 TELECOM ACCESS STANDARDS NEWSLETTER NO. 101 NOVEMBER 1997
CONTENTS 1. PTC 222: REQUIREMENTS FOR CUSTOMER PREMISES CABLE (2-4 PAIRS) As explained in Newsletter No. 99, Telecom is changing to 0.5 mm conductors for its premises cabling, despite the risks of problems due to installers connecting mixed gauges in our earlier 3-wire jackpoints. This change gives us the opportunity to introduce cabling with the much higher transmission performance needed to support future network services. The new 0.5 mm cable is intended primarily for new installations and additions where 2-wire jackpoints are being installed. Although it will be used mainly for low frequency applications in the immediate future, 2-pair Category 3 (for operation at up to 16 MHz) is now regarded as the minimum for new work. This will provide at least partial "future-proofing" to cope with the increasing need for more bandwidth and higher data rates. For maximum flexibility, this new specification covers a range of optional cable types for "general purpose cable". This can be of 2, 3 or 4 pairs and meet Category 3, 4 or 5. To align with best practice, 4-pair Category 5 cable (for operation at up to 100 MHz) is recommended for use where the customer is more concerned about the need for future service capability than first cost. This cable is expected to support all projected new services for at least 10 years. PTC 222 has now been published as a "draft for public comment" to cover these new cables. This Specification is now available from Access Standards at a price of $25, inclusive of GST and postage. Purchasers of the draft are invited to submit comments on the text. The above price includes the provision of a copy of the final published version at no additional cost. 2. PTC 204: AMENDMENT No. 1 With the move to 2-wiring, it becomes feasible to accept a 2-pair version of the older "voice frequency" cable defined in PTC 204. This brings the early specification into line with our proposed practice of running two pairs instead of three pairs (originally intended to support up to two 3-wired lines). While the 2-pair variant of 0.4 mm cable is being made eligible for Telepermit purposes, it is strongly recommended that the new 0.5 mm Category 3 cable should be used for all new installations and additional lines. Although 2-pair 0.4 mm cable could be used for extensions of simple one line installations without causing any difficulty, prospective users need to consider that cable is intended to be installed for a good many years. The marginal saving in first cost by using 2-pair 0.4 mm Category 1 cable for new work instead of 2-pair 0.5 mm Category 3 cable is swamped by the cost of installation. Unfortunately, there are conflicting interests. Many installers and customers concentrate on minimising first cost, but customers' service expectations are growing rapidly. Installers are thus not really helping customers if they save a dollar or two today and customers have to spend hundreds of dollars to replace their cable in a few years time. Cable suppliers are urged to make this point clear on all 2-pair 0.4 mm cable offered for sale. Since there are few companies supplying telephone cable and all these will almost certainly be purchasing PTC 222, the actual amendment to PTC 204 is not being supplied with all copies of this Newsletter. Instead, it will be sent out with the draft of PTC 222. Any other holders of PTC 204 who are interested in having a copy of the amendment can request one from Access Standards. The one page amendment will be supplied free of charge. Return to Contents3. PTC 200 CORRECTIONS It has been necessary to make some minor corrections to Specification PTC 200, issue 2, which was released only last month. Since there are no really significant changes and few copies have yet been circulated, we are not making this a formal amendment and copies of the amended pages will be sent out free of charge to registered purchasers of this specification. These pages are to be used to replace existing pages. The page headers show "November", whereas the original headers show "October". For the record, pending receipt of the amended pages, the changes are as follows:- (a) Text page 6-2, clause 6.3(2) & Fig. 6-1: The voltage limit on the recommended lower limit at 100 mA has been amended to read "6 V" instead of "10 V". The 10 V limit was not considered justifiable and was set for historical reasons. (b) Text page 7-9, clause 7.7.5: Spelling error in note. (c) Appendix 2, pages 1 & 2, clause (10) & Fig. A1(b): Amended to clear up anomaly between the clause wording and the associated Figure. (c) Appendix 2, page 17, sub-clauses 7.5.2(3) & (4): Sub-clause (3) renumbered (4) to align with the body of Specification. Procedure for testing to sub-clause (3) added. (d) Appendix 2, pages 18 - 22: Repaginated. (e) Appendix 3, pages 1 - 22: The following clauses have actually been amended. The remainder of changes are the result of minor spelling errors, editorial amendments, or repagination:- Clause 4.2(2): "dBm" amended to read "dBV". Clause 4.5.1(6) & (8): "Return Loss" amended to read "Minimum Return Loss". Clause 4.10(6): Receive Loudness Rating expanded to include results for minimum and maximum volume control. Clause 5.7.1(1) - (3): If keypad layout non-compliant, details of actual layout to be given. Clause 7.5.2(3): Wording amended to read, "Ringer shall not respond to ringing of 40 ms duration. If it does respond, state actual minimum duration to which it responds." Return to Contents4. CHANGING DATA SERVICE ACCESS NUMBERS The Telecom Pacnet, Transaction (EFTPOS) and Videotex services are currently accessed using codes in either the old 17XY series or the more recent 087XY series, as shown below. The need for the 17XY option is historical and dates back to the early 1970s when access via 087XY was constrained by toll barring facilities. The continued use of the 17XY series for access to these services is now inappropriate as this part of the numbering plan is reserved for the customer support services provided by network operators. e.g., Telecomís 120 service for customer faults, 123 and 125 for customer service, etc. Other network operators need to be able to provide similar services via 1-series numbers, including 17XY. For some time now, Telecom has been encouraging users of these data services to migrate from the 17XY to the 087XY access codes, especially when a customersí equipment is upgraded or replaced. No new services of this type will be offered on a 17XY code. If your customer's equipment is due for replacement or you are installing new equipment to access these services, please ensure that they are programmed to dial the 087XY access codes.
5. CDPD AND AMPS CELLULAR CONTROL CHANNELS Both the United States Federal Communications Commission and our Ministry of Commerce allocate two frequency bands, each of 333 channels, for AMPS cellular use. The A-band, using the radio spectrum 825 - 835 MHz (mobile transmit) and 870 - 880 MHz (base transmit) covers channels 1-312, plus 21 control channels (channels 313 - 333). The B-band, using the radio spectrum 835 - 845 MHz (mobile transmit) and 880 - 890 MHz (base transmit) covers channels 355 - 666 plus the 21 control channels from 334 - 354. In the USA, each band uses its own separate set of control channels. Telecom's cellular network is an Ericsson 882/884 system. It uses a different control channel set-up, in that the 21 B-band control channels are used to control all traffic channels between 1 and 666, even though these are spread over both bands. These analogue control channels are used for the dual mode analogue/digital cellphones to EIA/TIA specification IS 54B, as well as for analogue-only cellphones to EIA/TIA specification 553. Dual-mode cellphones built to the later EIA/TIA IS 136 specification use a separate group of digital control channels. Again there are differences between US and Telecom New Zealand practices. The US allocates a group of frequencies above the original B-band as control channels. Because this spectrum is already allocated to another network operator in New Zealand, Telecom is using a group of channels at the top of the B-band for this purpose. The group we are using initially is referred to in the IS 136 specification as "Relative Probability Block 4" (search probability block 13), corresponding to channels 641 - 666. Additionally, to support this mode of operation, a digital control channel "pointer" message is appended to all analogue control channel messages every 4.8 seconds. Some analogue phones may misunderstand this message and we check for this possibility in our testing process. These arrangements lead to some important differences between New Zealand and US AMPS cellphone practice for Cellular Digital Packet Data (CDPD) services. Telecom has allocated the original 21 A-band control channels exclusively for CDPD, whereas the US practice is to allocate any suitable available channels within the ranges 1-312 and 355 - 666. These two differing allocation arrangements need to be appreciated by CDPD suppliers if they are to avoid problems in New Zealand with equipment originally designed for the US market. Telecom is not the only exception to US practice. For example, the Australian AMPS analogue cellular network operated by Telstra uses the A - band control channels for both A and B-bands. This means that cellphones intended for use in both Australia and New Zealand have to be set up to work with either block of control channels. Like many other telecommunications standards issues, where each network evolves under different circumstances or constraints, it is not easy to fully harmonise arrangements even when there would be benefit in doing so. Return to Contents6. CDPD TELEPERMITS As announced in Newsletter No. 97, Telecom is conducting trials of CDPD devices in parallel with its own implementation of a service compliant with the CDPD Forum REV 1.1 Specification. Things are in a state of flux, as the various standards and implementations are still being developed and we have limited experience of the potential compatibility issues arising from this new service. A number of different CDPD modems have been offered for use on the Telecom network. Some of these provide a range of features, such as optional packet or circuit switched operation, optional connection to the PSTN, etc. The Limited Permit trial system is being adopted at this early stage, as there are still some aspects which are not fully defined and cannot easily be fully tested. Those suppliers who intend to market products when the service is formally launched are asked to make at least interim applications for their permits. Overseas suppliers of CDPD equipment may also submit applications and arrange the necessary compliance testing in advance of their appointing New Zealand representatives to act as Telepermit Holders. All applications, including those from companies which have already been trialling CDPD equipment, should be addressed to Access Standards at this stage. It should be noted that where a device provides for dual cellular/PSTN connection, it will need to be tested for compliance with Telecom requirements under both modes of operation. Thus, for PSTN use, compliance with PTC 200 is required; for cellular operation, the Limited Permit arrangements outlined in Newsletter No. 97 apply as an interim arrangement. Under the terms of New Zealand consumer protection legislation, any Telepermits issued will have to be conditional on the supplier agreeing to either warn customers about potential problems, or to address any problems that arise in service. In this respect, mutual interference between the CDPD modem, the cellphone and its associated PC or data terminal are possible complications. Needless to say, Telecom's tests on such matters as spurious emissions are made from a frequency management and network compatibility viewpoint. These tests cannot cover the wide range of equipment that might be used in any combination by customers. Susceptibility to RFI is not measured in this country, nor is there any recognised national standard at this time. As a result, there may be a lot of equipment in current use that reacts adversely to a CDPD device emitting what could be over 1 Watt of RF at a distance of only a few centimetres. Network compatibility issues can be assessed within New Zealand by Telecom testing staff, but they will also require a copy of the User Guide, Service manual, programming information and any other relevant information needed to correctly set up and operate the product in all of its connection modes. Prospective suppliers should note that, as part of its frequency management responsibilities, Telecom requires copies of FCC test results for both in-band and out-band radio emissions. Here again, the limits set for out-of-band emissions in New Zealand are somewhat tighter than those that apply in the USA. It should be noted that the maximum level permitted here is -50 dBW for any emissions outside the overall 825 - 890 MHz band allocated for AMPS operation. As with all Telepermits, a grant indicates only that Telecom agrees to the connection of a device to its network. It is neither an endorsement nor a warranty. It is certainly not a guarantee that a device will be compatible with all other products in service. These are matters for suppliers to sort out directly with their customers. Return to Contents7. DIRECT DIALLING IN (DDI) DIGIT EXPANSION As the result of changes being made to the NEAX 61E exchanges in our network, the number of digits that can be passed forward from the network to a PABX or any other customer equipment with a DDI interface is being increased from a maximum of 4 digits to a maximum of 7 digits. The minimum number of digits passed forward is 2. These changes will be progressive and will not necessarily apply at every 61E exchange from a specific date. The necessary amendments to our PTC Specifications to cover this change will be published in due course. Return to Contents8. ISDN D IRECT DIALLING INTelecom is introducing on Basic Rate Access (BRA) lines an ISDN equivalent of the Direct Dialling In (DDI) service provided on the PSTN. The initial installation is currently under trial and the service is expected to be available quite widely by early 1998. Primary Rate Access DDI has, of course, been available for some time. Manufacturers and suppliers of DDI-capable ISDN products are invited to set up their equipment and confirm its compatibility with this new service. Arrangements are being made for this to be done prior to the formal launch date. This should help to ensure that the necessary customer equipment will be available to support the service as soon as it is introduced. Like DDI on the PSTN, DDI for Basic Rate Access will allow a BRA subscriber to associate multiple directory numbers with a group of ISDN BRA lines. In fact, there can be up to 511 BRA lines in a DDI group and up to 2000 DDI numbers serving that group. A caller can thus dial directly to a specific extension on an ISDN Private Branch Exchange (ISPBX) or other private system using BRA lines, without assistance from the operator. It also allows a common set of numbers to be used across a group of BRA lines, as in PSTN DDI. As many of the last digits of the directory number as are needed to identify the called extension are passed to the customer's equipment during call establishment. From 2 to 7 digits can be forwarded, but the same number of digits applies to all lines within the one BRA group. Similarly, services are assigned to the interface or group of interfaces, so all DDI numbers within a group of interfaces will inherit the same set of services. ISDN DDI is based on the use of the ISDN called party number and the standard DDI service does not include subaddressing. It should not be confused with another similar method used to select a terminal on a passive bus. This is the supplementary service known as MSN (Multiple Subscriber Number). With MSN, up to eight numbers can be assigned to a single BRA line. However, these numbers cannot be shared between different BRA lines. The DDI and MSN services are thus mutually exclusive. However, subaddressing can be used with ISDN DDI as an additional service. When a call is made from a DDI line, the calling number associated with that call will relate to the actual extension making the call. As such, it can be any valid number for the DDI group irrespective of the particular line used for the call. For calls to the PSTN, the number displayed will be the directory number of the extension. For calls within a Centrex group, the calling number displayed is that used by the extension within the PABX. Following on from the explanation given in Newsletter No. 99, Telecom's ISDN DDI meets the requirements of ETSI Standard ETS 300 064 as well as ITU-T Recommendations I.251.1 and Q.951.1. Full details of the signalling requirements for ISDN DDI are included in TNA 134, which is available from Access Standards (see Newsletter 99 for further details). However, there is correction to be made with respect to ISDN DDI and this will be covered in Amendment No. 1 to the specification. All registered purchasers of the recently published TNA 134: 1997 will be sent copies of this amendment free of charge. To arrange a suitable booking, manufacturers and suppliers wishing to test their equipment should telephone either Ronnie Alban on (09) 355-3854 or Graham Ockleston, Manager Technical Evaluation, on (09) 355-3853. Return to Contents9. ISDN - INTERWORKING BETWEEN NETWORKS, PABX SYSTEMS, ETC A recently reported problem and its outcome may be of interest to other parties involved with ISDN operations and help them avoid the same difficulties. The situation reported was that if ISDN calls from the Telecom network into a PABX system with an ISDN interface were diverted by that PABX into the Telecom cellular network, the calls were being dropped. On the other hand, calls from the PABX direct to cellular worked well. Investigations showed that Timer 310 in the originating ISDN exchange was expiring and thus releasing the call. This occurred after 10 seconds because no signal was received to turn the timer off. It was initially thought that the basic cause was the lack of an ALERT Message from the cellular network. This message, which is passed back on ISDN calls to indicate that the called party's line is being rung, usually precedes either an ANSWER Message or a RELEASE message. The lack of an ALERT Message is not uncommon, as it can also arise when interworking between the ISDN and older technology exchanges. The normal signalling sequence for calls diverted by a customer are that the originating exchange sends a SETUP message to the PABX, which responds with a CALL PROCEEDING message. The called PABX sends a SETUP message forward to start the second call to, in this case, the cellular network. The Telecom exchange initially responds by returning a CALL PROCEEDING message. This is followed by a PROGRESS message, which indicates that it may be necessary for the caller to listen to in-band tones because the call is being connected to another network. Normally, the call would continue with an ANSWER message and, finally, a RELEASE message. What was missed is that the PROGRESS Message returned from the second call must be passed transparently by the PABX to the originating exchange in order to turn off Timer 310. In this particular case, the cellular network does not send back an ALERT message, so the second call normally has to await either an ANSWER or RELEASE message, which might take well over the 10 seconds setting of Timer 310. As a result, it is important that this timer is turned off by the PROGRESS message, which occurs early in the setting up of the second call. While this particular case related to a PABX diverting ISDN calls from the Telecom network to the cellular network, PABX suppliers and maintainers should note that relaying of signalling messages will be necessary in other situations. In view of this, the general principle is that PROGRESS messages should be returned whenever call diversions are involved. Details are provided in clause 5.1.6 of TNA 134. Note that Table 9-1B explaining timer controls is only a summary. It is necessary to go to the main text for to get the full picture. To avoid any confusion, I should stress that the Timer 310 referred to above is the one in the public exchange. Newsletter No 73 covered the resetting of Timer 310 in the customer's equipment to 30 seconds, following the ITU decision in 1994 to increase it to between 30 and 120 seconds. This increase was made to allow for the longer set-up times that may be involved when calls are diverted. The 1997 edition of TNA 134 includes this revised timer setting. Return to Contents10. MORE ON THE MODULAR PLUG STANDARDS SAGA In Newsletter 100, I omitted mentioning another standard which covers 8-way modular plugs and sockets. This is AS/NZS 4102, which is the Australia/New Zealand version of ISO/IEC 10173. This Standard deals specifically with the wiring terminations for ISDN Primary Access S/T interface. Like the other Standards, it provides full details of the dimensions of the plugs and sockets. This information aligns with that given in the other specifications and Standards I referred to. The transmit and receive pin-outs align with what I referred to as TNZ8/2, but AS/NZS 4102 also provides for optional shields and power sink/source on the pins which have no connections on TNZ8/2. One other point: be careful using the terms "RJ11", "RJ12" or "RJ45" when dealing with North American suppliers. They may not understand what we mean by these terms in New Zealand Australia! Return to ContentsDOUG BURRUS Manager, Access Standards |