uses of presentation layer

The OSI Model – The 7 Layers of Networking Explained in Plain English

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!

Prerequisites

You don’t need any prior programming or networking experience to understand this article. However, you will need:

• Basic familiarity with common networking terms (explained below)
• A curiosity about how things work :)

Learning Objectives

Over the course of this article, you will learn:

• What the OSI model is
• The purpose of each of the 7 layers
• The problems that can happen at each of the 7 layers
• The difference between TCP/IP model and the OSI model

Common Networking Terms

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.

What is the OSI Model?

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.

• Please | Physical Layer
• Do | Data Link Layer
• Not | Network Layer
• Tell (the) | Transport Layer
• Secret | Session Layer
• Password (to) | Presentation Layer
• Anyone | Application Layer

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.

OSI Layer 1

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:

• Nodes (devices) and networking hardware components. Devices include hubs, repeaters, routers, computers, printers, and so on. Hardware components that live inside of these devices include antennas, amplifiers, Network Interface Cards (NICs), and more.
• Device interface mechanics. How and where does a cable connect to a device (cable connector and device socket)? What is the size and shape of the connector, and how many pins does it have? What dictates when a pin is active or inactive?
• Functional and procedural logic. What is the function of each pin in the connector - send or receive? What procedural logic dictates the sequence of events so a node can start to communicate with another node on Layer 2?
• Cabling protocols and specifications. Ethernet (CAT), USB, Digital Subscriber Line (DSL) , and more. Specifications include maximum cable length, modulation techniques, radio specifications, line coding, and bits synchronization (more on that below).
• Cable types. Options include shielded or unshielded twisted pair, untwisted pair, coaxial and so on. Learn more about cable types here .
• Signal type. Baseband is a single bit stream at a time, like a railway track - one-way only. Broadband consists of multiple bit streams at the same time, like a bi-directional highway.
• Signal transmission method (may be wired or cable-free). Options include electrical (Ethernet), light (optical networks, fiber optics), radio waves (802.11 WiFi, a/b/g/n/ac/ax variants or Bluetooth). If cable-free, then also consider frequency: 2.5 GHz vs. 5 GHz. If it’s cabled, consider voltage. If cabled and Ethernet, also consider networking standards like 100BASE-T and related standards.

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.

How to Troubleshoot OSI Layer 1 Problems

Here are some Layer 1 problems to watch out for:

• Defunct cables, for example damaged wires or broken connectors
• Broken hardware network devices, for example damaged circuits
• Stuff being unplugged (...we’ve all been there)

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:

OSI Layer 2

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:

• Line discipline. Who should talk for how long? How long should nodes be able to transit information for?
• Flow control. How much data should be transmitted?
• Error control - detection and correction . All data transmission methods have potential for errors, from electrical spikes to dirty connectors. Once Layer 2 technologies tell network administrators about an issue on Layer 2 or Layer 1, the system administrator can correct for those errors on subsequent layers. Layer 2 is mostly concerned with error detection, not error correction. ( Source )

There are two distinct sublayers within Layer 2:

• Media Access Control (MAC): the MAC sublayer handles the assignment of a hardware identification number, called a MAC address, that uniquely identifies each device on a network. No two devices should have the same MAC address. The MAC address is assigned at the point of manufacturing. It is automatically recognized by most networks. MAC addresses live on Network Interface Cards (NICs). Switches keep track of all MAC addresses on a network. Learn more about MAC addresses on PC Mag and in this article . Learn more about network switches here .
• Logical Link Control (LLC): the LLC sublayer handles framing addressing and flow control. The speed depends on the link between nodes, for example Ethernet or Wifi.

The data unit on Layer 2 is a frame .

Each frame contains a frame header, body, and a frame trailer:

• Header: typically includes MAC addresses for the source and destination nodes.
• Body: consists of the bits being transmitted.
• Trailer: includes error detection information. When errors are detected, and depending on the implementation or configuration of a network or protocol, frames may be discarded or the error may be reported up to higher layers for further error correction. Examples of error detection mechanisms: Cyclic Redundancy Check (CRC) and Frame Check Sequence (FCS). Learn more about error detection techniques here .

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 .

How to Troubleshoot OSI Layer 2 Problems

Here are some Layer 2 problems to watch out for:

• All the problems that can occur on Layer 1
• Unsuccessful connections (sessions) between two nodes
• Sessions that are successfully established but intermittently fail
• Frame collisions

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.

OSI Layer 3

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.

How to Troubleshoot OSI Layer 3 Problems

Here are some Layer 3 problems to watch out for:

• All the problems that can crop up on previous layers :)
• Faulty or non-functional router or other node
• IP address is incorrectly configured

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.

OSI Layer 4

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 .

How to Troubleshoot OSI Layer 4 Problems

Here are some Layer 4 problems to watch out for:

• Blocked ports - check your Access Control Lists (ACL) & firewalls
• Quality of Service (QoS) settings. QoS is a feature of routers/switches that can prioritize traffic, and they can really muck things up. Learn more about QoS here .

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.

OSI Layer 5

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:

• Client and server model: the application requesting the information is called the client, and the application that has the requested information is called the server.
• Request and response model: while a session is being established and during a session, there is a constant back-and-forth of requests for information and responses containing that information or “hey, I don’t have what you’re requesting.”

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.

How to Troubleshoot OSI Layer 5 Problems

Here are some Layer 5 problems to watch out for:

• Servers are unavailable
• Servers are incorrectly configured, for example Apache or PHP configs
• Session failure - disconnect, timeout, and so on.

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 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:

• American Standard Code for Information Interchange (ASCII): this 7-bit encoding technique is the most widely used standard for character encoding. One superset is ISO-8859-1, which provides most of the characters necessary for languages spoken in Western Europe.
• Extended Binary-Coded Decimal Interchange Code (EBDCIC): designed by IBM for mainframe usage. This encoding is incompatible with other character encoding methods.
• Unicode: character encodings can be done with 32-, 16-, or 8-bit characters and attempts to accommodate every known, written alphabet.

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.

How to Troubleshoot OSI Layer 6 Problems

Here are some Layer 6 problems to watch out for:

• Non-existent or corrupted drivers
• Incorrect OS user access level

The Presentation Layer formats and encrypts data.

OSI Layer 7

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 )

How to Troubleshoot OSI Layer 7 Problems

Here are some Layer 7 problems to watch out for:

• All issues on previous layers
• Incorrectly configured software applications
• User error (... we’ve all been there)

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.

• What is the OSI model?
• What are each of the layers?
• How could I use this information to troubleshoot networking issues?

Congratulations - you’ve taken one step farther to understanding the glorious entity we call the Internet.

Learning Resources

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:

• The Illustrated Network, 2nd Edition
• Protocol Data Unit (PDU): https://www.geeksforgeeks.org/difference-between-segments-packets-and-frames/
• Troubleshooting Along the OSI Model: https://www.pearsonitcertification.com/articles/article.aspx?p=1730891
• The OSI Model Demystified: https://www.youtube.com/watch?v=HEEnLZV2wGI
• OSI Model for Dummies: https://www.dummies.com/programming/networking/layers-in-the-osi-model-of-a-computer-network/

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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• Physical Layer
• Data Link Layer
• Network Layer
• Transport Layer
• Session Layer
• Presentation Layer
• Application Layer

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.

1. Physical Layer

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.

2. Data Link Layer

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.

3. Network Layer

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.

4. Transport Layer

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.

5. Session Layer

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.

6. 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. 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.

7. Application Layer

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.

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Presentation Layer: What It Is, Design Issues, Functionalities

Description and Functions of Presentation Layer in the OSI model: In this tutorial, we are going to learn what the Presentation layer is and the Functions of the Presentation Layer in the OSI model in Computer Networking. We will also discuss the Design issues with the Presentation Layer and the working of the Presentation Layer with the help of its diagram. By Monika Jha Last updated : May 05, 2023

What is Presentation Layer?

The Presentation Layer is concerned with the syntax and semantics of the information exchanged between two communicating devices.

• The presentation layer takes care that the data is sent in that way the receiver of the data will understand the information (data) and will be able to use the data.
• Languages that are syntax can be different from the two communicating machines. In this condition, the presentation layer plays the role of translator between them.
• It is possible for two machines to communicate with different data representations, data structures to be exchanged can be defined in an abstract way.
• These abstract data structures will be managed by the presentation layer and this layer allows higher-level data structures (For example banking records), to be defined and exchanged.

This figure shows the relationship of the presentation layer to the session layer and application layer.

Design Issues with Presentation Layer

The following are the design issues with presentation layer:

• To manage and maintain the Syntax and Semantics of the information transmitted.
• Encoding data in a standard agreed-upon way just like a string, double, date, etc.
• It Performs Standard Encoding scheme on the wire.

Functionalities of the Presentation Layer

Specific functionalities of the presentation layer are as follows:

1. Translation

• The processes or running programs in two machines are usually exchanging the information in the form of numbers, character strings and so on before being transmitted. The information should be changed to bitstreams because different computers use different encoding schemes.
• The Presentation layer is responsible for compatibility between these encoding methods.
• The Presentation layer at the sender's side changes the information from its sender dependent format.
• The Presentation layer at the receiving machine changes the common format into its receivers dependent format.

Example: Convert ASCII code to EBCDIC code.

2. Encryption

• The system must be able to assure privacy regarding the message or information as it also carries sensitive information.
• Encryption means that the sender transforms the original information or message to another form, this data after encryption is known as the ciphertext and this ciphertext sends the resulting message out over the network.
• Decryption concerned with the transform of the message back to its original form. This decrypted data is known as plain text.

3. Compression

• Data Compression means reduces the number of bits to be transmitted by this reduce the bandwidth of the data.
• Data Compression becomes particularly important in the transmission of multimedia such as audio, video, text, etc.

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The OSI Model

What is the osi model.

How a single bit travels from one computer to the next is a complex concept. In 1984, the open systems interconnection (OSI) model was published as a framework for network communication. The model breaks down computer network communication into seven layers. All of the layers work together to create a digital message. The message is built as it moves down the protocol stack. However, it is not sent to another network until it reaches the physical layer.

The model helps IT, computer science, and cybersecurity professionals understand how a single bit travels from one computer to the next by breaking the system into these layers.

From physical devices to user interfaces (UI), this model explains the communication role of each layer in overall computer networking. This article will start by introducing the Physical Layer (Layer 1).

Layer 1: the physical layer

The physical layer is where data moves across network interfaces as digital signals. Additionally, this is where the transmitting and receiving of network communication occurs. Starting with the Application Layer the message moves down the OSI model, and it eventually reaches the Physical Layer for transmission. When the message is received by the physical layer, the message will then move up the OSI layers until it reaches the final application layer.

Layer 2: data-link layer

Electrical signals received (or transmitted) to the physical layer are linked and translated to digital logic in the data-Link layer . Computer devices may be networked at the Data-Link layer, but only as a Local Area Network (LAN). Connecting a LAN to another LAN occurs at Layer 3.

Within Layer 2, the Protocol Data Unit (PDU) known as a frame consists of a header, footer, and data. Understanding how a frame is structured is important for network traffic analysis.

Additionally, within Layer 2, physical addresses are assigned and are also known as MAC addresses and/or hardware addresses in networking. MAC addresses are unique to each device on a local network. They are 48-bits in length and are assigned in hexadecimal characters.

Some other things to note about Layer 2 is that there are a few protocols that reside in it that we should know about:

• Ethernet : The most common type of LAN, Ethernet is the standard used to connect computing devices, routers, and switches in a wired network.
• IEEE 802.11 : “Wi-Fi” or “Wireless LAN.”
• Fiber Distributed Data Interface (FDDI) : Network standard for fiber optic LAN connections.
• Link Layer Discovery Protocol (LLDP) : A Link Layer protocol used for advertising neighbors, identity, and capabilities on a LAN.
• Address Resolution Protocol (ARP) : Converts and links Internet Protocol (IP) addresses to MAC addresses on a LAN.
• Cisco Discovery Protocol (CDP) : Similar to LLDP, but Cisco proprietary. The protocol collects neighbor information of directly connected LAN devices.

Additionally, Layer 2 is split into two sublayers:

• Logical Link Control (LLC) : Responsible for establishing the logical link between devices on a local network.
• Media Access Control (MAC) : Responsible for the procedures used by devices across a network medium.

Layer 3: network layer

When we think of the internet, we are thinking of interconnected networks. Interconnecting networks refer to a Local Area Network (LAN) connection to neighboring or remote networks. Layer 3 of the OSI model, the network layer , is where internetworking takes place and is where logical addresses are assigned to networked devices. A primary function of this layer is to route network packets from one LAN to another. Routing requires IP addresses and logical mapping of other networks across the internet to properly deliver messages. Another important function of Layer 3 is its ability to fragment and reassemble large communication. When Layer 3 passes a message down to Layer 2 for transmission, message length limits may be encountered in some cases.

Additionally, Layer 3 is the layer where the protocols used to route communication between networks reside. A few common network protocols are:

• Internet Protocol (IP) : IPv4 and IPv6 are two versions of IP, and IPv4 is the most common protocol of the Internet .
• Internet Protocol Secure (IPSec) : A more secure version of IP which leverages cryptography.
• Routing Information Protocol (RIP) : Distance-vector routing protocol that uses hop count as a metric of routing.
• Enhanced Interior Gateway Routing Protocol (EiGRP) : Cisco proprietary. A distance-vectoring protocol used for automating network configurations and routing decisions.
• Internet Control Message Protocol (ICMP) : Network protocol used for error reporting of network issues.
• Border Gateway Protocol (BGP) : A routing protocol designed to exchange routing information automatically on the internet.

Within Layer 3, the Protocol Data Unit (PDU) is the packet . Packets encapsulate data intended for transmission with header and footer data.

The IPv4 protocol encapsulates data with IPv4 header information necessary for delivery. For example, the 32-bit packet format contains the source address, the destination address, protocol, time-to-live (TTL), etc. in the IPv4 header data.

Layer 4: transport layer

The transport layer , Layer 4, is responsible for being the go-between the abstract layers of the OSI model (Layers 7-5) and the concrete communication layers (Layers 3-1).

Depending on the type of application, the transportation of that application’s communication will need to be handled in a specific way. For example, basic web browsing communication uses Hypertext Transfer Protocol (HTTP) . HTTP communicates via a specific connection service type and port. The transport layer is responsible for delivering/receiving the HTTP communication and maintaining the connection throughout the HTTP communication.

The Protocol Data Unit (PDU) at Layer 4 is known as a data segment . Segmentation is the process of dividing raw data into smaller pieces. Once the raw data is packaged from the higher application layers it is segmented at the transport layer before being passed to the Network Layer.

The transport layer protocols are divided into two categories depending on their connection service type:

Connection-oriented services

This connection type establishes a logical connection between two devices prior to beginning communication across a network. Connection-oriented protocols typically maintain service connection by following a set of rules that initiate, negotiate, manage, and terminate the communication. The Transport Layer protocols will also retransmit any data that is received without acknowledgment. The most common Connection-Oriented protocol is the Transmission Control Protocol (TCP) and its process to manage a connection between two devices is called the Three-Way Handshake . In TCP communication, the communicating devices typically share a client/server relationship where a client initiates communication with a service. The handshake involves the process of sending special TCP messages to synchronize a state of negotiated connection in communication.

Connectionless services

In connectionless communication, the protocol does not establish a connection between client and server. Instead, once a request is made to the server, the server sends all data without initiation, negotiation, or management of connection. Connectionless protocols also do not attempt to correct any interruptions in data transmission. Once the server sends the data, the server is not concerned if the client receives it.

When TCP or UDP are used to establish communication, the communication is assigned a port as the Layer 4 address. A port is a logical assignment given to processes and their respective application protocols on a computing system. A few important facts to memorize about ports are:

• There are 65,535 valid port numbers available to assign to a communication process.
• Ports 0 - 1023 are Well-Known Ports : Assigned to universal TCP/IP application protocols. These protocols are the most common such as HTTPS, SSH, FTP, DNS, and the list goes on. They are registered to these protocols by a global
• Ports 1024 - 49,151 are Registered Ports : Reserved for application protocols that are not specified as universal TCP/IP application protocols.
• Ports 49,152 - 65,535 are Private/Dynamic Ports : These ports may be used for any process without the need to register the port with the global assigning authority.
• When TCP and IP are used together, a Layer 4 port and a Layer 3 IP address are assigned to the connection. This is called a socket. For example, 8.8.8.8:443 is a socket indicating that communication to IP address 8.8.8.8 is to connect to port 443 on the server.

Layer 5: session layer

The session layer starts, manages, and terminates sessions between end-user application processes. Sessions are considered the persistent connection between devices. A session is application-focused; sessions are not concerned with layers 1-4. Instead, the session layer controls dialog between two networked devices. It is considered to facilitate host-to-host communication. Sessions dialog may be controlled through synchronization checkpoints, and through management of communication modes. There are two modes of communication permitted at Layer 5:

• Half-Duplex : Communication travels in both directions between sender and receiver, but only one device may transmit a message at a time.
• Full-Duplex : Communication travels in both directions between sender and receiver, and messages may be sent simultaneously in either direction.

The session layer resembles a phone conversation. For example, when a person picks up a phone and calls someone else a session is created. Once the communication on the call is completed, the session is terminated by hanging up the phone. In computing, software applications are making the phone call and establishing a session.

Two common Layer 5 protocols still used today are:

• Remote Procedure Call (RPC)

Layer 6: presentation layer

The presentation layer is primarily responsible for presenting data so that the recipient will understand the data. Data formatting and encoding protocols apply at Layer 6 to ensure data is legible and presented properly in the application receiving it. Data compression is also a function of Layer 6. If necessary, data may be compressed to improve data throughput over network communication.

Some common Layer 6 protocols are ASCII , JPEG , GIF , MPEG , and PNG .

Another main function of the presentation layer is the encryption and decryption of data sent across a network. Most encryption communication protocols straddle multiple layers of the OSI model, but the actual encryption function is Layer 6.

Two of the most common secure communication protocols are:

• Transport Layer Security (TLS)
• Secure Socket Layer (SSL)

Layer 7: application layer

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.

For example, the user can craft messages and access the network from the application layer. A web browser application allows a user to access a web page. The user may input information and receive information through the web browser. However, the application layer protocol HTTP performs the network communication function. The web browser and HTTP work closely together, and the distinction between the two may be subtle. Yet, HTTP is the web browsing protocol for all web browser applications. In contrast, no single web browser software exclusively utilizes HTTP.

HTTP is one of many common application layer protocols. Below are a few additional protocols to know. It is also good practice to memorize the associated port assigned to the protocols:

The OSI model breaks down computer network communication into seven layers. All of the layers work together to create a digital message. Understanding the OSI model will help you communicate with other network technologists. Computer networking may seem complex, but, with a bit of study, you can gain this knowledge to become an effective Cybersecurity Analyst.

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• Key Terms - Computer Network
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Presentation Layer

• HTTP Protocol
• FTP Protocol
• SMTP Protocol
• POP Protocol
• SNMP Protocol
• Electronic Mail
• MIME Protocol
• World Wide Web
• DNS Protocol

In this tutorial, we will be covering the Presentation layer of the OSI reference model in Computer Networks.

The presentation layer is layer-6 of the OSI reference model . This layer mainly responds to the service requests from the application layer(that is layer-7) and issues the service requests to layer-6 that is (the session layer).

This layer mainly acts as the translator of the network. Another name of the presentation layer is the Syntax layer.

The primary goal of this layer is to take care of the syntax and semantics of the information exchanged between two communicating systems. The presentation layer takes care that the data is sent in such a way that the receiver will understand the information(data) and will be able to use the data. Languages(syntax) can be different between the two communicating systems. Under this condition, the presentation layer plays a role as translator.

In order to make it possible for computers with different data representations to communicate, the data structures to be exchanged can be defined in an abstract way. The presentation layer manages these abstract data structures and allows higher-level data structures(eg: banking records), to be defined and exchanged.

We can say that the presentation layer may represent or encode the data in various ways (like data compression, data encryption). But the receiving device mainly decodes or converts the encoded message into its original form.

For the same data, the sender and receiver must need to agree upon a messaging format that is commonly known as the Presentation format.

Also, the presentation layer is a part of the operating system that mainly converts the data from one presentation format to another presentation format.

Protocols used at the Presentation layer

Given below are some of the protocols used at the presentation layer:

AFP(Apple filling protocol)

Secure Socket Layer(SSL)

FTP(file transfer protocol)

Lightweight Presentation Protocol(LPP)

SSH(Secure shell)

Functions of Presentation Layer

Translation: Before being transmitted, the information in the form of characters and numbers should be changed to bitstreams. The presentation layer is responsible for interoperability between encoding methods as different computers use different encoding methods. It translates data between the formats the network requires and the format of the computer.

Encryption: It carries out encryption at the transmitter and decryption at the receiver.

Compression: It carries out data compression to reduce the bandwidth of the data to be transmitted. The primary role of Data compression is to reduce the number of bits to be 0transmitted. It is important in transmitting multimedia such as audio, video, text, etc.

Design Issues with Presentation Layer

To manage and maintain the Syntax and Semantics of the information transmitted.

Encoding data in a standard agreed-upon way. Eg: String, double, date, etc.

Perform Standard Encoding on the wire.

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Presentation Layer In OSI Model : A Comprehensive Guide

In the vast landscape of computer networks, the OSI (Open Systems Interconnection) model stands as a fundamental framework for understanding how data is transmitted from one device to another. Among its seven layers, the presentation layer holds an important place, acting as a translator and formatter to ensure seamless communication between different systems. Through this article, we will try to know what is presentation layer in OSI model, what is its role in the field of networking and what is its importance.

Table of Contents

What is the Presentation Layer?

The Presentation Layer, within the OSI (Open Systems Interconnection) model, is the sixth layer. It focuses on the representation of data, ensuring that information exchanged between applications is formatted appropriately for transmission and receipt across a network. This layer handles tasks such as data translation, encryption, compression, and formatting. Its primary function is to ensure that data remains readable and understandable by both the sender and receiver, regardless of differences in data formats. In essence, the Presentation Layer acts as a translator and formatter, facilitating seamless communication between different systems and enhancing the reliability and security of data transmission.

Working of Presentation Layer

The Presentation Layer acts like a language translator and document formatter in the OSI model. It takes data from applications and prepares it for transmission over the network by translating it into a language that both the sender and receiver understand. Think of it as converting a letter into a universal format before mailing it overseas. Additionally, the Presentation Layer ensures that the data looks right by formatting it properly, like adjusting the font and spacing in a document. It also adds extra security by encrypting the data if needed, making it like a secret code that only the intended recipient can understand. Lastly, it might shrink the data down to save space during transmission, similar to compressing a file before emailing it. In short, the Presentation Layer makes sure data is ready for its journey across the network, keeping it secure, readable, and efficient along the way.

Functions of the Presentation Layer

• Data Translation : Converting data from the format used by the application into a format suitable for transmission over the network, and vice versa, ensuring interoperability between different systems.
• Encryption and Decryption : Securing data during transmission by encrypting it before sending and decrypting it upon reception, ensuring confidentiality and integrity of the information.
• Data Compression : Reducing the size of data before transmission to optimize bandwidth usage and speed up the transfer process, improving network efficiency.
• Data Formatting: Formatting data according to predefined standards for transmission, including character encoding, data structure, and multimedia representation, ensuring compatibility between sender and receiver applications.
• Protocol Conversion : Adapting data between different network protocols or data formats, facilitating communication between systems with varying requirements or standards.
• Character Code Translation: Converting characters between different character sets or encoding schemes to ensure proper interpretation of text-based data across systems with different language or encoding preferences.

Protocols are Use in Presentation layer

The Presentation Layer primarily focuses on data representation and formatting rather than specific protocols. However, some protocols or standards are commonly associated with the Presentation Layer due to their role in data representation and formatting. Here are a few examples.

• MIME : MIME stands for Multipurpose Internet Mail Extensions. It’s a protocol that broadens the scope of email messages, enabling the use of text in various character sets beyond ASCII. Additionally, MIME facilitates the inclusion of attachments such as audio, video, images, and application programs within emails.
• SSL/TLS : SSL/TLS protocols provide secure communication over a computer network by encrypting data between the client and server, ensuring data confidentiality and integrity. While SSL/TLS operate at the Transport Layer, they often involve encryption and decryption processes associated with the Presentation Layer.
• ASCII (: ASCII and Unicode are character encoding standards that represent text characters using numerical codes. These standards ensure consistent representation of text characters across different systems and platforms, which is crucial for data interchange.
• JPEG, GIF, PNG : These image file formats are commonly used for encoding and transmitting images over networks. While the specifics of image compression and encoding are often handled by the Application Layer, the Presentation Layer ensures proper interpretation and formatting of these image data.
• PDF : PDF is a file format used to present and exchange documents reliably, independent of software, hardware, or operating systems. The Presentation Layer ensures proper interpretation and rendering of PDF documents for display or printing

the Presentation Layer of the OSI Model acts as a translator and formatter, ensuring that data exchanged between applications remains readable and compatible across diverse systems. By handling tasks such as data translation, encryption, compression, and formatting, it enhances the reliability, efficiency, and security of data transmission over networks. Essentially, the Presentation Layer plays a crucial role in facilitating seamless communication between different systems, ensuring that information is accurately represented and securely transmitted, thus contributing to the smooth functioning of modern networking environments.

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OSI model (Open Systems Interconnection)

• Andrew Froehlich, West Gate Networks
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What is OSI model (Open Systems Interconnection)?

OSI (Open Systems Interconnection) is a reference model for how applications communicate over a network. This model focuses on providing a visual design of how each communications layer is built on top of the other, starting with the physical cabling, all the way to the application that's trying to communicate with other devices on a network.

A reference model is a conceptual framework for understanding relationships. The purpose of the OSI reference model is to guide technology vendors and developers so the digital communications products and software programs they create can interoperate and to promote a clear framework that describes the functions of a networking or telecommunications system that's in use.

Most vendors involved in telecommunications try to describe their products and services in relation to the OSI model. This helps them differentiate among the various transport protocols, addressing schemes and communications packaging methods. And, although it's useful for guiding discussion and evaluation, the OSI model is theoretical in nature and should be used only as a general guide. That's because few network products or standard tools keep related functions together in well-defined layers, as is the case in the OSI model. The Transmission Control Protocol/Internet Protocol ( TCP/IP ) suite, for example, is the most widely used network protocol, but even it doesn't map cleanly to the OSI model.

History of the OSI model

In the 1970s, technology researchers began examining how computer systems could best communicate with each other. Over the next few years, several competing models were created and published to the community. However, it wasn't until 1984 when the International Organization for Standardization (ISO) took the best parts of competing networking reference models to propose OSI as a way to finally create a framework that technology companies around the world could use as the basis of their networking technologies .

From ISO's perspective, the easiest way to create a conceptual model was to organize the models into different abstraction layers required to organize and send data between computing systems. Looking inside each abstracted layer to see the details shows one part of this network communication process. Each layer can be thought of as a separate communication module or piece of the puzzle. But, to actually accomplish the goal of sending data from one device to another, each module must work together.

How the OSI model works

Information technology (IT) networking professionals use OSI to model or conceptualize how data is sent or received over a network. Understanding this is a foundational part of most IT networking certifications, including the Cisco Certified Network Associate (CCNA) and CompTIA Network+ certification programs. As mentioned, the model is designed to break down data transmission standards, processes and protocols over a series of seven layers, each of which is responsible for performing specific tasks concerning sending and receiving data.

The main concept of OSI is that the process of communication between two endpoints in a network can be divided into seven distinct groups of related functions, or layers. Each communicating user or program is on a device that can provide those seven layers of function.

In this architecture, each layer serves the layer above it and, in turn, is served by the layer below it. So, in a given message between users, there will be a flow of data down through the layers in the source computer, across the network and then up through the layers in the receiving computer. Only the application layer at the top of the stack doesn't provide services to a higher-level layer.

The seven layers of function are provided by a combination of applications, operating systems (OSes), network card device drivers, networking hardware and protocols that enable a system to transmit a signal over a network through various physical mediums, including twisted-pair copper, fiber optics, Wi-Fi or Long-Term Evolution (LTE) with 5G .

7 layers of the OSI model

What is the function of each layer of the OSI model? The seven Open Systems Interconnection layers are the following.

Layer 7. The application layer

The application layer enables the user -- human or software -- to interact with the application or network whenever the user elects to read messages, transfer files or perform other network-related tasks. Web browsers and other internet-connected apps, such as Outlook and Skype, use Layer 7 application protocols.

Layer 6. The presentation layer

The presentation layer translates or formats data for the application layer based on the semantics or syntax the application accepts. This layer also handles the encryption and decryption that the application layer requires.

Layer 5. The session layer

The session layer sets up, coordinates and terminates conversations between applications. Its services include authentication and reconnection after an interruption. This layer determines how long a system will wait for another application to respond. Examples of session layer protocols include X.225 and Zone Information Protocol (ZIP).

Layer 4. The transport layer

The transport layer is responsible for transferring data across a network and provides error-checking mechanisms and data flow controls. It determines how much data to send, where it gets sent and at what rate. TCP within the TCP/IP suite is the best-known example of the transport layer. This is where the communications select TCP port numbers to categorize and organize data transmissions across a network.

Layer 3. The network layer

The primary function of the network layer is to move data into and through other networks. Network layer protocols accomplish this by packaging data with correct network address information, selecting the appropriate network routes and forwarding the packaged data up the stack to the transport layer. From a TCP/IP perspective, this is where IP addresses are applied for routing purposes.

Layer 2. The data-link layer

The data-link , or protocol layer, in a program handles moving data into and out of a physical link in a network. This layer handles problems that occur as a result of bit transmission errors. It ensures that the pace of the data flow doesn't overwhelm the sending and receiving devices. This layer also permits the transmission of data to Layer 3, the network layer, where it's addressed and routed.

The data-link layer can be further divided into two sublayers. The higher layer, which is called logical link control (LLC), is responsible for multiplexing, flow control, acknowledgement and notifying upper layers if transmit/receive (TX/RX) errors occur.

The media access control sublayer is responsible for tracking data frames using MAC addresses of the sending and receiving hardware. It's also responsible for organizing each frame, marking the starting and ending bits and organizing timing regarding when each frame can be sent along the physical layer medium.

Layer 1. The physical layer

The physical layer transports data using electrical, mechanical or procedural interfaces. This layer is responsible for sending computer bits from one device to another along the network. It determines how physical connections to the network are set up and how bits are represented into predictable signals as they're transmitted either electrically, optically or via radio waves.

Cross-layer functions

Cross-layer functions, or services that may affect more than one layer, include the following:

• security service telecommunication as defined by the International Telecommunication Union Standardization Sector (ITU-T) X.800 recommendation;
• management functions that enable the configuration, instantiation, monitoring and terminating of the communications of two or more entities;
• Multiprotocol Label Switching ( MPLS ), which operates at an OSI model layer that lies between the Layer 2 data-link layer and the Layer 3 network layer -- MPLS can carry a variety of traffic, including Ethernet frames and IP packets;
• Address Resolution Protocol (ARP) translates IPv4 addresses (OSI Layer 3) into Ethernet MAC addresses (OSI Layer 2); and
• domain name system (DNS), which is an application layer service that's used to look up the IP address of a domain name.

Pros and cons of the OSI model

The OSI model has a number of advantages, including the following:

• It's considered a standard model in computer networking.
• The model supports connectionless , as well as connection-oriented, services. Users can take advantage of connectionless services when they need faster data transmissions over the internet and the connection-oriented model when they're looking for reliability.
• It has the flexibility to adapt to many protocols.
• The model is more adaptable and secure than having all services bundled in one layer.

The disadvantages of the OSI model include the following:

• It doesn't define any particular protocol.
• The session layer, which is used for session management, and the presentation layer, which deals with user interaction, aren't as useful as other layers in the OSI model.
• Some services are duplicated at various layers, such as the transport and data-link layers.
• Layers can't work in parallel; each layer must wait to receive data from the previous layer.

OSI model vs. TCP/IP model

The OSI reference model describes the functions of a telecommunication or networking system, while TCP/IP is a suite of communication protocols used to interconnect network devices on the internet. TCP/IP and OSI are the most broadly used networking models for communication.

The OSI and TCP/IP models have similarities and differences. The main similarity is in their construction, as both use layers, although the OSI model consists of seven layers, while TCP/IP consists of just four layers.

Another similarity is that the upper layer for each model is the application layer, which performs the same tasks in each model but may vary according to the information each receives.

The functions performed in each model are also similar because each uses a network and transport layer to operate. The OSI and TCP/IP model are mostly used to transmit data packets, although they each use different means and paths to reach their destinations.

Additional similarities between the OSI and TCP/IP models include the following:

• Both are logical models.
• Both define standards for networking.
• They each divide the network communication process in layers.
• Both provide frameworks for creating and implementing networking standards and devices.
• They enable one manufacturer to make devices and network components that can coexist and work with the devices and components made by other manufacturers.
• Both divide complex functions into simpler components.

Differences between the OSI and TCP/IP models include the following:

• OSI uses three layers -- application, presentation and session -- to define the functionality of upper layers, while TCP/IP uses only the application layer.
• OSI uses two separate layers -- physical and data-link -- to define the functionality of the bottom layers, while TCP/IP uses only the link layer.
• OSI uses the network layer to define the routing standards and protocols, while TCP/IP uses the internet layer.

Next: Explore 12 common network protocols all network engineers should know here .

Continue Reading About OSI model (Open Systems Interconnection)

• What is the difference between TCP/IP model vs. OSI model?
• Future of networking technology relies on 5G, edge computing
• 7 TCP/IP vulnerabilities and how to prevent them
• Edge computing and 5G bring the edge to remote workers
• SANs Institute OSI model overview

Related Terms

Dig deeper on network infrastructure.

An explanation of TCP/IP

Transmission Control Protocol (TCP)

encapsulation (object-orientated programming)

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What is the Presentation Layer in Programming?

Trevor Page

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The presentation layer is one of the three main layers in object-oriented programming.

The three main layers include:

• Presentation Layer
• Business Layer

Now, these three layers are typically related to enterprise web applications. It's a design pattern used to help separate your code out in three distinct areas that (if need be) can easily be switched out with another programming language or technology.

So if you keep all of your presentation layer code in one area of your application, switching presentation layer technologies shouldn't be too difficult.

Same rules apply to the business and data layers. If you separated your code out properly, switching databases shouldn't be too big of an issue.

Having said that, we'll be focusing on the presentation layer.

The four big players (in terms of technology) in the presentation layer are as follows:

Let’s dive into the overviews of each of these big players, shall we?

HTML (HyperText Markup Language) is a technology used to communicate with web browsers. All browsers follow the rules laid out in HTML (currently in its 5th iteration).

HTML defines a bunch of different HTML elements known as tags that are put together to make up the basic layout of a web page. These tags are used to define things like the title of the webpage (which appears in the tab of your browser), the actual text that appears on the page, images, buttons and more.

Thankfully HTML isn’t too tough to learn as it’s more of a game of memorizing the most popular tags and using them to create your simple web pages. HTML is not a programming language, as it doesn’t define variables, data types, control structure or the like. This is also what makes it fairly easy to learn.

We’ll be diving into examples of HTML “code” later, so stay tuned.

CSS (cascading style sheets) is used to add some “pizazz” to your web pages. CSS is used to add a design look and feel to your web pages through the use of its cascading rules. We won’t get into the exact rules that CSS uses to apply its designs just yet, but again, stay tuned for a more in depth explanation.

All you need to know is that CSS is used to make a web page look nice. You can use it to choose which parts of the web page should be which color, how big or small elements should be, what fonts should be used and more.

If you’ve ever landed on a web page that wasn’t able to properly load its CSS, you’d likely think that the website was completely broken. It is often fixed by forcing the page to reload and then the CSS usually gets picked up the second time and everything loads properly and the website goes back to looking great. This situation is quite rare, but I thought I’d mention it because it’s a great example of just how powerful CSS is.

JavaScript is used to make your web pages interactive. It allows you to put some real programming functionality into web pages (as HTML is not a programming language and thus cannot add real programming elements to a page).

Examples of what JavaScript can do is when you’re logging into an application and you forget to provide information in one of the fields. JavaScript can detect that you’ve forgotten to type in your username or password and can provide you with a prompt explaining that you need to fill in your username and password before you can continue.

JavaScript shouldn’t be confused with Java, as they are two different technologies. Java is part of the business layer and has no place in the presentation layer. Java is known as a server side language, as it exists and runs on servers. JavaScript is known as a client side technology, and thus lives where the “clients” are, which is inside the actual web browsers.

A good way to think of the difference between the two languages is that when you land on a web page and it loads in your browser, it will also load any JavaScript code inside the page and you’ll actually be able to access that code and read it. Whereas, you’d never be able to read the Java code, as it’s not loaded in your browser because it’s a server side technology.

That simple distinction between the two languages makes for two very different languages in terms of their use and functionality.

The syntax for JavaScript, however, is fairly similar to Java. This is nice since you’ll be able to look at a piece of JavaScript code and more or less understand what’s going on. So you should be able to pick up the JavaScript language a lot quicker if you already have a good command of the Java language.

JQuery is a technology that’s used in tandem with JavaScript. JQuery makes your life as a web programmer so much easier for one reason, it allows you to write code once and have it work across all the browsers.

In today’s world we have so many browsers that can be downloaded for free and used to peruse the web. This actually makes building websites a bit challenging, as every browser has made up their own minds on how to “render” an HTML web page.

This means that a webpage loaded on Safari might not look the same as if it’s loaded on Internet Explorer, or Firefox, or Chrome.

These inconsistencies drive web programmers crazy, so that’s why jQuery was introduced. It allows you to write your JavaScript in a sort of “browser agnostic” way. You can write it once, and jQuery will execute the code appropriately depending on which browser it’s loaded it. VERY COOL!

The best part of all of these technologies is that they are all free to use.

And thankfully, they are also free to learn via these tutorials!

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Difference between presentation layer and user-interface

What is the difference between a presentation layer and an user-interface?

• user-interface

4 Answers 4

They are close in execution, but they come from different directions. They aren't well defined, depending on the specific context, they may be almost identical or overlap only slightly.

Presentation layer is term in the taxonomy of code and associated resources.

User Interface is the implementation of the intended User Experience in terms of page layout, page transitions and page control elements. (I am using "page" loosely here - you can replace it with "form" or "window").

The distinction is important when you consider how a user interface gets created. If you come from the code, you are basically working with the needs and mechanisms of the code - what data is there to show? , and in what ways your code can change that?

If you come from the user, the questions are rather what data the does the user need? and what data the user wants to change?

(The first one isn't necessarily worse - it's perfect for users who have a good idea of the inner workings of the application, and it makes it often easier to make use of the full capabilities of the code.)

The link in the John's answer refers to the OSI model, which is not the term intended here IMHO.

I think presentation layer and UI are overlapping concepts, though not 100% overlapping.

Form one angle: The term presentation layer suggests a layered structure in the application, while the term UI does not suggest anything about the inner structure of the application.

From another angle: The term UI might only include the collection of controls and their event handlers, while the term presentation layer could include some deeper non visual parts of the application like ViewModels or Presenters.

The presentation layer delivers information to the application layer for display.

The presentation layer, in some cases, handles data translation to allow use on a particular system.

The user interface shows you the data once the presentation layer has done any translations it needs to.

More here: http://en.wikipedia.org/wiki/Presentation_Layer

Here's my own interpretation:

Presentation layer loosely refers to the layer which is responsible for somehow displaying the data for the users. It is often spoken of in the context of a software architecture along with other layers such persistence layer, business logic layer, etc, and rarely by itself.

User interface simply refers to the point of interfacing between the users and some software programs. User interface do not always have to have a nice graphical windows capabilities. A console program, one which runs on the prompt, is also said to have a user interface, just not a graphical one.

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Microsoft 365 Life Hacks > Presentations > How many slides does your presentation need?

How many slides does your presentation need?

When you’re creating a presentation, it’s important to consider the amount of information you’re sharing with your audience. You don’t want to overwhelm them, but you also want to be comprehensive and ensure that you’re covering all your bases. Whether you’re giving a 10, 15, or 30-minute presentation, see how many slides your presentation needs to get your point across.

Rules and guidance for PowerPoint presentations

PowerPoint is a powerful visual aid for introducing data, statistics, and new concepts to any audience. In PowerPoint, you can create as many slides as you want—which might sound tempting at first. But length doesn’t always guarantee a successful presentation . Most presentations last around 10-15 minutes, and anything longer than that (such as a 30-minute presentation) may have additional visual aids or speakers to enhance your message.

A handy rule to keep in mind is to spend about 1-2 minutes on each slide. This will give you ample time to convey your message, let data sink in, and allow you to memorize your presentation . When you limit each slide to this length of time, you also need to be selective about how much information you put on each slide and avoid overloading your audience.

For 10-minute presentations

Ten minutes is usually considered the shortest amount of time you need for a successful presentation. For a shorter 10-minute presentation, you’ll need to be selective with your content. Limit your slide count to approximately 7 to 10 slides.

For 15-minute presentations

When preparing for a 15-minute presentation, concise and focused content is key. Aim for around 10 to 15 slides to maintain a good pace, which will fit with the 1-2 minute per slide rule.

For 30-minute presentations

A longer presentation gives you more room to delve deeper into your topic. But to maintain audience engagement, you’ll need to add interactivity , audience participation, and elements like animations . Aim for around 20 to 30 slides, allowing for a balanced distribution of content without overwhelming your audience.

Tell your story with captivating presentations

Powerpoint empowers you to develop well-designed content across all your devices

Using the 10-20-30 rule

The 10-20-30 rule is an effective way to structure your presentation. It calls for no more than 10 slides and no longer than 20 minutes (as well as a 30-point font).

Tips for crafting an effective presentation

No matter how long a presentation is, there are guidelines for crafting one to enhance understanding and retention. Keep these tips in mind when creating your PowerPoint masterpiece:

• Avoid overload: Ensure that each slide communicates a single idea clearly, avoiding cluttered layouts or excessive text.
• Pay attention to structure: Think of slides as bullet points with introductions, endings, and deep dives within each subject.
• Add visual appeal: Incorporate images, charts, and graphics to convey information without using too many words to make your audience read.
• Engage with your audience: Encourage interaction through questions, polls, or storytelling techniques to keep your audience actively involved.
• Put in the practice: Familiarize yourself with your slides and practice your delivery to refine your timing and confidence.

Ultimately, the ideal number of slides for your presentation depends on the allocated time frame and how detailed your content is. By striking a balance between informative content and engaging delivery, you can create a compelling presentation that can teach your audience something new.

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Watch CBS News

Trump and Biden's first presidential debate of 2024, fact checked

By Arden Farhi , Hunter Woodall , Jui Sarwate , Julia Ingram , Layla Ferris , Laura Doan , James LaPorta , Daniel Klaidman , Alexander Tin , Pete Villasmil, Sierra Sanders

Updated on: June 28, 2024 / 9:46 AM EDT / CBS News

Here's the fact check of some of the statements made by President Biden and former President Donald Trump during the first 2024 presidential debate , which took place in Atlanta on Thursday, June 27. The two tangled on topics including immigration, the economy, abortion and their respective records. Mr. Biden seemed to ramble during many of his responses.

CBS News  covered the debate live as it happened . 

Trump claims "we had the greatest economy in the history of our country": False

Trump : "We had the greatest economy in the history of our country. And we have never done so well. Every- everybody was amazed by it. Other countries were copying us." 

Details : Trump's claim is false that during his presidency the U.S. had the greatest economy in the history of the country by many of the common metrics used to judge economic performance. The claim struggles when looking at GDP. If the 2020 pandemic  is excluded, growth after inflation under Trump averaged 2.49%, according to figures from the  World Bank . This is far from the GDP growth under Democratic President Bill Clinton of 3.88%, according to  World Bank data . Including the time period after COVID spread, that average drops to 1.18%. 

Trump's claim also falls short when compared to historical figures. Growth between 1962 to 1966 ranged from 4.4% to 6.6%. In 1950 and 1951, GDP ranged between 8.7% and 8%.

Under Mr. Biden, annual GDP growth is averaging 3.4%, according to the  Associated Press .

*An earlier version of this fact check misstated World Bank figures for growth after inflation under Trump at 2.65%, rather than 2.49%, and 1.45%, instead of 1.18%, and also rounded the growth number for Clinton. This has been updated.

Unemployment

Trump's claim is also false even when evaluating the unemployment rate.    In February 2020, a month before the COVID pandemic affected the economy, the unemployment rate stood at 3.5% — which was the lowest since December 1969 — but not the lowest ever. When Trump's term ended, the unemployment rate was 6.3%.

In 1953, the unemployment rate fell as low as 2.5%. Under Mr. Biden, the unemployment rate is 4%, according to the  most recent data  from May 2024. 

In January 2023 and again in April 2023, the unemployment rate was 3.4%, lower than the best month during Trump's term.

Stock market performance

On Jan. 19, 2021, the  S&P 500-stock average  closed at 67.8% above where it had been the day before Trump was inaugurated in 2017. 

According to  Investopedia ,  at the end of President Barack Obama's first term in office, the S&P closed 84.5% higher. Additionally the S&P gained 79% during President Bill Clinton's first term, and 70% during President Dwight Eisenhower's first term. So far, under President Biden, the  S&P 500 has increased almost 40% , according to calculations on June 13. 

By Laura Doan and Hunter Woodall 

Biden claims he's the only president this century that doesn't have troops dying anywhere in the world: False

Biden: "I'm the only president this century that doesn't have any — this decade — that doesn't have any troops dying anywhere in the world." 

Details : At least 16 U.S. service members have died while serving overseas during Mr. Biden's presidency. Thirteen U.S. service members  died  in an attack at the Kabul airport in Afghanistan in August 2021. Three soldiers were  killed  in an attack in Jordan in January of this year.

By Layla Ferris

Trump claims he did not refer to U.S. soldiers who were killed as "suckers and losers": False

Trump: "First of all, that was a made-up quote. 'Suckers and losers,' they made it up."

Details : Current and former U.S. military service members have detailed to CBS News multiple instances when Trump made disparaging remarks about members of the U.S. military who were captured or killed, including referring to the American war dead at the Aisle-Marne American Cemetery in France in 2018 as "losers" and "suckers."  

A senior Defense Department official and a former U.S. Marine Corps officer with direct knowledge of what was said detailed how Trump said he did not want to visit the cemetery because it was "filled with losers." These accounts were backed independently by two other officials — a former senior U.S. Army officer and a separate, former senior U.S. Marine Corps officer.   

In another conversation on the trip, Trump referred to the 1,800 Marines who died in the World War I battle of Belleau Wood as "suckers" for getting killed.  The Atlantic was first to report Trump's comments in 2020. His former chief of staff John Kelly later confirmed to CNN the essence of what Trump had said.

By James LaPorta and Sierra Sanders 

Biden claims 40% fewer people are crossing border illegally, better than when Trump was in office: Partially true         

Biden: "I've changed it in a way that now you're in a situation where there 40% fewer people coming across the border illegally; it's better than when he left office."

Details : Since Mr. Biden issued a  proclamation  banning most migrants from asylum at the U.S.-Mexico border in early June, illegal crossings there have dropped. In the past week, daily illegal border crossings have averaged roughly 2,000, according to internal Department of Homeland Security data obtained by CBS News. That's a 47% drop from the 3,800  daily average  in May.

During the height of a spike in migration faced by the Trump administration in 2019, Border Patrol recorded an average of 4,300 daily illegal crossings,  government data  show. But there were months during the  Covid-19 pandemic  when the Trump administration averaged fewer than 2,000 illegal border crossings.

By Camilo Montoya-Galvez

Trump claims migrants coming to U.S. and "killing our citizens at a level...we've never seen before": Misleading

Trump: "People are coming in and killing our citizens at a level like we've never seen before." 

Details :  Some migrants who are believed to have entered the U.S. along the southern border in recent years have been charged with murder and other heinous crimes in different parts of the country. They include the suspect in the high-profile murder of Georgia nursing student Laken Riley .

But while the data on this question is not comprehensive, available  studies  have found that migrants living in the country illegally do not commit crimes at a higher rate than native-born Americans. 

Government  statistics  also show a very small fraction of migrants processed by Border Patrol have criminal records in the U.S. or other countries that share information with American officials.

On COVID, Trump claims more people died under Biden administration than his: True, but needs context  

Trump: "Remember, more people died under his administration — even though we had largely fixed it — more people died under his administration than our administration, and we were right in the middle of it, something which a lot of people don't like to talk about. But [Biden] had far more people dying in his administration."

Details : More than 460,000 people had died from COVID-19 by the end of the week that Biden was inaugurated in 2021, while more than 725,000 have died in the three years since then, according to data from the  CDC . However, research has found that the counts of COVID-19 deaths, especially in the early days of the pandemic, were likely  undercounted .

By Julia Ingram and Jui Sarwate

In discussing abortion, Trump claims former Virginia governor, a Democrat, supported killing babies: False

Trump: "If you look at the former governor of Virginia, he was willing to do this — he said  'we'll put the baby aside and we'll determine what we'll do with the baby'.. .meaning we'll kill the baby."

Details : In a 2019 radio interview then-governor of Virginia Ralph Northam, in discussing late-term abortions,  addressed a hypothetical scenario in which a fetus was severely deformed or wasn't otherwise viable. He said, "the infant would be delivered, the infant would be kept comfortable, the infant would be resuscitated if that's what the mother and the family desired." 

Northam did not say the fetus should be killed. Killing a newborn baby — or infanticide — is illegal in every state, and not a single state is trying to change that. 

By Laura Doan and Daniel Klaidman

Trump claims Biden "went after" his political opponent in New York "hush money" case to damage him: False        

Trump: "[Biden] basically went after his political opponent (Trump) because he thought it was going to damage me, but when the public found out about these cases, 'cause they understand it better than he does, he has no idea what these cases are, but when they found out about these cases, you know what they did? My poll numbers went up, way up."

Details : There is no federal jurisdiction over a state case. The Manhattan district attorney's office is a  separate entity  from the U.S. Department of Justice. The department does not supervise the work of the Manhattan D.A.'s office, does not approve its charging decisions, and it does not try the D.A.'s cases.

By Pete Villasmil

Trump claims he brought insulin prices down for seniors: Misleading

Trump: "I'm the one that got the insulin down for the seniors. I took care of the seniors."

Details :  During Trump's time as president, Medicare created a voluntary program  in 2020  between some plans and insulin manufacturers that agreed to cap out-of-pocket costs for insulin at $35 per month. Around  half of  Medicare Advantage or stand-alone prescription drug plans ended up participating by 2021. 

David Ricks, CEO of insulin drugmaker Eli Lilly, has taken credit for pioneering the idea with Trump administration officials at a congressional  hearing  and in an  interview . In the same interview with STAT, Seema Verma, former Medicare agency chief in the Trump administration, gave Ricks the credit for the cap: "He is an unsung hero. He was actually the mastermind of all of this." 

Medicare  ended  the policy in 2023, after Mr. Biden signed into law the  Inflation Reduction Act , which capped insulin costs for Medicare beneficiaries — not just for the portion of plans participating in the program. The law capped insulin costs at the same amount of $35 per month.

By Alexander Tin and Hunter Woodall 

Trump claims Biden wants open borders: False

Trump: "He wants open borders. He wants our country to either be destroyed or he wants to pick up those people as voters." 

Details : When he took office, Mr. Biden reversed numerous Trump-era immigration policies, including a program that required migrants to await their asylum hearings in Mexico. U.S. Border Patrol has also reported record numbers of migrant apprehensions along the southern border during Mr. Biden's presidency. But Mr. Biden has never endorsed or implemented an "open borders" policy.

In fact, Mr. Biden has embraced some restrictive border policies that mirror rules enacted by his predecessor. In 2023, his administration published a regulation that disqualified migrants from asylum if they crossed into the country illegally after not seeking protection in a third country. 

Earlier this month, Mr. Biden enacted an even stricter policy: a proclamation that has partially shut down asylum processing along the border. His administration has also carried out over 4 million deportations, expulsions and returns of migrants since 2021, according to  government data .

Only U.S. citizens can vote in federal elections. Most who cross into the U.S. illegally are not on a path to permanent legal status, let alone citizenship. Even those who apply and win asylum — a process that typically takes years to complete — have to wait five years as permanent U.S. residents before applying for American citizenship. There's no evidence to suggest that the Biden administration's border policy is based on a desire to convert migrants into voters.

Biden claims Trump wants to get rid of Social Security: False        

Biden "[Trump] wants to get rid of Social Security. He thinks there's plenty to cut in social security. He's wanted to cut Social Security and Medicare, both times."

Details : Trump has repeatedly  said  he will try to protect Medicare and Social Security. Trump said in a March 21 Truth Social  post  that he would not "under any circumstance" allow Social Security to "be even touched" if he were president. Trump had said in a CNBC  interview  on March 11 that "there is a lot you can do" in terms of "cutting" spending under Social Security. Mr. Biden  said  the comments were proof Trump aimed to make cuts in the programs, but a Trump campaign spokesman  said  Trump was referring to "cutting waste and fraud," not Social Security entitlements.

Trump claims Biden has the "largest deficit" in history of U.S.: False

Trump: "But he's (Biden) got the largest deficit in the history of our country."

Details : The national deficit was the largest it had been in over two decades under Trump's administration, not Mr. Biden's, according to  data from the U.S. Treasury . The deficit peaked in fiscal year 2020 at $3.13 trillion, and declined to $1.7 trillion by the end of fiscal year 2023.

By Julia Ingram

• Presidential Debate
• Donald Trump

Arden Farhi is the senior White House producer at CBS News. He has covered several presidential campaigns and the Obama, Trump and Biden administrations. He also produces "The Takeout with Major Garrett."

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