We began this chapter with a look at the importance of network models, including the reasons for their modular nature. A look at the OSI model stressed the importance of understanding the concept of layered communication, protocol data units, and the functions of each layer. Do not underestimate the importance of remembering not only the […]

When it comes to network design, you’re pretty much left with two options – a flat design, or one that involves some type of hierarchy. A flat design can be very limiting in terms of performance and scalability, and in all but the smallest networks would not be recommended. For example, on a flat network […]

The primary reason for looking at any network model is to better understand how systems communicate. In real-life, network communication requires that data be encapsulated by the sender, transmitted over the network, and then de-encapsulated by the receiver. This is best illustrated by looking at what happens when one system running TCP/IP sends data to […]

The Department of Defence TCP/IP model is a 4-layer model that defines areas of responsibility much like the OSI, while providing insight into the functions of the different protocols that make up the TCP/IP suite. The model provides an excellent point of reference when compared to the OSI. We won’t look at all the details […]

The Physical layer of the OSI model is concerned with the electrical, optical, and mechanical properties of the network, including elements such as voltage, media, connector types, signal regeneration, and so forth. The physical layer doesn’t actually alter packets, but rather acts as the transmission facility over which the actual bits (1’s and 0’s) are […]

The Data Link Layer of the OSI model acts as an interface between the Network and Physical layers. The main responsibilities of the Data Link layer include:

Data framing and physical addressing. When data is passed to the Data Link layer, it is framed for transmission using various LAN and WAN protocols. This allows network protocols […]

The Network layer of the OSI model is commonly referred to as Layer 3, and has the following responsibilities:

Routing. When a host on one network wishes to exchange data with a host on another, packets will be sent to a router interface. After determining where the packet should be forwarded next using information found in […]

The Transport layer has three main responsibilities in terms of the exchange of data between systems. These include:

Data segmentation.
Establishment of end-to-end connections between hosts.
Using flow-control mechanisms to ensure that data is sent at rates that the receiver can handle.

Data Segmentation
At any given point in time there may be many applications passing data down to the […]

The Session layer is responsible for the creation, management, and termination of sessions between systems. A session is best described as a type of managed connection between systems for the purpose of a specific type of communication. For example, a session might be created for the purpose of user authentication, or to initiate a file […]

The Presentation layer is primarily responsible for data representation and formatting, ensuring that data can be viewed correctly. These formats are sometimes referred to as the “data syntax” of the applications in use. For example, different systems may use different schemes to represent data. While one system might use ASCII or EBCIDC, another might use […]