ISDN to Austpac Interconnection

ISDN provides a gateway to the Austpac network for low volume data.  The data
transfer is performed on the D channel instead of the two B channels.  This
frees the two B channels for voice services or for data transfers or any
combination of the two.

This application is particularly important where data integrity is crucial.
The X.25 error correction protocol is performed through the complete
connection.  This is provided by the Austpac service but only on the D channel
with the ISDN.  Error correction can be performed on the B channel of ISDN but
only end to end.  Sending the data across the D channel will let data be sent
across Austpac customers.

This feature can considerably rationalise the communications between a head
office and remote site.  There is also the migration path from the Austpac
connection to the use of the 64 kb/s B channel.  This extra bandwidth could
also be used for back-up of the host database.  There are many options that
are available with two 64 kb/s channels.

This feature is particularly important when voice facilities are the highest
priority.  When using the ISDN Spectrum service, a plethora of voice features
become available on each of the B channels with small volume data over the
D channel.

D Channel X.25

The D channel of the Microlink is used for signalling and call control of the
B channels.  This channel runs at 16 kb/s and allows the transmission of data
additional to that provided by the B channels.

For data transmission over the D channel, X.25 packets are used.  This feature
is particularly useful for low speed data transfer.

There is an interconnection to the Telecom packet-switched data service
Austpac.  This is useful for telemetry applications and particularly for the
retrieval and distribution of small amounts of data.

Telecom Australia has used this feature for the development of the new
Enhanced 000 service.  When a caller is identified the address of the caller
is sent to the required emergency service.  This will speed the dispatching
of the emergency service.

Figure 7.1 - PSTN connected to phones
	     DMS connected to PSTN
	     NT1 connected to DMS
	     DPN connected to DMS
	     PCTA connected to NT1
	     phone connected to PCTA
	     X.25 card in pc connected to DPN
	     DPN connected to AUSTPAC
	     AUSTPAC connected to gateway
	     gateway connected to remote databases

PCTA:		NCR ISDN card
PC:		NCR ISDN Terminal
Telephone:	Telecom ISDN Spectrum Black Phone
Software:	E000 software
DMS:		Digital Meridian Switch - Telecom Exchange Node
DPN:		Data Packet Network Node

Description:

The NCR ISDN terminal provides acess to the ISDN Spectrum service.  The
terminal is able to access both of the B channels.

The PCTA Card provides an applications programming intercafe (API) for
access to the D channel X.25 features.

The API can be programmed to send and receive data as desired for the
particular application.

The standard call establishment procedures for X.25 are to be performed
between the terminal and the database.  There are several remote databases
containing customer Id and addresses.  The application manages logon to
individual database as required.

In Enhanced 000 system, both B channels are used for voice connection.  When
a call is received by the 000 terminal, the application sends an enquiry to
the current remote database through the D channel.  Once the caller's
information is obtained, voice consultation call feature is activated to
connect to the ESO (Emergency Service Operator) with the data transferred
using D channel X.25 at the same time.

The remote stations do not require ISDN connections but do require an X.25
card to be placed in the computer.  The D channel access with the ISDN is
an extra feature used in conjunction with the other features of Spectrum
ISDN.

(something garbled in original document)

The setup of the NCR PCTA card is as shown in the user manuals.  The X.25
API procudures are outlined in the user manuals.

The conneciton to the Austpac service is performed from within the developed
application by calling the appropriate function in the API.

The connection protocol is standard X.25 packets via the D channel.