IS355 Seven Layers of the Open Systems Interconnection Reference (OSI) Model

Layer 7: Application

Core functionality:”Application Layer—This is responsible for interacting with end users. The Application Layer includes all programs on a computer that interact with the network; for example, your email software is included because it must transmit and receive messages over the network. A simple game like Solitaire doesn’t fit here because it does not require the network to operate.”

One protocol:BitTorrent, DNC, DSNP, DHCP, FTP, HTTP(S), IMAP, MIME, NNTP, NTP, POP3, RADIUS, RDP, SMTP, SOAP, Telnet

Common devices for each layer: Gateway, firewall, endpoint device (server, PC, mobile device, etc.)

Layer 6:Presentation

Core functionality:”This is responsible for the coding of data. The Presentation Layer includes file formats and character representations. From a security perspective, encryption generally takes place at the Presentation Layer”

One protocol:AFP, SSL, TLS

Common devices for each layer:Gateway, firewall, server, PC

Layer 5:Session

Core functionality:”This is responsible for maintaining communication sessions between computers. The Session Layer creates, maintains, and disconnects communications that take place between processes over the network.”

One protocol:L2F, L2TP, NetBIOS, NFS, RPC, SMB, SSH

Common devices for each layer:Gateway, firewall, server, PC

Layer 4:Transport

Core functionality:”This is responsible for breaking data into packets and properly transmitting them over the network. Flow control and error checking take place at the Transport Layer.”

One protocol:AH (over IP/IPSec), BGP, ESP (over IP/IPSec), TCP, UDP, SPXCT

Common devices for each layer:Gateway, firewall

Layer 3:Network

Core functionality:”This is responsible for the logical implementation of the network. One important feature of the Network Layer, covered later in this chapter, is logical addressing. In TCP/IP networking, logical addressing takes the familiar form of IP addresses.”

One protocol:ICMP, IGMP, IGRP, IPv4, IPv6, IPSec, IPX, GRE, OSPF, RIP

Common devices for each layer:Router, brouter, Layer 3 switch

Layer 2:Data Link

Core functionality:”This is responsible for transmitting information on computers connected to the same local area network (LAN). The Data Link Layer uses Media Access Control (MAC) addresses. Device manufacturers assign each hardware device a unique MAC address”

One protocol:ARP, Ethernet (IEEE 802.3), FDDI, Frame Relay, IND, L2TP, PPP, MAC, NPD, RARP, STP, Token Ring, VLAN, Wi-Fi (IEEE 802.11), WiMax (IEEE 802.16), X.25

Common devices for each layer:Bridge, modem, network card, Layer 2 switch

Layer 1:Physical

Core functionality:”This is responsible for the physical operation of the network. The Physical Layer must translate the binary ones and zeros of computer language into the language of the transport medium. In the case of copper network cables, it must translate computer data into electrical pulses. In the case of fiber optics, it must translate the data into bursts of light.”

One protocol:Bluetooth, DSL, Ethernet (Physical Layer), USB, Wi-Fi (Physical Layer)

Common devices for each layer:Hub, repeater, cable, fiber, wireless