Cisco Certification: The OSI Model, Part I

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Telepresence and Holography / Holograms - November 2008

Editor’s viewpoint on their differences, likenesses and future...

We all just recently viewed an historic CNN holographic interview on an historic Election Night. CNN stated this type of imaging has never been done before on National TV and I believe that. I haven’t seen anything like it. The live interview caught me by surprise and sure had the “wow” factor attached to it didn’t it? Here’s a link to the actual interview.

CNN Hologram Video

The question now has to be asked. Is it Telepresence?

I’m no expert on the subject but I’m going to throw my hat into the ring, go out on a limb and say yes, I believe it is. Although I know many video conferencing purists are rolling their eyes and grabbing their guns right about now with my statement.

While I do know that Telepresence still hasn’t been universally defined (Houston, we have a problem), here’s how I see it…. Broken down to its simplest form - “tele” (through electronic means) and “presence” (present). This is how I’m justifying my opinion by lumping holography and Telepresence together. Just as Telepresence is surely an offshoot of video conferencing, holographic imaging (like we viewed on CNN) surely has to be considered an offshoot of Telepresence. The interviewer was “telepresent” from Chicago and beamed into the CNN Election Headquarters. She was most assuredly - “telepresent”. There was negligible latency, the imaging was fantastic and both interviewers were rehearsed on what they would say. I’ve just recently read that CNN actually “downgraded” the experience to make it “movie” quality and not as good as it could have been. Maybe they thought us mere mortals would be shocked if they showed their complete hand. I have a feeling it was so big to them, they didn’t want it to get upstaged by the historic election. I’m willing to bet we’ll see the “true” power of this technology in the upcoming weeks and months when they can put the pedal to the medal and show it off without having it sidetracked.

What an amazing time for this technology (all differences and opinions aside). Telepresence Doctors, nurses, teachers, schools and healthcare (healthpresence) will benefit from the recent gains in this state-of-the-art industry whether holograms, Telepresence or holography. Airlines also have to see the threat to a portion of their business travel. Hell, who wants go through security and fly to Miami for a two-hour conference when you can look them in the eye via Telepresence?

Beam me up Scotty! Simply amazing…!

Visit the free Telepresence Forum for more information and discussion

Your Editor and Administrator - L II
"Ride on the Next Plane of Existence" TM

To conquer the Introduction To Cisco Networking exam, and to begin the process of becoming an expert network troubleshooter, you have to master the OSI model and learn what happens at each of the seven layers.

In this three-part series, we'll examine each level of the OSI model, paying particular attention to the details that will help you pass the CCNA exams and give you the foundation you need to become a true networking professional.

We'll start at the top layer, the Application layer.

It won't surprise you to find that the Application layer is the OSI model layer where most end users have interaction with said applications. Passing the CCNA exam is all in the details, though, and you need to know what happens at the Application layer, as well as the common and not-so-common applications that run at this layer.

The Application layer's tasks include identifying the remote communication partner, ensuring that the needed resources for communicating with that partner exist, and user authentication. If you're prompted for authentication, you're most likely at the Application layer of the OSI model.

Keep that in mind if asked to identify Application layer protocols. I've noticed that CCNA candidates tend to identify Telnet as running at the Application layer. That's an understandable misconception, since the first thing you enter in Telnet is an IP address, and it's often used to communicate with a router. However, keep in mind that Telnet is an Application layer service, not a Network layer service. You've got to authenticate to Telnet to a Cisco router in the first place, remember!

Other common applications that run at Layer 7 are Simple Mail Transfer Protocol (SMTP, port 25) and File Transfer Protocol (FTP, port 21).

In short, if an end user is interacting with a program, especially if they're being prompted for authentication by a program such as Telnet or FTP, they're working at the Application layer of the OSI model.

Let's take a look at the Presentation layer.

Layer 6 of the OSI model is the Presentation Layer. While we don't have a great deal of interaction with this layer, you need to know what happens at this layer to pass your Intro and CCNA exams.

The main purpose of the Presentation Layer is making sure that the communication that will be seen at the Application Layer is presented in the appropriate format.

That's all well and good, but what does it mean? J Have you ever opened a document with MS Word and gotten screens and screen of garbage? That's a presentation layer problem – the program being used to open the document is unable to present the data in an appropriate format.

The three major tasks of the Presentation layer:

1. Compatibility with the operating system.

2. Proper encapsulation of data for network transmission.

3. Data Formatting (ASCII, binary)

Encryption and compression of data is also handled at the presentation layer.

Let's keep working our way down the OSI Model. Next up, the Session Layer!

The Session layer of the OSI model basically acts as the manager for the entire model. Some have called it the PHB (Pointy-Haired Boss) of the OSI model if that helps you remember its role, that's fine with me!

The Session layer establishes, manages, and tears down connections between applications. The Session layer uses port numbers to keep multiple conversations between two end points separate. You may have heard the term well-known port-numbers before. That term refers to port numbers that are often-used and static in that they use the same port numbers every time. You'll be expected to know common well-known port numbers to pass your Intro exam, such as 23 for Telnet and 21 for FTP.

That's about all there is to Layer 5, the Session Layer. From here on out, there's more you need to know about each layer, and that starts with Layer 4 – the Transport Layer. We'll take a look at that layer in Part II of this OSI tutorial.

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage. The Bryant Advantage offers dozens of FREE CCNA and CCNP tutorials and articles. The Bryant Advantage sells the world's most comprehensive CCNA Study Guide in the world, and is the ONLY company specializing in CCNA and CCNP rack rentals, allowing candidates for these certifications to gain vital hands-on experience with full racks of Cisco routers and switches with labs and prices designed just for them. Visit his site at http://www.thebryantadvantage.com today!

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To learn more about Telepresence, the revolutionary new style of immersive video conferencing; visit these websites:

Telepresence - "Ride on the Next Plane of Existence" - Telepresence
Telepresence Web Portal - Telepresence Internet web portal
Telepresence Report - 24/7 breaking Telepresence related news and information
Via Telepresence - Video conferencing via Telepresence
Telepresence Forum - Free user discussion forum for everything Telepresence related
Telepresence Today - Telepresence information and editor qualified headline news
Telepresence Resource Directory - Telepresence web resource directory
Telepresence Tube - Telepresence videos, pictures and more