Cisco CCENT - CCNA Certification Exam Training - Introduction to the OSI model

As network administrators, we are going to be primarily interested in the first three layers of the OSI model - but for the CCENT and CCNA exam, we need to be involved all seven!

The OSI layers are often referred to by numbers, with the layer of application being level 7 ("L7"), the presentation layer being Layer 6, and so on until the end of the level 1, the physical layer. To get you used to this, I will refer to the layers with their names and numbers of all these tutorials.

The application layer

This is the layer in which the end users themselves interact with the network. Authentication services also operate at Layer 7.

Protocols and services that run at L7 include:

Email POP3 and SMTP protocols

Telnet

HTTP

File Transfer Protocol (FTP)

Simple Network Management Protocol (SNMP)

The presentation layer

This layer responds to one simple question: "How should this information be presented?" In addition to properly formatting the data, encryption occurs at this level.

The session layer

Level 5 is the "manager" of the bidirectional communication between two remote hosts. This is the level which manages the establishment, maintenance and teardown of communication between these two hosts.

The Transport Layer

TCP and UDP, both running at the transport layer, and we got to know both protocols in and out to pass the CCNA and CCENT exams. We will see in those protocols in a future tutorial.

The network layer

And 'at level 3 of the OSI model that you and I, as network administrators are beginning to have a great deal of interaction with the network. Internet Protocol (IP) works at this level, and since the routers operate here to L3, this layer is often called "the layer of routing".

In a nutshell, the routing is a process of two questions:

That there are valid paths from the local router to a particular destination?

What is the best way to go to get there?

The Data Link Layer

Switches operate at Layer 2, as well as wireless access points (WAP). We have four main features that run here, some of which may already be familiar with:

Ethernet

Data at high Link Control (HDLC)

Point-to-Point Protocol (PPP)

Frame Relay

The physical layer

When things get a bit 'complicated network, I like to remind myself that "it's all ones and zeroes!" Whatever the data of our users are creating, eventually is going to be "translated" into a series of 1 and 0. Once that is done, is the physical layer that handles the actual data transmission. Nothing to do with a physical cable - the pin connectors, the electrical current itself - is running at the physical level .......