| The use of Escape Codes for the purpose of interworking between PSPDNs
and ISDNs and the transition to TOA/NPI signalling format |
Number plan interworking
between the E.164 and X.121 numbering plans when calling to or from a terminal
on an X.25 network from or to a terminal on an ISDN is currently achieved by the
use of escape codes. The long term recommended signalling method for
interworking is use of the TOA/NPI signalling format within the X.25 protocol as
this method does not use escape codes. Details regarding number plan
interworking can be found in Recommendation X.122 / E.166
ITU-T Study Group 2
(responsible for the E.164 Numbering Plan) has decided that the E.164 Escape
Code �0� will be officially discontinued as from 31 December 2000 (see
Recommendation E.165.1) in order that digit �0� may be re-used as the first
digit of a E.164 Country Code at some time in the future. To ensure a smooth
transition to NPI/TOA signalling if and when required, Study Group 2 will inform
the telecommunications industry 3 years in advance of its intention to implement
an E.164 Country Code starting with digit �0�� which would conflict with
its use as an escape code. This notification has not yet been given.
Network operators and equipment
vendors should take careful note of the above agreement between Study Group 2
and Study Group 7 regarding the E.164 Escape Code �0�, the impact of which
is summarized as follows.
1) PSPDNs interworking with
ISDN terminals identified by 15 digit E.164 numbers require TOA/NPI signalling to be implemented.
2) PSPDNs interworking with
ISDN terminals identified by 14 or fewer digit E.164 numbers may continue to use escape codes as per current
practice, but may need to consider a transition plan to TOA/NPI
signalling.
a) As defined in ITU-T
Recommendation E.165.1, the E.164 Escape Code �0� will be formally discontinued as of 2359 hours
UTC, 31
December 2000. However the E.164 Escape Code �0� may be continued to
be used on an informal basis for the purpose of establishing calls from
ISDN terminals to PSPDN terminals in the case where the E.164 ISDN terminal
number length is not greater than 14 digits (see ITU-T
Recommendation X.122). At least 3 years notice will be given of any intended use
of digit �0� which would conflict with its use as an escape code. Network
operators and equipment vendors should check with the ITU-T to
ascertain the status/use of digit �0� within the Recommendation
E.164 framework.
b) The X.121 escape codes
remain in force.
For further information, you
may contact the Rapporteur for Question 3/7, Numbering and routing for public
data networks:
Mr. Peter R. HICKS
Telstra Research Laboratories
770 Blackburn Road
(PO Box 249 Rosebank MDC)
Clayton
Victoria 3168
Australia
Phone: +61 3 9253 6308
Fax: +61 3 9253 6777
Email: peter.hicks@team.telstra.com
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