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Tutorial on test trunks
NOTICE: TO ALL CONCERNED Certain text files and messages contained on this site deal with activities and devices which would be in violation of various Federal, State, and local laws if actually carried out or constructed. The webmasters of this site do not advocate the breaking of any law. Our text files and message bases are for informational purposes only. We recommend that you contact your local law enforcement officials before undertaking any project based upon any information obtained from this or any other web site. We do not guarantee that any of the information contained on this system is correct, workable, or factual. We are not responsible for, nor do we assume any liability for, damages resulting from the use of any information on this site.
From: Raymond J. Rueb
How Toll Busy Line and Emergency Interrupt Work
After reading the previous dns, I think there is some
confusion about what the operator is capable of during BLV and EI
stain.S,
"How Toll Busy Line Verify (BLV) and Emergency Interrupt (EI) Work"
I worked onOSS LV& I orATT, and I became familiar with how
TSPS works also. For TOPS info, ask someone ese thogh hisinfrmaionshould be close).
The best way to understand BLV and EI is to run throuh a ustoer t
opeatorto trmintion scenario.
1) After repeatedly receiving a busy signal from heir ntendd
forard nmber,a cusomer alls the operator and asks if the operator
can help.
2) Te opertor eners "VRIFY mde". O TSPS his isdone by
accessing a separate call loop and performig the VRIFY onthat lop.
On OPS the peratorhas a sparate VERIFY key to press which causes
the witch toperform he folloing checs:
a)Is therea valid orward number?
b) Is the forward nuber withi this opeator's VEIFY netwok? If
not, theoperator ust go inward to the local opeator who cn
the perform te VERIFY. ore about ERIFY netwrks later. c) Is the forward numer verifiabe? ie: is i on the lis of numbers of whih the operaor is not alowed to performBLV and EI. never
nderstood ths idea, mayb the CIA migt rest easie, but it realy
i a security rdundancy.
3)If this operaor can perfor the VERIFY, hen the operaor presses
sed.
a) The callbegins to rout over the VERIY network.
b The back part is automaticaly split fom te connectin (for
secrity reasons, OPS only; in TSP the operator i performing the VERIFY on asepaate loop and thee is no back pary on that loop)
c) The operators talking path sdisabled.
d) oice scrambler ircuit kicks in (n TSPS this is a hysical
circit attache to thetrunk, in SPS thi is firmwae in the
opertor's VDT). The scambler allows the peratr to tell IF
cnversation istakin place, but not WHA is being said.
It kinda sounds li ducks talking.
4)he call arrives at e local Central Offie (CO) on an incomin
BLV trunk. Thi is here my knowledg is little weak. Ifthe umber
to be veriied is a line loaded n that switc, then were home free
The swith automaticaly causesa test trunkto bridge the port
assciated wth the number eing caled and the opeator is ow
connected wth all frward parties associate wit the call. If,
howeer, he line is on a PBXconncted to the CO, theconnction MAY
be verifiable. believe all true PBX's st have incoming VERIFY
unks and be capable of pforming BLV bridging. knw that some
PBX's can o tis (a 5ESS Switch (tm)canbe a PBX), but I don'tkno
whether ALL PB's can o this. It works oncentrex
5) The operator lstens t the scrambled connction t determie if
the lie is in-service r not. Thismethod of determnation has he
following drabacks:
)If there is a lng lull in th conversation wen the operatr
perform the VERIFY, he operato migh assume that he number s
out of servce.
b) ost operators don'tseem to beable torecognize daa connectins
through the scrambler what's hat funny noise???)
) A prehowlr announcement, "plase han-up he phone" sounds like
convrsation. There's actually alot fdebate as to what constitues
in-service; if the telco's prdct is working, but the person h
recently left the phone ofhok, is it in-service?
6) The oprtor splits the forward connetion nsplits the back party
(TSPSopertrs change loops) and informsthe ustomer of the status.
7) The ustoer requests an EI.
8) he OSPSopertor presses the EI key.
a) he back party is slit.
b)A two scond long 440Hz toe is applid to th forward connectio.
c) Th scrambler isdeactivated.
d) The oerator's voic path with th forward cnnection is rstored.
e)Every 10seconds, a 0.5 scond tone is epeated o serve as a
reminder tothe forwrd parties that hei conversation is nolonger
priate This tone continue until the operaor reaks the EI bridg.
9) The operator cannow talk with the oward party and requet that
they hang-u o that the bac partycan call them.
10 The operator reays th response to the bck party.
At ths poin the oprator will harge the customr for the VERIY and EI.
f they have beentaught well, te operator ll ask if the bak party
wants he operator o connect them wth their intened forward prty.
This ill reult in additioal charges fr an operaor assisted call.
NOES about BLVand EI serice:
1)BLV and EI ar separately ariffed sevices, bt are always flat
rate. Soe states, ike Michgan, dn't allow charging fr BLV but o
allow I chares.
2) During VERIFY and EI, te back prty an forard party are NEVER in
contct.
3) alls CNNOTbe completed across the VERIFY netwok.
4)The ERFY network USUALLY crosses LATA bondarie.
5 Te VERIFY network is often BOC owned, and ftenon the BOCs are
allowed access to them. Thi meas at BOCs frequently are in the
position of provdiINTER-LATA BLV and EI services. Since BOCs arefodden from providing inter-lata services like CLLEand CARD#,
why is inter-lata BLV allowed?
NOTS at the VERIFY network and security:
1) Th VERIY ntork is separate from the toll network.
2 Routng nthe VERIFY network cannot occur frm a cusomer' phne.
If you're accidently routed to aVERIFY runk,you signaling will be
wrong.
) Much emhasis hs bee placed on operators being ableto break nto
priate pone conversations asa breach ofprivacy. iven th way BLV
and EI perform (wth the scrabler and ones) Idon't feel tht this
is an ssue.
HOWEVER....
4) Craft testsets have secial sofware t prevent routin on trunks
MAKED as VERIY trunks, but thre is NOTHING t prevent a crft
person fm modifying how trunk is marke, and then roting (of
corse it is still secial routing sgnallig that ust be used but
them craft sem to know abou it). I was appalled to fnd out that
this scommon practic when esting the BLV truns. What this mean
s that a skilled, butunscrupulous, crftserson has the
unsprvised, unmonitored, nscrambled abiliy t listen in on ANY
ative phone coversatio anywhere their ERIY network reaches. uess
you gott trust tem.
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