ONE:Now that you have read the chapter about the OSI model, how would you change it? Are there inefficiencies or redundancies in the model?

TWO:Learning Objectives

In this lab, you’ll examine the layers of the OSI seven-layer model and the TCP/IP model. When you’ve completed this lab you will be able to

● Explain why layered models are used to describe data communication.

● Identify each of the seven layers of the OSI model. 

Solution

1. How does the concept of layers describe flow of information or communications?

The ISO refers to open systems interconnection model commonly used to standardize and categorize the inner functions of the communication system by dividing it into different layers. This model consists of seven abstract layers with each playing a different function. The layer may serve the layer above it or the layer below it.  There is error-free communication within layers throughout the network, layers also provide a path needed by application to send or receive packets across the network. For example two instances in one layer are handled by a horizontal connection.

2. How are layers used to describe data communications?

The seven logical layers play a very great role in data communication. Each layer has a distinctive function to serve the later above it or the layer below it. The following are the seven logical layers of an ISO:

 Layer 1: Physical layer

Physical layer is composed of the physical requirements and electrical specifications of data connections. It establishes the devices and the medium of communication. It is usually concerned with establishing and termination connection between two connected nodes across the network thus making it essential to monitor flow control. The physical channel consists of cabling (such as copper or optical cables.), physical Ethernet layers such as Token Ring and FDDI, wireless networks  such as radio link and Bluetooth.

Layer 2: Data link layer

Data link layer provides a reliable connection between itself and physical layer. It detects and corrects errors that result from the physical layer. It is further subdivided into sub-layers:

Media Access control (MAC)layer- this layer is charged with the function of controlling  how computers gain access to data and regulates  the transmission of this information.

Logical link Control (LLC) layer-this layer is concerned with error detection and synchronization of packets.

Data link layer follows the point –to point protocol in the TCP/IP stack.

layer 3: network layer

The network layer provides a functional and steps by step mode of transfers variable data sequences called datagram from one node to the next across the same network. A network system consists of may be interconnected nodes. The nodes have different addresses that allow nodes to connect to it and transfer messages to the required destination node. The network layer has the capability of delivering message by splitting it into several fragments, where each fragment follows a separate route and reassembling the fragment upon reaching the destination while detecting and correcting errors.

Layer 4: transport layer

The transport layer provides a functional and steps by step method of transporting the datagram from the source to the terminus across one or more networks. Transport layer is responsible for control the reliability of links through segmentation/de segmentation and also error control. Some of these protocols are connection oriented or state oriented. Meaning that the transport layer can monitor the segments and resend those that fail to transmit. The transport layer also indicates accomplishment of a successful transmission and also allows the next data to be transmitted if no errors occurred. Transport layer is also responsible for creating packets from messages received from the application layer through a process called packet zing. Packetizing is the process of braking long messages into smaller ones for secure transmission. The transport layer protocol is categorized as the TCP/IP on the internet portal stack.

Layer 5: session layer

This layer is responsible for controlling connecting between computers.  It starts monitors and ends connections between remote and local applications. This happens through simplex, full-duplex and half-duplex operations by starting checkpoints, restarting, adjournment and termination of procedures. This layer responsible for the closure of the session that not in use, also known as transmission control protocol. It  very helpful in session check pointing and recovery. Finally this is very helpful in environments that use remote procedure calls.

Layer 6: presentation layer

This layer is responsible for establishing context relationship in application layers entities. The application layers entities can use different semantic and syntax if the layer provides a presentation mapping service between them. Incase mapping is available there an encapsulation of the presentation data units into session data units   and is passed down to the TCP/IP stack. The layer also encrypts data to be sent over the network  and then transforms it in a format that all application accepts. It also known as syntax layer.

Layer 7: application layer

This layer is the one closest to the end user, the ISO application layer interacts with the user directly through software applications. The software applications implement communication component in this layer and such programs are not within the ISO model. The application layer is responsible for identifying the communicating entities, ensuring availability of resources in communication and   ensuring synchronization during the communication.

3. What is a mnemonic used for remembering the OSI model?

The standard mnemonic trick used to remember the ISO model is shown below. It starts from the top to bottom.

[Application] All

[Presentation] Pros

[Session] Search

[Transport] Top

[Network] Notch

[Data Link] Donut

[Physical] Places

4. What is the OSI model and what are its benefits?

The ISO refers to open systems interconnection model commonly used to standardize and categorize the inner functions of the communication system by dividing it into different layers.Breaking down network into seven logical layers provides these advantages

• Reduces the complexity- it breaks network into small simpler communicating parts which help in component design, troubleshooting and development.
• Standardizes interfaces- it allows the network system to support many vendors/users and also allows the development.
• Facilitates modular engineering- provides different kinds of software and hardware to communicate across the network.
• Facilitate communication between layers-it allows connection of two different layers is thus promoting communication between them.
• Hiding (abstraction) of implementation details.

5. What is a PDU?

In the ISO model a PDU (protocol Data Unit) can be defined as the as information that contain controls  such a user data and address and is delivered among peer entities of the network system. It can likewise be characterized as a unit of data of a specified protocol of a given layer containing protocol control information such as user data.

6. Explain data encapsulation.

Data encapsulation in computer networking is a method designing communication protocol modular which isolates functions of the network model that are hidden by high level objects across the network. The more specific layer is referred as the lower layer while the abstracted layer is known as the upper layer.

7.the OSI model, how would you change it? Are there inefficiencies or redundancies in the model?

 The ISO model can be change by creating a network stack with three layers:

– Physical
– Network
– Application

This may be generally unsuitable for the functions performed by the stack. This is because every layer has its own function to either serve the layer above or below it. There are no much redundancies; those found are error detection and correction which increase its efficiency.

 

Task 2: Fill out the following table.

1. Under functions, please supply enough information to completely describe the function of each layer.
2. In the keywords column write a word or phrase to help you remember the purpose of the layer.
3. Under hardware, please list the network devices used at that layer.
4. For the protocols column, provide specific protocols that are used in the TCP/IP suite.

Note that layers 5-7 (Marked Red) do not have some of the categories such as PDU’s or hardware

	OSI model			TCP/IP model
	Name	PDU	Function	Keywords	Hardware	Protocols
7	Application		Provides an interface for interaction with network devices.	Interaction		DNS, HTTP,DHCP
6	Presentation		Data representation, encryption, and decryption	Representation		MIME,XDR
5	Session		Managing session between hosts.	Sessions		SAP,SOCKS
4	Transport	Segments	Delivery of packets between hosts applications	Applications	Bridge	TCP,UDP
3	Network	Packets	Addressing and routing	Routing	Router	IP,IPsec, ICMP
2	Data link	Frames	Reliable point-to-point data connection	Point-to-point	Switch	HDLC,PPP
1	Physical	Bits	Defines electrical and physical specifications of network devices.	Electrical	Fiber, copper cable	BLUETOOTH, DSL

 

Lab Materials and Setup

The materials you need for this lab are

● The Mike Meyers’ CompTIA Network+ Guide to Managing and Troubleshooting Networks textbook

● Pencil and paper

Instructions

Work through the following tasks to investigate the details of network data delivery using the OSI seven-layer model. 

Task 1: Answer the following questions.

1. How does the concept of layers describe flow of information or communications?

2. How are layers used to describe data communications? 

3. What is a mnemonic used for remembering the OSI model? 

4. What is the OSI model and what are its benefits?

5. What are some advantages of the OSI model? 

6. What is a PDU?

7. Explain data encapsulation. 

THREE:Use the following worksheet to complete the Hardware Lab. Make sure you also download the zip file with the images you will need for the lab. 

Attach your completed Hardware Lab worksheet to this drop box and submit it. Your submitted file can be in any of these formats: .doc, .docx, .rtf, or .pdf.

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