TELECOM ACCESS STANDARDS NEWSLETTER NO. 100 OCTOBER 1997 CONTENTS This issue is something of a landmark for the Telepermit system in that the Newsletter and the group itself were originally expected to survive for no more than 3 - 4 years. The original plan was for the group to set up CPE deregulation during 1987-89 and then step back from the operational aspects, leaving these to another group. When network deregulation was announced in 1988, the group took on the associated roles of publishing network interconnection specifications and was absorbed into the Corporate Policy area, so that the customer and network connection requirements could be dealt with in a consistent and coordinated way. We have subsequently become part of the "Network" division of Telecom. Like the group, the Newsletter also was originally expected to be published for only 3-4 years. When we first got under way, as the main author, I certainly never expected to be writing the 100th issue. Nevertheless, with network and new service developments and a massively increased range and number of CPE products, it looks as if there will be a continuing need to publish some sort of Newsletter to the industry. This should help to ensure that the many CPE suppliers now involved in the local market will continue to be able to provide products compatible with Telecom's network and service implementations. From comments received, it appears that these Newsletters are meeting their intended purpose of keeping the industry informed of developments and helping to avoid any serious compatibility problems. I certainly hope this is the case and, if not, that readers will let us know what improvements they would like to see for the next 100 issues - should we ever get that far! 2. CHARGES FOR INTERNATIONAL DIRECTORY ASSISTANCE SERVICEAs recently announced, Telecom will be introducing a call charge for international Directory Assistance calls from 1 December. This means that the service code "0172" may require toll-barring on any PABX systems that are currently set up to permit these calls. There is already a charge in place to business customers for the national Directory Assistance service available on "018". In many cases, all "01x" codes will already be toll-barred, especially the "017" codes, which relate to international services. Similarly, "018" may already be barred as this is already a charged service. However, some of the larger PABX systems may still be differentiating between such codes as "010" for operator assistance and "0172" for International Directory Assistance. Suppliers and maintainers are advised to note this change and be in a position to advise their customers with respect to additional toll barring measures that may be needed. 3. "RJ11, RJ12 AND RJ45" SOCKETS As a number of people have asked for an explanation of the terms used to describe the various "American" modular sockets, the following may be of general interest, as well as providing some background for Item 6. Part 68 of Volume 47 of the US Code of Federal Regulations (sometimes referred to on product labels as "FCC 68" or "Complies with FCC Part 68")defines in detail the mechanical specifications of the standard 6-way and 8-way North American modular sockets (which they refer to as "jacks") and their associated plugs. A smaller 4-way modular plug is commonly used for handsets and for line cord connections to the CPE, but not for connection to the fixed wiring. There are also "keyed" versions of these plugs and sockets, with slightly different plastic mouldings. These can be used for specific applications in North America, but we rarely see them in this country. All of these sockets can be installed or pre-wired with a wide range of options, integral switch contacts, etc. Some examples of these wiring and contact arrangements are defined in Part 68 of the Federal Regulations with specific "USOC" numbers. "USOC" is the "Universal Service Order Code" used in the North American market. The various standardised "socket/wiring/contact" combinations are each given one of these USOC "RJ-series" ("Registered Jack") numbers so that there is a common reference for ordering any particular type. These codes can also be used for specifying wiring installation requirements. e.g., the number of lines to be terminated on a single socket and on what pins they are to be terminated. For example, 6-way sockets are normally used for telephone line connections, but may have 2, 4 or 6 wires connected. The actual USOC codes for these are "RJ11", "RJ14" and "RJ25", whereas we usually refer to the 6-way socket as "RJ12" - hence one source of confusion. To further complicate matters, the 8-way and 4-way sockets are commonly termed "RJ45" and "RJ11" in New Zealand and Australia. Again, these are not the correct terms in North America. USOC codes are much more explicit and usually also have suffix letters. The suffix letter "C" is used to define a flush-mounted socket and "W" is used to define a wall-mounted socket. Other suffix examples are the "RJ38X" and "RJ48X", sometimes used here to provide by-pass arrangements for security alarm connections with line grabbing. The "X" indicates a series connection. Both are variants of the 8-way socket, with auxiliary shorting bars. In general, several different "RJ numbers" are used to define the many 6-way and 8-way socket variants. In New Zealand and Australia, we generally use the looser terms "RJ11", "RJ12" and "RJ45" to describe the sockets themselves, independent of how they are wired. AS/NZS 3080 ("Telecommunications Installations - Integrated telecommunications cabling systems for commercial premises" used for large buildings) defines commercial building cabling standards in this country. A companion standard, AS/NZS 3086 ("Telecommunications Installations - Integrated telecommunications cabling systems for small office/home office premises" or "SOHO" applications) covers what is likely to be a growing market for installers. These standards are both based on the use of "RJ45" sockets. However, prior to their publication, the North American cabling standard EIA/TIA 568 or its successor, EIA/TIA 568A, were the de facto standards for commercial cabling. These introduced two other confusing terms; "T568A" and "T568B". As with most standards, there is a need for compromise if all parties are to agree. Two major US cabling industry participants used different ways of allocating the four cable pairs to the pins of the 8-way socket. Both arrangements had to be "recognised" in the standard, but this led to confusion when both methods were used in the same building. The two methods were defined in EIA/TIA 568 as "T568A" and "T568B". To help avoid confusion here, AS/NZS 3080 clearly stipulates that the 568A arrangement is the preferred one for both Australia and New Zealand. What may not be realised is that not all of these sockets have the same electrical performance, even though they look the same. For example, AS/NZS 3080 defines significantly different performance requirements for Cat 3, 4 and 5 rated sockets and there are also some lower rated products on the market. In general, unless the components are clearly marked with a Category rating or they are from a known source, unmarked RJ45 sockets should be avoided if the customer has specified the required cable performance. To further complicate references, the same physical 8-way socket design is also defined in AS/NZS 3594 (ISO/IEC 8877) for ISDN installations and in IEC 603-7. 4. PLUG AND LINE CORD WIRINGNorth American modular plugs are designed for machine termination onto "flat" or "D-section" cord, as are our own BT 6-way plugs. As such, there are usually no variations when RJ plugs are fitted at both ends of a cord, other than for the number of conductors used in the cord. The wires lay parallel within the sheath of the cord with no twist. This means that there is an inherent reversal in the wire-pin allocations at the two ends of the cord. Where necessary, this reversal is accounted for in the CPE design. However, it is not usually critical in North American CPE as, for all three sizes of plug, the centre two pins are used for the line 1 pair. Their system is 2-wire in any case and the number of wires within the cord is not usually critical for single line CPE. The problems start when the cord is terminated with a North American modular plug at one end and a BT plug at the other. The BT plug uses pins 2 and 5 for the line pair, whether it is intended for 2-wire or 3-wire connection. In 3-wire connection, pin 4 is used for the third "ringing wire, usually with a 4-conductor cord. The cord itself is usually wired with pins 2, 3, 4 and 5 terminated in the BT plug and pins 5, 4, 3 and 2 terminated in the RJ plug. In this case, the connection of the ringing wire for 3-wire CPE is allowed for within the CPE. However, this is not always the case. With 2-wire connected CPE, the supplier may prefer to leave the CPE with the line connections on pins 3 and 4 of a 6-way RJ socket to avoid internal changes Instead, a cord is supplied with a "split" connection at one end, so that pins 3 and 4 of the RJ socket connect to pins 5 and 2 of the BT socket. Often, the wires that were terminated on 2 and 5 of the RJ plug are cut off and not connected in the BT plug. Because BT plugs are white and not transparent, these changes are rarely visible to a casual observer. Thus, all BT-RJ line cords are not identical, even though they look the same, so it is important to check the compatibility of a replacement line cord with an item of CPE. Don't write off the CPE as "faulty" if changing the line cord fails to fix a problem. While the usual detachable handset cord is wired with the 4-way plug at both ends, there is no standard stating which wires are to be used for the transmitter and receiver. This complicates the provision of headsets, the wiring of which needs to match the associated CPE. In any case, it is important that the headset be matched to the CPE for transmission performance as there is certainly no standard for the transmit and receive levels at the handset-telephone interface.
FIG.1 Socket pin numbering is as shown above, looking at the socket from the front, as when plugging in the CPE. BT sockets number left to right, with 6 at the latch. RJ sockets also number left to right (latch at the bottom). FIG. 2 8-way modular plugs machine-connected at each end of the cord lead to inherent reversal of pin-outs. A standard 4 - conductor cord normally connects to pins 3, 4, 5 and 6 at both ends. The same conditions apply with BT 6-way plugs at both ends.
FIG. 3 Simple 2-wire CPE connection cord. With an "RJ12" 6-way modular plug at one end, the two centre wires terminate on pins 3 &4. The outer wires may or may not be connected. The two central wires terminate on pins 5 &2 of the BT plug, leaving pins 3 & 4 unconnected. The outer wires may be cut off at the BT plug end, or may connect to pins 1 & 6. CAUTION: An "apparent 4-conductor cord" may only be a 2-conductor cord in practice and NOT be suitable for 3-wired CPE.
FIG. 4 Typical 3-wire CPE connection cord. The four wires usually terminate on pins 2, 3, 4 & 5 of the BT plug at the line end, although pin 3 is actually unused. With an "RJ12" 6-way modular plug at the CPE end of the cord, the wires from pins 2 and 5 of the BT plug may terminate on pins 3 &4, or the cord connections may be to pins 2, 3, 4 &5, as for RJ-RJ cordage, with any cross-connections made within the CPE itself. Again, any "apparent 4-conductor cord" may NOT be suitable for all types of 3-wired CPE. CAUTION: There is NO STANDARD connection arrangement for BT to RJ12 or for BT to RJ45 cordage. Unless it is known that the cord was supplied with the product, always check out the cordage before assuming that the CPE itself is faulty. 5. MIXING PLUGS AND SOCKETSThe 6-way plug and the 8-way socket are designed to be compatible and the component tolerances are carefully specified to ensure a reasonable fit. Also, all three types use the centre pins for terminating "line 1". Nevertheless, these required tolerances are not always achieved and the smaller plugs often fit only "more or less" into the larger sockets. As a result, contacts may not prove very reliable because of misalignment problems. There is also considerable risk of the plastic moulding of these smaller plugs over-stressing the outer contact springs in the socket so that when the correct matching plug is fitted the outer springs do not make reliable contact. All in all, it is strongly recommended that only the matching plug should be inserted into a modular socket and customers in buildings with generic or integrated cabling to AS/NZS 3080, AS/NZS 3086, or EIA/TIA 568A, should be warned not to insert 6-way plugs into their RJ45 wall sockets. Return to Contents 6. PROPOSED TELECOM SOCKET WIRING DESIGNATIONS FOR 2 MBIT/S NTU'sThe matters raised in Items 4 and 5 above arose from investigations into standardising the various network terminating units we provide for our "Wideband Digital Data Services", "Megalink", etc. There has been some confusion about pin numbering and the choice of terms to define our preferred wiring arrangements when dealing with different equipment suppliers, so we have been looking into fixing these problems. Unfortunately, our 2 Mbit/s NTU's do not always use the same pin-outs and there was a risk that future suppliers might provide even more pin-out variations. To avoid these complications and any risk of confusion with existing USOC numbers, we are proposing to adopt just three different physical interfaces for our G.703 2 Mbit/s terminations. Two of these use the 8-way modular socket with balanced 100Ω or 120 Ω balanced cable, the third uses the standard BNC connector for coaxial cable. To avoid any confusion with "RJ" or USOC codes, which do not appear to include direct equivalents, we are proposing to call these types TNZ8/1, TNZ8/2 and BNC terminations. The pin-outs are as shown below:- Type TNZ8/1 As currently used with Open Networks Type OA2048 2M NTUs
I omitted reporting in July that TELARC, the Testing Laboratories Accreditation Council, was split into two parts to separate its accreditation functions from its quality assessment functions. The laboratory accreditation part has been renamed "International Accreditation New Zealand". The quality assessment functions are now being handled by "Telarc New Zealand Ltd". This means that we will need to progressively change the various references in our publications to "TELARC" to ensure that readers understand that we are actually referring to what is now IANZ. 8. 56 KBIT/S MODEMSThere has been quite a lot of publicity about 56 kbit/s modems in the computer and general press and, no doubt, growing customer interest in the promised high performance of these modems. Test reports to date indicate that these modems meet our PTC specification requirements and Telepermits are being granted accordingly. Nevertheless, we are concerned that suppliers - and especially retailers - do not create some false expectations for their customers. There are two competing and currently incompatible systems at present and efforts to have the ITU establish a single common standard are somewhat stalled by a patent dispute in the USA. In the meantime, 56 kbit/s modems are intended to provide faster operation over the Internet. They provide up to 56 kbit/s for delivering data to the Internet customer and up to 33.6 kbit/s for data sent by the customer to the Internet, as shown below.
This does NOT mean that ALL Internet communications will go faster if the customer upgrades to a 56 kbit/s modem. Operation at the full rated speed is subject to the following conditions:-
ONLY when ALL of these conditions are satisfied will there be a reasonable probability that the customer will achieve "full speed" between the ISP and the modem. Even then, this does not mean that all Internet communications will run at 56 Kbit/s, nor will one customer be able to communicate with another at 56 kbit/s because these modems provide 56 kbit/s in only ONE direction. In any case, an end-to-end call between two modems involves at least two analogue/digital transforms and condition 3 is not met in these circumstances. Access Standards requires 56 kbit/s modem suppliers to ensure that their retailers make the above constraints known to their prospective customers. We are also recommending that they provide some sort of "Help Line" to their users to sort out any problems. Until Telecom and the industry have had some practical experience of 56 kbit/s operation, the percentage of customers' lines that cannot support 56 kbit/s operation is unknown. After all, the public network was designed to support toll quality voice, not these new data protocols. For example, we know that some customer lines do not meet condition 3, but this is not usually a problem for voice or other types of modem operation. Unfortunately, there are bound to be some customers who will not achieve "full speed" even when the other conditions are satisfied. We do not want Telecom's Faults Service to be called as the "first response" in the event of any problems. Even with lower speed modems, we receive complaints that reduced transmission rates are due to poor line conditions, only to find that a "good" modem performs at full speed on the line and no other remedial action is necessary. 9. REPRINTS OF EARLIER PTC SPECIFICATIONSIn case any readers are confused by the appearance of a number of our earlier specifications in A4 format, I should explain that these have simply been re-formatted with their original text to permit them to be fitted into our standard A4 loose-leaf folders. This work includes "sectionalising" the page numbers, as we have done for our recent publications. The only text changes made at this stage are to the lists of references and related documents. To avoid unnecessary confusion, the current PTC and TNA specifications are now shown. Typically, references to PTC 202, 206, 208, 211 and 212 are now shown as PTC 200. In the case of PTC 301, we have incorporated the Supplement issued in 1990 and the five published amendments into the main text. We have also put in a more extensive table of contents. Reformatting is the first stage of a general revision of these earlier documents. Many are little changed, despite their age. However, there have been some developments, which need to be covered by editorial changes when we carry out a full review of these earlier specifications. However, they are generally correct and there is a lot of more urgent work to be done at present. Re-publishing these original documents as "1997" versions would have implied that the documents have been revised and that they are completely up to date. DOUG BURRUS Manager, Access Standards |
