The OSI 7 Layer Model

Ben, Stuart, Charles

1) Physical Layer

● The physical, wired or wireless, transmitting of data.○ Type of medium

○ Electrical signals

● Implemented by the Network Interface Card (NIC)○ 802.3(wired ethernet)

○ 802.11 (WI-FI)

■ 2.4ghz & 5ghz

2) Data Link Layer

● The Data Link layer ensures that messages are delivered to the proper device on a LAN

using hardware (MAC) addresses

● Translates messages from the Network layer into bits for the Physical layer to transmit.

● The Data Link layer is responsible for the unique identification of each device that resides

on a local network.

3) Network Layer

● Manages communication between devices that are not in the same LAN.

● IP addresses record the logical address of each device.○ IPv4 32 Bits

■ Contains a subnet

● Division of the network into smaller groups

■ subnet mask

● Used to determine the network ID of the IPv4 address

○ IPv6 128 Bits

● Route-Update Packets maintain routing information on Layer 3 networking devices.○ RIP

○ EIGRP

○ OSPF

○ BGP

4) Transport Layer

● Logically assembles data into segments.

● TCP vs UDP

● TCP provides flow control.○ Data is sent in order.

○ Receiver confirms that they received the data.

○ Lost data is retransmitted.

● UDP is not concerned with whether or not the packets have been received by the

intended recipient

5) Session Layer

● Five main targets of the session layer○ Ensures data from different applications is sent to the correct location and is handled

properly.

○ The Session layer is responsible for setting up, managing, and then tearing down sessions

between Presentation layer entities.

○ It coordinates communication between systems and serves to organize their

communication by offering three different modes: simplex, half duplex, and full duplex.

○ Session layer basically keeps applications’ data separate from other applications’ data.

○ Deals with lost connections and what to do with them

6) Presentation Layer

● The Presentation layer gets its name from its purpose: it presents data to the Application

layer and is responsible for data translation and code formatting○ Data compression

○ Decompression

○ Encryption

○ Decryption.

7) Application Layer

The Application layer is responsible for identifying and establishing the availability of the

intended communication partner and determining whether sufficient resources for the

requested communication exist.

● Serves as an Interface between applications and rest of the OSI.○ Telnet - 23

○ File Transport Protocol (FTP) - 20/21

○ Simple Mail Transport Protocol (SMTP) - 24

○ Domain Name System (DNS) - 25

● High level API

PDU’s