98 lines
4.7 KiB
Plaintext
98 lines
4.7 KiB
Plaintext
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/-/ Understanding PBX Systems /-/
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Presented by Brainstorm Elite
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Computer Based PBX
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To get a better understanding of what a PBX can do, here are a few basic
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fundamentals. The modern PBX is a combined computer, mass storage device, and
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of course a switching system that can:
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{1} Produce itemized,automated billing procedures, to allow the
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identification and management of toll calls.
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{2} Combine daytime voice grade communication circuits into
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wideband data channels for night time high speed data transfers.
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{3} Handles Electronic Mail {including office memos}.
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{4} Combine Voice channels into a wideband audio/visual conference
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curcuit, with the ability to xfer and capture slides, flipcharts, pictures
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of any kind.
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Both the external and internal calling capacity of the PBX System must be
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carefully considered because many business operations run a very high ratio of
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internal station to station dialing and a low capacity system will not handle
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the requested traffic load.
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A critical factor is the number of trunks and the Central Office Facilities
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that are used for outside connections. Another is the number of junctions or
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{links} that make up the internal calling paths.
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To understand the services available on a typical computer run PBX it is
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necessary to introduce the subject of time division switching. In a time
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division switching network all connections. Called (of course) a
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time-division bus.
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Every line trunk that requires a connection with another is provided
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with a port circuit. All port circuirs have access to the time division bus
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through a time division switch.
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[When two ports require connection,their time division switches operate at
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a very high frequency (16,000 times per second). This technique, which is
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called 'speech sampling', allows many simultaneous connections over the same
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time division bus.
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The next critical item is circuit PACKS. The system elements that we will be
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describing in future tutorials {lines/trunks/switches,memory and control} are
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contained on plug in circuit packs. Each line circuit pack contains a number
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of lines, in example, four. But tha assignment of station numbers to actual
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phone line circuits is flexible.
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The system memory is contained in circuit packs which provide the call
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processing functions. The circuit packs are held in small frames called
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'carriers'. Within each carrier, the circuit packs are plugged into positions:
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the 'slots'. Every circuit can be addressed by, say a five digit number which
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tells its location by carrier-slot-circuit.... {starting to get the idea?}
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There can be three types of carriers in a modern PBX system:
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o Line Carriers
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o Trunk Carriers
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o Control Carriers
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The line carriers contain station lines. In AT&T's "Dimension" model, for
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example, a total of 52 to 64 lines are provided. The trunk carriers contain
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slots for 16 trunk circuit packs. The control carrier includes processor,
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memory, contvol circuitry, data channels for attendant console control and
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traffic measurement outputs.
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PBX Systems will directly reflect the types of services offered at the C.O.
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o CCSA
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o CCIS
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o Picturephones {sooner than you tlink my phriends}
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Common Control Switching Arrangements ( CCSA ) permit any unrestricted tele-
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phone station to call any othet internal or external system station by using
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the standard seven digit number. Alternate routing is a feature of CCSA service
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The interfacility, alternate routed calling paths are accomplished at the
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telephone company central office level, not at the PBX level.
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A system of interest to large scale telephone users is Common Channel Inter-
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office Signalling (CCIS). Ty0ically, this technique employs common channels to
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carry all interfacility signalling instructions: dial pulses, on hook (idle),
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off hook (busy), and so on, between two switching centers. { getting warm }.
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CCIS replaces older methods of interoffice signalling such as 'in band' and
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'out of band' techniques. By the way, real phreaks are selling their boxes
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to idiots who still think the're worth a lot...The former (in band) transmits
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signalling data within the normal conversation bandwidth. It's shortcoming is
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that false information may be transmitted due to unique tone or noise
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combinations set up in the talking path. {this is the official reasoning}
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Out of Band signalling techniques placed the interoffice data in special
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channels, generally adjacent to and immediately above the voice path. To pre-
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serve interchannel integrity,out of band signalling requires very effecient
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filtering or greater 'band guard' seperation between channels.
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** Brainstorm Elite 612-345-2815 **
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