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
NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.
Presentation Layer (Layer 6)
The presentation layer is
the sixth layer of the OSI Reference Model protocol stack, and second
from the top. It is different from the other layers in two key respects.
First, it has a much more limited and specific function than the other
layers; it's actually somewhat easy to describe, hurray! Second, it
is used much less often than the other layers; in many types of connections
it is not required.
The name of this layer suggests its
main function as well: it deals with the presentation of data.
More specifically, the presentation layer is charged with taking care
of any issues that might arise where data sent from one system needs
to be viewed in a different way by the other system. It also takes care
of any special processing that must be done to data from the time an
application tries to send it until the time it is sent over the network.
Presentation Layer Functions
Here are some of the specific types
of data handling issues that the presentation layer handles:
Presentation Layer Role in the OSI Model
- Translation: Networks can connect very
different types of computers together: PCs, Macintoshes, UNIX systems,
AS/400 servers and mainframes can all exist on the same network. These
systems have many distinct characteristics and represent data in different
ways; they may use different character sets for example. The presentation
layer handles the job of hiding these differences between machines.
- Compression: Compression (and decompression)
may be done at the presentation layer to improve the throughput of data.
(There are some who believe this is not, strictly speaking, a function
of the presentation layer.)
- Encryption: Some types of encryption (and
decryption) are performed at the presentation layer. This ensures the
security of the data as it travels down the protocol stack. For example,
one of the most popular encryption schemes that is usually associated
with the presentation layer is the Secure Sockets Layer (SSL) protocol.
Not all encryption is done at layer 6, however; some encryption is often
done at lower layers in the protocol stack, in technologies such as
The reason that the presentation
layer is not always used in network communications is that the jobs
mentioned above are simply not always needed. Compression and encryption
are usually considered optional, and translation features
are also only needed in certain circumstances. Another reason why the
presentation layer is sometimes not mentioned is that its functions
may be performed as part of the application layer.
The fact that the translation job
done by the presentation layer isn't always needed means that it is
common for it to be skipped by actual protocol stack implementations.
This means that protocols at layer seven may talk directly with those
at layer five. Once again, this is part of the reason why all of the
functions of layers five through seven may be included together in the
same software package, as described in the overview
of layers and layer groupings.
Key Concept: The sixth OSI model layer is called the presentation layer. Protocols at this layer take care of manipulation tasks that transform data from one representation to another, such as translation, compression and encryption. In many cases, no such functions are required in a particular networking stack; if so, there may not be any protocol active at layer six.
|If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!|
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.