TELECOM ACCESS STANDARDS NEWSLETTER NO. 119 February/March 2000 CONTENTS 1. MOBILE NUMBERING EXPANSION 2. TELEPERMIT RESERVATIONS AND NEW FORMS 3. ON-LINE PTC SPECIFICATIONS? 4. VOICE OVER PACKET OPERATION 5. D-AMPS MOBILE-ORIGINATED SHORT MESSAGE SERVICE 6. LABORATORY TESTING OF "UNSPECIFIED" FEATURES 7. HARVEST NZ LTD RELOCATION 8. PABX TRUNK LOCK-UPS 9. VACANCY FOR AN ENGINEER IN ACCESS STANDARDS RETURN TO MAIN INDEX 1. MOBILE NUMBERING EXPANSION It has been reported that some customers have been unable to call the recently introduced 7-digit mobile numbering range, "025 6xxx xxx". Investigations revealed that some PABX systems have not been programmed to provide access to this previously unused block of numbers. PABX suppliers and maintainers are asked to ensure that this block is opened for access in all systems. The same principle applies to all new number blocks activated by Telecom and other carriers. There can be many changes each year, so it would be a lot of work to keep all details up to date at every PABX. Unless there is a requirement to toll bar specific codes, the best approach for PABX maintainers may be to simply leave all codes commencing with digits 0 - 9 "open". 2. TELEPERMIT RESERVATIONS AND NEW FORMS We have published two new forms on our website to cover Telepermit reservations; one for general CPE and the other for cellular terminal equipment. While I am reluctant to grow the number of forms we use, as this can cause confusion - especially for new people entering the CPE business, we have aimed to make things clearer and more specific for particular classes of CPE. As suppliers will appreciate, where there are requests for reservations, they are usually made before we have access to the test reports. There is thus a risk that numbers will be allocated in the wrong PTC-series or that product names will be changed when they are finally brought to market. Our preference is to avoid the need for reservations by speeding up our processing of applications. However, where testing is still to be finalised we do not even have an application to process. If there is a genuine need to reserve a permit number to expedite market entry, we are happy to co-operate thorough our reservations process. However, it has disrupted our operations and only delayed other applicants when we provide a "fast track" reservation service and then not see the product enter the market until months later. As a result, we now make reservations valid for only 2 months in order to focus the service on those products which genuinely need to be "fast-tracked". Another problem for analogue CPE is the need for the RN to be assessed in accordance with PTC 200 test conditions. Since the RN needs to be shown on the Telepermit label, this part of the testing has to be done before the reservation can be granted. Applicants should note that a reservation is essentially no different from a full application in that both are based on contracts between the applicant and Telecom under which the applicant undertakes to comply with the conditions of the permit or reservation grant. This is why we have a formal declaration on each form and seek signed forms via mail or fax, rather than emailed copies. Those suppliers being issued with reserved Telepermit numbers are reminded that part of the declaration is an undertaking NOT to release product to market until the Telepermit has been formally granted. Any non-compliance with this condition will result in our refusal to grant further reserved numbers. 3. ON-LINE PTC SPECIFICATIONS? With everything going "on-line" these days, we have been conscious of our practice of limiting the availability of PTC and TNA specifications to printed paper copies. The reason for this has been our need to "pay our own way" within Telecom. We are now considering a progressive changeover to web publication. This has already proved reasonably successful for our Newsletters and other publications, especially as regards keeping information up-dated and having back-copies readily available. We have compared the payments we receive for publications relative to the payments received for Telepermits and have found that we could continue with our usual approach of "user pays" by making specifications free on our website, but increasing the cost of PTC grants by a nominal 16% - just $50 extra on the usual single-line product Telepermit. This approach would make our specifications available worldwide (not only free, but also more easily accessible) to industry participants. This should be particularly useful to those local agents who copy and post or courier the documents to their overseas principals. From our viewpoint, we would avoid the need to handle ordering enquiries, then print, store, pack, post and bill the documents. Since we introduced Telepermits in 1987 at a charge of $200, we have had only two price rises (an increase to $250 in 1990 and to $300 in 1995). An increase to $350, plus GST, would not seem unreasonable, especially if access to specifications and up-dates is provided free of charge. Our aim would be to publish the specifications in "pdf", so that the printed copies retain their original formats. For those few parties who still need paper copies, we would make them up on demand. However, the number of readers in this category must be close to nil these days, and special one-off print runs would justify an increased price. CPE suppliers are invited to comment on this proposal. If it gains general support, we propose phasing it in progressively. Those parties applying for Telepermits before the relevant PTC specification for their product has been published on-line, will continue to be charged for their Telepermit s at the current prices. 4. VOICE OVER PACKET OPERATION For some time now, we have been investigating Telepermit requirements for the new generation of CPE for Voice over Packet (Frame relay, Internet Protocol, etc), especially for PABX systems and proprietary telephone sets, which are now arriving here in increasing numbers. In the following , I refer to these systems as "VoP". Telecom is also, of course, looking into using VoP for public network applications. The VoP PABX systems that are here now have generally used 64 kbit/s speech encoding systems, so their performance is not too far removed from our standard PCM-based circuit-switched standards. However, systems using speech encoding at rates down to around 5 kbit/s are expected in the near future. The ITU have published a number of Recommendations on VoP operation; namely those in the G. series. G.109, G.113, G.114 and G.177 are some of the documents that lay out the principles involved in assessing quality of transmission. Another ITU Recommendation very worth reading for background on the principles of packetised voice transmission is G.764. Amongst other things, these ITU Recommendations deal with the concepts of overall speech quality - something that we, in Access Standards, are anxious to maintain as close as possible to present levels. VoP presents some interesting issues in overall speech performance. With data, even relatively long delays (perhaps hundreds of milliseconds) and the possibility of packets arriving in the wrong order are not usually a serious problem. The main issue is to ensure that packets are not lost, and buffers can introduce quite long relative delays to ensure they are all complete and re-assembled in the right order. Speech presents a quite different set of conditions. It is important for perceived quality that delays are not too long and that speech packets are delivered in the correct order to ensure there are no interruptions or garbling of speech. Delay is especially critical where the call is terminated on a 2-wire telephone and echo can be troublesome. Echo cancellers are thus necessary in many cases. On the other hand, speech signals are not critical for up to around 1% of lost packet frames because of the ability of the human ear to ignore very brief interruptions in transmission. How VoP encodes the speech signal and splits it into packets can vary widely. In effect, there are usually two encoding processes; the first digitises the signal and undertakes any compression, while the second removes idle (silent) periods and packetises the resulting digital signal. As mentioned above, the initial encoding can be at rates of between 5 and 64 kbit/s, with significant differences in perceived quality. These two processes have the main impact on speech quality, assuming that there is no further significant delay or further re-encoding processes in the call path, and no loss of packets due to traffic congestion. Unfortunately, on a "hybrid" point-to-point call across several private and public networks, these last constraints may be applicable. The ITU has drawn up its recommendations based on a "computational model for use in transmission planning" (Rec. G.107), in which it outlines the various impairments to speech quality and their causes. These are applied to practical operating conditions in Rec. G.113, which deals with the overall effect of the many and variable impairments in combination. Unfortunately, these models do not yet attempt to "allocate" impairments to the various stages of a VoP call, so we will need to set some arbitrary values to get things started. The traffic conditions and call paths vary widely in "real life" situations, especially with the growth of private networks and potential call diversions, plus the impact of heavy traffic or even congestion on packet flows. Many of the variables are thus outside the control of an equipment designer. For this reason, the test procedures of our draft PTC Specification for VoP products focus on the performance of an IP-telephone or Terminal Adapter to a Gateway (the device which interfaces with the PSTN) connected over a direct metallic call path. Our assumption is that, at this early stage with few VoP systems in service, the great majority of calls will either remain in their initial packet format end-to-end over a private network (which we are not directly concerned with for Telepermit purposes), or go through a single conversion to 64 kbit/s digital, for transmission over a circuit-switched public network. Where the interface between the VoP system and the PSTN is a digital trunk, this has to be synchronised with the public network, We expect to be publishing the "Draft for Industry Comment" of our VoP PTC Specification on our website some time soon and will seek input from those in the industry who have practical experience of the design and operation of these systems. Our aim is to develop a PTC Specification that will set reasonable conditions for the connection of VoP equipment, ensure compatibility with our network and, as far as possible, maintain present quality of service standards. More on the subject of VoP operation will be published in a future Newsletter. 5. D-AMPS MOBILE-ORIGINATED SHORT MESSAGE SERVICE Telecom is extending the existing Short Message Service (SMS) provided via its cellular network's Message Centre (MC) to support a Mobile Originated Short Message Service (MOSMS). These services cope with messages of up to 160 ASCII characters. As implied by its name, suitably equipped IS 136 D-AMPS handsets will be able to originate messages to other IS 136 mobiles. This applies whether or not the receiving IS 136 mobile is actually capable of originating such calls. This service has only recently been implemented in D-AMPS networks overseas and there is still a limited number of suitable equipped handsets on the local market. To give handset suppliers an opportunity to provide the necessary products to support this service, a brief specification and testing procedure is being drawn up as an interim measure, pending publication of a formal PTC Specification. Because it is of fairly limited reader interest, this interim specification is not being published in this Newsletter. Pending its publication on our website, interested parties are invited to email me for further information (doug.burrus@telecom.co.nz). 6. LABORATORY TESTING OF "UNSPECIFIED" FEATURES From time to time, products offer novel features as their selling points but, because they involve a new use for some network characteristic, these features have not been covered in the relevant PTC Specification. From the supplier's viewpoint, the feature may sound really useful, but it is pointless to stress an aspect of the product that has not been shown to be compatible with the Telecom network. This is especially true when a little research shows that successful and reliable operation of the feature is quite doubtful. Should the customer find that the product does not do what is claimed, the supplier is ultimately liable for remedying the position. We expect our accredited laboratories to raise any issues of this nature with us, so that we can evaluate the position. If the feature is compatible with the network and can be expected to operate reliably, then we will accept it, even though it may not be covered explicitly in our specifications. In some cases, we may need to amend the PTC specification to clarify the position. We cannot do this if the matter is hidden in some way. In a recent case, a test laboratory simply ignored the major marketing feature of a new product because it was not defined in the PTC Specification. Had we not queried the matter, the supplier could have been very embarrassed and put to some cost. Customers that purchased the product on the basis of the claimed feature would have had fair grounds for a claim when they found that it dropped the call each time it was used! This is one of the reasons that we request a product brochure and a User Manual as part of a Telepermit submission. 7. HARVEST NZ LTD RELOCATION The Telepermit testing laboratory operated under the Harvest Electronics name in past years is now re-named Harvest NZ Ltd and has re-located its premises to: Old ENZA Building Pragnell Street MASTERTON The mailing address is P O BOX 911, MASTERTON Their new telephone number is +64 6 370 1991 and their new fax number is +64 6 370 1993. This information is now also shown in the list of accredited laboratories on our website. The contact person for testing matters is Shane Harvey. 8. PABX TRUNK LOCK-UPS There have been reports recently of PABX trunks being locked up for long periods - sometimes weeks at a time. This not only prevents the customers concerned accessing their trunks at both the originating and terminating ends of the call, but may also result in the calling customer being billed for long duration calls. When the predominant use of the PSTN was for voice and no customers deliberately made day-long calls, Telecom was able to check out the relatively few calls which were reported by our exchanges as exceeding 24-hours. This allowed us to release lock-ups that had occurred. However, this process has been complicated by the increasing number of internet calls which are virtually continuous. As a result, there are internet calls that do need to be charged for very long durations and our staff can no longer assume that such calls are actually locked-up trunks. It appears that customers are not checking whether their PABX trunks are accessible until they find difficulty in gaining access to the network. In fact, lock-ups may not be detected at all in those cases where both customers have large traffic streams and large numbers of exchange lines. PABX maintainers are asked to check the status of their client's exchange lines and be on the look-out for any that are found busy with no speech or data signals present. Where such trunk conditions are found, it is recommended that test calls be set up to the trunk concerned to make sure it is giving the appropriate release signals back to the exchange. 9. VACANCY FOR AN ENGINEER IN ACCESS STANDARDS We are still on the look-out for a replacement Engineer, with either an Engineering degree or NZCE, or equivalents. As explained in Newsletter No. 118, the main attributes for work in Access Standards are a wide general experience in telecommunications and the ability to deal with the industry in a friendly and tactful manner. Above all, there is a need for the replacement staff member to be able to investigate new product features, developments in technologies and any other matters related to the preparation and publication of our PTC Specifications. Any telecommunications engineers with the right sort of background are invited to call me on (04) 382 5345, send me a fax to (04) 384 5368, or email me at "doug.burrus@telecom.co.nz". DOUG BURRUS Manager Access Standards