 |
|
Please Whitelist This Site?
I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)
If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.
If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.
Thanks for your understanding!
Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide
|
|
|
Custom Search
|
 |
The TCP/IP Guide 9 The Open System Interconnection (OSI) Reference Model 9 Key OSI Reference Model Concepts |
|
Data Encapsulation, Protocol Data Units (PDUs) and Service Data Units (SDUs)
(Page 3 of 3)
Use of PDU and SDU Terminology
The term “protocol data unit” is rather formal. You will see it used in standards and sometimes in discussions, but more often, the “plain” message terms, such as “frame” and “datagram”, are encountered, as discussed in the networking fundamentals topic on messages. Similarly, data encapsulated by these messages is not normally called a “service data unit” but rather simply the message body or payload, as discussed in the topic on message formatting. There are cases, however, where knowing the difference between an SDU and a PDU is important to understanding the technology. One example is the IEEE 802.11 physical layer; the 802.11 standards talk about SDUs and PDUs constantly.
|
Related Information: See the
|
Key Concept: The message used to communicate information for a particular protocol is called its protocol data unit (PDU) in OSI model terminology. That PDU is passed down to the next lower layer for transmission; since that layer is providing the service of handling that PDU, it is called the lower layer’s service data unit (SDU). The SDU is encapsulated into that layer’s own PDU and in turn sent to the next lower layer in the stack, proceeding until the physical layer is reached. The process is reversed on the recipient device. In summary: a layer N PDU is a layer N-1 SDU, which is encapsulated into a layer N-1 PDU.
|
| |||||||||||||||||||
Home - Table Of Contents - Contact Us
The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.