OSI Model by Nick Griffiths https://padlet.com/nickgriffiths141095/osiimodel Made with love en-us 2018-10-04 10:52:10 UTC 2024-05-24 20:04:57 UTC hello@padlet.com Layer 5 - Session Layer https://padlet.com/nickgriffiths141095/osiimodel/wish/289078673 The session layer is the fifth layer in the OSI model. It handles all of the connections between the computers. It can control these connections as well as track the dialog (sessions) between the computers. 

This layer also establishes the sessions between local and remote applications as well as controlling those connections. The session layer also creates procedures for check-pointing, restarting and termination. 
 
Sessions are commonly implemented on Web browsers using protocols such as AppleTalk and the Session Control Protocol. The session layer is also responsible for masking potential transport layer failures. The session layer creates a transmission bridge that can provide more efficient long-term transport.

The functions of the session layer are to set up and manage the communication between two applications. The session layer also helps mask communication failures and manages data synchronisation of multiple session streams.
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]]> 2018-10-04 12:17:59 UTC https://padlet.com/nickgriffiths141095/osiimodel/wish/289078673 Layer 1 https://padlet.com/nickgriffiths141095/osiimodel/wish/289079251 Layer 1 defines electrical and physical specifications for devices/nodes.  The physical layer takes what all the other layers have sent to them

The physical layer defines the relationship between a device and a cable. 

the physical layer provides bit by bit delivery e.g binary, start stop signalling and flow control, circuit switching, auto negotiation and transmission mode control.

Binary is the language in which computers and their internal hardware communicates. The circuits in a computer's processor are made up of billions of transistors which is a tiny switch that is a some examples of protocols that use the physical layer are digital subscriber line (DSI), USB, Bluetooth, Controller Area Network. 

Some of the major functions and services performed by the physical layer are:
  • Bit-by-bit or symbol-by-symbol delivery
  • Providing a standardised interface to a physical transmission medium
  • Modulation
  • Line coding
  • Bit synchronisation in synchronous serial communication
  • Start-stop signalling and flow control in asynchronous serial communication
  • Circuit switching
  • Multiplexing


]]> 2018-10-04 12:18:59 UTC https://padlet.com/nickgriffiths141095/osiimodel/wish/289079251 Layer 3 - Network https://padlet.com/nickgriffiths141095/osiimodel/wish/289079299 The third layer of the OSI model is the network layer, it is the layer where the switching and routing of packets takes place. Routers and switches are devices that perform packet routing and switching on this layer.

Packet switching is when a file is broken down into separate packets, and each packet has information such as the destination address, the source address, the total number of packets and the sequence number. After all the packets have been received, they are rearranged to form the original file.

In Internet Protocol All devices will have an IP address assigned to them for communicating on this layer with IP.
There are other types of network layer protocols but they are not commonly used due to the widespread usage of IP

 The network layer also handles addressing packets to the corresponding MAC (Media access control) address, so the packets know what device they are being routed to. 

Overall, the network layer of the OSI model is responsible for routing packets to the right place]]> 2018-10-04 12:19:04 UTC https://padlet.com/nickgriffiths141095/osiimodel/wish/289079299 Layer 2 - Data Link https://padlet.com/nickgriffiths141095/osiimodel/wish/289079313 The Data Link Layer is divided into 2 sub-layers, the Logic Link Control sub-layer, and the Media Access Control sub-layer.
Logic Link Control
The LLC sub-layer's is responsible for the exchange of data between the nodes on a network. 
Its main function is to manage the data and to make sure it is consistent and accurate, however it is also responsible for error-checking, and it checks each packet sent for errors, and if there is an error, then it asks for the data to be resent.
Media Access Control
On a network, the MAC layer will provide a MAC address for the computer, so that the NIC that the computer has will be recognised specifically - this means that the data will be sent to that MAC address. from the other computer's NIC. 
The MAC layer is responsible for moving data packets from a Network Interface Card (NIC) to another NIC across a channel.
Overall
Basically the Data Link Layer gets the data and records the MAC address it came from and is going to, then checks for errors and to make sure the data is consistent and accurate, and then it sends it to the network layer.

]]> 2018-10-04 12:19:06 UTC https://padlet.com/nickgriffiths141095/osiimodel/wish/289079313 Layer 7 - Application Layer https://padlet.com/nickgriffiths141095/osiimodel/wish/289079571 Only layer that interacts directly with the end user
The pass of control in the OSI model starts at Layer 7
The services which are provided by this layer can consist of:
- File transfer
- SMTP (Simple mail transfer protocol)
- Web chat
- Web surfing
- Email clients
- Network data sharing
- Virtual Terminals
DHCP - Dynamic Host Configuration Protocol is used to provide an Internet Protocol host with its IP address. (assigns and IP address to each device) According to all known laws of aviation, there is no way a bee should be able to fly. Its wings are too small to get its fat little body off the ground. The bee, of course, flies anyway because bees don't care what humans think is impossible.
HTTP- This stands for Hypertext Transfer Protocol. This being one of the most important protocols is the foundations of the WWW. HTTP is used as a request-response protocol. The importance comes from the amount of communication it enables between client and server.
The application layer relies on the rest of the layers/levels to complete these processes.

SMTP - Simple Mail Transfer Protocol - the standard for email transmission. It's always used by all mail servers when sending or receiving mail outside their own systems. There are three key command/reply sequences.
-MAIL, to establish the return address.
-RCPT, the recipient.
-DATA, the content of the mail.


]]> 2018-10-04 12:19:34 UTC https://padlet.com/nickgriffiths141095/osiimodel/wish/289079571 Layer 4 - Transport https://padlet.com/nickgriffiths141095/osiimodel/wish/289079873 In the OSI model Layer 4 is  known as the Transport Layer, and it's job role is for transferring information/data reliably between two endpoints  and this essentially deals and helps with picking up on errors such as deleted or duplicated packets. The required protocol properties is that it's fast, low overhead, does not require acknowledgements, does not resend lost data, delivers data and delivers the date as it arrives. 

It is good for traffic control and processing so there's no crashes. It makes sure the packet is securely transported and makes sure the packet is sent to the correct destination/IP. 

In cases where TCP is being used, packet segments that have been destroyed or lost in transit are re-transmitted to ensure that all of the data reaches the destination in tact so that when the packets are reassembled parts aren't missing. 

The transport layer is also responsible for segmenting data as it is sent out and reassembling it when it is received.

]]> 2018-10-04 12:20:13 UTC https://padlet.com/nickgriffiths141095/osiimodel/wish/289079873 Layer 6 https://padlet.com/nickgriffiths141095/osiimodel/wish/289079921 The presentation layer
It is part of the hot layer aspect of OSI model that covers applications, presentations and session/transport  layers  etc.

Simple Version:
Residing at Layer 6 of the Open Systems Interconnection (OSI) communications model, the presentation layer ensures that the communications that pass through it are in the appropriate form for the recipient application. In other words, it presents the data in a readable format from an application layer perspective. 

Example:
For example, a presentation layer program could format a File transfer request in binary code to ensure a successful file transfer. Because binary is the most rudimentary of computing languages, it ensures that the receiving device will be able to decipher and translate it into a format the application layer understands and is expecting.

In areas of security it has  data encryption and decryption: Encryption is needed for security purposes when sending data across networks. 
Encryption and decryption typically involves the secure sockets layer (SSL) protocol, which has become more popular when used by the presentation layer. 
]]> 2018-10-04 12:20:19 UTC https://padlet.com/nickgriffiths141095/osiimodel/wish/289079921