Ccna what is a pdu

Example, you could use any number of FTP programs, but the protocol used is an application layer protocol. File Transfer Protocol FTP is an application layer protocol which moves files between local and remote file systems. Data is data, and a model is a model.

The model describes what is done with data. I think you should stop right there. I feel you are about to go down an unproductive rabbit hole. The model takes the process and breaks it down into discreet steps, providing general terms of what is happening at each step but leaving enough flexibility so that within a particular step As such, the model is not supposed to provide fine details of what is transpiring at each step.

If it did so, you would lose your flexibility and lose your choices of which protocols you wanted to implement. MTU may or may not be a component of whatever protocol you select to use within a given layer of the model. For example, we know that Ethernet has a rule i. MTU that says that a maximum of bytes including the Ethernet header may be transmitted onto the wire and then the protocol must pause to give other NICs the opportunity to also transmit on the wire.

But that is a rule built into that specific protocol Ethernet. I could design my own DataLink Layer protocol called, "Keith's Protocol" that says my NIC can transmit for as long as it wants until all the data is transmitted. My protocol will have no MTU. If I have bits to transfer or 10,,, bits to transfer I'll keep going until I'm done.

However my protocol does the generic things described by the OSI Model as being in the DataLink Layer provides a L2 Source Destination Address, provides for error checking, knows how to encapsulate different kinds of data, hands data down to the Physical Layer, etc.

So the short answer to your question is no Any layer may, or may not implement, an MTU option. If you encounter a technical issue on the site, please open a support case. Communities: Chinese Japanese Korean. All Rights Reserved.

The Cisco Learning Network. Enterprise Certifications Community. View This Post. In this chapter, we will look at the layered models that are used in communication over networks. This will lead into detailed discussion on each of the layers so as to better understand them. To better understand the various protocols and how they work with each other, we use layered models.

A layered model shows how the protocols work at each layer as well as how the layers interact with the layers either above them or below them. However, these two models are different. The protocols that are defined in this model are usually based on vendor specifications. The OSI model is a reference model and it is used to provide or maintain consistency and standardization among the various protocols and services that are used in networks.

It does not give strict regulations on how or what protocols and services should work at each layer, rather, it works as a guideline. The reference model is aimed at giving clear understanding of what happens — the functions and processes at each layer, however, it does not say exactly how they should be implemented.

Network engineers use it in designing, operating and troubleshooting networking equipment where necessary. There are four categories as you can see from the output above. Network communications were first defined using this model and for successful communication to occur, the functions of each layer must be in place in a network.

From the output below, you can see the function of each and every layer of this model. The application layer, is the component that interfaces with the user, when you are using a web browser, this is a component of the application layer.

The transport layer defines the various ports and helps differentiate the different types of communication from a single user. You may be sending an email, browsing and listening to internet radio on one computer.

It is the work of the transport layer to differentiate the different types of communications. The transport layer also helps in interoperability between different network devices such as a PDA and a computer. The internet layer is meant to provide the best path to remote networks, this differentiates the different devices on a network.

If a message is to be sent from one computer to another on a remote network, it is the work of the internet layer to make sure the message gets to the intended recipient. You may compare the internet layer to an address you use when you want to send a letter. The network access layer acts as an interface between the hardware and software components in the network.

The application, transport and internet layers are all implemented by software, however, the network access translates the messages from these layers to a form that can be transmitted over various media such as fiber optic cables, copper wire and wirelessly.

If we want to send an email, for example, the steps shown below would be the functions of each layer for this communication. NOTE: encapsulation is a process of adding protocol specific information as well as converting a protocol data unit PDU into a form that conforms into the layer it is in. The OSI model provides an extensive list of functions and services that can occur at each layer. It also describes the interaction of each layer with the layers directly above and below it. In this model, as shown in the diagram above, the application and network access layer are broken down to define more functions.

The application layer is broken into the application, presentation and session layers, while the network access layer is broken up into the data link and the physical layers. At the data link and physical layer, the OSI model only describes how data is handled from the network layer to the physical layer.

It does not state what exactly happens at each of them. The functions at these layers are the same. The transport layer defines how communication between different user machines happens. At this layer, the rules define how messages are acknowledged, how the communication recovers from errors, and how the segments are arranged.