Lab 2.3.5 OSI Model  - Overview

Estimated time: 20 min.

Objectives:

This lab will help you develop a better understanding of the seven layers of the OSI model. You will identify the characteristics of each layer as well as the terminology at each layer. The OSI model was developed by the ISO to help provide a common framework for the development of both Local Area Networks (LANs) and Wide Area Networks (WANs). Most network architectures and companies do not adhere exactly to the OSI model but use it to describe their products and compare them to others. The OSI model helps us troubleshoot networking problems by breaking down the networking process (communication from hosts to servers) into distinct layers where functions must occur and identifying tools which can help to isolate the problem. An understanding of the OSI model is essential to success in the world of networking. This lab focuses on the Ethernet network architecture and the Internet Protocol suite (TCP/IP).

Tools / Preparation:

Task: Fill out the following charts based on your knowledge of the OSI model.
Explanation: Your understanding of the OSI model will greatly increase your ability to absorb and categorize networking information as you learn it. 

1.  List the 7 layers of the OSI model from the top to the bottom. Give a mnemonic word for each layer that can help you remember it and then list the keywords and phrases that describe the characteristics and function of each.

Layer #	Name	Mnemonic	Key Words and Description of Function
7
6
5
4
3
2
1

2. List the 7 layers of the OSI model and the encapsulation unit used to describe the data grouping at each layer.

Layer #	Name	Encapsulation Unit or Logical Grouping	Devices or Components that Operate at this Layer
7
6
5
4
3
2
1

EXERCISE 2.3.5 – OSI MODEL LAYERS – ANSWERS 

Step 1 

1.    List the 7 layers of the OSI model from the top to the bottom.  Give a mnemonic word for each layer that can help you remember it and then list the key terms and phrases that describe the characteristics and function of each. 

Layer #	Name	Mnemonic	Key Words and Description of Function
7	Application	All	Network processes to applications such as File, Print, Message, Database and Application services. Establishes availability of resources between two nodes.  (FTP and Telnet are examples)
6	Presentation	People	Data representation, coding (EBCDIC, ASCII),  Data transfer syntax, conversion, encryption, formatting and compression services.
5	Session	Seem	Interhost communication.  Establishes, maintains and terminates connections between applications.
4	Transport	To	End-to-End connections.  Segments and reassembles data in proper sequence.  Setup and teardown of “virtual Circuits” (connection oriented).  Can ensure segment delivery with error correction,  recovery and flow control.
3	Network	Need	Network / Host addresses and selection of best path through an Internetwork (Routing).  Encapsulates upper layer information into “packets”
2	Data Link	Data	Access to media. Adds frame header to upper layer in formation which contains the hardware address of the destination device or next device on the path. The data Link Layer is divided into 2 sub-layers. 1) The Logical Link Control (LLC) and 2) The Media Access Control (MAC).
1	Physical	Processing	Binary transmission signals and encoding.  Electrical (copper), light (fiber) and physical connections and media (cabling) between network devices.

2.   List the 7 layers of the OSI model and the encapsulation unit used to describe the data grouping at each layer.

Layer #	Name	Encapsulation Unit or Logical grouping	Devices or components that operate at this layer
7	Application	Data	Software (gateways)
6	Presentation	Data	Software
5	Session	Data	Software
4	Transport	Segments	Router
3	Network	Packets, Datagrams	Router
2	Data Link	Frames	NIC (LLC & MAC), Bridge, Switch
1	Physical	Bits	NIC (Physical connectors – BNC, RJ-45 etc.), Media (cable), Repeater, Hub, DCE & DTE