Zhone 891630, Справочное руководство системы

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2-20 IMACS System Release 5.1.9 Reference Guide
Model No.
Running Head
ISDN Primary Rate Interface (PRI) Server (884060) Applications
The cards provide flexible access to PRI-based ISDN services such as Switched 384, Switched
T1, and Switched 56/64. The PRI Server Card (PRI card) provides both local D channel
origination and termination and D channel consolidation. It offers a perfect alternative to
standalone ISDN access devices when other “non-ISDN” voice and data services must be
consolidated in addition to ISDN services.
The 884060 ISDN cards can be simultaneously connected to several network and user side
ISDN PRI facilities. The ISDN PRI card provides D channel support of both the network side
protocol and the user side protocol. Typically, the IAD with an ISDN PRI card, supplies the
network side protocol on a D channel connected to a PBX, and provides the user side protocol
on the D channel connected to a carrier switch.
The 884060 ISDN PRI server card can also be configured to route calls from a PBX, multiple
PBXs, and DTE devices to multiple ISDN service providers. services. The 884060 ISDN PRI
Server does not support BRI-to-PRI translation. This application is supported by the 65130
ISDN BRI-PRI translation software running on an 881162 ACS card.
2.5.1 NFAS (Non-Facility Associated Signaling)
All ISDN PRI cards can be configured to support NFAS (Non-Facility Associated Signaling).
The limit for NFAS is 191B+D in T1 environments (8 times 2 minus 1 D channel) and 239
B+D in E1 environments (8 times 30 time slots minus 1 D channel).
A basic ISDN PRI facility is a T1 link that consists of 23 B channels and 1 D channel
(23B+D), or an E1 link that consists of 30 B channels and 1 D channel (30B+D). Note that
one time slot on any E1 link is reserved for maintenance use and is neither a B channel nor a
D channel. The D channel provides signaling for all of the (23 or 30) B channels on the facility
carrying that D channel.
However, many ISDN applications have relatively low call rates (i.e., the D channel is not
very busy), but need more than 23 (or 30) B channels to carry user (bearer) traffic. In these
cases, a D channel can be set up to perform signaling not only for the B channels on its own
facility, but also for B channels on other facilities (i.e., other T1/E1 WAN links). When a D
channel is so provisioned, it is considered to be performing non-facility associated signaling
(NFAS).
The system is limited to 8 WAN links. Thus the system limit for NFAS is 191B+D in T1
environments (8 times 24 minus 1 D channel) and 239B+D in E1 environments (8 times 30
minus 1).
Although this Integrated Access System supports NFAS, it can only be implemented within
private networks or in public networks where it is supported by the service provider. Within
EC and EFTA countries NFAS is considered an EC-MOU2 supplementary service which is
still at the discussion stage and therefore is not supported by any of the European Service
Providers.