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|| Incoming Trunk Service Observing ||
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||            Written by            ||
][          The Executioner         ][
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||    [+] PhoneLine Phantoms [+]    ||
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    The ITSO (Incoming Trunk Service Observing) feature provides the
ability to perform service observing on incoming 2-wire trunk [per
trunk signalling or CCIS]. The ITSO feature provides a method to
determine how effectively the telefone system serves the customer.
This assists the telefone co. in maintaining network quality.
    
    The intent of servince observing is to evaluate the completion
performance of the office's subtending networks. All calls selected
for observation must originate from offices of equal or higher rank
in the toll heirarchy and must terminate in the area served by the
toll office. The ESS switch randomly selects calls for observation.
Only one call can be monitored at any given time for the ITSO
feature. Equipment malfunctions, network overloads, or other problems
preventing call completion are detected. The calls are also directly
monitored for transmission quality. Each service observing position,
located in the SES (Service Evaluation System) bureau is capable of
monitoring calls.
 
    The information required by the service observer is provided to
the SES bureau from the ESS switch via a dedicated data link and a
voice monitoring channel. A 1200 baud data link is used to transmit
call progress data and control signals between the ESS switch and the
SES bureau. The dedicated one-way voice channel is required for
monitoring voice transmission. The interface is capable of monitoring
one call at a time.
 
     The SES has complete control over the SES/ESS interface. The
observing feature is a demand system where the demand originates with
the SES. There are 5 possible control messages that the SES can send
to an ESS switch.  They are:
 
   1. ENABLE- This message is accepted when the interface is in the
idle state.  It directs the ESS switch to obtain the next observable
call.
 
   2. RELEASE- This message is used to release the present call and
return the interface to the idle state or to release the present test
and return to idle state.
 
   3. TONE TEST- This message is used ony if the interface is in the
idle state. It causes a 1-milliwatt tone to be applied to the voice
channel.
 
   4. TERMINATION TEST- This messages is only accepted if the
interface is in the idle state. It causes a quiet termination to be
applied to the voice channel for 30 seconds (unless a RELEASE order
is sent).
  
   5. DATA ECHO TEST- This message is accepted only if the interface
is in the idle state. It sends a message to the ESS switch to verify
the sanity of the data channel. The ESS switch appends a unique
2-character header to the received message and outputs the recieved
message to the data channel.
 
   There are 15 potential call progress messages that the ESS switch
can generate and send to the SES. They are:
 
   1. SEIZURE- This message indicates that the ESS switch has found a
candidate call. If the SES does not recieve this signal within a
period of time after being enabled, a RELEASE message is transmitted
be the SES.
 
   2. RELEASE AKNOWLEDE- This message is transmitted whenever the ESS
switch decodes a RELEASE signal deo the SES. The interface returns to
the idle state and the SES is allowed to attempt to observe a new
call.
 
   3. TERMINATION- This message is Xmited when the interface returns
to the idle state due to an abnormal ending of the call observation
in progress, or when the tone or termination test times out.
 
   4. INCOMING TRUNK DISCONNECT- This message is Xmitted to the SES
for every calling party on on-hook occurrence.
 
   5. ON-HOOK- This message is Xmitted to the SES for every called
party on-hook occurrence.
 
   6. OFF-HOOK- This message is xmitted to the SES for every called
party off-hook occurrence.
 
   7. EMERGENCY- This message indicates an emergency announcement is
being applied to the calling party.
 
   8. 60 IPM- This call progress message indicates that the busy tone
is being applied to the calling party.
 
   9. 120 IPM- This call progess message indicates that recoreder
tone is being applied to the calling party.
 
  10. NO CIRCUIT AVAILABLE- This call progress message indicates that
a no circuit available is being applied to the calling party.
 
  11. VACANT CODE ANNOUNCEMENT- This message indicates that a vacant
code announcement is being applied to the calling party.
 
  12. RECORDER- This message indicates that a recorder announcement
is being applied to the calling party.
 
  13. AUDIBLE RING- This message indicates that audible ringing is
being applied to the calling party. In the case of a locally
terminating call, the observer is not bridged onto the call until
after answer and is therefore unable to detect the actual audible
ringing.
 
  14. CALLED NUMBER DIGITS- This message contains the called number
of digits.
 
  15. DATA ECHO TEST- This contains the DATA ECHO TEST message.  {
The 4 states of SES/ESS interface are as follows:
 
        o Idle- This is the wait state of the interface. It is the
stae to which the interface returns after tests and completing
observations.
 
        o Active- This state is entered only when the ESS switch
recieves an ENABLE message frm the SES. Service observing is
performed in this state. This state is maintained for no moe than 3
minutes (2-wire trunks) after seizure.
 
        o Tone Test- This can only be entered from the idle state
upon receipt of a tone test order. In this state, a 1- milliwatt tone
is applied to the voice channel. The interface returns to the idle
state upon the RELEASE message or after a 30 second test.
 
        o Termination Test- This state can only be entered from the
idle state upon the TERM. TEST message. In this state a quiet term.
is applied to the voice channel. The interface returns to the idle
state upon the RELEASE or after 30 secs.
 
     Action to establish an observation is initiated when the SES
send an ENABLE message to the ESS switch. This message triggers the
switch to begin looking for an observable call. When the switch has
found a call, the SEIZURE and CALLED NUMBER DIGITS messages are
transmitted to the SES.
 
     From this point on, the SES observes the progress of the call
using the progress messages.
 
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=All sysops are allowed to put this =
=file on their BBS's.               =
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(C) 1985 Sexy-Exy & PLP          
 
Dedicated to Christi and Linda.
 
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