ATT System 25 Reference Manual

							Coverage, Group
terminal. If there is no idle Cover button on any covering terminal, either individual or group,
the call will not receive coverage and the calling party will receive Busy Tone.
Calls sent to coverage will continue to ring at single-line sender terminals but will cease
ringing at multiline sender terminals.
In the latter case, the calls will remain on the incoming
call appearance button, and that button’s status LED continues to reflect the status of the
call. In particular, covered calls to multiline sets remain available and can be entered by the
called (sender) station.
If a covered station activates the Send All Calls feature, calls will be directed to coverage
immediately, with or without a single-ring reminder, as administered.
A station can provide (or receive) Individual Coverage (see Coverage, Individual) and also be
a member of a Coverage Group (sender or receiver).
Unanswered calls to a station,
provided both Individual and Group Coverage, will first ring at the Individual Coverage station
and then, after a second delay cycle and still unanswered, will ring at the Group Coverage
station.
Calls from a covering station to a covered station will not be covered unless the covered
station has additional coverage.This is an important consideration when the attendant
provides coverage.
DGC Group Coverage
Calls proceeding to the DGC Coverage Receiver Group hunt in a circular fashion for the first
idle station, starting from the last station to receive a call. If all DGC members are busy,
both internal and external calls continue to ring and/or flash at the covered station and any
individual coverage receiver’s station(s) until a DGC station becomes idle. If a DGC group is
used for both DGC calls and group coverage, trunk calls into a DGC group have priority over
coverage calls.Calls sent by coverage to a DGC Coverage Group member station do not
receive additional coverage.
DGC groups cannot be coverage senders to another DGC Coverage Group. However, calls
made directly to a DGC member can be covered by another DGC Coverage Group.
Once a call has been redirected to a DGC Coverage Group member, the call is transferred to
the covering station.The call continues ringing until answered or dropped. The call is not
accessible at the covered station nor any individual coverage receiver once it is redirected to
an idle DGC station.If all DGC members are busy, the call remains accessible at the
covered station until a member is available.
DGC Coverage Groups count against the system specified maximum number of DGC groups,
but not against the number of Coverage Groups.The limit of eight receiving stations per
Coverage Group does not apply when administering a DGC group as a Coverage Group. A
maximum of twenty stations per DGC Coverage Receiver Group is allowed.
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							FEATURES AND SERVICES
Considerations
Coverage provides a way to redirect calls to alternate answering positions. The feature is
versatile enough to permit suitable alternate answering arrangements for virtually every level
of employee.Special functions, such as the Send All Calls feature, accommodate the day-
to-day variations that occur in an employee’s work schedule.
Interactions (Standard Group Coverage)
The following features interact with Standard Group Coverage.
Attendant Console, Direct Trunk: If the Direct Trunk attendant is a receiver for a Coverage
Group and extendsa call (using the Start button or Selector Console) that is
unanswered/busy to a member of the group, the call will return on the Return-On-Don’t-
Answer (RTN-DA) or Return-On-Busy (RTN-BUSY) button, not on the attendant’s COVER-
GRP button.
Automatic Intercom: Auto-Intercom calls do not receive coverage.
Bridging of System Access Buttons:An incoming call is given group coverage according to
the coverage specified for the principal.Calls appearing on Bridged Access buttons are not
extended to the coverage specified for those bridging stations.
Callback Queuing: Callback calls to the originator do not send ring signals to its coverage
stations. If a call is queued for a station, then one of the coverage stations becomes
available, the call remains queued for the originally-dialed station.
Coverage, Individual:Unanswered calls to a station, provided both Individual and Group
Coverage, will first ring at the Individual Coverage station and then, after a second delay
cycle and still unanswered, will ring at the Group Coverage station.
Coverage/Station Hunting: A call to a busy single-line voice terminal that is both a member
of a Station Hunting group and a coverage sender will first hunt for an idle station to service
the call. If none is available, the call will be sent to coverage.
Direct Group Calling (DGC): A call to a DGC group member will receive coverage if the
member is also a Coverage sender. Calls to a busy DGC group do not receive coverage.
Instead, after a predefined number of rings,the call will be transferred to delay
announcement (if provided), or ringing will be transferred to all button appearances of the
line.
Exclusion: If a coverage receiver invokes Exclusion after answering a coverage call, all other
terminals (including the attendant and the covered station) are excluded from the call. The
covered user cannot enter the call until EXCLUSION is pressed a second time by the
covering user.
Forwarding:When a station has both Coverage and Forwarding in effect, calls are routed
first to the forwarded-to station.If not answered there within an administered number of
rings, calls ring at the forwarding and coverage stations and stop ringing at the forwarded-to
station.
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							Coverage, Group
When forwarding to an outside number, coverage may only occur in one case: the forwarding
had been activated using a trunk group’s facility access code (not ARS), the forwarding
cannot be completed because the trunk group is busy, and the forwarding station is not
busy. In this case, the call will ring at the forwarding station and its coverage stations.
Hands-Free-Answer On Intercom: An incoming (inside) call will not receive coverage if auto-
answer is activated, since the set will answer the call (whether the user is present or not).
Leave Word Calling (LWC): A multiline voice terminal user can activate LWC for the called
party even if the call has gone to coverage.
Night Service:Directed Night Service calls do not receive coverage.
Personal Dial Codes: Calls directed to a station because another non-floating PDC is signed
in there do not receive the coverage treatment of the signed-in station, Such calls return to
their home station and receive that station’s coverage (immediately upon return). Calls to
signed-in floating PDCs, on the other hand, receive the same coverage treatment as any
other calls to the signed-into station.They, of course, have no home station to return to.
Personal Lines:Personal line calls receive the coverage of the principal (owner) station for
that line. Other line appearances (even if administered to ring) will not receive coverage.
Pickup: Pickup is independent of coverage.When a call is answered via Pickup, all Cover
buttons associated with the called party go idle.
Tie Trunks:Tie Trunk calls directed at a user with coverage receive normal coverage
treatment.
Transfer: When a covering station transfers a covered call to another station, the call will no
longer appear at the covering station’s Cover button or at the covered multiline station.
Interactions (DGC Group Coverage)
The following features interact with DGC Group Coverage.
Attendant Console, Switched Loop: If a SLAC is a member of a DGC Coverage Receiver
Group, any DGC Group Coverage call sent to this attendant will enter the common queue
and be treated as a coverage call, not as an Attendant—DGC call. Thus, the call will be
handled by whichever attendant is administered to receive coverage calls.
Attendant Direct Extension Selector Console: The Selector Console can be used to transfer
and place calls to a DGC Coverage Group provided the DGC group access code appears on
the console. The status LED of the DXS button lights steadily whenever all stations in the
DGC Coverage Group are busy.
Automatic Intercom: Auto Intercom calls do not receive coverage.
Bridging of System Access Buttons: An incoming call is given group coverage according to
the coverage specified for the principal. Calls appearing on Bridged Access buttons are not
extended to the coverage specified for those bridging stations.
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							FEATURES AND SERVICES
Callback Queuing: Callback calls to the originator do not send ring signals to its coverage
stations. If a call is queued for a station,then one of the coverage stations becomes
available, the call remains queued for the originally-dialed station.
Direct Station Selection (DSS): A DSS button can be assigned to a DGC Coverage Group.
The button lights whenever all DGC members are busy.
Flex DSS: A Flex DSS button can be assigned to a DGC Coverage Group.
Forwarding:When a station has both DGC Coverage and Forwarding in effect, calls are
routed first to the forwarded-to station. If not answered there within an administered number
of rings, calls ring at the forwarding station and DGC coverage group and stop ringing at the
forwarded-to station. Once the call is directed to a DGC group member, the call appearance
is removed from the forwarding station.
When forwarding to an outside number, coverage may only occur in one case: the forwarding
had been activated using a trunk group’s facility access code (not ARS), the forwarding
cannot be completed because the trunk group is busy, and the forwarding station is not
busy. In this case, the call will ring at the forwarding station and its DGC coverage group.
Once the call is directed to a DGC group member, the call appearance is removed from the
forwarding station.
Leave Word Calling (LWC): A multiline voice terminal user can activate LWC for the called
party even if the call has gone to coverage.
Night Service: Directed Night Service calls do not receive coverage.
Personal Line Access: All outside lines directed to a DGC group can be assigned to button
appearances in addition to the DGC assignment.If the outside lines appear at stations that
also have DGC coverage by the same group, then the operation is as follows:
When an incoming call is ringing in the DGC group, the status LEDs on the appearance
buttons light steadily, indicating that the line is busy.If the call goes unanswered after a
system-specified number of rings, then a delay announcement is provided. The caller is
subsequently put on hold and receives music if available. If the system is not equipped
with a delay announcement, the call begins to ring at all line appearances after the
system-specified number of rings.
If the outside lines are not directed to a DGC group, but are provided DGC Group
Coverage, the feature operation is the same as for incoming calls on SA keys except
that the call appearance remains accessible at the covered station after being directed to
a DGC Coverage Group member.
Pickup: A DGC Coverage Group member can also be in a Pickup group.
Station Hunting: Calls directed to a DGC Coverage Group will not hunt.
Trunk Groups: Trunks can be directly assigned to DGC groups that also act as coverage
group receivers.Among tie trunks, only automatic incoming tie trunks can be translated as
directed to a DGC Group.
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							Coverage, Group
Administration Requirements (Standard Group Coverage)
System:
l Provide Coverage ringing on internal calls (yes or no; default = yes).
If “no”, covered calls will flash but not ring at covering stations on internal calls.
l Number of rings before Coverage ringing starts on no answer (0-31; default = 2).
The status LEDs on Group Coverage buttons at covering stations begin flashing
immediately in all cases. Ringing, in addition to flashing, is always sent on external
calls, though it may not be accepted at the covering stations.
Voice Terminal Port:
l Coverage Sender group number (1-32; default = 1).
l Provide Coverage ringing on no answer (yes or no; default = yes).
If “no”, flashing LED is the only indication received at the covering station; the calling
party always hears ringing.
l Provide Coverage ringing on busy (yes or no; default = yes).
If “no”, flashing LED is the only indication received at the covering station.
The calling party always hears ringing.
l Coverage Receiver button
— Group Number (1-32)
— Allow Ring (yes or no; default = yes).
If “no”, flashing LED is only indication received at this covering station.
Administration Requirements (DGC Group Coverage)
The parameter to assign a coverage sender group has been expanded to include DGC
groups as coverage group receivers.DGC receiver groups are first set up as regular DGC
groups, numbered 1-32.DGC coverage groups can then be specified by using coverage
group numbers 101-132, where coverage group 101 has DGC group 1 as its receiver group,
coverage group 102 has DGC group 2 as its receiver group, etc. No button assignments are
required.
Send ringing options (on busy, on no answer, system-wide for internal calls) have no effect
for DGC group coverage; ringing is sent for all calls that go to coverage.
The system search of group coverage sender stations has been expanded to allow the
system administrator to enter a DGC Coverage Group and list all its sender stations by PDC.
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							FEATURES AND SERVICES
Coverage, Individual
Description
This feature is similar to Group Coverage, covered in the preceding feature description. The
primary difference is that Individual Coverage is a one-on-one type coverage between pairs
of stations.
An Individual Coverage (COVER-IND) button can be assigned on multiline voice terminals to
cover calls to a specific (single) voice terminal.The covering station can answer covered
calls by selecting COVER-IND. Each COVER-IND button can be programmed to ring or not
ring. If ringing is selected, the covering station will begin ringing after a specified number of
rings at the covered station.When the specified number of rings has occurred, covered
multiline voice terminals will stop ringing. Covered single-line voice terminals continue to ring
until the call is answered at a covering terminal. When the call is answered at the covering
station, the call remains accessible at the call appearance button of multiline voice terminals,
but is no longer accessible at single-line voice terminals.
Each COVER-IND button at a covering station represents one covered voice terminal. If
more than one voice terminal is to be covered, multiple buttons are required, one for each
station covered. A covering voice terminal may be assigned multiple COVER-IND buttons for
a particular station to cover multiple simultaneous calls to that station. The first button will
track the first call, the second button, the second call, etc.
Up to eight COVER-IND buttons can be assigned for each covered station.
There is no limitation on the number of stations that can receive Individual Coverage.
A voice terminal can receive both Individual Coverage and Group Coverage.
Refer to Messaging Services for a description of Coverage Message Waiting service, which
allows the covering station to control the status of the covered user’s Message LED.
Calls from a covering station to a covered station will not be covered unless the covered
station has additional coverage.This is an important consideration when the attendant
provides coverage.
Considerations
Coverage provides a way to redirect calls to alternate answering positions. The feature is
versatile enough to permit suitable alternate answering arrangements for virtually every level
of employee.Special functions, such as the Send All Calls feature, accommodate the day-
to-day variations that occur in an employee’s work schedule.
The Individual Coverage feature is not administrable on the Switched Loop Attendant
Console.
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							Coverage, Individual
Interactions
The following features interact with Individual Coverage.
Attendant Console, Direct Trunk: When a coverage call rings at a busy Attendant Console,
the attendant receives a single burst of ringing.If the call is still unanswered when the
attendant hangs up the other call, the Attendant Console will resume ringing.
Bridging of System Access Buttons:An incoming call is given individual coverage according
to the coverage specified for the principal.Calls appearing on Bridged Access buttons are
not extended to the coverage specified for those bridging stations.
Callback Queuing: Callback calls to the originator do not send ring signals to its coverage
station. If a call is queued for a station, then the coverage station becomes available, the call
remains queued for the originally-dialed station.
Coverage, Group:Unanswered calls to a station, provided both Individual and Group
Coverage, will first ring at the Individual Coverage station and then, after a second delay
cycle and still unanswered, will ring at the Group Coverage station.
Direct Station Selection (DSS): Calls placed via a DSS button to a user with Individual
Coverage will receive coverage.When a DSS button is used to activate the busy-to-idle
reminder for the user, the reminder is returned only when the user becomes idle, not when
an associated coverage user becomes idle.
Exclusion: If a covering station answers a coverage call and then invokes Exclusion, all
other reside stations, including the covered one, are excluded from the call.
Forwarding: When a station has both Coverage and Forwarding in effect, calls are routed
first to the forwarded-to station.If not answered there within an administered number of
rings, calls ring at the forwarding and coverage stations and stop ringing at the forwarded-to
station.
When forwarding to an outside number, coverage may only occur in one case: the forwarding
had been activated using a trunk group’s facility access code (not ARS), the forwarding
cannot be completed because the trunk group is busy, and the forwarding station is not
busy. In this case, the call will ring at the forwarding station and its coverage stations.
Hold: May be used by the covering user to place a coverage call on hold. The COVER-IND
button’s status LED winks at the covering station.At the covered station, if the call is on a
Personal Line button, the button’s status LED winks; if the call is on a SA button, the status
LED lights steadily. The held call will automatically leave the coverage terminal if picked up
by the covered user. The covering station will be unable to reenter the call.
Leave Word Calling (LWC): A multiline voice terminal user can activate LWC for the called
party even if the call has gone to coverage.
Transfer: When a covering station transfers a covered call to another station, the call will no
longer appear at the covering station’s Cover button or at the covered multiline station.
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							FEATURES AND SERVICES
Administration Requirements
Voice Terminal Port:
lIndividual Coverage button (button function # 12):
—
Individual Coverage PDC (1-9999).
—
Allow Ring (yes or no).
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							DS1 Facility Interface
DS1 Facility Interface
Description
The DS1 facility interface feature provides connectivity between System 25 and a T1 facility.
The DS1 facility is a transmission system to transport digital signals of the DS1 format. The
System 25 forms voice signals using the DS1 format. By using the DS1 format the following
advantages are provided; calls to other digital PBXs or central offices remain digital and
signals don’t need to be converted to analog for acceptance by the connecting tie or tandem
trunk. A T1 trunk can replace up to 24 analog loop-start, ground-start, direct-inward dialing,
tie, and off-premises station trunks and associated System 25 circuit packs. One T1 trunk
can transport a 1.544-Mbps signal consisting of twenty-four 64 kbps channels.
DS1 Format
The term DS1 format stands for Digital Signal 1.Twenty-four Digital Signal 0 signals, each
operating at 64 kbps plus framing bits, are multiplexed forming a DS1 signal of 1.544 Mbps.
Each DS0 channel within the DS1 signal corresponds to a port or a trunk.
Framing Formats
To identify each DS0 channel within the DS1 signal, the DS0 channels are segmented into
blocks of 193 bits (known as a frame). A frame consists of twenty-four 8-bit plus one
framing bit which is inserted at the beginning of each frame. A framing bit appears every
193rd bit of the DS1 signal. Frames repeat at a rate of 8000 per second. Each frame repeats
DS0 channels 1 through 24 of the DS1 signal sequentially.
Two framing formats exist, D4 and Extended Super Frame (ESF). System 25 accepts either,
and the selection must match the framing format at the far end.
A D4 frame consists of 24 eight-bit time slots and one framing bit that alternates between a
one and a zero every other frame.The receiver uses the framing information for
synchronizing to the start of each frame and to identify which frames contain signaling
information (see Robbed-bit signaling). The framing information repeats once every 12
frames, defining the D4 superframe.The advantage of this framing format is that it is
universally used by all DS1 equipment.
The ESF framing format extends the 12 frame superframe of D4 to a 24 frame extended
superframe, making significantly different use of the framing information. The ESF framing
format consists of a 24-bit pattern, with 6 of the bits used to synchronize to the start of each
frame and signaling frame. Six of the remaining 18 bits consist of an error detection code
known as a Cyclic Redundancy Check (sum) over the superframe. The remaining 12 bits are
used as a facility data link signal providing maintenance and facility supervision. The
advantage of ESF framing format is that it is able to detect more errors than D4 framing
format. However ESF is not universally used by DS1 equipment.
A Red alarm occurs when frame synchronization on the DS1 interface is lost.
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							FEATURES AND SERVICES
Signaling Types
Signaling types refers to signaling used by DS1 on the T1 facility. Two signaling types can be
used in System 25, Robbed-bit and Common Channel.
Robbed-bit signaling (RBS) robs or replaces the least significant bit (of each DS0 channel’s
8-bit word in every 6th frame) with that channel’s signaling information. For D4 frame format,
that means the 6th and 12th frame carry RBS. For ESF frame format, this means the 6th,
12th, 18th, and 24th frames carry RBS. Robbed-bit signaling can not be used when the DS1
carries 64 kbps data and therefore limits the channel’s use to voice and analog voiceband
data applications.
Common Channel signaling places the signaling bits for DS0 channels 1 through 23 into the
8-bit word of the 24th channel. This restricts the DS1 from using the 24th channel for voice
or data transmission.This signaling type is known as Digital Multiplexed Interface Bit
Oriented Signaling (DMI-BOS). Common channel signaling is acceptable when DS1 is used
in a data application.
A Remote Multiframe alarm occurs when Common Channel signaling is used and the far end
is unable to synchronize to the multiframe pattern in its incoming signal.
Line Coding Formats
The DS1 signal consists of a continuous stream of 1’s and 0’s. The bit stream is encoded
into bipolar pulses for transmission purposes. Actually, only the 1’s create bipolar pulses
while 0’s are represented as the absence of a bipolar pulse. The line coding formats serve
to guarantee that the bit stream maintains a minimum number of 1’s. In the T1 carrier
system, this is known as the ones-density requirement. A Blue alarm occurs when an all
ones pattern including the framing bits is received.There are two line coding formats, Zero
Code Suppression (ZCS) and Bipolar 8 Zero Suppression (B8ZS).
The Zero Code Suppression line coding format monitors the transmit bit stream and forcibly
changes one of the zeros to a 1 when a string of 8 or more zeros are transmitted. When
RBS signaling is used, the overwritten bit has no effect on voice and voiceband data.
However, when common channel signaling is used, the ZCS format destroys digital data.
The Bipolar 8 Zero Suppression line coding format allows strings of 8 zeros in the DS1
signal, but encodes them into a unique binary sequence (known as a bipolar violation). These
special sequences are then detected at the receiving end and converted back to the correct
sequence.Many of the network interface and transmission equipment devices currently
installed will not pass bipolar violations (while some will correct the violation). B8ZS offers no
advantage for voice or voice grade data, and must be used on unrestricted digital data
applications.
Digital Network Synchronization
The term synchronization refers to an arrangement where digital facilities operate from a
common clock. Whenever digital signals are transmitted over a communication link, the
receiving end must be kept in step or synchronized with the transmitting end in order to
receive the digital signals.This is referred to as link synchronization.
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