osi / tcp model


the OSI Model

The OSI model is an abstract conceptualization of the processes that make the Internet work.

Interpreting and applying the model to the real-world Internet is sometimes subjective.

Layer 7 - The Application layer:

Data generated by and usable by software applications. The main protocol used at this layer is HTTP.


Examples:

HTTP - Hyper Text Transfer Protocol

FTP - File Transfer Protocol

SMTP - SImple Mail Transfer Protocol

DNS - Domain Name Services

DHCP - Dynamic Host Configuration Protocol

IMAP - Internet Message Access Protocol

IRC - Internet Relay Caht

Bitcoin

BitTorrent

RDP - Remote Desktop Protocol

NFS - Network FIle System

NIS - Network Information SYstem

SMTP - Simple Mail Transfer Protocol

SNTP - Simple Network Time Protocol

SSH - Secure Shell / Remote Telnet

Layer 6 - The Presentation layer:

Data is translated into a form the application can accept. Some authorities consider HTTPS encryption and decryption to take place at this layer.


Examples:

AFP - Apple Filing Protocol

ICA - Independent Computing Architecture (Citrix system core protocol)

LPP - Lightweidth Presentation Protocol

Layer 5 - The Session layer:

Controls connections between computers (this can also be handled at layer 4 by the TCP protocol).


Examples:

NetBIOS - Network Basic Input/Output System

PAP - Password Authentication Protocol

PPTP - Point to Point Tunneling Protocol

RPC - Remote Procedure Call Protocol


Layer 4 - The Transport layer:

Provides the means for transmitting data between the two connected parties, as well as controlling the quality of service. The main protocols used here are TCP and UDP.


Examples:

TCP - Transmission Control Protocol

UDP - User Datagram Protocol

MPTCP - Multipath TCP

Layer 3 - The Network layer:

Handles the routing and sending of data between different networks. The most important protocols at this layer are IP and ICMP.


Protocols that work on WANS

Examples:

IPV4/IPV6

ICMP - Internet Control Message Protocol

IGMP - Internet Group Meanagement Protocol

IPsec - Internet Protocol Security


Layer 2.5 - (The ARP layer)

ARP allows an IPv4 to be encapsulated inside a frame.

Devices on a network maintain an ARP Cache (Table) which contains a list of IP to MAC address associations

ARP Cache age out entries about every 90 seconds to force ARP to continually re-resolve the Cache/Table data.

  • This is not to be confused with the MAC address table of a switch, which is separate.

  • The MAC address table maps the MAC to a port on a switch.

  • The ARP cache (table) maps the MAC to IP of connected devices.

  • Switches do not need an ARP table except when using SSH.


Packets are stored within frames when passed through a network.

Below is an example of the contents of an IP packet.


The Frame: | Destination MAC Address | Source MAC Address | Layer 3 Protocol |

The Packet inside the Frame: | Source IP Address | Destination IP Address | TTL | Other | ICMP |


Detail of Frame:

Destination MAC Address: Where the frame is being sent

Source MAC Address: Where the frame came from

Layer 3 Protocol: ARP, ICMP

The IP Packet:



Layer 2 - The Data link layer:

Handles communications between devices on the same network. If layer 3 is like the address on a piece of mail, then layer 2 is like indicating the office number or apartment number at that address. Ethernet is the protocol most used here.


Layer 2 = Protocols that work on LANS

Examples:

PING - Packet Inter Networking Grouper

Ethernet - Broadcast / Flood / Multicast (LAN)

IEEE 802.11 Wireless LAN

IEEE 802.2 - provides LLC funstions to IEEE 802 MAC layers

Token Ring


Layer 1 - The Physical layer:

Packets are converted into electrical, radio, or optical pulses and transmitted as bits (the smallest possible units of information) over wires, radio waves, or cables.


Examples:

Blue Tooth

Physical Ethernet - (10BASE5, 100BASE-TX, 100BASE-FX, 1000BASE-T, 1000BASE-SX)

802.11 WiFi-Physical Layer

ISDN - Integrated Services Digital Network

USB - Physical

Hardware - Router, Switch, Firewall

TCP IP Model

The TCP/IP model is an alternative model of how the Internet works. It divides the processes involved into four layers instead of seven.

layer 4 - The Application layer:

This corresponds, approximately, to layer 7 in the OSI model.

Data generated by and usable by software applications. The main protocol used at this layer is HTTP.

OSI layers 5 and 6 in the TCP/IP model are no longer necessary in the modern Internet, and/or actually belong to layers 7 and 4 (represented by layers 4 and 3 in the TCP/IP model).


Examples:

HTTP - Hyper Text Transfer Protocol

FTP - File Transfer Protocol

SMTP - SImple Mail Transfer Protocol

DNS - Domain Name Services

DHCP - Dynamic Host Configuration Protocol

IMAP - Internet Message Access Protocol

IRC - Internet Relay Caht

Bitcoin

BitTorrent

RDP - Remote Desktop Protocol

NFS - Network FIle System

NIS - Network Information SYstem

SMTP - Simple Mail Transfer Protocol

SNTP - Simple Network Time Protocol

SSH - Secure Shell / Remote Telnet

AFP - Apple Filing Protocol

ICA - Independent Computing Architecture (Citrix system core protocol)

LPP - Lightweidth Presentation Protocol

Layer 3 - The Transport layer:

This Corresponds to layer 4 in the OSI model.

Provides the means for transmitting data between the two connected parties, as well as controlling the quality of service. The main protocols used here are TCP and UDP.


Examples:

TCP - Transmission Control Protocol

UDP - User Datagram Protocol

MPTCP - Multipath TCP

NetBIOS - Network Basic Input/Output System

PAP - Password Authentication Protocol

PPTP - Point to Point Tunneling Protocol

RPC - Remote Procedure Call Protocol


Layer 2 - The Internet layer:

This Corresponds to layer 3 in the OSI model.

Handles the routing and sending of data between different networks. The most important protocols at this layer are IP and ICMP.


Examples:

IPV4/IPV6

ICMP - Internet Control Message Protocol

IGMP - Internet Group Meanagement Protocol

IPsec - Internet Protocol Security

LAYER 1 - Network access layer:

Combines the processes of layers 1 and 2 in the OSI model.

Packets are converted into electrical, radio, or optical pulses and transmitted as bits (the smallest possible units of information) over wires, radio waves, or cables. Handles communications between devices on the same network.

Ethernet is the protocol most used here.


Examples:

Blue Tooth

Physical Ethernet - (10BASE5, 100BASE-TX, 100BASE-FX, 1000BASE-T, 1000BASE-SX)

802.11 WiFi-Physical Layer

ISDN - Integrated Services Digital Network

USB - Physical

Hardware - Router, Switch, Firewall

Ethernet

IEEE 802.11 Wireless LAN

IEEE 802.2 - provides LLC funstions to IEEE 802 MAC layers

Token Ring