85 lines
2.7 KiB
HTML
85 lines
2.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>VoIP Howto: Communications using PSTN line</TITLE>
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<A HREF="VoIP-HOWTO-9.html">Next</A>
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<A HREF="VoIP-HOWTO.html#toc8">Contents</A>
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<HR>
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<H2><A NAME="s8">8. Communications using PSTN line</A></H2>
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<H2><A NAME="ss8.1">8.1 Overview</A>
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</H2>
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<P>VoIP becomes very interesting when you start to use PSTN lines
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to call other people in the world, directly to their home telephone.
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<H2><A NAME="ss8.2">8.2 Scenario</A>
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</H2>
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<P>A typical application is like that:
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<P>
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<PRE>
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Home telephone1 -- (PSTN) -- PC1 -- (Internet) -- PC2 -- (PSTN) -- Home telephone2
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</PRE>
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<P>
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<OL>
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<LI>Home Telephone1 make a calls to PC1 phone number (using PSTN
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line, I mean classic telephone line).</LI>
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<LI>PC1 answer to it.</LI>
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<LI>Home telephone1 must tell PC1 what gateway use (PC2 in this case)
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by giving the IP address (from DTMF keyboard) and/or what number
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call (in this case Home telephone2).</LI>
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<LI>After that PC1 will start to make an H323 call to PC2, then it
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will pass Home telephone2 to PC2 to make it call it throught PSTN
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line.</LI>
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<LI>Home telephone2 answers to call and communication between Home
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telephone1 and Home telephone2 begins.</LI>
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</OL>
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<H2><A NAME="ss8.3">8.3 What can be changed in this configuration? </A>
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</H2>
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<P>
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<OL>
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<LI>You may use a PBX to select many lines to access many PC1 gateway
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(for example one to call within your state, one to go accross Europe,
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and so on...): typically you don't have to change this, cause cost
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is always the same.</LI>
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<LI>You can select (after called your PC1 gateway) every PC2 you
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want (for example a PC2 living in England to call an English person
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so that you'd pay only intra-country costs).</LI>
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</OL>
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<P>So your decision will be taken considering PSTN line costs. In
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fact what VoIP does is the convert this:
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<P>
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<PRE>
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Home Telephone1 --- (PSTN) --- Home Telephone2
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PSTN great distance calling cost
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</PRE>
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<P>into this:
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<P>
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<PRE>
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Home Telephone1 --- (PSTN) --- PC1 +
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PC2 ---- (PSTN) --- Home Telephone2 =
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--------------------------------------
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2 PSTN short distance calling costs
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</PRE>
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<P>To save money you need that:
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<P>
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<PRE>
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2 PSTN short distance calling costs < PSTN great distance calling cost
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</PRE>
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<P>Typically "short distance calling" refers to a "city cal" while "great
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distance calling" can be an "intercontinental call"!
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