Ethernet, Hub & Switch Applets
   


Introduction


Theoretical Background

Components of the applet

Ethernet

Hub

Switch

Start the Ethernet applet  
 

Start the Hub applet  
 

  Start the Switch applet  
 


Basic knowledge about Ethernet

Ethernet technology predates the Institute of Electrical and Electronics Engineers (IEEE) LAN standards committee. Therefore, the first Ethernet standard was developed by a vendor consortium made up of Digital Equipment Corp. (DEC), Intel, and Xerox. Taking the first initial of each company, the first Ethernet standard became known as the DIX Standard. This was the first open standard for LAN technology ever published.

Two versions of the DIX standard were proposed and the IEEE 802 committee made the creating of open standards for LANs one's job. The first “Ethernet-like” IEEE standard was published in 1985 and formally called the “IEEE 802.3 Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer” specifications. The Ethernet system consists of three basic elements:

  • The physical media used to carry Ethernet signals between computers.
  • A set of media access control rules embedded in each Ethernet interface that allow multiple computers to access the shared Ethernet channel.
  • An Ethernet frame that consists of a standardized set of fields used to carry data over the system.

    Ethernet uses a bus topology, which is a networking architecture that is linear, usually by using one or more pieces of cable (Bus Element) to form a single line (Bus Segment), or bus. The signals (Signal) sent by one station (Host) extend the length of this cable to be heard by other stations. Taking this into account and doing a first level decomposition of the IEEE 802.3 (CSMA/CD) Protocol, following components can be identified:


Components
 

Component

Symbol

Description

Host

 

Represent a computer that access the shared Ethernet channel.

Arrow

 

Represent the data flow within a host. A sender is represented through a down directed arrow, while a receiver is represented through a up directed arrow.

Bus Element

 

Represent the smallest entity of the ethernet channel.

Signal

 

Represent the state of the ethernet channel. Blue means normal transmission, red means a collision, while yellow means padding.

Bus Segment

 

Is composed out of several bus elements. Each bus segment has four I/O possibilities: top, bottom, left, and right. A bus segment is traversed by the signal.


Ethernet
 

Each of these components has been developed as a JavaBean. These components are the basic elements to implement an applet visualizing the diverse functionality of Ethernet. The visualization window is divided into three main areas according to the iTBeanKit:

  1. the “MainPanel”, where the hosts are connected to the bus and the animation takes place
  2. the “ParameterPanel”, where some of the interaction parameters can be adjusted, and
  3. the “TextArea” where the textual explanation of the animation can be drawn, in order to facilitate the understanding.

In addition to these three panel, the VCR, and the menu can be seen. In the VCR we notice two disabled buttons, which means that the interaction with them is not possible. This is either because the functionality is not implemented, or it does not make sense to use this buttons in the context, within which the applet is integrated.

 

    Start the applet  
     


Hub
 

The same basic elements were used for the implementation of the applet visualizing the functionality of a Hub.

A Hub is a central device that connects stations following a star topology as an architecture. Signals sent by a station must pass through (and are usually regenerated by) these central Hubs. Since all stations are linked through the Hub, the architecture resembles a star.  only difference to the Ethernet applet described above, from the software engineering and reusability point of view was the controller unit, which implemented the logical structure that connect the diverse components.

    Start the applet  
     


Switch
 

As an alternative to the Hub, Switch is an option to be taken into account. It optimizes connections with the whole bandwidth for all hosts. Its installation causes no big trouble as one has only to take the cables out of the old Hub and install them instead in the Switch. One has to take also the fact in consideration that Hubs are far less expensive than Switches are. The data transmission between two hosts generates traffic only in it's correspondent segment and not in the whole channel. Bandwidth is not shared, so every single host has 100% bandwidth towards the Switch.

From the functionality point of view, a Switch can be seen as a learning Hub. As soon as a Switch receives a data package it learns the direction of the source host from which the data package came. The data packages wanted to be sent next time to that host will be directed to the port of the host, which the Switch learned from the previous data received. We find out that a Switch operates as a Hub when it has no information. We may also say that a Hub is a non intelligent Switch. This memory has an “ageing time”.

 

 

    Start the applet