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|| Incoming Trunk Service Observing ||
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||            Written by            ||
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][          The Egocutioner         ][
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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 service 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 hierarchy 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 fro 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 only 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 received 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 receive this signal within a period of
 time after being enabled, a RELEASE message is transmitted be the SES.

       2. RELEASE ACKNOWLEDGE- 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 Xmitted when the interface returns
too the idles 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 progress message indicates that recorder 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 state to
which the interface returns after tests and completing observations.

        o Active- This state is entered only when the ESS switch receives an
ENABLE message from the SES. Service observing is performed in this state.
This state is maintained for no more 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

