OSI Model

7 ApplicationResponsible for making or receiving a network request and a typically the networking software. For example, a web server, FTP Server, and DNS Server run at thihs layer.-Closest to the end user
-Communicates with software application
-HTTP, HTTPS are protocols used
-Doesn’t include the applications itself but just the protocol
-Identifies communication partners and synchronises them. 
6 PresentationResponsible for formatting the information so that the information is understood on the receiving system. Examples of formatting are compression and encryption.-Data in the application layer is in “application format”. It needs to be translated to a different format to be sent over the network
-The presentation layer’s job is to translate between application and network formats
-For example, encryption of data as it is sent, and decryption of data as it is received
-Also translates between different Application Layer formats
5 SessionResponsible for opening, closing, and managing a connection (a session) to another system or device.-Controls dialogue or sessions between communicating hosts
-Establishes, manages, terminates connection between the local application
4 TransportResponsible for breaking the information down into smaller pieces so that it can be sent along the network in parts. This layer is also responsible for ensuring that the information reaches the destination-Segments and reassembles data for communications between end hosts
-Breaks large pieces of data into smaller segments which can be more easily sent over the network and are less likely to cause transmission problem if error occur
-Provide host-host communication.
3 NetworkResponsible for routing of information and logical addressing. A router runs at this layer, and, the IP protocol runs at this layer, which provides logical address (ip address).-Provides connectivity between end hosts on different networks (i.e. outside of the LAN)
Provides logical addressing (IP Addresses)
-Provides path selection between source and destination
-Routers operate at Layer 3
Converts the segments into packets
2 Data LinkPrepares the information to hit the physical network by placing the data into packets. The data link layer also provides the physical addressing (MAC Address), so any device that works with a MAC address runs at this layer (such as a network card, switch and bridge).-Provides node to node connectivity and data transfer like PC to switch, switch to router, router to router
-Defines how data is formatted for transmission over a physical medium for eg, copper UTP cables 
-Detects and possibly corrects Physical Layer errors
-Uses layer 2 addressing, separate from layer 3 addressing
Switches operate at Layer 2
1 PhysicalDeals with the network media such as cabling and connectors. The physical layer is also responsible for sending the electrical signal on the wire. Any deice that works with the electrical signal runs at this layer such as a hub or repeater.-Defines physical characteristics of the medium used to transfer data between devices
For example, voltage levels, maximum transmission distances, physical connectors, cable specifications etc
-Digital bits are converted into electrical (for wired connections) or radio (for wireless connections signals)
-All of the information related to UTP copper cable and fiber optic cable are related to Physical layer
OSI LayerPDU (Protocol Data units)
7 ApplicationData
6 PresentationData
5 SessionData
4 TransportSegment
3 NetworkPacket
2 Data LinkFrame
1 PhysicalFrame


OSI ModelTCP/IP Model
7 Application

6 Presentation
5 Session
4 TransportTransport
3 NetworkInternet
2 Data Link
1 Physical

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