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". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||^$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!

Enjoy The TCP/IP Guide? Get the complete PDF!
The TCP/IP Guide

Custom Search

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

Previous Topic/Section
OSI Reference Model Layer Mnemonics
Previous Page
Pages in Current Topic/Section
Next Page
TCP/IP Protocol Suite and Architecture
Next Topic/Section

OSI Reference Model Layer Summary

To assist you in quickly comparing the layers of the OSI Reference Model, and understanding where they are different and how they relate to each other, I have created the summary chart shown in Table 18. It shows each layer's name and number, describes its key responsibilities, talks about what type of data is generally handled at each layer, and also what the scope of each layer is in approximate terms. I also show some of the more common protocols that are associated with each layer.

I will say here that “standard disclaimers apply”. I don't want to repeat all of the caveats I mentioned elsewhere in discussions of the OSI model, but know that they apply here as well. Namely: the layers aren't always hard-fast, I haven't listed every single protocol here, some may really fit into more than one layer, and so on. In particular, note that many of the technologies listed as being in the data link layer are there because that is the layer where their primary functionality resides. In reality, most of these technologies include components in other layers, especially the physical layer.

Table 18: OSI Reference Model Layer Summary



Layer Name

Key Responsibilities

Data Type Handled


Common Protocols and Technologies

Lower Layers



Encoding and Signaling; Physical Data Transmission; Hardware Specifications; Topology and Design


Electrical or light signals sent between local devices

(Physical layers of most of the technologies listed for the data link layer)


Data Link

Logical Link Control; Media Access Control; Data Framing; Addressing; Error Detection and Handling; Defining Requirements of Physical Layer


Low-level data messages between local devices

IEEE 802.2 LLC, Ethernet Family; Token Ring; FDDI and CDDI; IEEE 802.11 (WLAN, Wi-Fi); HomePNA; HomeRF; ATM; SLIP and PPP



Logical Addressing; Routing; Datagram Encapsulation; Fragmentation and Reassembly; Error Handling and Diagnostics

Datagrams / Packets

Messages between local or remote devices

IP; IPv6; IP NAT; IPsec; Mobile IP; ICMP; IPX; DLC; PLP; Routing protocols such as RIP and BGP



Process-Level Addressing; Multiplexing/Demultiplexing; Connections; Segmentation and Reassembly;
Acknowledgments and Retransmissions;
Flow Control

Datagrams / Segments

Communication between software processes


Upper Layers



Session Establishment, Management and Termination


Sessions between local or remote devices

NetBIOS, Sockets, Named Pipes, RPC



Data Translation; Compression and Encryption

Encoded User Data

Application data representations

SSL; Shells and Redirectors; MIME



User Application Services

User Data

Application data



Previous Topic/Section
OSI Reference Model Layer Mnemonics
Previous Page
Pages in Current Topic/Section
Next Page
TCP/IP Protocol Suite and Architecture
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 (
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.