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This article explains the Open Systems Interconnection (OSI) model and the 7 layers of networking, in plain English.
The OSI model is a conceptual framework that is used to describe how a network functions. In plain English, the OSI model helped standardize the way computer systems send information to each other.
Learning networking is a bit like learning a language - there are lots of standards and then some exceptions. Therefore, it’s important to really understand that the OSI model is not a set of rules. It is a tool for understanding how networks function.
Once you learn the OSI model, you will be able to further understand and appreciate this glorious entity we call the Internet, as well as be able to troubleshoot networking issues with greater fluency and ease.
All hail the Internet!
You don’t need any prior programming or networking experience to understand this article. However, you will need:
Over the course of this article, you will learn:
Here are some common networking terms that you should be familiar with to get the most out of this article. I’ll use these terms when I talk about OSI layers next.
A node is a physical electronic device hooked up to a network, for example a computer, printer, router, and so on. If set up properly, a node is capable of sending and/or receiving information over a network.
Nodes may be set up adjacent to one other, wherein Node A can connect directly to Node B, or there may be an intermediate node, like a switch or a router, set up between Node A and Node B.
Typically, routers connect networks to the Internet and switches operate within a network to facilitate intra-network communication. Learn more about hub vs. switch vs. router.
Here's an example:
For the nitpicky among us (yep, I see you), host is another term that you will encounter in networking. I will define a host as a type of node that requires an IP address. All hosts are nodes, but not all nodes are hosts. Please Tweet angrily at me if you disagree.
Links connect nodes on a network. Links can be wired, like Ethernet, or cable-free, like WiFi.
Links to can either be point-to-point, where Node A is connected to Node B, or multipoint, where Node A is connected to Node B and Node C.
When we’re talking about information being transmitted, this may also be described as a one-to-one vs. a one-to-many relationship.
A protocol is a mutually agreed upon set of rules that allows two nodes on a network to exchange data.
“A protocol defines the rules governing the syntax (what can be communicated), semantics (how it can be communicated), and synchronization (when and at what speed it can be communicated) of the communications procedure. Protocols can be implemented on hardware, software, or a combination of both. Protocols can be created by anyone, but the most widely adopted protocols are based on standards.” - The Illustrated Network.
Both wired and cable-free links can have protocols.
While anyone can create a protocol, the most widely adopted protocols are often based on standards published by Internet organizations such as the Internet Engineering Task Force (IETF).
A network is a general term for a group of computers, printers, or any other device that wants to share data.
Network types include LAN, HAN, CAN, MAN, WAN, BAN, or VPN. Think I’m just randomly rhyming things with the word can ? I can ’t say I am - these are all real network types. Learn more here .
Topology describes how nodes and links fit together in a network configuration, often depicted in a diagram. Here are some common network topology types:
A network consists of nodes, links between nodes, and protocols that govern data transmission between nodes.
At whatever scale and complexity networks get to, you will understand what’s happening in all computer networks by learning the OSI model and 7 layers of networking.
The OSI model consists of 7 layers of networking.
First, what’s a layer?
No, a layer - not a lair . Here there are no dragons.
A layer is a way of categorizing and grouping functionality and behavior on and of a network.
In the OSI model, layers are organized from the most tangible and most physical, to less tangible and less physical but closer to the end user.
Each layer abstracts lower level functionality away until by the time you get to the highest layer. All the details and inner workings of all the other layers are hidden from the end user.
How to remember all the names of the layers? Easy.
Keep in mind that while certain technologies, like protocols, may logically “belong to” one layer more than another, not all technologies fit neatly into a single layer in the OSI model. For example, Ethernet, 802.11 (Wifi) and the Address Resolution Protocol (ARP) procedure operate on >1 layer.
The OSI is a model and a tool, not a set of rules.
Layer 1 is the physical layer . There’s a lot of technology in Layer 1 - everything from physical network devices, cabling, to how the cables hook up to the devices. Plus if we don’t need cables, what the signal type and transmission methods are (for example, wireless broadband).
Instead of listing every type of technology in Layer 1, I’ve created broader categories for these technologies. I encourage readers to learn more about each of these categories:
The data unit on Layer 1 is the bit.
A bit the smallest unit of transmittable digital information. Bits are binary, so either a 0 or a 1. Bytes, consisting of 8 bits, are used to represent single characters, like a letter, numeral, or symbol.
Bits are sent to and from hardware devices in accordance with the supported data rate (transmission rate, in number of bits per second or millisecond) and are synchronized so the number of bits sent and received per unit of time remains consistent (this is called bit synchronization). The way bits are transmitted depends on the signal transmission method.
Nodes can send, receive, or send and receive bits. If they can only do one, then the node uses a simplex mode. If they can do both, then the node uses a duplex mode. If a node can send and receive at the same time, it’s full-duplex – if not, it’s just half-duplex.
The original Ethernet was half-duplex. Full-duplex Ethernet is an option now, given the right equipment.
Here are some Layer 1 problems to watch out for:
If there are issues in Layer 1, anything beyond Layer 1 will not function properly.
Layer 1 contains the infrastructure that makes communication on networks possible.
It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating physical links between network devices. - Source
Fun fact: deep-sea communications cables transmit data around the world. This map will blow your mind: https://www.submarinecablemap.com/
And because you made it this far, here’s a koala:
Layer 2 is the data link layer . Layer 2 defines how data is formatted for transmission, how much data can flow between nodes, for how long, and what to do when errors are detected in this flow.
In more official tech terms:
There are two distinct sublayers within Layer 2:
The data unit on Layer 2 is a frame .
Each frame contains a frame header, body, and a frame trailer:
Typically there is a maximum frame size limit, called an Maximum Transmission Unit, MTU. Jumbo frames exceed the standard MTU, learn more about jumbo frames here .
Here are some Layer 2 problems to watch out for:
The Data Link Layer allows nodes to communicate with each other within a local area network. The foundations of line discipline, flow control, and error control are established in this layer.
Layer 3 is the network layer . This is where we send information between and across networks through the use of routers. Instead of just node-to-node communication, we can now do network-to-network communication.
Routers are the workhorse of Layer 3 - we couldn’t have Layer 3 without them. They move data packets across multiple networks.
Not only do they connect to Internet Service Providers (ISPs) to provide access to the Internet, they also keep track of what’s on its network (remember that switches keep track of all MAC addresses on a network), what other networks it’s connected to, and the different paths for routing data packets across these networks.
Routers store all of this addressing and routing information in routing tables.
Here’s a simple example of a routing table:
The data unit on Layer 3 is the data packet . Typically, each data packet contains a frame plus an IP address information wrapper. In other words, frames are encapsulated by Layer 3 addressing information.
The data being transmitted in a packet is also sometimes called the payload . While each packet has everything it needs to get to its destination, whether or not it makes it there is another story.
Layer 3 transmissions are connectionless, or best effort - they don't do anything but send the traffic where it’s supposed to go. More on data transport protocols on Layer 4.
Once a node is connected to the Internet, it is assigned an Internet Protocol (IP) address, which looks either like 172.16. 254.1 (IPv4 address convention) or like 2001:0db8:85a3:0000:0000:8a2e:0370:7334 (IPv6 address convention). Routers use IP addresses in their routing tables.
IP addresses are associated with the physical node’s MAC address via the Address Resolution Protocol (ARP), which resolves MAC addresses with the node’s corresponding IP address.
ARP is conventionally considered part of Layer 2, but since IP addresses don’t exist until Layer 3, it’s also part of Layer 3.
Here are some Layer 3 problems to watch out for:
Many answers to Layer 3 questions will require the use of command-line tools like ping , trace , show ip route , or show ip protocols . Learn more about troubleshooting on layer 1-3 here .
The Network Layer allows nodes to connect to the Internet and send information across different networks.
Layer 4 is the transport layer . This where we dive into the nitty gritty specifics of the connection between two nodes and how information is transmitted between them. It builds on the functions of Layer 2 - line discipline, flow control, and error control.
This layer is also responsible for data packet segmentation, or how data packets are broken up and sent over the network.
Unlike the previous layer, Layer 4 also has an understanding of the whole message, not just the contents of each individual data packet. With this understanding, Layer 4 is able to manage network congestion by not sending all the packets at once.
The data units of Layer 4 go by a few names. For TCP, the data unit is a packet. For UDP, a packet is referred to as a datagram. I’ll just use the term data packet here for the sake of simplicity.
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are two of the most well-known protocols in Layer 4.
TCP, a connection-oriented protocol, prioritizes data quality over speed.
TCP explicitly establishes a connection with the destination node and requires a handshake between the source and destination nodes when data is transmitted. The handshake confirms that data was received. If the destination node does not receive all of the data, TCP will ask for a retry.
TCP also ensures that packets are delivered or reassembled in the correct order. Learn more about TCP here .
UDP, a connectionless protocol, prioritizes speed over data quality. UDP does not require a handshake, which is why it’s called connectionless.
Because UDP doesn’t have to wait for this acknowledgement, it can send data at a faster rate, but not all of the data may be successfully transmitted and we’d never know.
If information is split up into multiple datagrams, unless those datagrams contain a sequence number, UDP does not ensure that packets are reassembled in the correct order. Learn more about UDP here .
TCP and UDP both send data to specific ports on a network device, which has an IP address. The combination of the IP address and the port number is called a socket.
Learn more about sockets here .
Learn more about the differences and similarities between these two protocols here .
Here are some Layer 4 problems to watch out for:
The Transport Layer provides end-to-end transmission of a message by segmenting a message into multiple data packets; the layer supports connection-oriented and connectionless communication.
Layer 5 is the session layer . This layer establishes, maintains, and terminates sessions.
A session is a mutually agreed upon connection that is established between two network applications. Not two nodes! Nope, we’ve moved on from nodes. They were so Layer 4.
Just kidding, we still have nodes, but Layer 5 doesn’t need to retain the concept of a node because that’s been abstracted out (taken care of) by previous layers.
So a session is a connection that is established between two specific end-user applications. There are two important concepts to consider here:
Sessions may be open for a very short amount of time or a long amount of time. They may fail sometimes, too.
Depending on the protocol in question, various failure resolution processes may kick in. Depending on the applications/protocols/hardware in use, sessions may support simplex, half-duplex, or full-duplex modes.
Examples of protocols on Layer 5 include Network Basic Input Output System (NetBIOS) and Remote Procedure Call Protocol (RPC), and many others.
From here on out (layer 5 and up), networks are focused on ways of making connections to end-user applications and displaying data to the user.
Here are some Layer 5 problems to watch out for:
The Session Layer initiates, maintains, and terminates connections between two end-user applications. It responds to requests from the presentation layer and issues requests to the transport layer.
Layer 6 is the presentation layer . This layer is responsible for data formatting, such as character encoding and conversions, and data encryption.
The operating system that hosts the end-user application is typically involved in Layer 6 processes. This functionality is not always implemented in a network protocol.
Layer 6 makes sure that end-user applications operating on Layer 7 can successfully consume data and, of course, eventually display it.
There are three data formatting methods to be aware of:
Learn more about character encoding methods in this article , and also here .
Encryption: SSL or TLS encryption protocols live on Layer 6. These encryption protocols help ensure that transmitted data is less vulnerable to malicious actors by providing authentication and data encryption for nodes operating on a network. TLS is the successor to SSL.
Here are some Layer 6 problems to watch out for:
The Presentation Layer formats and encrypts data.
Layer 7 is the application layer .
True to its name, this is the layer that is ultimately responsible for supporting services used by end-user applications. Applications include software programs that are installed on the operating system, like Internet browsers (for example, Firefox) or word processing programs (for example, Microsoft Word).
Applications can perform specialized network functions under the hood and require specialized services that fall under the umbrella of Layer 7.
Electronic mail programs, for example, are specifically created to run over a network and utilize networking functionality, such as email protocols, which fall under Layer 7.
Applications will also control end-user interaction, such as security checks (for example, MFA), identification of two participants, initiation of an exchange of information, and so on.
Protocols that operate on this level include File Transfer Protocol (FTP), Secure Shell (SSH), Simple Mail Transfer Protocol (SMTP), Internet Message Access Protocol (IMAP), Domain Name Service (DNS), and Hypertext Transfer Protocol (HTTP).
While each of these protocols serve different functions and operate differently, on a high level they all facilitate the communication of information. ( Source )
Here are some Layer 7 problems to watch out for:
The Application Layer owns the services and functions that end-user applications need to work. It does not include the applications themselves.
Our Layer 1 koala is all grown up.
Learning check - can you apply makeup to a koala?
Don’t have a koala?
Well - answer these questions instead. It’s the next best thing, I promise.
Congratulations - you’ve taken one step farther to understanding the glorious entity we call the Internet.
Many, very smart people have written entire books about the OSI model or entire books about specific layers. I encourage readers to check out any O’Reilly-published books about the subject or about network engineering in general.
Here are some resources I used when writing this article:
Chloe Tucker is an artist and computer science enthusiast based in Portland, Oregon. As a former educator, she's continuously searching for the intersection of learning and teaching, or technology and art. Reach out to her on Twitter @_chloetucker and check out her website at chloe.dev .
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So I feel I pretty well understand the application layer, and everything below (and including) the transport layer.
The session and presentation layers, though, I don't fully understand. I've read the simplistic descriptions in Wikipedia, but it doesn't have an example of why separating out those layers is useful.
The session layer is meant to store states between two connections, like what we use cookies for when working with web programming.
The presentation layer is meant to convert between different formats. This was simpler when the only format that was worried about was character encoding, ie ASCII and EBCDIC. When you consider all of the different formats that we have today(Quicktime, Flash, Pdf) centralizing this layer is out of the question.
TCP/IP doesn't make any allocation to these layers, since they are really out of the scope of a networking protocol. It's up to the applications that take advantage of the stack to implement these.
The reasons there aren't any examples on wikipedia is that there aren't a whole lot of examples of the OSI network model, period.
OSI has once again created a standard nobody uses, so nobody really know how one should use it.
Layers 5-6 are not commonly used in today's web applications, so you don't hear much about them. The TCP/IP stack is slightly different than a pure OSI Model.
One of the reasons TCP/IP is used today instead of OSI is it was too bloated and theoretical, the session and presentation layer aren't really needed as separate layers as it turned out.
I think that presentation layer protocols define the format of data. This means protocols like XML or ASN.1. You could argue that video/audio codecs are part of the presentation layer Although this is probably heading towards the application layer.
I can't help you with the session layer. That has always baffled me.
To be honest, there are very vague boundaries in everything above the transport layer. This is because it is usually handled by a single software application. Also, these layers are not directly associated with transporting data from A to B. Layers 4 and below each have a very specific purpose in moving the data e.g. switching, routing, ensuring data integrity etc. This makes it easier to distinguish between these layers.
Presentation Layer The Presentation Layer represents the area that is independent of data representation at the application layer - in general, it represents the preparation or translation of application format to network format, or from network formatting to application format. In other words, the layer “presents” data for the application or the network. A good example of this is encryption and decryption of data for secure transmission - this happens at Layer 6.
Session Layer When two devices, computers or servers need to “speak” with one another, a session needs to be created, and this is done at the Session Layer. Functions at this layer involve setup, coordination (how long should a system wait for a response, for example) and termination between the applications at each end of the session.
For the presentation layer :because most of communication done between heterogeneous systems (Operating Systems,programing langages,cpu architectures)we need to use a unified idepedent specification .like ANS1 ans BRE.
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The Open Systems Interconnection (OSI) networking model defines a conceptual framework for communications between computer systems. The model is an ISO standard which identifies seven fundamental networking layers, from the physical hardware up to high-level software applications.
Each layer in the model handles a specific networking function. The standard helps administrators to visualize networks, isolate problems, and understand the use cases for new technologies. Many network equipment vendors advertise the OSI layer that their products are designed to slot into.
OSI was adopted as an international standard in 1984. It remains relevant today despite the changes to network implementation that have occurred since first publication. Cloud, edge, and IoT can all be accommodated within the model.
In this article, we'll explain each of the seven OSI layers in turn. We'll start from the lowest level, labelled as Layer 1.
All networking begins with physical equipment. This layer encapsulates the hardware involved in the communications, such as switches and cables. Data is transferred as a stream of binary digits - 0 or 1 - that the hardware prepares from input it's been fed. The physical layer specifies the electrical signals that are used to encode the data over the wire, such as a 5-volt pulse to indicate a binary "1."
Errors in the physical layer tend to result in data not being transferred at all. There could be a break in the connection due to a missing plug or incorrect power supply. Problems can also arise when two components disagree on the physical encoding of data values. In the case of wireless connections, a weak signal can lead to bit loss during transmission.
The model's second layer concerns communication between two devices that are directly connected to each other in the same network. It's responsible for establishing a link that allows data to be exchanged using an agreed protocol. Many network switches operate at Layer 2.
The data link layer will eventually pass bits to the physical layer. As it sits above the hardware, the data link layer can perform basic error detection and correction in response to physical transfer issues. There are two sub-layers that define these responsibilities: Logical Link Control (LLC) that handles frame synchronization and error detection, and Media Access Control (MAC) which uses MAC addresses to constrain how devices acquire permission to transfer data.
The network layer is the first level to support data transfer between two separately maintained networks. It's redundant in situations where all your devices exist on the same network.
Data that comes to the network layer from higher levels is first broken up into packets suitable for transmission. Packets received from the remote network in response are reassembled into usable data.
The network layer is where several important protocols are first encountered. These include IP (for determining the path to a destination), ICMP, routing, and virtual LAN. Together these mechanisms facilitate inter-network communications with a familiar degree of usability. However operations at this level aren't necessarily reliable: messages aren't required to succeed and may not necessarily be retried.
The transport layer provides higher-level abstractions for coordinating data transfers between devices. Transport controllers determine where data will be sent and the rate it should be transferred at.
Layer 4 is where TCP and UDP are implemented, providing the port numbers that allow devices to expose multiple communication channels. Load balancing is often situated at Layer 4 as a result, allowing traffic to be routed between ports on a target device.
Transport mechanisms are expected to guarantee successful communication. Stringent error controls are applied to recover from packet loss and retry failed transfers. Flow control is enforced so the sender doesn't overwhelm the remote device by sending data more quickly than the available bandwidth permits.
Layer 5 creates ongoing communication sessions between two devices. Sessions are used to negotiate new connections, agree on their duration, and gracefully close down the connection once the data exchange is complete. This layer ensures that sessions remain open long enough to transfer all the data that's being sent.
Checkpoint control is another responsibility that's held by Layer 5. Sessions can define checkpoints to facilitate progress updates and resumable transmissions. A new checkpoint could be set every few megabytes for a file upload, allowing the sender to continue from a particular point if the transfer gets interrupted.
Many significant protocols operate at Layer 5 including authentication and logon technologies such as LDAP and NetBIOS. These establish semi-permanent communication channels for managing an end user session on a specific device.
The presentation layer handles preparation of data for the application layer that comes next in the model. After data has made it up from the hardware, through the data link, and across the transport, it's almost ready to be consumed by high-level components. The presentation layer completes the process by performing any formatting tasks that may be required.
Decryption, decoding, and decompression are three common operations found at this level. The presentation layer processes received data into formats that can be eventually utilized by a client application. Similarly, outward-bound data is reformatted into compressed and encrypted structures that are suitable for network transmission.
TLS is one major technology that's part of the presentation layer. Certificate verification and data decryption is handled before requests reach the network client, allowing information to be consumed with confidence that it's authentic.
The application layer is the top of the stack. It represents the functionality that's perceived by network end users. Applications in the OSI model provide a convenient end-to-end interface to facilitate complete data transfers, without making you think about hardware, data links, sessions, and compression.
Despite its name, this layer doesn't relate to client-side software such as your web browser or email client. An application in OSI terms is a protocol that caters for the complete communication of complex data through layers 1-6.
HTTP, FTP, DHCP, DNS, and SSH all exist at the application layer. These are high-level mechanisms which permit direct transfers of user data between an origin device and a remote server. You only need minimal knowledge of the workings of the other layers.
The seven OSI layers describe the transfer of data through computer networks. Understanding the functions and responsibilities of each layer can help you identify the source of problems and assess the intended use case for new components.
OSI is an abstract model that doesn't directly map to the specific networking implementations commonly used today. As an example, the TCP/IP protocol works on its own simpler system of four layers: Network Access, Internet, Transport, and Application. These abstract and absorb the equivalent OSI layers: the application layer spans OSI L5 to L7, while L1 and L2 are combined in TCP/IP's concept of Network Access.
OSI remains applicable despite its lack of direct real-world application. It's been around so long that it's widely understood among administrators from all backgrounds. Its relatively high level of abstraction has also ensured it's remained relevant in the face of new networking paradigms, many of which have targeted Layer 3 and above. An awareness of the seven layers and their responsibilities can still help you appreciate the flow of data through a network while uncovering integration opportunities for new components.
Layer 7 refers to the Application Layer in the OSI networking model. It is the top layer of this network model and deals with standard protocols that users interact with directly, such as HTTP traffic for web browsing.
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The Open Systems Interconnection (OSI) model is a conceptual model for how network traffic is structured. The seven layers of the OSI model include:
Layer 7 is the highest layer of the OSI model and deals with applications that interact with the user directly.
Lower application levels of the OSI model are concerned with ensuring that data gets where it needs to go and is formatted appropriately. Layer 7 is where applications that interact with the user operate. For instance, when browsing the web, a user will be using the HTTPS web protocol to communicate with the remote web server.
HTTPS is a Layer 7 protocol whose traffic is encapsulated within lower-layer protocols, such as:
These protocols are responsible for ensuring that data gets from a particular application on the client computer to a particular application on the server, while HTTPS carries the actual data that makes the web browsing session work.
An organization may choose to implement load balancing at Layer 7 of the OSI model. This means that legitimate traffic for a single application is distributed across multiple different servers, ensuring that they’re not overloaded.
Therefore, load balancing improves overall application performance. From a user’s perspective, all of the servers behind a Layer 7 load balancer are indistinguishable since they’d have the same public-facing IP address and port numbers. But, the load balancer can route the traffic to servers based on utilization.
Additionally, the load balancer may use cookies or other information included in requests to ensure that traffic from the same session goes to the same server, enabling caching and optimizing the service.
Load balancing can also happen at Layer 4, the Transport Layer of the OSI model. In this case, different upstream servers would use different TCP/ UDP ports, enabling a load balancer to quickly send traffic from the same session to the same server without inspecting its actual contents. However, this approach offers less granular control over the sessions sent to each backend server.
Layer 7 is also relevant in the context of distributed denial-of-service (DDoS) attacks . In DDoS application layer attacks, an attacker-controlled botnet attempts to render a target service unavailable to users and customers. DDoS attacks can occur at multiple different layers of the OSI model. One approach is to attempt to overwhelm a system with the sheer volume of requests.
These attacks operate at Layers 3 (Network) and 4 (Transport) of the OSI model. For instance, a SYN flood attack exhausts the number of TCP sessions that a server keeps open at one time.
A SYN Flood is a type of DDoS attack that overwhelms a server with connection requests, making the server unavailable to legitimate customers.
However, in the case of SYN Flood attacks, the DDoS attacker sends a barrage of SYN requests to the server but purposefully does not reply with a final ACK to any of the SYN-ACK messages sent by the server. As a result, the server is stuck waiting for a large volume of ACK responses that never arrive from the client.
This process overwhelms the servers’ limited compute resources as they are tied up trying to manage a huge volume of half-open connections. This is why SYN Flood attacks are also known as ‘half-open attacks’.
Layer 7 DDoS attacks are designed to exploit vulnerabilities and bottlenecks in particular applications or services. For example, HTTP flood attacks try to send a web server more HTTP requests than it can handle. This may be substantially less than the number of simultaneous TCP sessions it can handle, making this a more efficient attack.
Different types of DDoS attacks have to be handled at different OSI layers. While many application firewalls can handle Layer 3/4 attacks, protecting against Layer 7 attacks requires a Layer 7 firewall that inspects and understands application-layer data.
Companies can suffer cyberattacks that operate at multiple different layers of the OSI model. For example, DDOS attacks can be performed at Layers 3, 4, or 7. Each of these types of attacks operates differently, and a network security solution providing protection only at Layers 3 and 4 will be blind to attacks occurring at Layer 7.
Check Point next-generation firewalls (NGFWs) provide protection at multiple layers of the OSI model, including the ability to inspect and understand network packet payloads to offer application-layer protection. Learn more about the Layer 7 protection that Check Point Quantum Force NGFWs provides by signing up for a free demo .
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TCP/IP stands for Transport Control Protocol/Internet Protocol. TCP/IP suite is considered as a basis on which a virtual network exists. TCP/IP makes use of client-server model for communication where service is provided by the server to the client or other systems. TCP/IP protocol consists of four layers. TCP/IP defines the rules, standards, and formats in which the message is transmitted from one system to another. Whenever any packet is transmitted over the internet it then passes through all the layers of the TCP/IP model. While a packet is being transmitted from one layer to another, each layer removes its header information.
There are four layers in the TCP/IP model. Each layer works in order to coordinate another layer above or below it. Below is a detailed description of each layer.
Layers of TCP/IP
Network access layer is the lowest layer of TCP/IP model. It is a combination of data link layer and physical layer present in the OSI model. The main function of network access layer is to transmit the information from one system to another that are connected in the same network.
Internet layer is also known as network layer. Internet layer ensures that data is sent accurately and fastly by controlling the flow and routing of traffic. If the internet traffic is more it takes more time to transfer the data.
Transport layer is responsible to provide a reliable connection between two communicating devices. In the incoming data is divided into packets by the transport layer and makes an acknowledgement when packet is received from the sender. UDP and TCP protocols are used in transport layer.
Application layer is the top most layer in TCP/IP model. Application layer provides the devices to access network and applications such as emails, cloud storage etc. While communicating from one application layer protocol to another application layer the information is forwarded to transport layer.
Application layer is the top most layer of TCP/IP model. This layer performs all the task that are performed by the session layer, presentation layer and application layer. The protocols used at application layer conveys the user request to transport layer. These protocols help to transfer mail, sharing of file and terminal login. Below are the protocols used at application layer of TCP/IP Model.
HTTP stands for Hypertext Transfer Protocol. This protocol is majorly used for exchanging the hyper text on different systems. HTTP is a request response protocol. With the help of Uniform Resource Locators(URLs) HTTP resources are identifiable on the networks. HTTP is considered as a base of World Wide Web (WWW). For example, HTTP is used for transferring the web pages. HTTP protocol transmits the data in MIME-like format. A HTTP request consists of HTTP version type, a URL, an HTTP method, HTTP request headers and optional HTTP body. HTTP request carries a sequence of data that is in encoded format.
TELNET protocol is also known as Remote login protocol. This protocol is used for accessing the remote end protocols. TELNET protocol allows the users client to interactively log in to the server host. TELNET defines a device that is known as NVT(Network Virtual Terminal). This NVT device provides with a standard network representation of a terminal. TELNET protocol also consists of features for the client and server for negotiating the options that can enhance their communications. Once the client and server agrees upon certain condition they can initiate their communication. When the connection between client and server is established successfully it is being presented to the Operating System of telnet server.
FTP stands for File Transfer Protocol. In order to perform file operations FTP allows the users to log into remote host. Various file operations supported by FTP are copying files to remote host, copying files from remote host, listing the remote directories, delete and rename remote directories. In order to provide reliable transportation of data FTP makes use of Transport Control Protocol( TCP ). When a successful connection is being established between FTP client and the server FTP makes an request for username and password for accessing the server host. This authorisation provides with security by denying the access to unauthorised user. FTP protocol supports various types of file formats that includes binary and ASCII format.
SMTP stands for simple mail transfer protocol. This protocol is used for transferring the mails. It works on store and forward model. Within the working of a network this mail being used twice. First it is used between the sender and senders mail server. At second time it is used between the two mail servers. In this protocol the transfer is of mails is being done by the Message Transfer Agents(MTA). Therefore the system that wants to send the mail from one system to another they must have client message transfer agents and server message transfer agents. When any client sends a mail to server it keeps a copy of mail until the mail is successfully received by the server client. IT makes use of TCP for reliable transmission of data.
DNS stands for Domain Name System. DNS is a decentralised naming system used by the computer system and other devices over the internet. It translates the domain name into IP address and IP address into domain name. The advantage provided by DNS is that the user need not to remember the IP address, but Domain name is sufficient. Once the user searches for particular website using domain name, this DNS query is being sent to DNS server that maps the IP address against domain name. When it gets the address an HTTP session is then built with the IP address. The protocols supported by Domain Name System are TCP and UDP. These domains are classified into three types namely generic domain, country domain and inverse domain.
DHCP stands for Dynamic Host Configuration Protocol. DHCP is a network management protocol at the application layer of TCP/IP model. The Internet Protocol can allocate IP address to the devices connected in network so that they can communicate with each other with the help of Dynamic Host Configuration Protocol. DHCP assigns a unique IP address to all the host connected in the network. It aslo assigns other network address such as subnet mask, router address and DNS address. For example a network consists of 10,000 devices in the network. Assigning a unique IP address to each device manually is a difficult and time consuming task. Therefore DHCP protocol is used to assign IP address and other related information to all the devices connected in the network.
1. network switches can operate in which layers .
Network switches can operate at data link layer or network layer. Data link layer forwards the data based on the MAC address of of destination and network layer switches forwards the data based on the destination of IP address.
VLAN stands for Virtual Local Area Network. It is a virtualized connection that is used to connect various devices in the one logical network that are in different LAN networks.
The maximum size of TCP header is 60 bytes and minimum size is 20 bytes.
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Telnet (Telecommunication Network): Telnet protocol was introduced in 1969, and it offers the command line interface for making communication along with remote device or server. Tox: The Tox protocol is sometimes regarded as part of both the presentation and application layer, and it is used for sending peer-to-peer instant-messaging as well as video calling.
Prerequisite : OSI Model. Introduction : Presentation Layer is the 6th layer in the Open System Interconnection (OSI) model. This layer is also known as Translation layer, as this layer serves as a data translator for the network. The data which this layer receives from the Application Layer is extracted and manipulated here as per the required ...
The presentation layer is the lowest layer at which application programmers consider data structure and presentation, instead of simply sending data in the form of datagrams or packets between hosts. This layer deals with issues of string representation - whether they use the Pascal method (an integer length field followed by the specified ...
For example, HyperText Transfer Protocol (HTTP), generally regarded as an application-layer protocol, has presentation-layer aspects such as the ability to identify character encoding for proper conversion, which is then done in the application layer. The presentation layer is the lowest layer at which application programmers consider data ...
The Presentation Layer, situated at Layer 6 of the OSI model, acts as an intermediary between the Application Layer (Layer 7) and the Session Layer (Layer 5). Its primary function is to ensure ...
The presentation layer is located at Layer 6 of the OSI model. The tool that manages Hypertext Transfer Protocol ( HTTP) is an example of a program that loosely adheres to the presentation layer of OSI. Although it's technically considered an application-layer protocol per the TCP/IP model, HTTP includes presentation layer services within it.
The presentation layer is the sixth layer of the OSI Reference Model protocol stack, and second from the top. It is different from the other layers in two key respects. First, it has a much more limited and specific function than the other layers; it's actually somewhat easy to describe, hurray! Second, it is used much less often than the other ...
In this article, we'll explain what the presentation layer is, how it works, and its functions and protocols. What is the presentation layer? The presentation layer is the sixth layer in the OSI model. Known as a translator, it converts data into an accurate, well-defined, standard format after it receives it from the application layer.
When the presentation layer receives data from the application layer, to be sent over the network, it makes sure that the data is in the proper format. If it is not, the presentation layer converts the data to the proper format. ... Presentation Layer Protocols. The OSI Model provides a conceptual framework for communication between computers ...
Layer 6 OSI Model. An example of a program that loosely adheres to layer 6 of OSI is the tool that manages the Hypertext Transfer Protocol (HTTP) — although it's technically considered an application-layer protocol per the TCP/IP model. However, HTTP includes presentation layer services within it.
The presentation layer is the sixth layer of the OSI Reference model. It defines how data and information is transmitted and presented to the user. It translates data and format code in such a way that it is correctly used by the application layer. It identifies the syntaxes that different applications use and formats data using those syntaxes.
The presentation layer is known as a translator because it converts data from a complex format into one that the application layer understands. Presentation layer protocols include MIDI, MPEG, TDI ...
The presentation layer translates information in a way that the application layer understands. Likewise, this layer translates information from the application layer to the session layer. Some examples of presentation layer protocols are SSL, HTTP/ HTML (agent), FTP (server), AppleTalk Filing Protocol,Telnet, and so on.
The Presentation layer has the simplest function of any piece of the OSI model. ... The Application layer supplies network services to end-user applications. Network services are protocols that work with the user's data. For example, in a web browser application, the Application layer protocol HTTP packages the data needed to send and receive ...
OSI model, the transport layer is only connection-oriented. A layer of the TCP/IP model is both connection-oriented and connectionless. In OSI model, data link layer and physical are separate layers. In TCP data link layer and physical layer are combined as a single host-to-network layer. The minimum size of the OSI header is 5 bytes.
The presentation layer handles protocol conversion, data encryption, data decryption, data compression, data decompression, incompatibility of data representation between operating systems, and graphic commands. The presentation layer transforms data into the form that the application layer accepts, to be sent across a network.
In synchronizing communication, all communication between applications requires cooperation that is managed by the application layer. Some examples of application layer implementations include Telnet, File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP). 1.2 Presentation layer. Manages the presentation of the information in an ...
The topmost layer of the OSI model is the application layer. On computer systems, applications display information to the user via the UI. Note: Software applications running on a computer are NOT considered to reside in the application layer. Instead, they leverage application layer services and protocols that enable network communication.
The presentation layer is the 6 th layer from the bottom in the OSI model. This layer presents the incoming data from the application layer of the sender machine to the receiver machine. It converts one format of data to another format of data if both sender and receiver understand different formats; hence this layer is also called the ...
The Session Layer initiates, maintains, and terminates connections between two end-user applications. It responds to requests from the presentation layer and issues requests to the transport layer. OSI Layer 6. Layer 6 is the presentation layer. This layer is responsible for data formatting, such as character encoding and conversions, and data ...
This means protocols like XML or ASN.1. You could argue that video/audio codecs are part of the presentation layer Although this is probably heading towards the application layer. I can't help you with the session layer. That has always baffled me. To be honest, there are very vague boundaries in everything above the transport layer.
Presentation Layer The presentation layer handles preparation of data for the application layer that comes next in the model. After data has made it up from the hardware, through the data link, and across the transport, it's almost ready to be consumed by high-level components. ... An application in OSI terms is a protocol that caters for the ...
Presentation Layer: Performs data encryption, ... HTTPS is a Layer 7 protocol whose traffic is encapsulated within lower-layer protocols, such as: ... In DDoS application layer attacks, an attacker-controlled botnet attempts to render a target service unavailable to users and customers. DDoS attacks can occur at multiple different layers of the ...
Application layer is the top most layer of TCP/IP model. This layer performs all the task that are performed by the session layer, presentation layer and application layer. The protocols used at application layer conveys the user request to transport layer. These protocols help to transfer mail, sharing of file and terminal login.