TELECOM ACCESS STANDARDS NEWSLETTER NO. 130 November 2001 CONTENTS 1. TELEPHONE LOUDNESS RATING CHANGES 2. HOW THE LR CHANGES IMPACT ON VOICE QUALITY 3. FALSE EMERGENCY SERVICE CALLS 4. CDMA/AMPS MOBILE PHONE POWER BOOSTERS 5. JACKPOINT COATING MATERIALS 6. LEVELS AND PAD SETTINGS FOR VOICE MESSAGING SYSTEMS 7. CALL CHARGING AND NETWORK NUMBERING RETURN TO MAIN INDEX 1. TELEPHONE LOUDNESS RATING CHANGES Voice-over-packet technology in various forms (VoP, VoIP, VoATM, VoADSL, etc) is now being introduced into both private and public telecommunications networks. In the following, I will refer to the various technologies in a generic way, as "VoP" (Voice over Packet) This trend to VoP will accelerate as the potential cost and service advantages become more widely known. However, careful management of voice transmission levels is needed to ensure that end-to-end voice quality is not unduly compromised by any additional delay, distortion or other impairments introduced into connections by VoP technology. This also applies to digital cellular mobile systems (GSM, D-AMPS, and CDMA) all of which have transmission characteristics different to those of a circuit-switched network. Connections that are either too loud or too quiet adversely affect the users' ability to converse. Newsletter No. 129 explained the increased significance of "loudness" and mentioned the need to aim for the optimum loudness rating limits for telephones. This is a preparatory step towards maintaining voice quality in a VoP environment. Because Loudness Ratings can be particularly confusing for many readers, I will use the terms "quieter" or "louder", as well as the actual SLR (Send Loudness Rating) and RLR (Receive Loudness Rating) figures. The confusion comes about because LR's are a measure of the loss in "loudness" between the talkers mouth and the listeners ear. A "higher" positive value (or a lower negative value) thus represents an increase in loss and a quieter connection. Conversely, a "lower" positive value (or a higher negative value) represents a decrease in loss and a louder connection. Analogue telephones PTC 200 specifies the currently acceptable range of Send and Receive Loudness Ratings, which were last revised in 1993 to cover the introduction of limited current feed bridges and to allow for quieter telephones. At present, PTC 200 permits a tolerance range of + 6 /- 3 dB for SLR and + 5.5/ - 3.5 dB for RLR about the target design values of + 5 dB and - 6.5 dB respectively. The aim at that time was to use the opportunity provided by our digitisation of the inter-exchange network to permit a wider range of North American mass-market voice products to be connected to the Telecom network. These generally provide quieter (higher SLR value) performance than the telephones traditionally supplied by Telecom. Because many of the telephones being manufactured were aimed at the very large North American market, it was expected that this change would allow a wider range of models to be connected here. Now that we need to prepare for the VoP world, it is proposed that PTC 200 will again be revised. This time, the aim is to more closely focus the permissible Send and Receive Loudness Ratings around the optimum values determined in accordance with ITU-T recommendations, by reducing the tolerances to ± 3 dB. The acceptable Receive Loudness rating will of course, be extended for telephones with user-adjustable receive amplification. The new values for analogue voice products will be:- SLR = Minimum (Loudest) + 2.0 dB (no change)   Objective + 5.0 dB (no change)   Maximum (Quietest) + 8.0 dB (currently + 11 dB) RLR = Minimum (Loudest) - 9.5 dB (currently -10 dB) - 14.0 dB with receive volume control (no change)   Objective - 6.5 dB (no change)   Maximum (Quietest) - 3.5 dB (currently -1 dB) Any voice call comprises the sending and receiving telephones, plus the lines at each end and the exchange network itself. In setting out the Telecom Transmission Plan, the full range of possible connection conditions is taken into account. The loudness loss of a call from end-to-end, i.e. from the talkers mouth to the listeners ear, is assessed in terms of the Overall Loudness Rating (OLR) and the effect of the above changes is to reduce the maximum OLR on a worst case connection by 5.5 dB. A check of the last 55 approved Telepermit applications for telephones showed that only 7 would fall outside the SLR limits now being proposed. Most are a good fit with the new RLR values and many of the more recent telephones have receive volume controls that can be adjusted across the required range. Since these changes draw Telecom requirements into line with the internationally recommended performance, it is not expected that many voice products will be restricted from gaining a Telepermit. Also, of course, manufacturers have the option of adjusting loudness ratings of their telephones during manufacture if they find that this is needed. Digital telephones Digital telephones include all 4-wire telephones such as ISDN, native IP, and cellular mobile. Loudness ratings for these are all set during manufacture. On an all-digital connection, the overall loudness is set entirely by the characteristics of the telephones themselves, as there are no variable 2-wire line losses to take into account. It is important that the potential transmission advantage of digital 4-wire telephones is not lost through unduly wide limits or inadequate controls. As with analogue telephones, the Telepermit requirements will be amended to permit a reduced tolerance of ± 3 dB. The new values for digital voice products will be:- SLR = 8.0 ± 3.0 dB (the current range is 8.0 ± 4.5 dB) RLR = 2.0 ± 3.0 dB (the current range is 2.0 ± 4.5 dB) Timing As is usual practice, reasonable notice is being given of the implementation of the new LR values. These will come into force for new Telepermit applications on 1 April 2002. Expiry of earlier Telepermits Telepermits granted after 1 January 1999 are valid for a period of no more than 5 years. Telephones Telepermitted from that date will expire from 2004 onwards and, if they are still in production, they will need to comply with the Telepermit requirements current at the time their Telepermits come up for renewal. Similarly, to avoid any anomalies, Telephones Telepermitted prior to 1 January 1999 will also be required to comply with the new LR values by 1 January 2004 - assuming any are still in production. In all cases, Telepermit holders are urged to take steps to make their products comply with the new LR values at the earliest opportunity, as this will benefit their customers. Industry comment Industry comment is invited on the above proposal, as it is important that all suppliers of voice products appreciate the issues and have some involvement with these changes. VoP technology is coming fast and we need to prepare now for the transmission changes it will introduce. As explained, more closely defined Loudness Ratings are a key to making the best of this new technology, especially during the transition from circuit to packet switching and the world's networks are a mixture of analogue, digital, packet and circuit switched. 2. HOW THE LR CHANGES IMPACT ON VOICE QUALITY The primary objective of the above changes is to improve the quality of worst case connections. The improvements will be progressive, as only those existing products which already comply with the new LR values and those future products formally required to comply with the new specifications will have any impact. As explained above, Overall Loudness Rating (OLR) is the sum of the SLR, RLR and any network losses. The higher the value of OLR the quieter the connection. The following graph illustrates the relationship between OLR and the R value, as determined by the ITU E model. Newsletter No. 129 outlined the many factors involved in assessing the actual R value for a call and all of these impairments further reduce the R values. Excluding these other factors for simplicity, it can be seen that the slope of the right hand side of the curve is constant for a wide range of OLR. What is important is that every 1 dB reduction in OLR at the worst case end of the range corresponds with a 1.5 improvement in R value. The above changes have reduced the tolerances on both SLR and RLR on the "quiet side", and hence the OLR of a worst case PSTN-PSTN call will progressively improve in loudness by 5.5 dB. This is equivalent to an increase in R-value of around 8. In a VoP world, or any other circumstances where the nature of the call introduces additional impairments such that call quality would otherwise be considered unsatisfactory, these extra R units will become very significant. In the longer term, when more and more calls are digital end-to-end and most voice equipment complies with the optimum digital levels of SLR = 8 dB and RLR = 2 dB, the Loudness Ratings at least will be helping to achieve maximum call quality. 3. FALSE EMERGENCY SERVICE CALLS It has been reported that there is an increasing number of false or unnecessary calls to our "111" Emergency Service. Investigations showed that these are being generated by cellphones, but not as malicious or deliberately stupid calls. The actual cause was customers who had either programmed their "one button emergency call feature" or failed to deactivate this feature after it had been set as a default feature by the supplier. In many cases, the users were not even aware that the feature existed. If the user is sitting on or leaning against some hard object that presses against the relevant keypad button for more than a few seconds, a pre-programmed cellphone in their pocket can generate a "111" call without the user even realising. These "no speech" calls lead to a lot of concern and wasted time for our operators, as they do not know whether a caller is genuinely unable to speak or the call is unintended. While sorting this out, they are unavailable to handle genuine emergency calls. Telecom's recommendation is that the "one button emergency call feature" should always be disabled to avoid such false calls. Although it might seem a fairly unlikely event, with over two million cellphones now in service even a low probability can result in a large number of such unwanted calls. Cellphone suppliers/retailers are asked to ensure that the feature is not set up as a default on new cellphones and to make sure their customers are aware of this problem. It can apply to any cellphones used in New Zealand, not just those used by Telecom customers. 4. CDMA/AMPS MOBILE PHONE POWER BOOSTERS It was recently reported that "cdma/AMPS mobile phone power boosters" are being offered for sale. In New Zealand, these devices can only connect to the Telecom Mobile network to have any practical functionality, but none of these products have so far been granted Telepermits. Under the provisions of S.6 of the Telecommunications Act 1987 and Telecom's management rights under the Radiocommunications Act 1989, these units MUST NOT be connected to the Telecom network. Telecom provides for Telepermits to be granted to devices which meet the appropriate technical specifications for connection to its network. However, these "boosters", which are essentially bothway RF amplifiers, do not provide for the uplink (mobile unit to base station direction) power level to be under the control of the actual network. This is vital to the correct operation of a cellular radio system and a firm requirement of the relevant standard, EIA.TIA IS 95. These devices can output full RF power independent of whether they are used close to a cellsite or remote from it. In doing so, they will cause interference to network services for other users. Such boosters are sometimes used as network equipment where it is necessary to improve local services, but they are used at specific sites and with properly designed antenna systems to avoid interference to other users. Their use by mobile customers in any location and without such constraints is unacceptable. In February, the Australian Communications Authority published its intention of banning the use of such boosters unless adequate power control features have been incorporated into their design. That ban came into force in May and such devices may not be sold or used in Australia without formal ACA approval. "Cellphone power boosters", "antenna amplifiers" and like items are NOT permitted to be connected to, or to be used in conjunction with the Telecom mobile network until such time as Telecom has been satisfied that the products have been shown to meet the relevant technical specifications for connection to its network. Where it is considered that a device does comply, a "Telepermit" will need to be applied for and be granted before such products may be used on the Telecom mobile networks. 5. JACKPOINT COATING MATERIALS Telecom has approved a new coating material for its 2-wire jackpoints. This is "Certonal TL6x", manufactured by Acota Ltd in the UK. This material and 3M Co's "Fluorad FC722", are the only products formally accepted as coating materials for this purpose. Telecom recognises the assistance provided by Acota over recent months in helping to bring improvements in the jackpoint manufacturing process. What has become clear as a result of our investigations is that manufacturers have to pay particular attention to two aspects, which were not clearly identified when the draft specification was originally published in 1997. These are:- a. the drying process, which takes place after the printed circuit boards have been cleaned of flux residues. Thorough drying is essential for the coating material to properly adhere to the surfaces of the components, especially in the very confined spaces within the IDC connectors and the area where the socket contact springs emerge from the plastic separators; and b. careful control of the coating material to ensure that the solids/solvent ratio is kept within precise limits. If there is too little solids content, the coating effectiveness and service life is reduced. If there is too high a solids content, the material has reduced ability to penetrate into the above critical confined areas, which have proved to be common locations for corrosion to start. All suppliers of Telepermitted jackpoints have already been advised of the need to take special care in these areas and PTC 223 is now being updated to cover the processes in more detail and include additional "accepted components". In view of the critical nature of these issues on customer service reliability, suppliers will be required to certify that their manufacturing processes comply with the revised edition of PTC 223 on or before 1 April 2002. Since the original draft edition required suppliers to ensure that the cleaning and coating process "complies with the coating manufacturer's specifications", this is a change in detail rather than a change in the basic manufacturing principles. 6. LEVELS AND PAD SETTINGS FOR VOICE MESSAGING SYSTEMS Further to the article on this matter in Newsletter No.129, we have been asked whether the same level and pad settings apply to voice messaging systems connected behind a PABX or private network. Voice messaging systems are a little different in that they not only receive a call from anywhere in the world at a level dependent on the call path, but also have to re-transmit the received message at a level appropriate to a new call originated by the same customer. If this is not done, the message suffers the combined losses of two separate calls and could become unintelligible. The draft Supplement to PTC 109, which is currently published on the Access Standards website www.telepermit.co.nz has been revised to better illustrate the settings required for voice messaging systems. 7. CALL CHARGING AND NETWORK NUMBERING Details on call charging and network numbering for the PSTN were originally published by Access Standards on behalf of our Network Interconnection Group. With the advent of the internet and web publishing, the original printed version is no longer being up-dated. Instead, this information is now published free of charge on the main Telecom website, with the following URL:- http://www.telecom.co.nz/content/0,2502,200655-1553,00.html This page covers not only the telephone numbering scheme, but also lists area and access codes, residential and business "distance steps" and Telecom's toll charging structure. The page also has links to other useful Telecom information, such as the Telecom List of Charges. DOUG BURRUS Manager Access Standards