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The Digital Future
Of The Telephone Network Bibliography(and comments on the works listed)Abbreviations frequently used:
1.0 Background1.1 Notes on Distance Dialing, 1975. AT&T. 1.2 Transmission Systems for Communications. Revised 4th Edition: Bell Telephone Laboratories, 1971. 1.3 Communication System Engineering Handbook. Edited by D.H. Hamsher. McGraw Hill, 1967. 1.4 Design Background for Telephone Switching. L.F. Goeller. Lee's ABC of the Telephone, 1977. 1.5 Proceedings of the IEEE, Sept., 1977: Special Issue on Telecommunications Circuit Switching. Edited by A.E. Joel. 2.0 Toll Switching2.1 Special Issue on No. 4 ESS. BSTJ, Sept. 1977. 2.2 Special Issue on No. 4 ESS. BLR, Dec. 1977. 2.3 Special Issue on the 1A Processor. BSTJ, Feb. 1977. 2.4 Keeping No. 4 Crossbar Young and Responsive: R.C. Snare. BLR, Nov. 1975. 2.5 Special Issue on TSPS. BSTJ, Dec. 1970. 2.6 "SP-1 TOPS." E. Bierman. Telesis, Jan./Feb., 1974. 2.7 No. 3 EAX (Automatic Electric). Session 27, ICC 77. 3.0 Common Channel Interoffice Signaling (CCIS)3.1 Special Issue on CCIS. BSTJ, Feb. 1978. 3.2 CCIS Implementation Enhanced by No. 4A Crossbar: R.S Little. BLR, May 1978. 3.3 "What is this thing Called 'CCIS'?" J.M. Heller. Telephony, Dec. 27, 1976. 3.4 Telephone Sets, Station Carrier, Concentrators and Loop Plant Special Issue on Loop Plant. BSTJ, April 1978. 3.5 Physical and Transmission Characteristics of Customer Loop Plant: P.A. Gresh. BSTJ, Dec. 1969. 3.6 ISSLS 78 Conference Record. International Symposium on Subscriber Loops and Services. Published by IEEE. 3.7 Special Issue on Exchange Plant. BLR, Feb. 1972. 3.8 Digital Multiplexer for Expanded Rural Service: I.M. McNair. BLR, March 1972. 3.9 Subscriber Loop Carrier Gets Even Better: S.J. Brolin et al. BLR, May 1977. 3.10 Loop Switching System Triples Cable Capacity: J.M. Brown. BLR, May 1978. 3.11 An Improved Telephone Set: Inglis and Tuffnell. BSTJ, April 1951. 3.12 An Improved Circuit for the Telephone Set: A.F. Bennett. BSTJ, May 1953. 4.0 User Interface4.10 The User Interface...SL-1 Terminals: J. Audette et al. Telesis, Fall, 1975. 4.11 The Electronic Telephone Emerges: P. Luff. Telesis, Feb. 1978. 4 12 A Self-multiplexing, Self-concentrating Digital Telephone: T.R. Balkeslee. NTC 77 Conference Record, Session39-6. 4.13 The Dimension PBX: A.M. Gerrish et al. BLR, Sept. 1975. The Dimension Console: J.H. Coyne et al. BLR, Oct. 1976. Maintaining the Dimension 400 PBX: E.J. Braun. BLR, Oct. 1976. 4.14 "The Digital Decision" or Assessing the Digital/Analog Tradeoffs: M.D. Blackwell. Telephone Engineer & Management, March 15, 1978. 5.0 Analog ESS5.1 Special Issue on No. 1 ESS. BSTJ, Sept. 1964. 5.2 Special Issue on No. 1 ESS. BLR, June 1965. 5.3 Special Issue on No. 2 ESS. BSTJ, Oct. 1969. 5.4 No. 3 ESS Improves Telephone Service for Country Customers: R.W. Foster. BLR, Oct. 1977. 6.0 T-Carrier6.1 PCM and Digital Transmission: G.H. Bennett. Marconi Instruments, Northvale, NJ, 1976 (Book). 6.2 D2 Channel Bank: BSTJ, Oct. 1972. 6.3 D3 Channel Bank: Albert et al. BLR, March 1977. 6.4 The Evolving Digital Network: V. I. Johannes. BLR, Nov. 1976. 6.5 1A Radio Digital Terminals Put "Data Under Voice": Grady and Knapp. BLR, May 1974. 6.6 Mixing Data and Voice on the T1 Line: Mackey et al. BLR, Feb. 1975. 6.7 TIC Carrier: The T1 Doubler: J.F. Graczyk et al. BLR, June 1975. 6.8 T4M: New Superhighway for Metropolitan Communications: J.M. Sipress. BLR, Oct. 1975. 6.9 The Digital Data System: Moster and Parom. BLR, Dec.1975. 7.0 Loss-Noise-Echo Studies7.1 Models for the Subjective Effects of Loss, Noise and Talker Echo on Telephone Connections: J.F. Cavanaugh et al. BSTJ, Nov. 1976. 7.2 Loss-Noise-Echo Study of the DDD Network: T.C. Spang. BSTJ, Jan. 1976.7.3 Is Transmission Satisfactory? J.L. Sullivan. BLR, March 1974. 8.0 Digital Class 5 Offices and the Switched Digital Network8.1 The Switched Digital Network Plan: J.E. Abate et al. Transmission Factors for Local Switched Digital Network: L.S. Dibiasco. Telephony, Oct. 24, 1977. 8.2 Grade of Service Considerations in Developing the Digital World: J. Schick. Telephony, May 15, 1978. 8.3 A PCM Switching System for all Uses: Pickett and Skaperda (North Electric). A Bid for the Digital Future: G.J. Smith (Stromberg-Carlson). A Digital World...The Way of the Future: Rendall and Soni (Northern Telecom). Telephony, July 19, 1976. 8.4 Class 5 Digital Switching...Where Does It Stand Today? A.R. Meier. Telephony, July 11, 1977. Digital Class 5 Switching...Round 2 (Letters in response to Meier article). Telephony, Sept. 5, 1977. 8.5 Considerations in the Evolution to Digital Telephony: D.G. Messerschmitt. IEEE Communications Transmission Seminar, Princeton, March 20, 1978. 8.6 Putting the Digital Telecommunications Network Together. Session 26, ICC 77. 8 7 Agenda and Record of Meeting Held Dec. 9, 1976 (Digital Loss Plan Workshop) between USITA and AT&T. 8.8 General Specification for Digital, Stored Program Controlled Central Office Equipment. REA Form 522, Draft - March 1978. 9.0 The Stored Program Controlled Network9.1 The DDD Network Goes Electronic. Session 35, ICC 77. 9.2 Technology of the •80s: W.O. Baker (interview). Telephony, June 12, 1978. 9.3 Stored Program Savings (letter); I. Dorros. IEEE Spectrum, May, 1977. Digital Telephone (letters in response): Glover and Morison. IEEE Spectrum, August 1977. 10.0 The Main Distributing Frame10.1 Distributing Frames...The Bottleneck and How to Stretch It: Session 13, ICC 76. 10.2 Taming a Giant...The Main Frame Solution: G. Crowe. A Modern MDF—A Main Distributing Frame You Can Live With: Ashby and DeBortoli. Telesis, Feb. 1978. 10.3 MDF...A Slow Starter Comes on Strong: R. Blain. Telephony, Dec. 16, 1974. 11.0 Echo Suppressors11.1 New Rules for Echo Suppressors in the DDD Network: Hatch and Ruppel. BLR, Dec. 1974. 11.2 Digital Echo Suppressors. Session 36, ICC 76. 11.3 Improving Transmission of Domestic Satellite Circuits: Holder and Lopiparo. BLR, Sept. 1977. 11.4 Suppressing Echoes Digital Style: Drechsler et al. BLR, June 1978. 12.0 Other Services and Networks12.1 Transaction Telephone Gets the Facts at Point of Sale: V.S. Borison. BLR, Oct. 1975. Transaction Network...Data Communications for Metropolitan Areas. L.R. Pamm. BLR, Jan. 1977. 12.2 Transaction Network Service - AT&T's Major New Entry into Data Communications: K. Kozarsky. PROBE Research, Millburn, N.J., 1978. 12.3 AT&T Tariff Filings Near on Advanced Com System. Electronic News (p. 36), March 13, 1978. 12.4 Computer-Communication Network Design and Analysis: M. Schwartz. Prentice Hall, Inc., Englewood, NJ, 1977. 12.5 A Short History of Facsimile: G.M. Stamps. Business Communications Review, July/August, 1977. 12.6 Private Line Interconnection: Bell System Transmission Engineering Technical Reference. PUB 43201, June 1970. 12.7 Dimension PBX Electronic Tandem Switching. AT&T Advertising Brochures, May 1978. 12.8 CO Switching: Is It a CU Ripoff? L.F. Goeller. Business Communications Review, September/October, 1977. CommentsThe Background References, 1.1-1.5, are listed merely to assist someone new to the field. Notes on Distance Dialing, in particular, is required reading. It is the document published by AT&T to make sure all the Independent (non-Bell) telephone companies know how to interface with the toll network. The latest edition, 1975, is a little out of date on the topic at hand: digital switching and transmission. Turning to Toll Switching, three special issues of the BSTJ document the No. 4 ESS: References 2.1, 2.3 and 3.1. The 1A Processor issue is included for completeness (2.3); one can understand No. 4 ESS without detailed knowledge of its processor. The interaction between No. 4 Crossbar, No. 4 ESS and CCIS is particularly interesting. By and large, the articles in 3.1 are of the most value, but 3.2 and 3.3 are easier reading. The 3.3 reference is a particularly good summary of the subject. Note that CCIS greatly reduces the cost of analog trunks by omitting the SF signaling sets and the wiring and cross-connect frames related to them. This makes analog trunks more competitive against digital (T) trunks. However, CCIS gives digital trunks all 8 bits all the time, improving signal to noise performance (assuming all 8 bits are available in the first place). Digital trunks really don't need CCIS. A di-group of 24 voice channels on T-carrier could pull out all 24 signaling bits and run 1333 words of 24 bits each, every second. This is a lot of bytes. Reference 2.5, in addition to describing TSPS, mentions use of T-carrier in very nearly this way to control remote operator positions (Reference 2.6 as well as some material in 1.4), allows the reader to compare the Northern Telecom TOPS to the Bell TSPS. Reference 2.7 shows another digital architecture to compare with No. 4 ESS. The references in sections 4 and 5 give, among other things, a feel for how difficult it will be for the Bell System to go digital to the Class 5 office and beyond. The three ESSs (5.1-5.4) are all analog, and No. 3, in particular, is designed for the rural market where everybody else is going digital. But No. 3 ESS isn't all; references 4.4, 4.5 and 4.6 show the extent to which analog station carrier, hard wire concentrators and non-PCM digital techniques are committing the local plant to something forever incompatible with No. 4 ESS. Articles in reference 4.1 cover the same material in greater depth; half of 4.1 is used to justify the economics of non-PCM local plant. Reference 4.3, record of a yearly conference, contains a wealth of other possibilities and viewpoints. The Dimension PBX, a major player in the anti-digital drama, is documented in the articles listed in Reference 4.13. Although the Bell Labs authors were quite careful never to refer to Dimension as Digital, outside commentators were by no means so discriminating. Reference 4.14, however, shows the anti-digital attitude in full flower: Dimension is defended as being better because it is NOT digital. This article is very well written, and illustrates the dilemma of the potential customer for digital communications. The whole issue of Telephone Engineer and Management is well worth reading since it is the annual PBX evaluation issue and contains a number of interesting articles. References 4.8-4.11 show the past and possibly the future history of the telephone set. The existing 500-type telephone is a marvel, but it is over 25 years old. In the past 25 years, transistors have come of age and faded before their children. The time is right for an electronic telephone set. References 4.10 and 4.11 show the Northern Telecom (Bell of Canada) approach. Key telephone sets, important to business users, are replaced with a PBX/voice-terminal combination in the SL-1 that is quite remarkable (other manufacturers, notably Rolm, have even more advanced units). But the electronic telephone in Reference 4.11 is, if anything, even more interesting. By NOT using traditional coils, capacitors, microphones, etc., it appears that the telephone on the customer end of the loop can do a lot more to improve transmission than even the smartest line circuit at the switch. Apparently the electronic set improves return loss (reduces echo at the 4/2-wire interface) and does a better job of compensating for loop length than existing (non-electronic) equipment. The alternative, finding a better matching network for use in a digital switch, is of great interest as well. The North Electric approach is described in Reference 4.3, Session 10.1, while the Bell approach is covered in References 8.1 (second article), and 8.7. Reference 4.2 shows the nature of customer loops and the kind of return loss the present system provides; one wonders how the analog network can function under the circumstances. Reference 4.12 discusses PCM coding in the telephone set, and the use of one wire-pair to serve a number of PCM phones in TDM. Although the multiplexing of several phones on one pair may be a little intricate, per-line coding is here. Advertisements in Telephony, May 29, 1978, page 4 and June 12, 1978, page 4 again, tout the wares of Siliconix and Intel respectively. These ads doubtless represent the leading edge of the per-telephone electronics of the future. The T-carrier references, 6.1-6.9, give some general information on PCM, both American and CCITT. Reference 6.4 does not really deal with an evolving digital network, but rather with the way T-carrier bit streams are being multiplexed together to get faster and faster bit streams. 6.5 discusses DUV, or how to use available frequency space on an analog radio carrier to stick in a little digital modulation at minimal incremental cost (sic transit gloria Datran). Reference 6.6 is interesting, but various ads and brochures from Vidar (TRW) for Vicom SMT equipment show better what can be done to mix and match high and low speed data with voice on T lines. References 6.7 and 6.8 simply make bigger and bigger pipes, while 6.9 discusses DDS as a fixed data-line service. References 7 and 8 get to the heart of the matter. 7.1 describes at some length the way the user preference transmission models are set up and standardized. The problem of rating subjective opinions about transmission quality, considering the number of different technical impairments that can be injected into a communication system, is not to be taken lightly, and the work described here deserves the highest possible praise.* But a major segment of the paper is devoted to an in-house problem: why did tests at Murray Hill produce different results from similar tests with the same program after it was moved to the Holmdel Laboratory? The fact that the differences are reported says a lot for the honesty of the experimenters although it might cause some concern about the utility of the results.
Reference 7.2 describes the study that worked out the fixed-loss digital network plan and arranged its compatibility with the VNL analog network plan. 7.3 is a more popular treatment of the whole subject. Since most of this work is used to justify 0 cross-office loss in Digital Class 5 switches built and used by other telephone administrations. Section 7 of Reference 1 should also be reviewed. In particular, Figure 5, page 7, shows that the present VNL approach provides appreciably more loss than is required in connections shorter than, say, 800 miles. Comparison of the bland acceptance of this loss with the rigid attitude delineated in Reference 8.7 and discussed in 8.2 and 8.4 concerning the heinous crime of inserting stabilizing loss in a digital Class 5 switch again is cause for wonder. It is important to remember that nobody is talking about increasing customer-to-customer loss on either toll or local calls. What is under discussion is the senseless decree that 4-wire local digital switches belonging to non-Bell companies must hang on the edge of instability. The two referenced articles, back to back in 8.1, discuss the future all-digital network. The first article is reprinted from Reference 2.1, but the second mounts an attack on loss in a Class 5 office, apparently under the assumption that 2-wire analog toll connection trunks will remain and customer loops will be unaffected by station carrier, remote concentrators and electronic telephone sets. Reference 8.2 (author with TRW) reviews the situation, and suggests programmable insertion of digital pads. This will probably work—as long as true digital data (without modems) is not being transmitted. Some further discussion, again emphasizing the Bell attitude that any extra loss in a local switch automatically equates to extra loss in customer-to-customer connections, is offered in 8.4. Reference 8.4, however, spends a certain amount of time discussing the differences in the switch architecture offered by Independent Telephone manufacturers. Three separate systems are covered in reference 8.3, and the letters in the second part of 8.4 show how staunchly each design group will defend its own approach. In any event, it is amusing to compare the announcement of digital switching with an historical article of mine two weeks earlier in the July 5 anniversary issue of Telephony. I must say I was gratified by seeing my predictions for the future so promptly verified. Reference 4.3, Session 9.1, reviews various possible ways of designing local digital switches, and mentions the metallic switch concentrator that many of us feel could be useful if existing dial pulsing, power ringing, high-voltage coin control and test access are to be preserved. Reference 8.5 shows some of the considerations, problems and other factors in dealing with digital implementation, while 8.6 gives an idea of how different design groups are approaching the all-digital future. Reference 8.7 shows the hardening of AT&T's heart against Class 5 loss, and 8.8 shows how REA, not taking as limited a view of toll connecting trunks and customer loops in the presence of a digital switch as AT&T does, is permitting some loss. Nobody, however, seems to agree with me that all digital signals should be at the same level to simplify testing. The outgoing switch, even if it doesn't exist, still seems to be at 0 TLP in a Class 5 office. It is interesting to note that a milliwatt tone, used for testing, exceeds the amplitude limits permitted to interconnected PBXs and thus is one of the "harms" that AT&T feels may befall its sacred network. To find AT&T's witty rejoinder to the digital future, read the articles in Reference 9.1. A digital toll network is conceded as long as it looks like analog to the Class 5 offices. The biggie is CCIS (References 3.X) which will permit many new features. New features will yield far greater return than equipment savings (Reference 3.1, page 252), but it becomes pretty clear that the features involved deal with network administration, ease of handling credit card, third party and collect billing information, improvements in IN-wats, traveling class marks and the thwarting of Blue Boxers. User-related features are mentioned, but seem trivial: distinctive ringing for certain calling numbers (for example—and then only when CCIS reaches Class 5 offices). Even reduced call set-up time is of far more value to the telco than to the customer, since the time saved accumulates primarily for the former. In any event, the emphasis in the SPC network is on return from features rather than savings in hardware. Although some mention is made of channel bank elimination in the Switched Digital Network and the more rapid expansion of T-carrier (see, in particular. Reference 8.6, session 26.3) as a result of No. 4 ESSs being installed, the DIGITAL nature of the future is minimized. Indeed, customer features, whatever the telephone industry chooses to believe they may be, are seen as needing only analog facilities (Reference 4.3, Session 7.1). Thus modem manufacturers can sleep easily for many years to come. To demonstrate further this attitude, W.O. Baker, in Reference 9.2, iterates the savings the Bell System can realize with analog switching, indicating that the Independent Industry is on the verge of heresy. Going one step further, the first letter in Reference 9.3 shows the belief that stored program makes the savings and not digital switching. The answering letters should, it is hoped, put the argument to rest but they don't. Although it is unlikely that a digital switch will be appreciably less expensive than an analog ESS, it would seem to me that a toss-up should come down in favor of the future and not the past. We already know what we CAN'T do with analog switches. To summarize, it appears that digital switching saves in equipment costs (copper, signaling sets, carrier terminal equipment, modems, etc. For PBX trunk savings, see, in particular. Reference 4.3, Session 2.5.) but stored program control, shared by analog and digital switches alike, reduces maintenance and operating costs, and facilitates traffic handling. I would opt for digital, but I don't have to justify 1500 obsolete, immortal analog ESS machines to the FCC and the various state public utility commissions. The MDF, in References 10.X, is interesting in this context since digital switching tends to eliminate MDFs. This leads to various problems, not the least of which is how you patch sub-multiplexed data channels on a single voice 64 kb/s connection. Reference 10.2 notwithstanding, something has to give in the MDF department as the digital future rolls on. The MDF problem in No. 4 ESS is discussed in Reference 2.1, page 1083 ff. Echo suppressors (References 11.X), particularly using digital techniques, are vital on long haul connections. Since any connection via a satellite is something like 44,000 miles long, the (analog) network of the future will have to have more echo suppressors than at present. Traveling class marks, possible with CCIS, will be necessary to make sure that no more than one bird-hop and/or one echo-suppressor are in each connection. What will happen with speaker phones beats me, since each speaker phone contains, of necessity, half of an echo suppressor. The many new networks that are springing up are discussed in Reference 12.X, while Reference 6.9 adds a summary of AT&T's DDS network. The Transaction Network, 12.1 and 2, shows one present application of digital communications over the public network; 12.3 makes one wonder just what is waiting in the wings.* Reference 12.4 discusses in some depth the now-defunct Datran network, and two networks of the "value-added" type. Reference 12.5 shows, among other things, how much revenue the telephone industry has lost by forbidding the connection of traffic-generating "foreign attachments." Facsimile at the moment may well be the biggest non-voice use of the switched public network. Having been evolved to fit the telephone network, it lends strength to the Bell assertions that a digital network is not needed. One cannot help but wonder what a digital fax on a 64 kb/s channel could do.
Reference 12.6 is one of the few treatments available of transmission in private switched tie line networks. Tie line networks differ from the public network in that, for cost minimization, both PBX extensions and tie trunks should usually be switched by the same machine. Reference 12.7 apparently recognized this and indicates that Dimension is now going to be permitted to shoot down CCSA in just the same way it is shooting down Centrex. Reference 12.8 lists some of the problems with current CCSA offerings. One would have thought that No. 4 ESS could have made CCSA reach its full potential. Well—that's still in the future. And the analog 2-wire Dimension may pre-select a return to the analog past. [ Top ] [ Table of Contents ] |
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Copyright 2005 Lee Goeller. All Rights Reserved. |