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.

The Book is Here... and Now On Sale!

Get The TCP/IP Guide for your own computer.
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  The Open System Interconnection (OSI) Reference Model
      9  Key OSI Reference Model Concepts

Previous Topic/Section
Interfaces: Vertical (Adjacent Layer) Communication
Previous Page
Pages in Current Topic/Section
1
2
Next Page
Data Encapsulation, Protocol Data Units (PDUs) and Service Data Units (SDUs)
Next Topic/Section

Protocols: Horizontal (Corresponding Layer) Communication
(Page 1 of 2)

Each layer in the OSI Reference Model has a particular role (or roles)—a set of general tasks for which it is responsible. On each system on the network, hardware and software are running at many of the different levels in the model. The routines doing a particular job on machine “A” are designed to communicate with similar or complementary ones that are running on machine “B”. This horizontal communication is the very heart of what networking is about. It is what enables Web browsers and Web servers to talk, email applications to exchange messages, and so much more.

OSI Protocols

Of course, all types of communication function only if everyone agrees to the same methods of accomplishing it. Each set of rules describing one type of communication is called a protocol. You can think of a protocol as being like a language or a set of instructions. Each function or service of a network has its own language; like human languages, some are similar to each other while others are quite unique.

If you've done any reading at all about networks, you have probably seen the term “protocol” many, many times. Like the word “interface”, the word “protocol” can have many meanings. In fact, it is so fundamental to networking, and used in so many different ways, that I have a topic devoted to it in the chapter on Networking Fundamentals.

All that aside, we must remember that the OSI Reference Model is intended to be a formal way of describing networks. As such, the term “protocol” has a formal meaning in the context of the model. It refers specifically to a set of communication rules, instructions and/or procedures that describe communication between specific software or hardware elements running at the same layer on different machines within a network.


Previous Topic/Section
Interfaces: Vertical (Adjacent Layer) Communication
Previous Page
Pages in Current Topic/Section
1
2
Next Page
Data Encapsulation, Protocol Data Units (PDUs) and Service Data Units (SDUs)
Next Topic/Section

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!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



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.