CHAPTER 2 |
13
INSTALLATION AND CONFIGURATION
Example Option 3: Service delivered over the Public Internet
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From the Internet Service Provider (ISP) we order a circuit to be delivered on Ethernet to be used to telephony only.
Bandwidth, jitter, and a Service Level agreement should be taken into account.
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From the Internet Telephone Service Provider (ITSP) we need to order a trunk with an adequate number of channels and
a block of DID numbers.
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From your distributor we order: (after a consultation with a Telos Applications Engineer)
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Appropriately sized Asterisk PBX machine with enough Ethernet ports
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Telos VX Enterprise or Prime+ Engine
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Telos xNodes if necessary
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Qualified Network switch for L audio if not existing or too small
Here’s how it this all works in practice once installed:
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A listener dials 311 555-2300 (your studios number).
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That number is recognized by Telco and is connected to a
virtual
(SIP) trunk to your facility across the public Internet.
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The telco connects to your Asterisk PBX over this connection and sends the DID number to the PBX on the far end of the Trunk.
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The PBX uses those digits to route the call further. (to the correct extension in most cases)
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The PBX rings the desired extension and causes ringback tone to be sent to the calling party until the called party answers.
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When the call is answered, a two-way audio path is cut through and the network is signaled that answer supervision
should be returned, charging the calling party of the call.
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When the call has ended, the stream is torn down and the customer billed.
If there was more than one appearance of the called extension on any particular phone (more line buttons), more calls could be
passed to that extension. This would continue until no more channels were available, or an artificial limit in the Asterisk PBX,
Trunk, or Telco would cause the “busy here” message to be sent back to the calling parties PBX or Central Office.
This means that:
1.
We can now build our own hunt groups
2.
We can change the hunt group size on the fly in most cases.
3.
It is critical to fully consider network engineering and security ramifications in design of the system because it’s delivered
as IP and we are fully responsible for the security risks and performance of the system.
Advantages: Probable lowest monthly cost. Instant provisioning. (short lead time if adequate Internet circuit is present at
the site already).
Disadvantages: Riskiest type of installation for security. Riskiest type of installation for performance.
Fully considering and planning for proper Network security is absolutely critical when attaching
anything to the public Internet. This cannot be overstated. If not handled correctly, huge bills from
service providers, interruptions in service and very embarrassing public hacking episodes could be in
your future. Your employer counts on you to minimize their exposure to fraud and embarrassment.
Please take this seriously. Telos can help. Discuss your implementation with an Applications Engineer
before system deployment.
