True VoIP should really be based on the SIP system which is the recognized standard.Any SIP compatible device can talk to any other; you don't even use a PC. Any SIPtelephone can call another right over the internet, you don't need any additionalequipment or even a phone provider. Just plug your SIP phone into the internetconnection, configure it and then dial the other person right over the internet. _In allVoIP systems, your voice is converted into packets of data, like little files, and thentransmitted to the recipient over the internet and decoded back into your voice at theother end. To make it quicker, these packets are compressed before transmission, a bitlike zipping a file.
Actual Cost of VoIP:
The promise of free international calls whenever you want them probably sounds alittle too good to be true – there must be a catch, right? Well, yes and no. Provided youonly wish to use VoIP to communicate with other VoIP users, everything is verystraightforward. If however you want to be able to use VoIP to make and receive callsto and from people who don’t have VoIP, you’ll need to subscribe to a gateway servicethat provides a bridge between VoIP and the conventional phone networks.
Getting Started with VoIP:
Getting started with VoIP could hardly be simpler. Assuming you already have the twomost important ingredients (a Windows or Mac computer and a broadband Internetconnection), all you need to get started is the following
Some free phone or messaging software.
Headphones or speakers (headphones are best because they won’tcause as much feedback).
Appendix K Answers to Checkpoints
1.12 The original value is overwritten.1.13 A compiler
is a program that translates source code into an executable form.1.14 Syntax
are mistakes that the programmer has made that violate the rulesof the programming language. These errors must be corrected before the com-piler can translate the source code.1.15 The Java compiler translates Java source code into byte code, which is an inter-mediate language. The Java Virtual Machine executes the byte code instructions.1.16 The Java Virtual Machine (JVM) is a program that reads Java byte code instruc-tions and executes them as they are read. In other words, it interprets byte codeinstructions. You can think of the JVM as a program that simulates a computerwhose machine language is Java byte code.1.17 The program’s purpose, input, process, and output.1.18 Before you create a program on the computer, it is often a good idea to imaginewhat the computer screen will look like while the program is running. If it helps,draw pictures of the screen, with sample input and output, at various points inthe program.1.19 A cross between human language and a programming language. Pseudocode isespecially helpful when designing an algorithm. Although the computer can’tunderstand pseudocode, programmers often find it helpful to write an algorithmin a language that’s “almost” a programming language, but still very similar tonatural language.1.20 A compiler
translates source code into an executable form.1.21 A runtime error is an error that occurs while the program is running. These areusually logical errors, such as mathematical mistakes.1.22 Syntax errors are found by the compiler.1.23 You can provide sample data and predict what the output should be. If the pro-gram does not produce the correct output, a logical error is present in the pro-gram.1.24 Data and the code that operates on the data.1.25 The data contained in an object.1.26 The procedures, or behaviors, that an object performs.1.27 Encapsulation refers to the combining of data and code into a single object.1.28 Data hiding refers to an object’s ability to hide its data from code that is outsidethe object. Only the object’s methods may then directly access and make changesto the object’s data. An object typically hides its data, but allows outside code toaccess the methods that operate on the data.