7. TNA 134 - CODING OF CALLED AND CALLING PARTY NUMBERS IN DSS1
As TNA 134 does not explicitly cover the coding of called and calling party numbers for Centrex and VPN (Virtual Private Network) interfaces in Digital Signalling System No. 1, this article explains the position in some detail.
On a public ISDN line, the ISDN numbering plan defined by ITU-T Recommendation E.164 applies. Numbers may be dialled as a local (directory) number, a national number, or an international number.
On a Centrex or VPN line, a private numbering plan applies. This numbering plan is unique to each customer. The same number for a different customer will connect to a completely different line. To call a public number from a Centrex or VPN line, an escape prefix is used to indicate that the number following is a public (E.164) number. This escape digit is normally the digit "1".
As the result of these basic differences, the following coding arrangements apply:
A. Called party number information element
i. Originating access
Public ISDN Line
A "Numbering plan identification" of E.164 or unknown is valid. E.164 is assumed if unknown is used.
If "Type of number" is coded subscriber, national or international the digits must be coded as shown below without any prefixes.
Type of number ..... Digits .............................................. Example
Subscriber ................ directory ........................................................ 888 1234
National ................... area code + directory .......................................... 4 888 1234
International .............. Country code + area code + directory ....................... 64 4 888 1234
"Type of number" may be coded unknown, in which case the digits may be:
- a directory number,
- prefix "0" followed by a national number,
- prefix "00" followed by an international number.
Centrex and VPN Lines
A "Numbering plan identification" of unknown or private numbering plan is valid.
The"Type of number" should be coded unknown and the digits coded:
- an intercom (private) number,
- prefix "1" followed by a public number.
ii. Terminating access
This applies to public, Centrex and VPN lines.
The "Numbering plan identification" is always coded E.164.
The "Type of number" is coded:
- subscriber if line does not have DDI (Direct Dial In) assigned,
- unknown if line has DDI assigned.
The number digits sent are:
- directory number if line does not have DDI assigned,
- the last n digits of the directory number as specified if the line has DDI assigned.
B. Calling party number information element
i. Originating access
For public, Centrex and VPN lines the subscriber number is passed from the user to the network (currently 7 digits). Currently the "Numbering plan identification" and "Type of number" are not checked, but should be restricted to:
.... Numbering plan identification ........ unknown .... or .... E.164
.... Type of number ........................ unknown .... or .... subscriber
ii. Terminating access
The coding of the Calling party number information element from the network to the user varies depending on the call type. If the call originated in another network (in New Zealand or overseas) the coding will be dependent on the information received from that network. The Calling party number information element will normally be coded:
Type of Call ........... Numbering plan identification ........ Type of number ........ Digits
Centrex intercom call ........................ unknown ...............................unknown ...............
intercom number
Public and VPN .............................. E.164 .................................. National .................
national number
.................................................. E.164 .................................. International ............
international number
The above information will be incorporated into the next edition of TNA 134.
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8. CELLPHONE NUMBER DISPLAYS
Most users can determine the cellphone's directory number by keying "Recall #", although others may key in different codes to display their number. The numbers displayed by AMPS cellphones used on the Telecom network have led to a number of queries lately. The most frequent question was in relation to the anomalous display of the new 025 2xxx xxx number range, which was announced in Newsletter No. 89. In brief, "Why are these numbers displayed as "530 1 xxx xxx" and not "64 25 2xx xxxx?" To answer this question, it is best to outline how the overall mobile numbering system works.
ITU Recommendation E.212 defines the structure of a mobile's number, formally known as the International Mobile Station Identity (IMSI), in three parts. These are the Mobile Country Code (MCC), the Mobile Network Code (MNC) and the Mobile Station Identity Number (MSIN). These numbers are NOT the same as the usual international telephone number. This is why a user does not see the digits "64 25 xxx xxx" displayed.
Our numbers are allocated according to a worldwide numbering scheme under which the country code "530" is allocated for New Zealand cellphones ( as another example, Australia is allocated "505"). The Mobile Network Code for our 6-digit network is "0" , but this is often suppressed. Thus, a 6-digit number may be displayed as "530 0 xxx xxx" or "530 xxx xxx".
A new Mobile Network Code had to be allocated for the 7-digit part of the Telecom network and, while "2" would have been the obvious choice, this had already been assigned. As a result, "1" had to be allocated and, unlike the "0", this is not suppressed by the cellphone display. Unfortunately, we cannot change the international system, so customers and other involved parties will need to accept that although the number is displayed in the format "530 1 xxx xxx", this really does correspond with the more familiar "25 2xx xxxx" and there is no error in the display.
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9. INTRODUCTION OF "EXTENSION BILLING" FOR ISDN PRA CUSTOMERS
Telecom will soon be introducing Extension Billing for customers who have PABX systems connected via Telecom's Primary Rate Access ISDN service.
The new service means that the Telecom bill will group calls by the Direct Dial In (DDI) extension which made them. This will enable businesses to trace all calls made by extensions and to compare costs and usage extension by extension.
Extension Billing will make it easier to pass on the cost of calls to clients. The service also makes it possible for businesses to share PABXs, because costs can be allocated accurately.
To receive Extension Billing, customers must have
an ISDN Primary Rate connection, and
a PABX model which supports ISDN and 'A' party number forwarding, and
Direct Dial In (DDI) lines.
The signalling protocol for user provided numbers is defined in TNA 135, and it is likely that some PRA ISDN capable PBX systems already have this protocol in place. In some PABXs, it may be necessary to have the protocol activated. This means ISDN capable PABX suppliers can expect to receive enquiries from customers once the service is available.
For further information contact Gillian May, Telecom Marketing, on 0800 GILLIAN (0800 44 55 42).
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10. "FAXABILITY" FOR DATA MODEMS
Telecom's DA-4 Distinctive Ring cadence has so far been promoted primarily as an inherent part of the "FaxAbility" service. Nevertheless, use with a facsimile machine is NOT the only option. "FaxAbility" is equally applicable to any type of data call or to any needs for a second number and ring cadence to permit incoming call discrimination.
Where modems or other CPE have the capability to support ring cadence discrimination and this feature is shown by laboratory test reports to be compliant with Telecom ringing cadences, the supplier is welcome to submit these reports to Access Standards. Given our confirmation, Telecom's Services Division will accept applications from the Telepermit holder for the right to make use of Telecom's registered "FaxAbility" logo in marketing the product. There is NO charge, but such use MUST first be authorised by Telecom.
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11. SOHO STANDARD
The new SOHO (Small Office/Home Office) cabling standard mentioned in Newsletter No. 93 has been published as AS/NZS 3086: 1996 and is now available from Standards New Zealand Customer Services. The price is $32.40 for members or $40.50 for non-members, inclusive of GST. This new Standard and any others required can be ordered from Standards New Zealand by fax on (04) 498 5994 or by phone on (04) 498 5991.
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12. TNA 139: WARNING
Telecom's TNA 139 was published in 1992 to explain the differences between Telecom's ISDN, which is based on the 1988 ITU Blue Book and Telecom Australia's ISDN, which was based on the ITU Red Book. Since Telstra's announcement that they will be introducing "ETSI ISDN", we have had numerous enquiries from prospective purchasers of TNA 139, thinking that the document gives information relative to the ETSI version. This is not the case. Once we have further information on the Telstra ISDN, we may be able to publish a new comparison document. At this stage, we do not know which of the 300 or so ETSI ISDN specifications Telstra actually supports.
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DOUG BURRUS
Manager
Access Standards
OCTOBER/NOVEMBER 1996
