keystrokes for the insertion and deletion of word, move the sensor etc. A good way to get over such problems in data is to determine an abstract network online terminal, so editors and other programs can be written for each corresponding. To take care of each terminal type, one area of the software must be written to map the network digital terminal functions to the real terminal. For example, when moving the cursor editor electronic terminal into the left area of the display screen, the software should issue the appropriate command sequence to achieve the cursor. All electronic terminal software is in the application layer.

Another program layer function is file transfer. File systems from one another have different naming conventions, how expressing the lines of text message are different, etc. Transfer documents from a system different to other systems that require treatment to triumph over the lack of this compatible. The duty is also employment request layer, such as electronic mail, remote job accessibility, directory lookup, and various general goal facilities and other special goal facilities.


The procedure for sending a data to be delivered to the recipient. Sender processes submitting data to the application form layer, which in turn add an individual application header, the AH (which might also be empty), the front end and submit the leads to the demonstration layer. Presentation layer can form these data in various ways and could just add a header at the front end, which is given by the treatment layer. It is important to keep in mind that the demonstration layer is unaware of the data which are designated AH by request layer is the data users really are.

The process of granting this header repeated until the data grows to the physical layer, where data will be sent to other machines. On these machines, all headers were be removed one at a time until reaching the admissions process.

Figure1. 3 Examples of the way the OSI model used

The key here is that although actual data transmission is each layer is designed as though the transmission involved took place horizontally. For instance, when transportation layer delivery get a note from the treatment layer, carry layer will affix the move layer header and delivers it to the device transportation layer.


Computer networks are a tool, known also as nodes, associated with press liaison. Node may consist of a computer, computer printer or other device to send and receive data produced by other nodes, nodes in the network. Media Liaison, also called communication media.

On today, there are various types of networks, including local area network (LAN) and wide area network (WAN). The greatest network on earth is the web.

Edit Development. Network started with a small building, the connection about ten computer systems and a printer. The technology that prevails at the time the computer is linked to limit the quantity and amount of communications cable that may be allowed on the network. In the early nineties the communication cable connection can be pulled up to now about 600 feet to the extension of around 30 computers only. This network is well suited for a small firm known as local area network (LAN). LANs typically connect devices in a building or a building. A LAN can be built only with two pcs and a printing device or can be extended only in one building to include audio tracks and video software. LAN size is limited to a distance of several kilometers only. LAN with data rates from 4 Mbps to 100 Mbps. Network links from different countries has established the introduction of LAN to the wide area network (WAN). WAN can be mailing data, audio tracks and video tutorial at distances up for a country or continent or about the planet.


Briefly explain at least four (4) topologies of systems and suggest how we apply these topologies in networking.


Network can be of the following three types:

Local Area Network:

Figure: 2. 1 Local Area Network

Local Area Network (LAN) is a limited range of physical barriers like a laboratory, a university or building. In a typical LAN construction, one of the computers used as record server document server that functions to keep all the program that manages the network. All pcs are linked to the server record known as a workstation. Computer workstation comprising a pc specifications less than the server and also may have software on the disk severity. Cable television used to connect the LAN via network card installed on each computer.

Metropolitan Area Network:

Figure : 2. 2 Metropolitan Area Network

Town Area Network (MAN) protects a wider physical area as a region or city. Common area network hooking up lots of Local Area Network in a place to enable posting of information transported. Universities and federal government agencies Endemic Area Network to talk to the other neighborhoods and "private sectors. "

One example is the MAN MIND Network, positioned in Pasco County, Florida which allows communication between the Central Pasco Mass media Center Main Shape using a telephone line, coaxial wire, and cellular communication providers.

Wide Area Network:

Figure : 2. 3 Wide Area Network

Widespread Area Network (WAN) includes a wider area as circumstances, nation and world. To make a WAN requires systems across the sea or the use of microwave or satellite tv.

Use WAN permits communication between your expresses can be put in place quickly.

Configuring the WAN is complex and requires a hardware multiplexing multiplexer for LAN and MAN links for access to a comprehensive marketing communications network including the Internet.

Network Topology:

Figure : 3. 1 Network Topology

ЇїЅA computer network system using communication range that connects computer systems to each otherЇїЅ. [5] There are many methods you can use for the communication and is recognized as topology. Topology can be viewed as as a online shape or structure of any network. This form actually does not match the actual physical design of the devices on the computer network. The pcs on the house network can be set up in a group shape but it generally does not necessarily mean so it presents a engagement ring topology.

There are few types of topologies for computer networks, particularly: -

Star Network Topology

Figure :3. 1. 1 Legend Network Topology

Star topology is a network where all computer systems or other devices connected to the central distribution system, known as the Hub or Move. Hub or Turn is accountable for taking care of the computer network. All messages or data that is sent to a central control hub for avoid collisions from occurring. A couple of two operations that employed by the hub or switch that is functioning broadcast and the procedures of the change switching. ЇїЅCirculation procedures, hub or swap can make the delivery of data received in one station to all or any the routes joining them. In transition functions, the hub or swap will save the info received and transmits the data by way of a receiving stationЇїЅ. [3] Each node can be linked to the network and can be removed at any time without affecting the complete system of straight by. Furthermore, if one node does not work, it will not influence other computer networks. Any damage to the connection between the hub nodes will not affect the machine as a whole, but if the damage happened on the hub, the whole system will also be affected. The primary weakness of the topology is the fact it requires a reasonably high cost because of all systems linked to it computer systems, scanners, printers, etc. requires its own cable.

Ring Network Topology

Figure :3. 1. 2 Diamond ring Network Topology

In geographic area networks where the ring topology can be used, each computer is linked to the network in a sealed loop or engagement ring. The Information or data to be transferred in order according to the same journey in the same band. Network technology was first used by IBM systems with Type I in the category of cable shielded Twisted Couple STP. Each data node will be checked by delivery location. If not the same node strike, it'll be submitted to the next node and this will continue before delivery address the same node reach. ЇїЅAs the data is moved by the same way as the sequence of the potential for violations of data that are like the network and can be removed anytime without affecting the complete system of immediately byЇїЅ. [6] However, one problem that arises is if a node fails, the entire network will most likely also be affected.

Arrangement of nodes in this topology is almost the same literally as legend topology; only a logical was a band. The attachment is required in this topology is named Multi Station Gain access to Product (MSAU). MSAU is installed in a ring-shaped network where it is several unit. Only if one device only used the physical topology is similar to the star interconnection.

Bus Network Topology

Figure :3. 1. 3 Bus Network Topology

Bus topology, are also known as the Ethernet utilizing a line length where each node with regards to him. Data will be directed by each node in the trust that it generally does not collide with data transmitted from other nodes. If it happens, the node will attempt again until successful.

Weakness of the bus topology is within conditions of maintenance. It really is quite difficult to maintain in view of the bond is by means of a series. In the event of damage to any range at any node, it'll cause the whole system will not work. In addition to accurately identify things or nodes those are broken. Each node can be connected to the network and can be removed anytime without affecting the complete system directly. Furthermore, if one node does not work nor would it influence other computer sites. The other edge will there be in this topology is the fact it uses a single cable tv and requires no additional hardware to develop the network. But it does not need a very high cost for maintenance purposes.

Tree Network Topology

Figure :3. 1. 4 Tree Network Topology

The tree topology is actually a hybrid of the bus and star layouts. Additionally it is known as a hierarchical topology and has a central main node that is linked to one or more nodes of a lesser hierarchy. ЇїЅIn a symmetrical hierarchy, each node in the network has a particular fixed range of nodes connected to prospects at less levelЇїЅ. [3] Aside from these basic types of network topologies, there are hybrid network topologies, which are comprised of a combination of several basic topologies. These network mappings aim at harnessing the features of each of the basic topologies used in them. Network topologies are the physical plans of network nodes and wires. What is interesting is that the inanimate nodes and cables flip 'live' for the transmission of information.

Mesh Network Topology

Figure :3. 1. 5 Mesh Network Topology

In a full mesh network, each network node is linked to every other node in the network. Due to this design of nodes, it becomes easy for a simultaneous transmitting of signals in one node to many other nodes. In a very partially linked mesh network, only some of the network nodes are connected to more than one node. ЇїЅThis is beneficial over a fully connected mesh in conditions of redundancy induced by the point-to-point links between all the nodesЇїЅ. [5] The nodes of a mesh network require having some type of routing logic so that the signals and the info traveling within the network take the shortest course during each one of the transmissions.


Topologies are substance of computer sites design. Efficient networks can only just be built based on the complete knowledge and understanding of above mentioned topologies. Understanding of every communication device is of similar importance to support you in finding your best option for your network requirements. Most effective networks can be built with complete knowledge and understanding of computer network devices and how they are designed, any mistake in choosing improper techniques, device etc can only be the misuse of time, resources and efforts.


Figure 1. 1. OSI Reference point Model

Application Software Overlay



Transport Data Transport Undercoat


Data Link


Table 1. 2 Parting of top coating and bottom level of the OSI model

Figure1. 3 Examples of how the OSI model used

Figure: 2. 1 Local Area Network

Figure : 2. 2 Metropolitan Area Network

Figure : 2. 3 Wide Area Network

Figure : 3. 1 Network Topology

Figure :3. 1. 1 Superstar Network Topology

Figure :3. 1. 2 Ring Network Topology

Figure :3. 1. 3 Bus Network Topology

Figure :3. 1. 4 Tree Network Topology

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