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75 lines
3.3 KiB
Twig
Executable File
75 lines
3.3 KiB
Twig
Executable File
id: how
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layout: default.twig
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title: How it Works
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---
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<p>
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In the simplest configuration, EnvayaSMS only needs to be installed on one phone.
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Suppose that you have installed EnvayaSMS on an Android phone in Dar es Salaam,
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Tanzania, with phone number <code>+255987654321</code> (local number <code>0987654321</code>),
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with GSM service from Vodacom.
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</p>
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<p>
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Suppose also that your web server is <code>example.com</code>, and its servers are located in a datacenter in London.
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</p>
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<p>
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In Dar es Salaam, you would put the Android phone in an office with internet access and a Wi-Fi router,
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and connect the phone to the Wi-Fi network. (Wi-Fi is not strictly necessary, since EnvayaSMS will also
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work over the phone's mobile data connection, but Wi-Fi is likely to be faster, cheaper, and more reliable.)
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</p>
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<p>
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Then your network would look like this:
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<br />
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<img src='/media/topology.png' width='650' height='262' />
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</p>
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<p>
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Typically your organization will need only one phone running EnvayaSMS in a
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particular country. However, it is possible to use multiple phones to load-balance requests
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for higher throughput, to offer different user services, or to serve different mobile networks.
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</p>
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<h3>Receiving incoming SMS and sending replies</h3>
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<p>Here is an example of how EnvayaSMS would forward an incoming SMS to your server, and send a SMS back as a reply:</p>
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<ol>
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<li>User in Tanzania, using Nokia phone with phone number <code>0555551234</code>, sends SMS message to <code>0987654321</code></li>
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<li>Your Android phone at <code>0987654321</code> receives SMS</li>
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<li>EnvayaSMS sends SMS to <code>example.com</code> via HTTP</li>
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<li>example.com processes the message and returns SMS reply in HTTP response</li>
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<li>EnvayaSMS forwards SMS reply to <code>0555551234</code></li>
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</ol>
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<p>
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Since users generally are charged only for outgoing messages in Tanzania, the user would be charged
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for sending one local SMS message, and your phone would also be charged for sending one local SMS message.
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</p>
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<h3>Sending outgoing SMS notifications</h3>
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<p>EnvayaSMS uses a different process to send SMS notifications that were not in response to an incoming message.</p>
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<p>Assume now that <code>example.com</code> has multiple phones using EnvayaSMS in different countries,
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and it is configured to send all messages to phone numbers with a <code>255</code> prefix (Tanzania's country code)
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via the cell phone with number <code>+255987654321</code>.
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<ol>
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<li><code>example.com</code> wants to send an SMS message to <code>+255555551234</code></li>
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<li><code>example.com</code> identifies that the recipient number has a <code>255</code>
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prefix, and chooses sender phone number <code>+255987654321</code></li>
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<li>The next time EnvayaSMS polls <code>example.com</code> for queued outgoing messages
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for its phone number <code>+255987654321</code>, the server responds with
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the message to send
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</li>
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<li>EnvayaSMS forwards the message to <code>0555551234</code></li>
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<li>EnvayaSMS notifies <code>example.com</code> via HTTP that message was sent</li>
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<li><code>example.com</code> removes the SMS message from its queue of outgoing messages.</li>
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</ol>
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<p>
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In these examples, even though SMS messages are being communicated between Dar es Salaam and London,
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all SMS messages are sent domestically and are not charged as international SMS messages.
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</p> |