Network+ - The Seven-Layer OSI Model

All People Seem To Need Data Processing.

APPLICATION, PRESENTATION, SESSION, TRANSPORT, NETWORK, DATA LINK, PHYSICAL.

Layer 3: Network Layer - IP address

An address assigned to each node on a network, which the Network layer uses to uniquely identify them on the network.

Layer 5: Session Layer

Describes how data between applications is synced and recovered if messages don't arrive intact at the receiving application. For example, the Skype application works with the operating system to establish and maintain a session between two end points for as long as a voice conversation or video conference is in progress.

Layer 7: Application Layer

Describes the interface between two applications, each on separate computers. Protocols used at this layer, including HTTP, SMTP, POP3, IMAP4, FTP, Telnet, and RDP.

Layer 4: Transport Layer - UDP (User Datagram Protocol)

Does not guarantee delivery by first connecting and checking whether data is received. UDP is used for broadcasting, such as streaming video or audio over the web, where guaranteed delivery is not as important as fast transmission. UDP is also used to monitor network traffic.

OSI (Open Systems Interconnection) reference model

Early in the evolution of networking, a seven-layer model was developed to categorize the layers of communication.

Layer 3: Network Layer - packet.

IP adds its own Network layer header to the segment or datagram.

Layer 3: Network Layer - fragmentation.

If a Network layer protocol is aware that a packet is larger than the maximum size for its network, it will divide the packet into smaller packets.

Layer 4: Transport Layer - segments.

If the message is too large to transport on the network, TCP divides it into smaller messages

Layer 4: Transport Layer - datagram.

In UDP, the message is called.

Layer 2: Data Link Layer

Layers 2 and 1 are responsible for interfacing with the physical hardware only on the local network. The protocols at these layers are programmed into the firmware of a computer's NIC and other networking hardware.

Layer 4: Transport Layer - TCP (Transmission Control Protocol)

Makes a connection with the end host, checks whether the data is received, and resends it if it is not. TCP is used by applications such as web browsers and email. Guaranteed delivery takes longer and is used when it is important to know that the data reached its destination.

Layer 7: Application Layer - Application programs

Provide services to a user, such as a browser and web server using the HTTP Application layer protocol.

Layer 7: Application Layer - Utility programs

Provide services to the system, such as SNMP (Simple Network Management Protocol) programs that monitor and gather information about network traffic and can alert network administrators about adverse conditions that need attention.

Layer 2: Data Link Layer - trailer.

Puts its own control information in a Data Link layer header and also attaches control information to the end of the packet

Layer 6: Presentation Layer

Responsible for reformatting, compressing, and/or encrypting data in a way that the application on the receiving end can read. For example, an email message can be encrypted at the Presentation layer by the email client or by the operating system.

Layer 4: Transport Layer

Responsible for transporting Application layer payloads from one application to another. The two main Transport layer protocols are TCP, which guarantees delivery, and UDP.

Layer 3: Network Layer

Sometimes called the Internet layer, is responsible for moving messages from one node to another until they reach the destination host.

Layer 4: Transport Layer - port.

The Transport layer header addresses the receiving application by a number.

Layer 2: Data Link Layer - frame.

The entire Data Link layer message.

Layer 2: Data Link Layer - MAC (Media Access Control) address

The frame header contains the hardware addresses of the source and destination NICs.

Layer 3: Network Layer - IP (Internet Protocol).

The principal protocol used by the Network layer.

Layer 4: Transport Layer - encapsulation

The process of adding a header to the data inherited from the layer.

Layer 4: Transport Layer - header

The protocols add their own control information in an area at the beginning of the payload to create a message ready to be transmitted to the Network layer.

Layer 1: Physical Layer

The simplest layer of all and is responsible only for sending bits via a wired or wireless transmission.

PDU (protocol data unit).

There are several different names for a group of bits as it moves from one layer to the next and from one LAN to the next. Although technicians loosely call this group of bits a message or a transmission.