Zhone Technologies IMACS Network Device - Manual (Page 75)

Zhone Technologies, Inc. IMACS Product Book, Version 4
March 2001 Page 71
Three ISDN PRI Server Cards are supported:
•
8840A ISDN PRI Server Card with 1 D Channel
•
8840B ISDN PRI Server Card with 2 D Channels
•
8840C ISDN PRI Server Card with 8 D Channels
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. The PRI Server card is available in three different software versions based on the number of D
channels (1, 2, or 8) to be supported. 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 8840B and 8840C 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 IMACS 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 8840C ISDN PRI server card, which supports eight (8) D-channels can be configured to route calls from a PBX,
multiple PBXs, and DTE devices to multiple ISDN service providers. The 8840x ISDN PRI Server does not support
BRI-to-PRI translation. This application is supported by the 65100 ISDN BRI-PRI translation software running on
an 8811xx ACS card.
NFAS (Non-Facility Associated Signaling)
All ISDN PRI cards can be configured to support NFAS (Non-Facility Associated Signaling). The IMACS limit for
NFAS is 191B+D in T1 environments (8 times 24 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 framing
and 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 IMACS is limited to 8 WAN links. Thus the IMACS 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 IMACS supports NFAS, it can only be implemented within private networks or in public networks where
the service provider supports it. 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.
Remote Login
In addition to carrying ISDN signaling information, the D channel can also be used to log into a remote system unit
to check card status, and perform necessary system maintenance. This unique application does not require B
channel allocation. The ISDN call is placed on the D channel to the ISDN network and routed to the D channel of
the remote unit. Coordination with the ISDN facility provider is necessary to obtain the number for the remote
system unit.