ATT Definity Addendum 1 For Ds1, Dmi, Isdn Pri Instructions Manual

							INTRODUCTION1-29
The ISDN-PRI level-3 messages are a collection of IEs that are defined in the Q.931 recommendations.
Each message has at least one IE. IEs are transmitted and received over the D-channel. IEs contain
three headers: protocol discriminator, call reference, and message type. Figure 1-9, ISDN Message
Signaling Format, shows the message-signaling format.½
FIRST OCTET
PROTOCOL DISCRIMINATOR
CALL REFERENCE
MESSAGE TYPE
INFORMATION ELEMENTS
(OPTIONAL)
INFORMATION ELEMENTS
LAST OCTET
Figure 1-9. ISDN Message Signaling Format
IEs may be one or more octets long, depending on the element type. There are 133 different IE
identifiers (called codepoints) grouped into eight functional categories (codesets 0 through 7).
How trunk groups are constructed and how ISDN-supported features are administered determines which
B-channels may be selected to originate and terminate a particular call. Generally, any B-channel may
be used with both originating and terminating calls so a particular channel may support a variety of
applications and trunk types. In Generic 2, this capability is called ISDN dynamic; in Generic 1, it is
called call-by-call (CBC). For both Generic 1 and Generic 2, this feature is called CBC Service
Selection.
Administration software also allows services to be dedicated to specific channels by assigning a channel
to a particular trunk type. In this way, the switch always provides enough trunks for a particular type of
service. Channels administered for specific services are not available for ISDN-dynamic uses.
With CBC Service Selection, calls requesting various types of services are routed, on a call-by-call
basis, over the same ISDN channels. To distinguish between various types of calls, the service type is
specified as a part of the message. Also included are BCC and NSF IEs.
The NSF IE identifies the feature or service provided by the network carrier (such as MEGACOM
service from AT&T). The called-party IE is used to specify routing digits such as the North American
dialing plan or RNX.½
½
½
½
½
½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							1-30INTRODUCTION
Except for DCS, the originating and terminating switches do channel negotiation to select a channel that
is compatible with both endpoints. Channel negotiation gives some control of the B-channel used for a
call. If the originating endpoint chooses a B-channel that is unacceptable to the terminating endpoint
(for example, planned use of the channel by the terminating endpoint), then the terminating endpoint can
request a change in the channel to be used for that call.
Although Q.931 recommendations allow for an asymmetrical design (that is, a user-to-network protocol),
most ISDN-PRI procedures on System 85 R2V4, Generic 1, and Generic 2 can be used symmetrically.
These communications systems can be administered as either the user side or as the network side.
When accessing a 4ESS switch, 5ESS® switch, or vendor-compatible toll-office or CO, the customer-
premises switch must have a user-side interface. For ISDN-PRI links between two private network
switches, one link must be administered for the user side and the other for the network side.
Differences between the user side and network side are primarily related to resolving occurrences of
glare. Glare is a condition where both switches try to originate a call on the same channel
simultaneously. The network side always gains control of the channel and the user side backs down
(terminals are excused from certain protocol functions).
Linking dissimilar networks to provide end-to-end call or feature processing is called interworking.
Calls from non-ISDN facilities (analog trunks and/or DMI-BOS trunks) may be connected to ISDN
facilities to provide end-to-end tandemed connections. The switch provides the required signal
conversions through interworking routines. The switch features and services that may be used depend
on an extension’s COS assignment and other administration options.
Depending on other administration options, message-associated user-to-user information (MAUUI) or
user-to-user information (UUI) may be transmitted from one user endpoint to the other. UUI transfer
includes the display of such things as calling number and calling party name.
Equipment manufacturers interpret the ISDN-PRI protocol in different ways. As a result, equipment
(and various equipment releases) use different approaches. Currently, one significant difference occurs
in codesets 6 and 7. System 85 R2V4 transfers UUI via codeset 7. System 85 R2V4 transfers network
specific information in codeset 7 according to the initial definition of ISDN. Generic 2 transfers
network-specific information in codeset 6 leaving codeset 7 available for user-specific information.
NOTE: Codesets 1 through 5 are reserved for future standards expansion.½
½
½
½
½
*½
½
½
CBC Service Selection
CBC trunk groups eliminate the need for dedicating specific B-channels to a particular service. CBC
Service Selection can dynamically select individual B-channels (from a group of B-channels) and
allocate those B-channels to any of the subscribed services. The selected B-channel may function as a
specific trunk type (for a specific service) during one call, then later the same B-channel may function as
a different trunk type (for a different service) during another call. The primary advantages of CBC
Service Selection include:½
½
½
½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							INTRODUCTION1-31
lMore efficient and effective use of ISDN-PRI network access trunks
lMore access trunks available for call routing (providing an improvement in the grade of service)
lReduction (usually) in the number of access trunks needed to provide the required grade of service,
because of the increase in efficiency
CBC Service Selection is a public network ISDN feature. The AT&T ISDN network provides CBC
Service Selection for AT&T ISDN nodal services (such as MEGACOM service, MEGACOM 800
service, Software Defined Network (SDN), ACCUNET switched digital service, and switched digital
international). To use CBC Service Selection, the customer-premises switch must manage access to
these nodal services. System 85 R2V4, Generic 1, and Generic 2 all provide CBC service selection.½
½
Because of architectural differences, these communications systems provide different levels of
implementation.
From the customer-premises switch perspective, a CBC trunk group may be designed to support
incoming nodal services, outgoing nodal services, or both.
System 85 R2V4/Generic 2 — CBC Implementation½
½
The following describes details of CBC on System 85 R2V4 and Generic 2:½
1.
2.
3.
4.With System 85, station identification number/automatic number identification (SID-ANI) can be
requested on per trunk group basis but not from the network on a per call basis. Therefore, if the
particular trunk group provides CBC service selection, then all calls, regardless of the particular
nodal service, must provide SID-ANI.
At service provisioning time, the customer will determine whether to subscribe to this network
service. From the AT&T network perspective, this service is available in either of two formats:
lSID-ANI provided on every call
lSID-ANI provided on request, call by call
Regardless of which format is selected, ANI or SID can be ordered exclusively, or the service can
be ordered as ANI preferred but will accept SID.
Except for trunk type 120, Generic 2 does not use the NSF value for processing incoming calls.
Incoming calls are routed based on the number of digits delivered and the format of those digits.
These conditions (the number and format of the digits) may impose restraints on the use and
administration of CBC Service Selection.
System 85 R2V4 introduced a new trunk type known as ISDN-dynamic. ISDN-dynamic trunk
types can only be used with ISDN-PRI facilities. Most other trunk types may be used with
ISDN-PRI as well as other facilities. ISDN-dynamic trunk types are useful where more than one
trunk type is needed, only one trunk group is available, and provisional routing digits are
inadequate for the current application.
Each AT&T ISDN-PRI nodal service (MEGACOM 800, SDN, ACCUNET switched digital
service) may be provisioned to deliver from 0 to 7 digits.½
½
½
½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							1-32INTRODUCTION
Generic 1 — CBC Implementation½
The following describes details of CBC on Generic 1:
1.
2.
3.The SID-ANI number can be received either per trunk group or per call
When receiving calls over a CBC trunk group, define the usage-allocation plans. These plans
prevent a particular nodal service from monopolizing a trunk group or being deprived of the
minimum number of trunks.
On Generic 1, the “service type” field on the trunk group form permits entries such as CBC,
access, tie, and tandem. When CBC is administered, the call-processing software analyzes the
NSF (for incoming calls) for called party number or length. The other entries do not analyze the
NSF but permit CBC Service Selection.½
Networking Restrictions and ISDN-PRI Limitations
ISDN-PRI has the following limitations:
1.
2.
3.
4.ISDN-PRI facilities cannot be used to connect a main and a satellite (such as a main/satellite
trunk). Therefore, it is recommended that AAR be used with ISDN-PRI trunks to provide private
network facilities.
Even though main/satellite trunks cannot be used over ISDN-PRI facilities, the main/satellite
feature may still exist on a switch that uses ISDN. For example, ISDN-PRI facilities may be used
to access the public network using the ARS software while non-ISDN-PRI trunks (such as
main/satellite trunks) may be used to connect subtending switches to the main switch. Calls may
originate and terminate on the satellite or on the tandem through the main, and route onto the
ISDN public network via ISDN-PRI trunks.
Centralized Attendant Service (CAS) uses a trunk type that does not use ISDN-PRI signaling.
Therefore, CAS is unavailable with ISDN-PRI facilities.
Distributed communications system (DCS) network configurations are supported over ISDN-PRI
facilities. However, a separate DCIU signaling link is required. This separate signaling link may*½
½
be a B-channel that is used as a DSC or an analog facility.
ISDN-PRI and DCS are two separate networking services. If DCS is used over an ISDN-PRI
trunk, in most cases the DCS display appears instead of the ISDN-PRI messages.
With ISDN-PRI, the calling party information is sent to the called party and the called party
information is returned to the calling party.
When ISDN-PRI and DCS are found in the same network, certain features predominate based on
the handling of the called number. Refer to DEFINITY Communication System Generic 2.1 to
Generic 1.1 with DCS (555-037-238) for more information regarding this networking arrangement.½
½
½
½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							INTRODUCTION1-33
Interworking between ISDN-PRI and DCS is a complex issue that is beyond the scope of this
document. However, for pure ISDN-PRI or combined ISDN-PRI/DCS networks, several new
ISDN feature and service options are available. These include: 5.½
l
l
l
l
l
l
l
lCall routing based on BC
End-to-end ISDN connectivity routing
BC passed on a call-by-call basis
User-to-user information transport
Locally provided tones
Controlled initialization of trunks to in-service at provisioning time
Two-way busy out of trunks
Digital demand transmission  test½
½
½
½
½
½
With interworking, the following types of calls are possible:
lCalls between non-ISDN endpoints and ISDN endpoints (BRI terminals)
lCalls between non-ISDN trunks and ISDN trunks
lCalls between non-ISDN trunks and ISDN endpoints
lCalls between non-ISDN endpoints and ISDN trunks
Part of this capability is the automatic insertion of conversion resources (modem pool) based on
the bearer capability rather than trunk type (see also the codeset mapping description in the
Procedure 280 Word 1 heading of chapter 7, Administration Options and Requirements).
NOTE: For Generic 2, AVD trunk characteristics no longer govern modem pool insertion.
For Generic 1, AVD is used for non-ISDN trunks.
Generally, DCS networks may overlay on an electronic tandem network (ETN) or main/satellite
network. For DCS call routing, ETNs use AAR to complete DCS calls while main/satellite
networks use multidigit steering software to complete DCS calls. Therefore, if DCS trunks are
provided over ISDN-PRI facilities, then the switch must be configured with AAR. (See item 1 of
this list for more information.)
When Generic 2 connects to a System 85 R2V4 using ISDN-PRI facilities to provide DCS service,
then the originating extension will not receive display updates as the call progresses (for example,
to call coverage or is forwarded). The DCS leave word calling feature is only applicable for 4- or
5-digit extension numbers; it will not function with 7- or 10-digit public- or private-network
numbers.½
½
½
½
½
6.
7.½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							1-34INTRODUCTION
Full DCS feature transparency is provided between two or more Generic 2s interconnected with
ISDN-PRI facilities. The supported voice terminal features include:
lAbbreviated dialing
lAlphanumeric display (DCS)½
½
lAutomatic callback
lCall coverage
lCall forwarding — all calls
lCall waiting — terminating
lCall waiting — conference
lPriority calls
lDistinctive ringing
lLeave word — calling (no AP)
lLeave word — call transfer
8.When ISDN-PRI facilities connect an ETN main to an ETN tandem, the main must do additional
routing since cut-through operation is not permitted. Dialed digits must first be collected and then
the setup message transmitted to the tandem.
Automatic Voice Networks (AUTOVON), tandem tie-trunk networks (TTTN), and Common-Control
Switching Arrangement (CCSA) or Enhanced Private Switched Communications Service (EPSCS)
networks that use E&M trunks cannot be served by ISDN-PRI trunks. DS1 facilities that use robbed-bit
inband signaling will work. Generic 2.1 without universal modules will support AUTOVON service;
Generic 2.1 Issue 3.0 with universal modules will also support AUTOVON service.
ANI (also known as the calling number identifier or CNI and as the calling line ID or CLID) is
currently regulated on a state-by-state basis. When maintenance people are troubleshooting intrastate
ANI-related problems, these regulations may or may not permit ANI to be passed.½
½
½
½
½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							2. NETWORK CONNECTIONS AND CONFIGURATIONS
This chapter provides a description of common connection arrangements with System 85 R2V4,
DEFINITY® Communications System Generic 1 and Generic 2. These connections include private
network, public network, and those made through digital signal level 1 (DS1) auxiliary equipment. Also
included is a description of the services provided by each connection, any option restrictions, and
relevant synchronization issues.½
The equipment used for completing the end-to-end connection may include any of the options described
in chapter 3, DS1 Transmission and Cabling. These options permit distances between endpoints of a
few feet to thousands of miles. Detailed information, such as that required to install and administer a
connection, is contained in chapter 6, Port Types/Installation Compatibilities, and chapter 7,
Administration Options and Requirments. Common field problems relating to these connections are
described in Appendix B, Sample Installation and Maintenance Problems. A complete description of
synchronization is provided in chapter 5, Synchronization of Digital Facilities, and loss adjustments are
described in chapter 4, The Digital Loss Plan.
NETWORK DIFFICULTIES
Two of the many difficulties that can exist on public and private networks are hyperactivity and glare.
Before describing connection arrangements, the methods for dealing with these two difficulties is
discussed.
Hyperactivity
When a DS1 facility generates an abnormally high stimulus rate originating from an individual source
over a certain amount of time (such as rapid on-hook and off-hook conditions), it is said to be
hyperactive. The call-processing software can not handle the flood of stimuli, resulting in dial-tone
delays. Hyperactivity can be caused by bit errors on the facility, misoptioned equipment, or hardware
failures. Severe or long-lasting hyperactivity can overload the communications system with more
messages than it can processs. Without intervention and corrective action, this could result in½
degradation or even loss of service on the switch.
On Generic 2, special software handles hyperactivity by executing the following steps:½
1.
2.
3.
4.Detecting the presence of possible hyperactivity
Identifying a suspected source of hyperactivity
Examing the suspected source
Arresting the message flow from the suspected port, usually protecting the communications system
from excessive stimuli
ADDENDUM 1 (December 1990) to 555-025-101, Issue 42-1 
						

							2-2NETWORK CONNECTIONS AND CONFIGURATIONS
5.
6.
7.Counting the number of messages and comparing this to other trunks
Determining whether a channel is hyperactive
Maintenance busying out a virtual trunk group with hyperactive channels or returning cleared
channels to normal service
For more information about troubleshooting hyperactivity, refer to DEFINITY Communications
System Generic 2 Maintenance Repair Strategies (555-104-118).½
Normal, though temporarily high, levels of ISDN-PRI D-channel signaling can sometimes create
apparent hyperactivity. This happens most often with nonfacility-associated signaling (NFAS) when
many B-channels are associated with a particular D-channel. This problem is handled similarly to that
described above with the exception that hyperactive D-channels are removed from service (associated
B-channels are busied out). Usually, but not always, this problem is transient and disappears before a
yellow alarm is sent. If this is a chronic problem in a particular configuration, administration of the
NFAS B-channel group can be an effective solution.½
½
½
½
Another category of hyperactivity involves digital communications protocol (DCP) equipment. DCP
hyperactivity is not directly relevant to DS1, digital multiplexed interface (DMI), or ISDN-PRI, and is
not discussed in detail here. DCP hyperactivity and DS1 hyperactivity are handled similarly.
Glare
Glare is the simultaneous seizure of a two-way trunk by two communications systems, resulting in a
standoff. Because of ISDN’s inherent negotiation capabilities, glare handling on ISDN-PRI trunks is
different from that for other trunks. When both sides of the trunk are seized at the same time and setup
messages cross on the D-channel, two rules are used to decide which side wins (succeeds in making
a call on that channel) and which side loses (backs off or moves to a different trunk).½
The first rule is evaluated using a parameter indicated in the Channel-ID information element (IE), called
the preferred/exclusive option. This option specifies that either the channel is the only one that can be
used for this call, or that the call can be completed over a different channel, specified by the destination
switch, if the indicated channel is busy. The full benefits of using the preferred option are only reached
if both switches can negotiate. A System 85 or Generic 2, having full negotiation capabilities, always
sends a preferred indication, with one exception.½
½
NOTE: In a DCS environment negotiation is impossible, so the exclusive option is used.½
The 4ESS, in ISDN Phase 2, always uses the preferred option. In terms of glare, if both calls are
exclusive, or both calls are preferred, the second rule (described below) is used to decide which call
wins. If one call is exclusive and the other preferred, the exclusive call wins the trunk.
The second rule is based on the translation field Interface Type in procedure 262, word 1, which is set to
either network or user. This field always has opposite settings on either side of the PRI. When a
System 85 R2V4 or Generic 2 is connected to the AT&T public network or a central office (CO), it is
translated as user. Otherwise, such as when several switches are networked together, the choice of
network or user is optional. When glare occurs and both calls are preferred or both are exclusive, the
network side wins.½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							NETWORK CONNECTIONS AND CONFIGURATIONS2-11
The assignment of CEM channels must be coordinated with the DS1/DMI-BOS channel assignments on
the switch. This is necessary so that only voice and voice-grade data channels are compressed and so
that digital data or 24th-signaling channels pass through uncompressed.
The CEM does not place any restriction on a DS1/DMI-BOS between the switch and the CEM.
Therefore, this interface may use either D4 or ESF framing, 24th-channel or robbed-bit signaling, and
either ZCS or B8ZS line coding. However, CEMs have the following considerations:
lThe type of signaling used on the compressed DS1/DMI-BOS facility
lThe selection of compressed and uncompressed channels
lThe use of echo cancelers
lThe use of a processor that allows remote administration and maintenance of the CEM
Only the first two options will be discussed here. The other options, along with additional specific
information, may be obtained from CEM: Description, Installation, and Maintenance (365-287-100)
and BCM32000 Solitaire: Description, Installation, and Maintenance (365-287-115).
Three types of mutually exclusive signaling are used with the compressed DS1 facility between the two
CEMs. These signaling types are different from the signaling types used by DS1/DMI-BOS. The first
type of signaling is variable bit-robbed (VBR). It is similar to RBS in that it is an inband type of
signaling. The VBR type is sometimes also called RBS, even though it is a different type from that
associated with DS1/DMI-BOS. When VBR signaling is used:
lVBR signaling is the default signaling type supplied with the basic CEM unit
lVBR signaling is the only signaling type that allows a DS1 facility to carry the maximum of 48
compressed voice or voice-grade data channels
lTandem connections (over several DS1/DMI facilities) can significantly affect signal quality
lAll uncompressed channels (that is, digital data channels and the 24th signaling channel) must be
provided on the same DS1/DMI.
NOTE: VBR signaling should not be used for out-of-band signaling applications or used when½
½
½
½
½
the compressed facility connects to a DACS.½
½
The second signaling format is called bundling. It is similar to 24th-channel signaling in that
compressed channels are grouped into bundles of 12; 11 carry voice or voice-grade data and the 12th
(called a delta channel) carries signaling for the other 11. The important points associated with
bundling signaling are as follows:
1.
2.
3.
4.It is the recommended signaling type for most applications
Hardware in addition to that provided with the basic CEM unit must be ordered
The maximum number of compressed channels that a CEM accommodates is reduced to 44
It is the only signaling method that allows compressed DS1 channels to be cross-connected
through a DACS½
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4 
						

							2-12NETWORK CONNECTIONS AND CONFIGURATIONS
5.
6.It is the only signaling type that permits uncompressed channels, from both DS1/DMI-BOSes, to
be connected to the CEM. Bundling is required when both DS1/DMI-BOSes operate with 24th-
channel signaling.
It is required when the CEM is used with a CDM
The third signaling format is called DMI-46. This format uses DMI-BOS over the 24th channel of the
compressed facility, leaving 46 compressed channels available for voice. DMI-46 is usually selected
only when the facilities to the switch use RBS signaling.½
½
½
The method for selecting the channels that are to be compressed and the channels that are to pass
through uncompressed depends on the type of signaling used. Both methods are described as follows.
If VBR signaling is used, the assignment of compressed and uncompressed channels on one of the two
input DS1/DMI-BOS facilities is done using 12 front-panel switches. The assignment of the other input
DS1/DMI-BOS facility is done by default by the CEM. If bundling is used, four templates are used to
assign status to each of the four 12 compressed-channel bundles. There are 6 front-panel switches per
bundle. These switches select 1 of 64 possible templates per bundle. The templates define the status
(compressed or uncompressed) of each channel, the signaling format that is being used, and the channels
that have signaling disabled.½
Regarding alarms, the CEM provides six relay contact closures. They are used to indicate major alarm
conditions. The contacts should be wired individually to the external alarm interface of the switch, or at
the minimum should be connected in parallel to one external alarm input of the switch.½
ISDN-PRI PRIVATE-NETWORK CONNECTIONS
Private-network connections only include connections to other customer-premises switches.½
System 85 R2 to a System 85 R2V4, Generic 1, or Generic 2½
These connections are the most frequently used private network configurations. Typically, digital tie
trunks are used to connect the switches. However, other trunk types, such as ISDN-dynamic trunk type
120, may be used. These trunks may be used to transmit voice, voice-grade data, and digital data.
If the two switches are colocated, then there are no network facilities between the switches, and any
combination of signaling, framing, and line coding may be used. Excluding the user/network option, all
other options should be administered identically for both switches.
Whenever carrier facilities are used to connect the ISDN-PRI endpoints, the carrier facilities may place
limitations (if there are any) on the permitted options. When two or more switches are connected, they
must be synchronized; one switch must be chosen as the timing master, and the other must derive timing
from the master. Chapter 5, Synchronization of Digital Facilities, describes synchronization procedures.
ADDENDUM 1 (December 1990) to 555-025-101, Issue 4