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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) decided that the E.164 Escape Code ‘0’ would 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, if required. 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 17 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’ was 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 3/17, Numbering and routing for public data networks:

Mr. Peter R. HICKS
Telstra Research Laboratories
770 Blackburn Road
(PO Box 249 Rosebank MDC)
Victoria 3168
Phone: +61 3 9253 6308
Fax: +61 3 9253 6777


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