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BLV is 'Busy Line Verification'. That is, discovering if a line is
busy/not busy. BLV is the telco term, but it has been called Verification,
Autoverify, Emergency Interrupt, break into a line, REMOB, and others. BLV is
the result of a TSPS that uses a Stored Program Control System (SPCS) called
the Generic 9 program. Before the rise of TSPS in 1969, cordboard operators
did the verification process. The introduction of BLV via TSPS brought about
more operator security features. The Generic 9 SPCS and hardware was first
installed in Tucson, Daytona, and Columbus, Ohio, in 1979. By now virtually
every TSPS has the Generic 9 program.
A TSPS operator does the actual verification. If caller A was in the 815
Area code, and caller B was in the 314 Area code, A would dial 0 to reach a
TSPS in his area code, 815. Now, A, the customer, would tell the operator he
wished an emergency interrupt on B's number, 314+555+1000. The 815 TSPS op who
answered A's call cannot do the interrupt outside of her own area code, (her
service area), so she would call an Inward Operator for B's area code, 314,
with KP+314+TTC+121+ST, where the TTC is a Terminating Toll Center code that
is needed in some areas. Now a TSPS operator in the 314 area code would be
reached by the 815 TSPS, but a lamp on the particular operators console would
tell her she was being reached with an Inward routing. The 815 operator then
would say something along the lines of she needed an interrupt on
314+555+1000, and her customers name was J. Smith. Now, the 314 Inward (which
is really a TSPS) would dial B's number, in a normal Operator Direct Distance
Dialing (ODDD) fashion. If the line wasn't busy, then the 314 Inward would
report this to the 815 TSPS, who would then report to the customer (caller A)
that 314+555+1000 wasn't busy and he could call as normal. However if the
given number (in this case, 314+555+1000) was busy, then several things would
happen and the process of BLV and EMER INT would begin. The 314 Inward would
seize a Verification trunk (or BLV trunk) to the toll office that served the
local loop of the requested number (555+1000). Now another feature of TSPS
checks the line asked to be verified against a list of lines that can't be
verified, such as radio stations, police, etc. If the line number a customer
gives is on the list then the verification cannot be done, and the operator
tells the customer.
Now the TSPS operator would press her VFY (VeriFY) key on the TSPS
console, and the equipment would outpulse (onto the BLV trunk)
KP+0XX+PRE+SUFF+ST. The KP being Key Pulse, the 0XX being a 'screening code'
that protects against trunk mismatching, the PRE being the Prefix of the
requested number (555), the SUFF being the Suffix of the requested number
(1000), and the ST being STart, which tells the Verification trunk that no
more MF digits follow. The screening code is there to keep a normal Toll
Network (used in regular calls) trunk from accidentally connecting to a
Verification trunk. If this screening code wasn't present, and a trunk
mismatch did occur, someone calling a friend in the same area code might just
happen to be connected to his friends line, and find himself in the middle of
a conversation. But, the Verification trunk is waiting for an 0XX sequence,
and a normal call on a Toll Network trunk does not outpulse an 0XX first.
(Example: You live at 914+555+1000, and wish to call 914+666+0000. The routing
for your call would be KP+666+0000+ST. The BLV trunk cannot accept a 666 in
place of the proper 0XX routing, and thus would give the caller a re-order
tone.) Also, note that the outpulsing sequence onto a BLV trunk can't contain
an Area Code. This is the reason why if a customer requests an interrupt
outside of his own NPA, the TSPS operator must call an Inward for the area
code that can outpulse onto the proper trunk. If a TSPS in 815 tried to do an
interrupt on a trunk in 314, it would not work. This proves that there is a
BLV network for each NPA, and if you somehow gain access to a BLV trunk, you
could only use it for interrupts within the NPA that the trunk was located in.
BLV trunks 'hunt' to find the right trunks to the right Class 5 End Office
that serves the given local loop. The same outpulsing sequence is passed along
BLV trunks until the BLV trunk serving the Toll Office that serves the given
End Office is found.
There is usually one BLV trunk per 10,000 lines (exchange). So, if a Toll
Office served ten End Offices, that Toll Office would have 100,000 local loops
that it served, and have 10 BLV trunks running from TSPS to that Toll Office.
Now, the operator (in using the VFY key) can hear what is going on on the
line, (modem, voice, or a permanent signal, indicating a phone off-hook) and
take appropriate action. She can't hear what's taking place on the line
clearly, however. A speech scrambler circuit within the operator console
generates a scramble on the line while the operator is doing a VFY. The
scramble is there to keep operators from listening in on people, but it is not
enough to keep an op from being able to tell if a conversation, modem signal,
or a dial tone is present upon the line. If the operator hears a permanent
signal, she can only report back to the customer that either the phone is
off-hook, or there is a problem with the line, and she can't do anything about
it. In the case of caller A and B, the 314 Inward would tell the 815 TSPS, and
the 815 TSPS would tell the customer. If there is a conversation on line, the
operator presses a key marked EMER INT (EMERgency INTerrupt) on her console.
This causes the operator to be added into a three way port on the busy line.
The EMER INT key also deactivates the speech scrambling circuit and activates
an alerting tone that can be heard by the called customer. The alerting tone
that is played every 10 seconds tells the customer that an operator is on the
line. Some areas don't have the alerting tone, however. Now, the operator
would say 'Is this XXX-XXXX?' where XXX-XXXX would be the Prefix and Suffix of
the number that the original customer requesting the interrupt gave the
original TSPS. The customer would confirm the operator had the correct line.
Then the Op says 'You have a call waiting from (customers name). Will you
accept?'. This gives the customer the chance to say 'Yes' and let the calling
party be connected to him, while the previous party would be disconnected. If
the customer says 'No', then the operator tells the person who requested the
interrupt that the called customer would not accept. The operator can just
inform the busy party that someone needed to contact him or her, and have the
people hang up, and then notify the requesting customer that the line is free.
Or, the operator can connect the calling party and the interrupted party
without loss of connection.
The charges for this service (in my area at least) run 1.00 for asking the