Welcome to TCP/IP Part 1

In Part 4 and Part 5 of the Internetworking series we brushed on the TCP/IP, DoD, and OSI Models that are used within internetworking communications, before going any further it would be wise to touch base on these subjects again and then carry on with the TCP/IP in more depth.

Internetworking Part 4

Now is a good time to introduce the networking reference models that permit the communications within our internetworking up through the previous sessions (Part 3).

In the beginning, most computers were only able to communicate with other computers from the same manufacturer.  In the 1970s the Open Systems Interconnection (OSI) reference model was created to overcome these communications problems.  There are other models  in use such as the DoD Reference and the Cisco Hierarchical Models, which we will discuss.

First, the OSI Model.  This is a reference model, or set of guidelines, that application developers can use in the creation and implementation of applications that run on a network, which provides a  framework within which network standards can be managed.

The OSI model has 7 distinct layers, which are divided in to two groups. The upper group (top 3 layers) define how the end-to-end host applications will communicate with each other.  The bottom group (bottom 4 layers)  define how the data is to be handles and transmitted between the hosts, end-to-end.  The top group are the Application, Presentation, and Session layers; the bottom group  The following operate at all seven layers of the OSI model:  Network management stations (NMSs); web and application servers; gateways (not default gateways); and network hosts.

The upper layers:  Application layer, Presentation layer, and the Session layer furnishes a user interface, “presents” data to the application layer, and maintains data separation between different applications.

The Application Layer:  This is where you (the user) has a direct connection to the computer by inputting data, or making requests.  This layer is also responsible for resolving the availability of communication and sufficiency of resources for data input.  The protocols associated with this layer are HTTP, FTP, and SMTP.

The Presentation Layer:  As mentioned before, this layer “presents” the data to the Application layer, which is where its name originates.  It is also in control of the data translation, code formatting and conversion functions (i.e., receives generically formatted data and converst it to its original format).  The protocols associated with this layer are ASCII, EBCDIC, JPEG, GIF, and MPEG.

The Session Layer:  This layer’s operation is to create, organize, and disassemble between Presentation layer components.  In essence, this layer can open many “seesions” and will keep all of those “sessions” and their respective data separate.

Internetworking Part 5

The lower layers, or the Transport Set, are for the transportation of the segments, packets, frames, and bits.

Transport Layer (Layer 4) provides for reliable or unreliable delivery and performs error correction before retransmit.  This layer segments and reassembles data into data stream by providing end-to-end  data transport service which creates a logical connection between the sending and destination hosts.

Network Layer (Layer 3) provides for logical addressing, which the routers use for path determination.  This layer manages device addressing, tracks the location of devices on the internetwork, and determines the best path available.

Data Link Layer (Layer 2) combines packets into bytes and bytes into frames, provides access to media using MAC address, performs error detection – not correction.  This layer provides for the transmission of data and handles error notification, topology of the network, and flow control.

Physical Layer (Layer 1) moves the bits between devices, specifies wire speed, voltage, and the pin-out of cable.  Sends and receives bits, some use tones, and others can use variations of voltage or signals

Data integrity is maintained through flow control whose purpose is to govern the amount of data sent by the sender.

Connection-Oriented Communication is where the transmitting device first creates a session with its peer system through a call setup, or three-way handshake.  The three-way handshake is a series of synchronization, negotiation, synchronization, acknowledgement, connection, and finally data transfer.


See also: Part 1, Part 2, Part 3

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1. Indianapolis: Cisco Press.

Internetworking Part 10

Cisco Three-Layer Hierarchical Model

This is the last part of the Internetworking series and we will move on to another area of Cisco CCENT/CCNA Certification.

We have been exposed to hierarchies all throughout our lives.  Hierarchies work within the human race as well as the electronic and computer fields…this is just how everything seems to work, meaning through a set and organized fashion.  Well, not so much with the human race, but you get the idea.

There are three layers to the Cisco Hierarchical Model, which essentially equates to a pyramid:

  • The core layer: backbone
  • The distribution layer: routing
  • The access layer: switching

Each layer has specific duties and responsibilities.

  1. The Core Layer, or the backbone, is truly the core of the network itself because it is responsible for the transporting of large amounts of traffic and must do it both reliably and quickly.  If there is a failure at the core, then potentially every user may be affected.  So, latency and and speed are a big concern to keep in mind.
  2. The Distribution Layer also referred to as the workgroup which provides routing.  This is the layer where all user data is processed which forwards requests if necessary.  The main function is to provide routing, filtering, WAN access and to determine how packets will access the core, if necessary.
  3. The Access Layer and is sometimes referred to as the desktop layer.  The network resources most users need will be available local to this layer.  Some functions are as follows:
  • Use of access control and policies, which are a continuation from the distribution layer
  • Segmentation or the creation of separate collision domains
  • Workgroup connectivity via the distribution layer

Though, I have not seen any reference to this 3 layer hierarchical model, as it is more than likely Cisco proprietary – because it is a Cisco test, it is testable.  But my personal & non-professional, opinion is that you will not see much of this outside of an all Cisco system.

See also: Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8, Part 9

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.


CCENT/CCNA Certification


Well, I have decided to follow a different path in preparing for the CCNA.  As I have already obtained my CCENT Certification using the Todd Lammle book for the single test CCNA 640-802, without too much difficulty…other than my own foolishness, etc…but I thought I would try the Wendell Odom books through Ciscopress, Official Cert Guides CCNA1 and CCNA2 (640-822 and 640-816 test).  Both authors are CCIEs and are very well qualified for the task.  But each test is structured differently; in-fact, there are certain things that are not on the single test method and are on the dual test method – which for a person such as myself could be an advantage by being introduced to those few items of study.  I have read both good and bad things about the books, but who is ever really a good critic.  Especially when you buy a book, as many of us do, and we mistakenly believe the knowledge will somehow magically be imparted upon us.  So, I will give it a try.  I have not made it past the first chapter yet, but I do like it’s layout so far.  Of course, it does help to skim through the book initially.  I felt it was a nominal investment in my future.

Network VisualizerUp until now, I have used a lab simulator program to play with the many interconnections between the Cisco Routers and Switches.




However, I thought it would be better to have a physical connection to the hardware by obtaining a Cisco CCNA Certification LabI felt it would be better, for me, to have hands on.  Sometimes I just don’t “get it” because I have no connection to what is actually going on.  That is probably one of my biggest problems.  Unlike the books, this will be a rather hefty investment, with a wide range of costs and options; ranging from $199-$1400+.