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A class is a description of the data and processes of an object. The class’s declaration establishes the attributes that each of the objects of the class will have, and the methods that it can invoke.
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-If it isn't specified otherwise, the attributes and methods defined in a class will be private. This means that the variables can only be accessed and changed by the methods of the class (*constructors*, *setters*, and *getters*, among others).
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+The attributes and methods of a class can have one the following levels of access: private, protected and public. An object's **public** data members can be read or modified by any function that has access to the object (including external functions). An object's **private** data members can only be read or modified through the object's **member** functions . Unless specified otherwise, the attributes and methods defined in a class will be **private**. Protected members allow read/write access from member functions and those of inherited classes.
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The following is the skeleton of the declaration of a class:
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The Internet packets must also specify the application that is sending the information and the application that must receive it. We can think of the Internet addresses like home postal mail addresses, and that the applications that send and receive the information are the persons that send and receive postal letters. To send a letter via postal mail, the recipient of the letter must be specified. This corresponds to the application that receives the information. To identify the source and destination application, the Internet protocol uses what is known as *port numbers*. This way, looking the packet information, the source and destination addresses and ports can be identified.
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-For instance, when your lab computer communicates with the server for Moodle, the packets that carry the information from your computer to the web server contains the source address, which is the address of the lab computer, and the destination address which is the Moodle server. The source port is the port of your web browser and the destination port is the port of the Moodle web server.
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+For instance, when your lab computer communicates with the Moodle server, the packets that carry the information from your computer to the web server contain the source address, which is the address of the lab computer, and the destination address which is the Moodle server. The source port is the port of your web browser and the destination port is the port of the Moodle web server.
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-The Internet addresses occupy 4 bytes (32 bits), and usually are presented to users as strings of 4 decimal values. Each decimal value between 0 and 255 is the decimal representation of one of the 4 bytes: "(0-255).(0-255).(0-255).(0-255)". Some examples of IP addresses are: `10.0.1.10`, `192.168.10.11`, `136.145.54.10`.
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+Internet addresses occupy 4 bytes (32 bits), and usually are presented to users as strings of 4 decimal values. Each decimal value between 0 and 255 is the decimal representation of one of the 4 bytes: "(0-255).(0-255).(0-255).(0-255)". Some examples of IP addresses are: `10.0.1.10`, `192.168.10.11`, `136.145.54.10`.
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-Port numbers are composed of 2 bytes or 16 bits. Therefore port numbers range from 0-65535. There are ports numbers assigned to known application services such as number 22 for ssh, 23 for telnet, 25 for smtp, 80 for http, and so on.
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+Port numbers are composed of 2 bytes or 16 bits and range from 0-65535. There are ports numbers assigned to known application services such as number 22 for ssh, 23 for telnet, 25 for smtp, 80 for http, and so on.
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-To complicate things a little bit, each computer network card has an unique identifier that is used for the communication between you computer and the network device that routes the network traffic from the Internet and local network to your computer and vice-versa (*Ethernet protocol*). This unique identifier is known as the Hardware address (a.k.a *Multiple Access Controll (MAC) address*), is represented using 6 bytes (48 bits), and is presented to the users as strings of 6 hexadecimal values (each pair of hexadecimal digits corresponds to 1 byte). Each hex value is the hex representation of the 6 bytes: "(00-ff):(00-ff):(00-ff):(00-ff):(00-ff):(00-ff)". Some examples of MAC addresses are: `e0:f8:47:01:e9:90` and `70:ad:60:ff:fe:dd:79:d8`.
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+To complicate things a little bit, each computer network card has an unique identifier that is used for the communication between your computer and the network device that routes the network traffic from the Internet and local network to your computer and vice-versa (*Ethernet protocol*). This unique identifier is known as the Hardware address (a.k.a *Multiple Access Controll (MAC) address*), is represented using 6 bytes (48 bits), and is presented to the users as strings of 6 hexadecimal values (each pair of hexadecimal digits corresponds to 1 byte). Each hex value is the hex representation of the 6 bytes: "(00-ff):(00-ff):(00-ff):(00-ff):(00-ff):(00-ff)". Some examples of MAC addresses are: `e0:f8:47:01:e9:90` and `70:ad:60:ff:fe:dd:79:d8`.
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+!INCLUDE "../../eip-diagnostic/simple-sniffer/en/diag-simple-sniffer-02.html"
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+<br>
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+---
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## Laboratory Session:
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