capas del modelo OSI

1.- Capas del Modelo OSI y sus funciones.

* Aplication Layer -> Provides services to application processes such as e-mail, file transfer, and terminal emulation that are outside of the OSI model. It identifies and establishes the resources required to connect with available communication partners. It establishes an agreement on procedures for error recovery and for control of data integrity. It interfaces directly to, and performs common application services for, the applicatión processes.

* Presentation Layer-> Standarizes user data formats for use in different types of system. Encodes and Decodes user dat, encrypts and decrypts; compresses and decompresses data.

* Session Layer-> Manages user sessions and dialogues. Manages links between applications.

* Transport Layer-> Manages end-to-end message delivery over the network. Can provide reliable and secuential paket delivery trough error recovery and flow control mechanisims

* Network Layer -> Provides logical network addressing. Routed packets between networks based on logical addressing.

* Data Link Layer-> Defines procedures for operating the communication links. Detects and corrects frame transmit errors. Adds physical addresses to frames.

* Physical Layer-> DEfines physical means of sending data over network devices. Interfaces between network medium and devices. Defines optical, electrical, and mechanical characteristics for both wired and wireless media. Includes all forms of electromagnetic transmission such as light, electricity, infrared and radio waves.

2.- ¿Qué protocolos ocupan las capas superiores e inferiores?

The seven layers are dividen in: upper layers & lower layers



upper layer --> Layers above the Transport layerof the OSI Model.
Deal with application functionality
Are implemented only in software

lower layer--> Layers below the session layer
Handles data transport
Physical & Data Link Layers are implemented in both software and hardware

End stations - work with the 7 layers
Networking devices - work with the two lower layers
Hubs - work on Layer 1
Swithches - work on Layers 1&2
Routers - Layres 1,2 &3
Firewalls - Layers 1,2,3&4

OSI Model Protocols and Technologies
* Upper layers create the data
Layers 7, 6, and 5 are responsible for ensuring that the message is placed in a format that can be understood by the application running on the destination host. This process is called encoding. The upper layers then send the encoded messages to the lower layers for transport across the network.

Application Layer -> The application (e-mail) initiates the communication process...
Presentation Layer -> Format and encode the data for the transmission. Encrypt and compress the data
Session Layer -> Establishes and monitors e-mail session with the destination.

* Layer 4 packages the data for end-to-end transport
breaks the message down into smaller segments.
Functions in the transport layer indicate the type of delivery service.
therefore packet delivery is acknowledged by the destination
are implemented in software that runs on the source and destination hosts
problems that occur at Layer 4 can be caused by improperly configured firewall filter lists.

* Layer 3 adds the network IP address information
The email data received from the transport layer is put into a packet that contains a header with the source and destination network IP addresses.
Routers use the destination address to direct the packets across the network along the appropriate path.
Problems can be caused when the IP address in incorrect.

* Layer 2 adds the data link layer header and trailer
Each network device in the path from the source to the destination encapsulates the packet into a frame. The frame contains the physical address of the next directly-connected network device on the link.
Each device in the chosen network path requires framing so that it can connect to the next device.
Switches & NICs use the information in the frame to deliver the message to the correct destination