====== Basic Networking ======

===== OSI Model =====

A conceptual model of networking based on seven "layers":

^ **#** ^  Layer  ^  Description  ^
| 7 | **Application** | Provides networking options (an interface to transmit data) to programs running on the computer. |
| 6 | **Presentation** | Translates the data into a standardized format (so the receiving machine can read it); it also handles encryption, compression, or other transformations of the data.|
| 5 | **Session** | Sets up and maintains a connection with the other computer across the network (connection is unique to this communication). |
| 4 | **Transport** | Decides on a transport protocol (TCP or UDP) and then divides up the data to be sent over the network (TCP: segments; UDP: datagrams). |
| 3 | **Network** | [router level] Locates the destination computer via logical addressing (i.e., IP Addresses). |
| 2 | **Data Link** | [switch level] Identifies the MAC/hardware addresses of the machines on the network (mapping each IP Address to the device's MAC/hardware address). Runs a CRC for data integrity and then presents the data in a suitable format for transmission.|
| 1 | **Physical** | The hardware that communicates with electrical impules (1's and 0's) or light (on and off).|

The machine that receives the transmssion does so on Layer 1, then passes the data up the stack to Layer 2, etc.

===== TCP/IP Model =====

^ **#** ^  Layer  ^  Description  ^
| 4 | **Application** | Provides applications with standardized data exchange via protocols like HTTP, FTP, POP3, SMTP, and SNMP. The payload is the actual application data. |
| 3 | **Transport** | Responsible for maintaining end-to-end communications across the network via TCP and UDP protocols. |
| 2 | **Internet** | Deals with packets and connects independent networks to transport the packets across network boundaries via protocols like ICMP. |
| 1 | **Network Access** | The "physical" or "link" layer; defines the networking methods within the scope of the local network link on which hosts communicate without intervening routers. Protocol: Ethernet. |

===== OSI & TCP/IP =====

^ OSI MODEL ^ TCP/IP MODEL ^
| 7. Application  | 4. Application       |
| 6. Presentation | :::                  |
| 5. Session      | :::                  |
| 4. Transport    | 3. Transport         |
| 3. Network      | 2. Internet          |
| 2. Data Link    | 1. Network Interface |
| 1. Physical     | :::                  |

  * The TCP/IP model was introduced first (in 1982 by the US DoD) and is the standard upon which modern networking is based.
  * The OSI model was developed later as a more comprehensive guide for learning.