Experienced Member. Platinum Expert. Gold Member. Regular Member. Platinum Member. Share this page:. Share this page on Presales info. Follow us on Twitter Youtube. Rate 0. Anguraj Posts: 56 Rating: 0. Suggestion To thank Quote Answer. Rate 2. Dear Anguraj, well, let me try. If you find my contribution helpful please RATE it :. Rate 1. There is no bad feedback! Please rate! Hi mopS04, thank you. I know this is an old post, but why shouldn't profinet be routable?
Considering now the communication between two entities of the same level logical communication , it generally takes place through the exchange of messages that are called Protocol Data Units PDU. A Protocol Data Unit PDU is therefore the unit of information exchanged between two peer entities in a layered network architecture. To make an analogy, the PDU could be the single SMS exchanged between two people peer entity who have an exchange of messages through their mobile phones.
Just as SMS have a predetermined maximum length bytes and can contain only a certain type of data characters , so too PDUs have a predetermined format based on the particular communication protocol. Some PDUs can be used to send or receive control information e. However, from the point of view of the format, all PDUs of a certain protocol have the same structure, regardless of their purpose. In practice, a PDU used to manage a communication is indistinguishable in form from a data exchange PDU and both are treated exactly the same way by the lower levels.
Again using a metaphor, the postman does not care what is the content of a certain letter to be delivered or its purpose.
In any case, each PDU generally consists of two parts:. The header can be assimilated to the address on an envelope, while the data part corresponds to the content of a letter. In order to reach the recipient i.
When moving from one level to the next, a new header is added to the PDU and the PDU itself is treated as the new piece of data. This process is called encapsulation. Look at the following figure:. In a symmetrical and reverse way, when the message arrives at the recipient, each level examines the corresponding header and removes it from the message itself.
The encapsulation process is closely related to the concept of information hiding. Each level uses its own communication protocols, but the structure and content of the messages exchanged are of no interest to the other levels. On the recipient side, the message will be unpacked, it will arrive at the physical level, it will go up the top of the stack from level to level up to the application level.
If the sender sends a message at level N, the recipient will always receive this message at level N. Next » « Previous.
Table of Contents. For example, on local networks: IEEE The definition of the rules for access to the services offered by a layer constitutes the interface between that layer and the upper layer, and is the only thing that the upper layer must know Each layer realizes the services for the upper layer by communicating logically with the peer layer of the remote node, through a set of rules called protocol.
The exchange of data with the peer layer is carried out physically using the services of the underlying layer. Transform a transmission of raw bits between adjacent nodes into an error-controlled transmission line analysis It performs functions such as division of data into frames error checking acknowledge receipt flow control handshacking access control to the transmission medium MAC address: Medium Access Control of the network card Frame delimitation, bit ordering, subdivision into fields, addresses, etc.
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