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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Page 45
Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Page 46
Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Page 47
Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Page 48
Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Page 50
Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Page 51
Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Page 52
Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
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Suggested Citation:"A.1.1 Wire Mediums and Terminals." Transportation Research Board. 1996. Communication Mediums for Signal, ITS, and Freeway Surveillance Systems: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6338.
×
Page 62

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

A.~.1 Wire Mediums and Terminals Wire mediums have more Man 100 years of successful communication deployments. A good overview is presented in Communications Handboolfor Traffic Control Systems, FHWA 1993. This section will not repeat Hat information, but will provide supplemental information, organized under He following categones: · TWP cable plants; · Wavelike modems; · High speed TWP circuits (SDL`S/HDLS); and · T! Hierarchy and digitized voice. A.~.~.1 TWP Cable Plants Twisted Wire Pair CTWP) cable plants have been deployed by He telephone industry for more than 100 years and Heir chata~enstics have been extensively studied for voice, data via analog wavelike modems, and T! circuits [2l, [31. More recently, motivated by He Internet and "video-on-demand," lower cost high speed techniques have been developed for deployment over existing telephone company cable plants [41. We will briefly discuss the characteristics of TWP, essentially adapting He discussion in [41. Communication capabilities and distances supportable by IWP are usually determined by the impairments presented In Table A.~.~.~-~. Prior to He 1984 divestiture, private lines were specified by FCC Tariff No. 260 which contained line conditioning specifications. Those intended for voice and data were defined as 3002 channels and specified a basic channel and types of "C" conditioning. An overview of these specifications is presented in Table A.~.~.~-2. These are end-to-end connection specifications with IWP often only serving He user-to-network portion of the link. Private ITS circuits consisting of TWP and private T1/SONET networks are usually of hider quality. These specifications are shU quoted although individual service providers may provide Heir own specifications. It is a good quality of service reference. ~:`NCHRP\Phase2~pt NCHRP 3-51 · Phase 2 final Report A1-2

Table A.~.~.~1 TWP Impairments | Propagation Loss | Attenuation of signal amplitude ty epically as a function of distance. Influenced by gauge of lWP. _.. . . Amplitude Distortion Signal distortion due to differing signal attenuation as a function of frequency over the signal bandwidth. The ideal channel would have constant attenuation over all frequencies in the signal bandwidth. . Phase Distortion Phase delay of the signal as a function of frequency. A equivalent is envelope (or group) delay which is the derivative of phase. Phase delay is expressed in seconds per km (or mile). The ideal would be linear phase delay as function of frequency or constant group delay. . . . _ . _ Cross Talk Interference Coupling of signals on different TWP within a cable. Near-end cross talk (NEXT) occurs near the transmitter. Far-End Cross Talk (FEXT) occurs near the receiver. In high count TWP cables, crosstalk is often the major determinant of throughput capacity. Gauge Changes The public telephone network typically changes to higher gauge and lower pair count cable on runs from Central Office (CO) to user. In private networks such as ITS systems, gauge changes are often not employed. Impedance Mismatches Occurs at endpoints of loops where impedance change. _ ..._ _ Temperature Changes Change is resistance and, to a lesser extent, inductance of a TWP as a result of temperature variation. Thermal Noise Browlan motion of electrons in copper. In high count TWP cables, cross talk is frequency Me major determinant of throughput capacity. TWP has been employed extensively in llS-related signal systems. TWP bandwidth and supportable bit rates decreases u ith length. Also attenuation increases win increasing frequency. Table A.-~.~.~-3 contains reference on TWP cable specification, TWP cable construction and installation, and TWP transmission systems. c;`NCHRP^ase:~p ~NCHRP 3-51 · Phase 2 final Report A1-3

Table A.~.~.~2 Line Conditioning Specifications . . _ . . 1 mplitude Distortion: AKenuationa I Phase Distortion: Envelope Delayb L . . Frequency Variation Frequency Variation Range (Hz) (dB) Range (Hz) (as) Basic 3002 300-500 -3 to +12 800-2600 1750 500-2500 -2 to +8 2500-3000 -3 to +12 C1 300 - 1000 -2 to +6 800-1000 1750 1000-2400 -1 to +3 1000-2400 1000 2400-2700 -2 to +6 2400-2600 1750 . ~ 2700-3000 ~ -3to+12 C2 300-500 -2 to +6 500-600 3000 500-2800 -1 to +3 600-1000 15050 2800-3000 -2 to +6 1000-2600 500 2600-2800 3000 , C4 300-500 -2 to +6 500-600 3000 500-3000 -2 to +3 600-800 1500 3000-3200 -2 to +6 800-1000 500 1000-2600 300 2600-2800 500 2800-3000 1500 The loss at 1004 Hz is specified as 16 + 4 dB, and losses at other frequencies are referenced to We 1004 Hz loss. Maximum delay variation within specified band. c:wc~.~t NC^P3-51 · P~2F ~A1-4

Table A.~.~.~3 TWP Standards and Related Specification [1] | Insulated Cable Engineers Association. Standard for Polyolefin Insulated Communication Cables for Outdoor Use. ANSI/ICEAS-56-434-1983. Available from ICEA. [2] Insulated Cable Engineers Association. Standards for Telecommunications Cable, Filled, Polyolefin Insulated, Copper Conductor Technical Requirements. ANSI/ICEA S-84-608-1988. Available from ICEA. [3] | Insulated able engineers association. Standard for Telecommunications Cable, Aircore, Polyolefin Insulated, Copper Conductor Technical Requirements. ANSI/ICEA S-85-625-1989. Available fro ICEA. [4] | Insulated able Engineers Association. Standard for Telecommunications Cable, Buried Distribution and Service Wire Technical Requirements. ANSI/ICEA S-86 634-1991. AvailablefromlCEA . . . [5] | REA Sp6 :ification for Filled Telephone Cables, Bulletin 345-67. PE-39, Jan. 1987. Available from Rural Electrification Administration (REA). [6] REA Specification for Filled Telephone Cables with Expanded Insulation, Bulletin 1753F-208, June 1993. [7] REA Specification for Aerial and Underground Telephone Cable, Bulletin 345-13. PE-22, Jan. 1983. [8] | REASpe,ificationforSelf-SupportingCable,Builetin345-29. PE-38,Feb.1982. [9] Generic Requirements for Metallic Telecommunications Cables. Bellcore Technical Reference TR-TSY-000421, Sept. 1991. [10] | PIC Fille ASP Cable. Bellcore Technical Reference TR-TSY-000100, June 1 988. [11] | Aircore IC ALPETH Cable. Bellcore Technical Reference TR-TSY-000101, June 1988. [12] | PIC Self upport Cable. Bellcore Technical Reference TR-TSY-000102, June 1988. [13] Underground Foam-Skin PIC Bonded STALPETH Cable. Bellcore Technical Reference TR-TSY-000106, June 1988. [14] | PlCFille Screened ASP Cable. BellcoreTechnicalReferenceTR-TSY-000109, June 1988. [15] PIC Riser Cable. Bellcore Technical Reference TR-TSY-0001 1 1, June 1988. [16] l Generi equirements for Multiple Pair Buned Wire. Bellcore Technical Reference TR-TSY-000124, Sept. 1991. [17~ ~Red TE&CM Section 635: Construction of Aerial Cable Plant. Feb. 1962, with 1966 and 1979 addenda. Available from REA. ;`NC~Phasc:.rp' NCHRP3-51e Phase2F~nalReport Al-S

[18] [19] [20] Outside Plant Engineering Handbook. AT&T Document Development Organization, 1990. _ Hamsher, D. Communication System Engineering Handbook. McGraw-Hill Book Company, 1967 Transmission Systems for Communications. Bell Telephone Laboratories, Inc. 1982. Available from AT&T Customer Information Center. [21] REATE&CM Section 406: Transmission Facility Data. Aug. 1977. Available from REA. References rid Communications Handboolfor Traffic Control Systems, FlIWA Report No. FE1WA-SA- 93-052, April 1993. [2] Subscriber Loop Signaling and Transmission Handbook: Analog, Whitham D. Reeve, ~ k'F'.E Press, 1992. [3] Subscriber Loop Signaling aru] Transmission Handbook: Digital, Whitham D. Reeve, TIME Press, 1995. [4] 'Yhe H1)SL. Environment," HERE Journal on SelectedFAreas in Communications, Vol. 9, #6;Aug.l991. A.~.~.2 WireIine Modems Wireline modem technology has advanced significantly In the last 10 to 12 years coinciding roughly win We divestiture of Regional Bell Operating Companies (RBOCs) In 1984 and win somewhat earlier court decisions permuting attachment of customer equipment (e.g., modems, answenug machines, cordless phones, etc.) to commercial telephone lines. Equally important has been He emergence of He Personal Computer (PC) and He 'demand for remote access to data of all tYDes. Within As timeframe, low cost standard-compliant modems in the $100 to $500 puce range have evolved from speeds of 300/1200 bits per second (bps) to the current International Telecommunication Union (FLU) V.34 with an upper speed of 28,800 bps. It should be noted that some suppliers have developed propnetaTy modems, often for special t:\NCHRP`Phasc2.rp ~NCHRP 3-51 · Phase 2 Anal Report A1-6

military applications, but market demand has been minimal due to customer preferences for standards and multi-vendor interoperability. Primarily due to the extensive use of point-to-poirlt multidrop circuits in widely deployed signal systems, Me transportation community has not been able to take advantage of these advances. This section win present an oversew of current modem technology and He features and specifications that determine appropriate uses in traditional and emerging ITS applications. Recommendations on how ITS can better use modem technology win also be presented. A.~.~.2.! Modem Technology Overview MOdulate/DEModulate (Modem) technology was created to permit the transmission of digital data over the analog voice telephone network. A typical voice telephone connection provides a communication channel within the audio frequency band between approximately 200 Hz and 3700 Hz (3500 Hz bandwidths. A modem modulates a earner (i.e., a sine waveform) USA the digital data, using techniques generally similar to the FM modulation employed in commercial broadcasting but win different technical details. I;M modulation has carriers and modulation bands in He 88 - 108 MHZ RF band while modems are in He audio band. ~ technical communication terminology, modems are double sideband passband signals win symmetrical sidebands on each side of He camer frequency. The details of the camer, sidebands, and bandw~d~s of signals modulated by digital data is beyond He scope or Intent of this work; however, extensive literature is available on He theory and concepts of digital data modulation. Terminology Following are key modem definitions Hat define He applicability of a modem standard and compliant products for a given application: Bit rate (Rid or speed, is the number of bits per second (bps) Hat He modem is capable of supporting. It should be noted Cat baud rate is often incorrec~dy used interchangeably win bit rate. ~:`NCH~2.rp: NCHRP 3-51 · Phase 2 final Report A1-7

Symbol rate (Rs) sometimes caned baud rate, indicates symbols per second and the symbol penod Is (= I/ Rs) is Me time that each symbol is transmitted before changing to the next symbol. Each symbol may encode one or more bits per symbol (:Bs). Thus, Rb = Rs x Bs. Carrier frequency (fc) and modulation bandwidth 03W) define We audio spectrum required to transmit modulated data. The BW is principally determined by We symbol rate (Rs). The banded required is typicalRy 1 to 2 times We symbol rate and depends on We modulation format and We fiItenng employed in the modem transmitter. Additionally, Frequency Shift Key (FSK) modulation typically requires more bandwidth for a given symbol rate than phase modulation formats such as Phase Shift Key (PSK) and Quadrature Amplitude Modulation (QAM). The BW is symmetrical and centered at the camer frequency (fc). Modulation format defines the bits per symbol (Bs). The trend has been to increase the bits per symbol while holding the symbol rate relatively constant. Example modulation formats are presented in Table A.~.~.2.~-~. Table A.~.~.2.~1 Example Modulation Formats Modulation Format Frequency Shift Key (FSK) Binary(2) PSK (BPSK) Quadrature(4) PSK (QPSK) 16 QAM 1 Bits per symbol period, B' # Symbols = 2BS 1 2 Figure A.~.~.2.~-1 presents example FSK, PSK, and QAM modulation formats. FSK is an older modulation technique that typically employees two tones separated in frequency by an integer multiple (almost always I) of the symbol rate. FSKs bandwidth is significantly greater Han Me symbol rate. Although conceptually it can use more than two tones, in practice FSK typically uses two tones for one bit/symbol. FSK modulation is suitable for simple demodulation without canter synchronization which is advantageous in multidrop circuits where turnaround is important. Additionally, FSK and its variations have constant amplitude and are suitable for low-power linear amplifiers in battery powered mobile wireless applications. L:WC~RE~Pha=.rp ~NCHRP 3-51 · Phase 2 F~1 Report A1-8

x 111 ~ - x x . - J ~ rim y ~ ~ U) ~ \ <,, m I C~ 1 4 . _ I CO Q n ~_` _ J ~ I m - A) \ En ~ u' m I ~ m · Y ~ \ En ~ i,, m I Ad Q a) Z llJ O _ ._ ~ llJ m z Y 11 ~ 11 CC o . . x I ~.U) ~ 0 > 11 x . - o m L~J U) ~ \ . Q ~ m r n (n I CL CM · m ~ m llJ llJ C) ~ J J 0 Q m · · ~ \ (n m - llJ u) <: I r, ~ m y ~ ~ cn ~ \ ui ~ c~, m · ~ ~ cn ~: o z o ~: o z z 0 y 0 ~ ~n ~ ~L ° IL o X 0 m \ m C N L.'

It should be noted that PSK Ed QAM are more modem phase modulation formats and require less bandwidth Can FSK for equivalent symbol rates. Thus, PSK and QAM are He modulation formats extensively employed in higher speecI wireline modems and microwave transmissions. A specific signal-to-no~se ratio (SNR) is required to achieve an acceptable Bit-Error-Rate (BER). In modems, BERs in practice are typically io-3 to lo-6. Me required Sew to support an acceptable BER is most heavily influenced by the symbol rate and Be modulation format which collectively defines Be bit rate. A higher SNR is required to support higher symbol rates and greater bits per symbol. Representative SNRs for commercially available modems are presented in Tables A.~.~.4.~-! and A.~.~.4.~-2. The teens 2-wire or 4-w~re refer to Be number of twisted wire pairs that connect the modem to the communication network. Since each connection is typically fun duplex, a squire connection implies two physically separate end-to-end communication circuits between modems. It should be noted that public telephone voice networks typically have only one Twisted Wire Pair (TWP) between the network and the telephone handsets or modems on customer premises. This method is illustrated in Figure A.~.~.2.~-2. A hybrid balancing network is employed In each handset or modem to properly balance the levels of local and remote voice signals; however, this balancing network is inadequate for modem data signals. It should be noted Mat most public network connections mix Me transm~ttreceive signals only on a single TWP between the central office and the customer premises. More expensive, 4-Wire (2 TWP) circuits can often be procured from public telephone service providers and are common in private networks. Method of achieving two-way communication is an important consideration in modem technology. The important definitions are as follows: · Simplex: One-way communication ondy (i.e., User A to User B) · Half duplex: Two-way commu~cadon, but one-way at a time (i.e., alternates User A to User B. then User B to User A, etc.) L:~h~.~t NCHRP 3-51 · PI 2 Few Ream A1-10

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· Full duplex: Simultaneous two-way communication Full duplex actually requires two communication channels, one for each direction. Full duplex operation of data modems can be achieved in sever ways (see Figure A.~.~.2.~-3~: I. Split band modulation techniques over a single TWP where each direction occupies a different portion of the audio band. For example: one direction is between 400 and 1400 Hz, while the other direction is between 1600 and 3300. This works for lower-speed modems with symbol rates below approximately 600 symbols/second (or typically 2400 bits per second). At higher rates the spectrums overlap and corrupt each other. Thus, above approximately 2400 bps, only half duplex or simplex is possible by split band techniques. 2. Echo canceling (EC) techniques over a single TWP are employed for symbol rates above approximately 600 symbols/second. In EC, sophisticated signal processing filtering algorithms are employed to generate and subtract the approximately known outbound local signal from the received signal leaving a sufficiently dominant remote signal to be demodulated. EC requires a time consuming training sequence on the establishment of every connection. 3. 4-w~res (or 2 TWP) are employed for We entire communication link; one pair for each direction. This totally avoids We problem of two potentially interfenng signals on a single TWP and is usually We preferred solution in private networks, where extra pairs in cables typically do not add significant incremental cost. Furthermore, the need for the torte consuming training of an echo canceler is eliminated. Dial-up or dedicated typically refers to whether or not a modem has the capability to dial or answer data calls over the public network. Modems for dedicated circuits generally work over leased or private circuits that may be of higher (sometimes referred to as special) quality than He typical dial-up circuit. These dedicated circuits do not usually require dial or answer capabilities u\NCHRP\.Phas~.rpr NCHRP 3-51 · Phase 2 Tonal Report A1-12

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as the end-to-end circuits are usually continuously connected. It should be noted Cat dial-up connections over the public telephone network typically require several seconds and are often not suitable for critical real-dine data. The predominant standard for computer supported modem control/configuration is Be Hayes "A£' command set. Adaptive equalization is generally required at bit rates above 2400 bps. A communication circuit distorts the amplitude and phase of a signal differently as a function of frequency (see Figure A.1.1.2.1-4~. An ideal communication channel would have constant amplitude across Me banded of We modulated signals. Similarly, He ideal commun~cadon channel would have no phase distortion over Han delay (i.e., linear phase or equivalently constant group delay). Real comrnun~cation channels have neither constant amplitude nor constant delay as a function of frequency. The adaptive equalizer is a trainable filter that measures and corrects these distortions by approximating, as closely as possible, an inverting filter (see Figure A.1.1.2.1-4). A training sequence is required on He establishment of a modem connection to measure the distortion and to allow the adaptive equalizer (or filter) to adapt to an initial inverting approximation. Adaption usually continues during data transmission, even after initial gaining, to account for changing circuits. Typically, the adaptive equalizer perfonnance requirements Increase as He bit rate increases. Transmitter output power expressed in dBm (decibel relative to one milliwatt). The FCC part 68 requires Hat a modem's transmit power be no greater Han - 9 dBm when connected to He public telephone network. A private network may or may not have a similar restriction. Modems intended for private networks may support commit powers from -15 dBm to +10 dBm. The greater He power, He greater He distance without repeaters. Turnaround or startup time is the amount of time (after dial-up, if required) for a modem to commence data transmission. This time is influenced by: · Symbol clock synchronization of He receiver clock wig He transmitter clock. · Carrier acquisition of the transmitter carrier frequency and phase by He receiver. · The training of He adaptive equalizer to correct channel distortions. · Tra~n~ng of He echo canceler, if employed. ~ :\NCHRP~Phas~rpr NCHRP 3-51 ~ Phase 2 Filial Report A1-14

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Handshaking exchange of supported bit rates and negotiation to employ the highest mutually supported rate. Advanced dial-up modems will measure circuit quality and select He highest rate sustainable by the circuit. This turnaround or startup time can range from 10 milliseconds (me) for simpler low speed, private wire FSK modems to 5 to 10 seconds for sophisticated, high speed, QAM, dial-up modems, requiring significant training and handshaking. Trellis coding is a sophisticated error protection technique embedded in He modulation Hat is increasingly required as modem speed exceeds 4800 bps, such as why the ITU V.32 and V.34 series standards. The technical details are beyond the scope of this material; however, several factors are significant for transportation applications: · High quality private or leased circuits may not require trellis coding. Most commercial networks will require trellis coding, especially long distance, and international. Many modems can disable trellis coding. · Trellis decoding at the receiver employs a decoding algorithm caned a viterbi decoder that introduces many symbols of delay from reception to availability of decoded data. Therefore, trellis modulation is not well suited to real-dine mulddropped operations. A.1.1.2.2 Modem Link Analysis A link budget establishes the distances that modems will support. In mulddrop applications, He link budget is a secondary determinant of He number of supported drops per TWP. A link budget establishes that the transmitter launch power, minus the circuit losses, is greater Man He modem receiver sensitivity. The losses in a TWP communication circuit include: 1. The IMP loss which is a fimction of length of He circuit, the frequency of the transmitted signal, the bandwidth of He transmitted signal, and He gauge and construction of He TWP employed. There are many sources of tables, graphs, and/or formulas on TWP attenuation. For planning purposes, approximate attenuation in He voice frequency band for TWP is as follows: L:~h~.~' NCH~3-51. P0e2F'~Re"n A1-16

Gauge 26 AWG 24 AWG 22 AWG 19 AWG Attenuation 5.2 dB/~le 4.0 dBImile 2.8 dB/mile I.S dB/mile It is recommended, however, that Me data supplied by We manufacturer of We TWP cable be used for actual design. 2. Drop (or insertions loss associated wig the connection of a modem to a circuit. These losses can range from .3 to .5 dB per modem (or drop) with .5 dB being a good planning value. For iDustradve purposes, Table A.~.~.2.2-! presents link budget analysis for two modem circuits with We foDo~g configuration and parameters. Table A.~.~.2.2~1 Example Link Budge! for Modems over TWP Parameter Mode! 400 Modem ITU V.29 (Bell Standard 202) 9600 bps, DAM modulation 1200 bps FSK modulation , Launch power (dBm) O dBm O dBm Number of drons . Droploss ~ .5dB .5x7=3.5dB .5x7=3.5dB per drop Length (miles) 10 ~ Distance loss ~ 2.8 28 dB 22.4 dB dB/mile. Total Receive Power O dBm - 28 - 3.5 = - 31.5 dBm O dBm - 22.4 - 3.5 = - 25.4 dBm Receiver Sensitivity - 40 dBm - 28 dBm Link margin (dBm ~' 5 dB:r t~D dSm) = 85 - 25.4 dBm - (-28 dBm) = 2.5 dB receive - sensitivity) dB Comment Positive so okay Positive so okay, but typically specify at least 5 dB link margin to account for statistical variations and aging and degradation of components and equipment. * It should be noted that a V29 modem uses 16 QAM (24 = 16 or Bs = 4) modulation at a R-s = 2400 symbol/second rate so Mat the bit rate is Rb = 4 x 2400 = 9600. The actual L:~h=~.= NC^P3-51e P~2F~Re ~A1-17

bandwidth will be approximately 3000 Hz (i.e., 1 to 2 times 2400 symbols/second) Hz and centered at He catner frequency of 1700 Hz. This bandwidth is somewhat greater Han He bandwidth Hat a 1200 bps FSK modem requires, and the actual loss in dB/mile will be somewhat greater. For detailed design, the actual modulation frequency band that a modem requires should be obtained from He modem manufacturer and the estimated dimple loss for this frequency band should be obtained from the TWP cable manufacturer, especialRy for long circuits win tight link budgets. A.~.~.2.3 Modem in Mu/fiaJrop Operations The transportation industry has extensively employed modems in mulddrop configurations as illustrated in Figure A.1.1.23-1. A multidrop circuit is much like a voice party line in Hat more Han two modems share a common TWP (or 2 TWP for 4-wire, full duplex) to avoid He expense of dedicated TWPs between sites. Typically, a single master serves as access allocator for multiple remote staves. The master addresses messages to slaves including polls Hat authorize a slave to send a message on He circuit. Thus, the master manages and allocates access to a link. The critical considerations in He design of mulddrop modems over TWP include: I. Frequency of polling requirements and message lengths of master-to-slave and slave-to- master communications. 2. The supported bit rates of He modem. The turnaround time of modems from receive-to-transmit and ~ansmit-to-receive. Since multiple modems share a circuit and only one transmitter can be active at a time, this turnaround can be a dominant consideration as He desired number of slaves per circuit increases and He polling frequency increases. The older simpler FSK modems support faster turnaround times at He expense of lower bit rates. The turnaround time of a modem is determined by: a. Symbol timing recovery, required in all modems. ~:`NCHRP\Phase2.rpr NCHRP 3-51 · Phase 2 Fmal Report A1-18

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b. Carner recovery - required in aB modems except FSK modems. Even FSK modem performance is improved on marginal circuits with coherent carrier recovery at the expense of turnaround time. c. Adaptive equalizer training. Adaptive equalizers are not a requirement for Tower speed FSK, PSK, or (somedmes) QAM modems. In addition, many higher speed PSK and QAM modems will operate on higher quality leased andlor private lines without adaptive equalization. It should be noted Hat modem operation over private networks often involves Aced circuits (as opposed to dial-up connections) with munimal var~abon from transmission to transmission. Thus, infrequent periodic startup trading may suffice if a modem has memory to store Be equalizer parameters. ~ mulddrop circuits, He master would have to remember He equalizer parameters for each slave. At present there is no known modem manufacturer that provides this capability, although it is technologically feasible. Modem manufacturer recommendations should be evaluated in determining He need for adaptive equalization. d. If 2-wire, fuB-duplex, echo canceling is employed, He echo canceler must be trained (or adapted) to He specific circuit of operation. The preferred filil duplex method for private networks is 4-wire which avoids He need for echo canceling and training time. e. Handshaking to select operating models) such as speed, error control, and protection, etc. This is not usually needed on private networks win consistent and known operating requirements. These should be preset by modem configuration. 4. 2-Wire or 4-u~re and Fin or half duplex. Full duplex permits simultaneous transmission in bow directions and Bus higher performance. Except in the most cost sensitive applications, 4-we should be employed in private networks for full duplex operation. 5. The public telephone networks support voice band signals with He highest frequency of approximately 3500 Hz. The transmission and switching equipment employed actually filter (or remove) any content above this frequency. Private networks employing similar equipment also filter these voice and modem signals; however, He TWP connecting the telephone handset or modem to the electronics of He network can have substantially wider L:~CH~h=~t NCH~3-51 · P0e2~Re~n A1-20

bandw~d~. Thus, FSK modems connected only by TWP in private networks can operate at higher bit rates, and resuldng higher bandwidths. It must be noted that no standards exist at these speeds and modem vendors have typically (m~n~maDy) modified lower speed standards for these higher speeds. 6. Modem transmitter launch power in dBm, typically O dBm +/- 15 dBm. 7. The modem receiver sensitivity is We minimum power level in dBm Bat the receiver will decode at a specified bit error rate (BER), typically ~ in {03 bits or i0-3 . Typic sensitivity values for modems are - 25 to 30 dBm for higher speed modems and can be in excess of 40 dBm for low speed FSK modems. Thus, multidrop modem design involves two analyses: link budget and throughput vs. number of supported drops per TWP. Link budget calculations are applicable in both multidrop and non-multidrop applications and are discussed in Section A.!.I.2.2. Throughput in multidropped circuits often determines the number of drops that may be supported on common TWP. The factors Rat determine this number include: . The bit rate of the modem, Rib in bits/second; · The modem turnaround time, T'. at is assumed Rat transm~t/receive and receive/transmit turnaround times are the slimed; · The average number of bytes: master-to-slave (Bym) and slave-to-master (Bys). (This should include all address, control, error protection, application, etc. bytes. It should also include Be opening flag but not the closing flag.~; 4. Full or half duplex circuit. Of fun duplex, a master can skip a next slave and continue transmuting to Be current addressed slave. The next slave can commence transmission on Be closing flag of the transmission to Be current addressed slave.~; c:\NCHRP`Phasc:.~r NCHRP3-51 · Phase2F-~nalReport A1-21

The number of bits per byte (BIT). For most asynchronous communication links, this will be 11 bits/byte which includes 8 bits plus 1 start bit, 1 stop bit, and 1 panty bit. Table A.~.~.2.3-! is an analysis of number of drops for model 400 modems and Me 9600 bps, V.29 modem. Table A.~.2.3~1 Example Mullidrop Analysis Parameter/Calculation Mode'400 Modem ITU V.29 (Bell Standard 202) 9600 bps, CAM modulation 1200 bps, FSK modulation Bit Rate: Rb in bits/second 1200 bps 9600 bps ._ Modem Tumaround Time: To 10 ms (millisecond 10~) 25 ms Number of bytes: master-to- 15 15 slave, BYm . . _ Number of bytes: slave-to- 10 10 master, BYs . . __ Polling Frequency, Tpo' 1 per second 1 per second . Number of bits per byte, BITS 11 11 . Single master transmission time Tm = BYm x BITS / Rb = 1 35.5 ms =1 5 x 11 / 1 200 = 1 7.2 ms = 1 5 x 11 / 9600 Ttot,n = Tm + T' with tumaround: = 145.5 ms per transmission = 42.2 ms per transmission Single slave transmission time Ts=BYsxBITSIR~: 91.7ms=10x11/1200 11.5ms=10x11/9600 Ttots = Ts + To with tumaround: 101.7 ms per transmission 36.5 ms per transmission Time for closing flag byte: Tf 9.2 ms = 1.2 ms = BITS/Rb 1 1111200 1 11/9600 _ Total Drops: Full Duplex = 6 drops = 23 drops = Tpd, /(Max Of(Ttot,,, or Ttots) + T.) 1/~145.5 ~ 9.2) x 103 1/~42.2 ~ 1.2) x 103 Rounded down Total Drops: Half Duplex = 3 drops = 12 drops = Tpo'' /(Ttotm + Ttots + 2xTf) 1/~1 45.5 + 1 01 .7 + 2 X 9.2) X 1/~42.2 ~ 36.5 + 2 x 1 .2) x 103 Rounded down 103 :`NCHRP`Ph~.rp' NCHRP3-S1e Phase2F~nalReport A1-22

A.1.1.2.4 Modem Standards and Products The modem industry has profited greatly from the establishment of international standards. Prior to the divestiture of the Regional Bell Operating Companies (RBOCs) by AT&T, there were Bed standards in the U.S. and CCLl l (The International Telegraph and Telephone Consultative Committee, now referred to as International Telecommunication Union or ITU) used intemabonally. Since about 1984, all significant new modem standards and widely deployed products have complied with ITU standards; however, He Must of Be commercial market has been dial-up, high-speed, modems that are not weD suited to the popular multidropped configurations of the transportation industry. Thus, a standards review must include Be older, generally lower speed, modems from Be Bell era. Table A.~.~.2.4-1 and A.~.~.2.4-2 are overviews of the modem standards. Table A.~.~.2.4-1 addresses standards win origins form He early 1960s to approximately 1985. These modems involve a suppler set of defining parameters. Table A.~.~.2.4-2 addresses the V.32, V.17, and V.34 modem families which achieved higher speeds with new techniques and require an expanded set of defining parameters. In addidon to He above interoperability standards, Here are many other supporting modem standards defining such functions as synchronous/asynchronous conversion, automode for speed/standard negotiation, error protocols, and compression. An overview of these supporting standards is presented in Table A.~.~.2.4-3. A.~.~.2.S V.32 and U34 Modems Prior to the 1984 [rut V.32 standard, the following deficiencies existed in modem products: I. Full duplex could only be achieved by 4-uire or split band over 2-wire. The highest speed fills duplex, spilt band modem was the 2400 bps, ITU V.22bis with a symbol rate of 600 symbols/second. Higher speeds could only be obtained web 4-wire, fun duplex, or 2-wire, half duplex (e.g., V.291. L:\NCHRP\Phasc2.rpt NC~3-51e P0e2F~Re"~ A1-23

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2. 4 Bits/symbo] (e.g., 4 bits/symbol x 2400 symbols/second = 9600 bits/second for example V.29) was Me highest modem speed and this did not work well on lower quality public telephone circuits (especially long distance and international). It should be noted Mat Me highest commonly employed symbol rate was 2400 symbols/second in order to stay within Me available 3000-3500 hertz bank. It should be noted Mat Me FLU V.29 standard recommended use is on "4-w~re, leased circuits," but also states Mat "use on lower quality circuits is not precluded." Subsequently, V.29 has been extensively employed over the switched public network as Me 9600 bps standard for facsimile. 3. There was no faBback standard for negotiated operation when c~ing/answenng modems. Supported multiple standards (e.g., ZOO, 1200, 2400, 9600, etc.), but not a common highest speed, or fallback operations to lower speeds when circuit quality is inadequate for higher speeds. 1 In Me early 1980s, work began on ITU V.32, that defined fig duplex, Rewire, operation. The characteristics and technologies of V.32-compliant products include: I. FuN duplex operation over Me General Switched Telenhone Networks [(GSTN (Public) rid ~ ~ ~ ~ PSTN in U.S., or commercial dial-up)] network or on po~nt-to-point (not multidropped) 2- w~re leased telephone circuits 2. Echo canceling that permits full duplex operation over 2-Wire (see Figure A.~.~.2.~-31. 3. Bit rates of 4800, 7200, 9600 bps (note: this is 2x,- 3x, and 4x Me 2400 symbols/second). Most commercial modems also integrate He popular V.22bis ,2400 bps; Bell 212, 1200 bps; and Bell 103, 300 bps standards, but users had to manually select these standards. 4. Quadrature Amplitude Modulation (QAM) at a symbol rate of 2400 symbols/second. 5. Carrier frequency of 1800 +/- 1 Hertz at He transmitter. The receiver must tolerate 1800 +/ 7 Hertz to account for frequency offset in the network. L::~NCHRPPhase2.~p ~NCHRP 3-51 · Phase 2 Fmal Report A1-29

6. Synchronous or optional asynchronous mode of operation. Although optional, asynchronous is the dominant commercial mode. 7. Higher performance adaptive equalizers that can more effectively correct the distortions of lower quality GAIN circuits. S. Sophisticated trellis coding, (optional) error protection algorithms that permitted 4 bits/symbol (and higher3 at acceptable BER over lower quality GSTN circuits. Although optional in Me standard, it is demanded as a commercial product feature. 9. Exchange of rate sequences during start-up to establish bit rate, coding, and other special facilities. Limited retrain capabilities are defined for use when required to interrupt data transmission. 10. Evolution of microprocessor and digital signal processing semiconductor products to enable cost effective implementation of the above. VirulaBy all modems are now implemented in software (sometimes caned firmware). FLU V.32bis (1991) is essentially the same, but adds 12.0 and 14.4 kbps (1000 bits per second) bit rates. V.32bis also defines an automode capability to automatically detect and interoperate with legacy V.22bis, 212, and 103 modems during start-up. V.32ter (1993) is a manufacturers defacto standard (not formally ITU) that adds 16.S and 19.2 kbps bit rates. V.32ter was developed for higher bit rate options when the V.34 standard development was delayed. The V.32 standards family all operate at a symbol rate of 2400 symbols/second and carrier frequency of 1800 Hertz. The greater bit rates are achieved by increasing He number of bits/symbol as presented in Table A.~.~.2.4-2. Thus, increasing bit rates require higher quality circuits for data transmission at acceptable BER. Trellis coding is a sophisticated error control aigori~n Hat is integrated with modulation to achieve substantially improved BER over lower quality circuits. It accomplishes this by adding one bit/symbol at He transmitter with restricted, but well conceived, symbol histones. At He receiver, averaging over many symbol periods (creating delay) is employed to decode symbols with less error. Thus, a trellis coded 9,600 bps, V.32, modem actually uses 5 bits/symbol (4 for L:WCH~h=~.~t NCH"3-51 · P~e2F~Re~n A1-30

data and 1 for trellis error coding). This is often referred to as Trellis Coded Modulation (TCM). Trellis coding is often an essential enabling technology on lower quality circuits usually found in commercial dial-up networks, but is often less essential on Me higher quality circuits available in leased and private networks. Trellis coding achieves equivalent BER communication with 3-6 dB lower SNR circuits than non-treHis modulation techniques. In general, as Me bits/symbol (and resulting bit rate) increases, Me benefits and necessity of trellis coding increases. The details of the theory and trade-offs of trellis coding is beyond the scope of this text. Unfortunately, (restraining and negotiation adds significant delay on startup of each connection. The startup sequence for the V.32 family is illustrated in Figure A.1.1.2.~-1. The T in the figure is the symbol period 4.1666 millisecond (= 1/2400 = 4.166 10-3 seconds). The resulting total delays can be on Me order of 5 -10 seconds. Additionally, Pelvis coding adds delay during actual data transmission. These delays make standard V.32 (and V.34) modem products unsuitable for multidrop applications as Hey are usually accomplished on restart of every drop. The rru V.34 modem furler extends Me achievable bit rates to 28.8 kbps. The standards activities on V.34 occurred in the early 199Os with foal approval in September, 1994. Enhanced capabilities and technologies of the V.34 family include: Bit rates, in addition to the V.32 family bit rates, are 16.S, 19,2, 21.6, 24.0, 26.4, and 28.8 kbps. These are achieved with the vanable symbol rates listed below and win bits/symbol ranging from 3 to 10 bitsIsymbol win one bit allocated for trellis encoding. Additionally, V.34 permits asymmetrical bit rates (not supported in Me V.32 standards) on bow transmit and receive so that each direction can use the maximum bit rate possible. . Vanable symbol rate including mandatory 2400, 3000, and 3200 symbols/second and optional 2743, 2800, and 3429 symbols/second. (V.32 filmily uses only 2400 bits/symbol.) It should be noted that the symbol rate is Me principle determinant of bandwidth (! to 2 times symbol rate with 1.1 to 1.2 typical for the V.32 and V.34 families). ~ general, it is preferable to have a higher symbol rate (available channel bandwidth permitting) and a lower bits/symbol rate because a higher bits/symbol rate requires higher SNP for equivalent BER decoding. ~:\NCHRP`Phase2.rp' NCHRP 3-51 · Phase 2 Fmal Report A1-31

1 1 '1 1 1 ' Em m LLJ Cad ·_ en a) 1 _. ~- 1 l T ~1 ~ ~ r Ln Cam it ~ r _ O Z An' 1 1 1 1 1 m LLJ U) En 1~ _~ T . ~ , ~ ~ _, ~1 r -~ ~ (D T <D Low 1 o Go ~1 Us o _ c~ a) _ cn - ~) E ° o o - o Go Al Lo T +1 _ Al Lo > v to a' - J CJ a) ~ ~o o o ° a) v +1 o. - ~D = c) ~ - -oc o ~ O D v ~·- ~ ~ ._ >`~ ~ O ._ 0 ._ ~C) O O C > ~O ~ O- _ cn - a)·_ co =5 O O D V O ~ 03 .e O O _O o_o O C~C) O ~ O 'V ~ U' o.C O ~ ~= C:~` a) ~ Q) O ~ C ) ~ 0 C 0 -O D C . O · CO C5- D ~ m-~a~c ~ ~ ~ ~ tn ' O ~ ~ 0~ 20 ~ 11 ~ i_ ~ ~ ~ o U) I (OD 4:L) O O C' ~ C' `.= V .C~ ~ C) .c U) ~ mm r~ C~ Z 1cn Z o~ ,ty' ~ ~ <: ~ u, ~ ~ L.1 m C _ ~ _ ~ ~ IL Q C~ CO j ~ I O N 111 ~ Z .= C, C,8 _ _

. Vanable camer frequencies. (V.32 employs 1800 Hertz only.) The selected camer frequency is a function of symbol rate and one of two frequencies according to channel characteristics. This allows the modulated spectrum to be generally placed where there is least noise and distortion. · An enhanced trellis coding algorithm (4-dimensional versus 2-dimensional for V.32~. The V.34 trellis aphorism has superior performance over the V.32 trellis, but both require only one additional bit/symbol for error coding. The V.32 trellis algorithm provides approximately 4 dB of additional SNR protection for equivalent BER compared to non- trellis standard QAM. The V.34 trellis aigonthm provides approximately 6 dB. . Transmitter pre-emphasis Hat pennits part of the equalization to be accomplished at the transmitter and, ~us, achieves much better performance in the high attenuation part of He available spectrum. A non-linear equalization method, or preceding, is employed to reduce equalizer noise enhancement caused by amplitude distortion. The receiver still has its adaptive equalizer, but receives a higher quality signal. · Constellation shaping Hat places in non-un~fonn spacing the amplitude and phase of the Quadrature Amplitude Modulation (QAM) symbols to minimize Heir susceptibility to noise. Non-linear encoding is employed for distortion immunity. The constellation size determines He bits/symbol as previously discussed. Transmit power control to account for difference in modulation parameters. The inclusion of the primary data channel "d an optional 200 bps auxiliary channel in a frame format. The auxiliary channel is independent of He plenary channel and can be used for modem control/link data, network management, or over functions. This win be of significant benefit when modems are employed win bridges and routers for remote network access. · Line probing during startup and actual data communication to measure actual circuit quality and then the selection of the best data mode modulation parameters. Included is a falIback to lower speeds if higher speeds are not possible on He circuit. L.:~NCHRP`Phase2.rp: NCHRP 3-51 · Phase 2 Fmal RepoIt A1-33

The V.34 modem standard Is a significant advance in modem technology based on extensive research by commercial modem vendors. It achieves performance close to the theoretical limit of Me data transmission on typical telephone circuits. V.32/V.34 modems have not been extensively employed in traditional signal systems due to the extensive employment of multidrop circuits Mat are better accomplished with the older FSK, FLU V.29, and rru V.33 modems Mat support faster turnarounds; however, ITS is evolving to ATIS systems where the Raveling public will remotely dial into infonnation services. The V.32/V.34 Moslems will be significant enabling technologies for these applications. A.~.~.2.6 The Wire/ine Communication Channe/and Modem Testing Standards Commercial public telephone service has been available for more Man a hundred years. Data comrnun~cation over Me public telephone via modem networks has been in development for approximately 40 years. Significant info~abon has been developed through the years conceding data communications over Me analog Public Switched Telephone Network (PSTN) within the U.S. In recent years, the PSTN characteristics have changed significantly. Today, other Man the 2-wire pair connecting a subscnber's modem (or telephone handset) to the telephone company's local cent office, Me network is usually totally digital. The analog subscriber signals are digitized at the local center office, then switched and transmitted dignitary to Me other subscriber. (Refer back to Figure A.~.~.2.~-21. In Me evolution from the analog network to Me digital network, end-to-end connections usually involved multiple conversions from analog to digital to analog with each conversion adding distortion and lowenng the quality of Me circuit. Today, Me network including local, national, and international calls, p~om~nantly involves only one conversion at each end of the connection. This has substantially changed and improved circuit quality and suitability for data communication. Although slow in evolving, Integrated Digital Service Network MISDO) provides standards for dig~hz~ng Me subscriber link and will be discussed elsewhere. ISDN permits end-to-end digital connections over PSTN. In this section, we will discuss the following PSTN network parameters and characteristics that impact modem data communication. We will discuss Me traditional as well as the modem, widely available, CO (Central Office)-to-CO digital network. L:WC~h~t NCH" 3-51 · PI 2 Few Ream A1-34

Typical PSTN impairments are presented in Table A.~.~.2.6-~. Table A.~.~.2.6~1 Public Service Telephone Network (PSTN) Impairments , Impairment ~ OTh:~! Ran ~ ~ Vows Noise Rectum Onud And 5 to 35 dm (SNR), or interference, often referred to ~0 to -60 dBm as white noise, expressed as signal-to-noise in dB or equivalently referenced to the receive level in dBm. Loss (total signal Signal transmit level minus -5 to 40 dB loss, or loss, not function of receive level in dB. Often -15 to 40 dBm receive level. time or frequency; equivalently expressed as often referred to a receive level in dBm. 1003 Hz loss) Total delay Delay independent of 0 - 1000 ms frequency of signal from transmitter to receiver. Attenuation (vs. Amplitude distortion as Be e F g u m ~ ~ 1 ~ ~ frequency) function of frequency, typically 300 - 500 Hz - 3 ~ 12 db referenced to 1 kHz tone 500 - 2500 Hz - 2 + 8 db expressed in dB. fib Envelop delay (or Delay distortion as a function BW - Z60D ~ 17~ m Absconds phase) distortion (vs. of frequency referenced to 1.8 frequency) Hz signal expressed in milliseconds. Frequency offset Frequency offset in Hz at w- 7 Hz receiver of 1 kHz transmit tone .. Phase jitter Fluctuation or deviation of zero 0-10 degrees / O - 120 Hz crossing of 1 kHz from expected value. Intermodulation Spurious signals at the sum and difference of frequencies 30 - 60 dB 3~ harmonic presence in the signal caused by non-lineariities. Near echo A reflection of the transmit -5 - ZO signal at the local hybrid where a 4-wire signal is converted to a 2-wire signal. Far echo Reflection of the transmit - 15 to 40 dB signal at the remote hybrid. _ Tim i ng Loss of network tim in g N ct s ~ e c h e d slips/transients synchronization of a digital sianai . ~:`NCHRP\Phase2.rpt NCHRP 3-51 · Phase 2 Final Report A1-35

Combinations of these impairments with varying parameters specify the quality of circuits for data communication with modems. PSTN circuits have evolved over the years from all analog circuits with predominantly analog microwave long distance circuits to PSTN circuits which today are predominantly digital circuits with digital fiber for long distance. Most PSTN cans involve analog on 2-wire pairs only from the customer premises to the central office. Severe impairments of analog circuits do not exist on digital circuits and include frequency offset, forms of phase jitter, and related impairments. This provides a high quality end-to-end circuit with mpainnents being concerned with He analog TWPs on each end and He digitization process at each end. Although becoming less prevalent, some connections can involve '~anscoding" where He signal is converted to analog and back to digital one or more times. This degrades He quality of He circuit. In response to He need for consistent modem testing for He new ITU V.34 modem standard, He Telecommunication Industry Association/Electronic Industry Association (TIA/ElA) has recently developed modem testing standards. These are: 1. UA Telecommunication System Bulletin TSB-37A, Telephone Network Transmission Modelfor Evaluating Modem Performance, September, 1994, Telecommunication Industry Association Engineenug Department. This bulletin specifies various line impairments including signal attenuation, noise, jitter, amplitude distortion and delay distortion, and specifies combinations of line impairment parameters most commonly found within the U.S. 2. TIA Telecommunication System BuBedn TSB-38, Test Procedure for Evaluation of 2 Wire (Full) Duplex Modems, September, 1994, Telecommunication Industry Association Engineering Department. This bulletin relates to test modems using the impairments specified in TSB-37A or over impairment suites. 3. International Telecommunication Union aTu' V.56bis, Network Transmission Modelfor Evaluating Modem Performance Over 2-Wire Voice Grade Connections. This document supplements He models in TSB-37A to address international circuits and includes satellite circuits. ~:\NC~Phase2.rp: NCHEP 3-51 · Phase 2 Final Report A1-36

These standards present models of circuits and testing methodology that are representative of the circuits found in current public networks wig emphases on digital switching and transmission circuits. Of significance to ITS is the good presentation of models for wire loop plants which is applicable to many private wire ITS TWP cable plants. A.~.~.2.7 Modem Opporfunities and Considerations for/TS . There are many opportunities and considerations for Me ITS community to improve deployed modem technology. These~nclude: · Employing a Rewire private network adds very modest incremental costs and has significant benefits. FuR duplex operation is possible without echo canceling at higher bit rates than is possible with Unwire split band modems. FSK modems have been extensively deployed in mulddrop configurations due to rapid turnaround time. FSK is a spechaBy inefficient modulation technique and requires greater band for a given symbol rate; however, a TWP-only circuit (no digitization and switching) has greater bandwidth Man Me typical 3500 Hertz telephone circuit. Figure A.~.~.2.7-1 illustrates these alternatives. Thus, FSK modems over TWP can support greater bit rates; however, Me supportable distances decrease as the increased bandwidth incurs greater attenuation per mile. . . The lTU V.29 modem is a more spectrally efficient (QAM modulation) modem Mat has not been widely deployed in ITS applications. V.29 is a modem standard intended for private or leased circuits and is suitable for mulddropped applications. Commercial products are available wig turnaround times of approximately 20 milliseconds (10-3 seconds) compared wig Me available 10 milliseconds of model 400, FSK modems. It has ITS potential as it will support 9600 pbs over higher quality private, leased, or public circuits. Even more specially efficient phase modulation techniques such as QAM and trellis coding modulation (TCM) employed in Me V.32 and V.34 have not been employed in multidropped signal systems because of turnaround time; however, these modems might be adapted for mulddrop circuits if: :\NCHRP`Phase2.rpr NCHRP 3-51 · Phase 2 Final Report A1-37

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a. 4-Wire is employed eliminating the need for echo canceling. b. The equalizer parameters for each drop are stored in He master modem, negating He need for retraining for each drop (except an initial Gaining for each drop). c. They do not employ the TCM which requires delay; however, this may limit He maximum bit rate. d. They eliminate the startup sequence except for the first (special) transmission, which initializes all parameters. f. It were possible to synchronize the slave modem's camer and symbol clock to a master modem reference, thus eliminating or m~nirnizing the master's relock lime to a multidrop slave's restart on pod. No products exist that can offer these capabilities; however, most modems are firmware based and, with the exception of item f, He above are not significant modifications. It should also be noted that FWP-only circuits, with larger bandwidths (i.e., greater Han 3500 kHz), could support higher bit rates by increasing He symbol rate and using more bits/symbol on He higher quality circuit. Interested manufacturers would need to be identified and motivated. These modifications, while close to V.32/V.34, would require special standards to ensure mul~vendor interoperability. The temperature requirements of ITS (40 to 70 Degrees Centigrade) cannot always be accommodates! in commercial grade products. The semiconductor products which are used in modem products are not always available in extended temperature grades. There is a need for special ITS modem standards. ITS mode} 400 vendors have provided modems web speeds above the 1200 bps of He defining FSK, Bell 202 modem standard. This has been accomplished by increasing He symbol rate and resuldng bit rate to 2400 bps and 9600 bps. The 9600 bps will only work over TWP, since a 9600 symbol/second rate requires a bandwidth greater than 3500 Hertz. No standards exist for these useful products. L:~h~.~t NIP 3-51 · PI 2 Few Ream A1-39

A.~.~.3 High~speed TWP Circuits (SDES/HDES ~ Wire has been the medium for 4 kHz analog voice transmission since He telephone was invented in the I800s. In He 1950s, when T] digital circuits at the DS-! rate of 1.5644 Mbps were developed, the 4 kHz bandwidth for voice was maintained. The codec (CODer-DECoder) that converts analog voice to a digital signal, first filters He analog voice signal to less Han 4000 Hertz prior to digitization (DS-0 at 64,000 bps). Thus, all digitized telephone transmission, multiplexing, and switching circuits are only capable of transmitting voice and Reline modem signals with bandwidths of less than 4000 Hertz. However, the TWP (collectively referred to as loop plant) that connects subscriber telephone sets to the telephone company central office has substantially greater bandwidth and can support substantially higher digital bit rates Han modems. The telephone industry and supporting equipment vendors have developed many products and services to provide higher bit rates over TWP-only circuits. These include: Repeatered T! camers; High Bit rate Digital Subscriber Line (HDSL); Asymmetric Digital Subscriber (ADSL); and Basic ISDN (2 B+D) and Primary ISDN (23 B+D). In addition to commercial commuuncabon service availability, these circuits are based on standards Hat include design methodologies. Although not widely deployed In ITS-related applications today, He circuits offer many benefits and moot become He future low-cost technologies as digital technologies are extended to telephone subscriber premises for new services such as Intemet access, v~deo-on-demand, etc. Repeater TI-camers typically provide a 1,544 Mbps (DS-~) bit rate. Section A.1.~.4 discusses the Tl digital hierarchy. Design of repeater T1-camer links is well understood based on design methodologies win origins in the 1960s. Key considerations in design are: Link loss (i.e., attenuation); Repeater spacing; L.\NCHRP\.Phase2.rp ~NCHRP3-51a Phase2FmalReport Al-40

Bit Error Rate (BER) requirements; Wire selection; Near-end (NEXT) and Far-end (FEXT) crosstalk interference; and TWO cable plant design. Table A.~.~.3-! lists the most pertinent references on repeatered TI-cartiers. Unfortunately, DS-! repeatered TI-carTier circuits have not proven cost effective for ubiquitous subscriber installations because: Lines must be qualified (i.e., tested); Cable plants must often be redesigned and conditioned; and Repeaters must be installed about every 6,000 feet. The high bit rate digital subscriber line (HDSL) technology was developed to provide a cost effective solution for DS-! subscriber loops to homes or businesses using existing TWP. Extensive surveys were conducted on the installed 1~WP loop plants deployed by telephone companies to determine their composition. Then HDSL, was developed and tested win the goal of achieving: No line qualifying (i.e., install and operate); No conditioning; No repeaters for links up to 9,000 to 12,000 feet; BER less than 1 in 107 (fiber quality); Suitable for 80-90% of installed T1 circuits and more than 60% of TWP loops, and Requires 2 TWP (i.e., 4 wires) Me same as T! links. ~:wC~Phase2.rp ~NCHRP3-51. Phase2FmalReport A1-41

Table A.~.~.3~1 High Speed TWP Circuit References (pg ~ of 2) Repeatered T1 ~ Carrier Circuits Reference American National Standard for Telecommunications. Carrier-to-Customer Installation DSI Metallic Intefface. ANSI T1.403-1989. Cravis, H., Crater, T. "Engineering of T1 Carrier System Repeatered Lines." Bell System Technical Journal, Vol. XLII, No. 2, March 1963. Functional Cnteria for the DSI Intefface Connector. BELLCORE Technical Reference RR- TSY-000312, March 1988. Tl Digital Line, Transmission and Outside Plant Design Procedures: Carrier Engineering. AT&T 855-351-101, July 1990. n Outstate Digital Line, Transmission and Outside Plant Design Procedures: Carrier | I Engineering. AT&T 855-351-200, April 1981. l HDSL References Generic Requirements for High-Bit-Rate Digital Subscriber Lines. BELLCORE Technical Advisory TA-NWT-001210, October 1991. "High Bit Rate Digital Subscriber Line: A Review of HDSL Progress," Joseph W. Lechleider, IEEE`JSAC, August 1991, pp. 769-784. High-capacity Digital Special Access Sen/ic~Transmission Parameter Limits and Intefface Combinations. BELLCORE Technical Reference TR-iNS-000342, February 1 991 . Available from BELLCORE Customer Service. Using HDSL Technology as a Transition Strategy to FlTL,n Kostalek, R. Presentation No. 112 at 1992 SuperCom/lCC'92, Chicago, Illinois. ADSL References Asymmetric Digital Subscriber Line fADSLJ Metallic dataface, ANSI T1 E1 .4/94-007R8, 1994. Asymmetric Digital Subscriber Line (ADSL): Technology and System Considerations. BELLCORE Special Report SR-TSV-002240, June 1992. Sistanizadeh, K. Spectral Compatibility of ADSL with Basic Rate DSLs, HDSLs, and T1 Lines. Section 4 of BELLCORE Special Report SR-TSV-00240, June 1992. :\NCHRP\Phas~.rp' NCHRP3-51e Phase2FinalReport A1-42

Table A.~.~.3-1 High Speed TWP Circuit References (pg 2 of 2) Basic Rate (BRI) References American National Standard for Telecommunications. Integrated Services Digital Network (ISDN9: Basic Access Interface for Use on Metallic Loops for application on the Network Side of the NT (Layer 1 Specification). AMSO T1-601-l see. Digital Networks, Digital Sections and Digital Line Systems. CCITT Blue Book, Vol. 111, Fascicle 111.5, Geneva, 1989. Available from NTIS, Order No. PB89-143895. General Requirements for ISDN Basic Access Digital Subscriber Lines. BELLCORE Technical Reference TR-NWT-000393, January 1991. Available fro BELLCORE Customer Service. Integrated Digital Loop Carrier System Generic Requirements, Objectives, and Interface. BELLCORE Technical Reference TR-TSY-000303, September 1986, Revision 4, August 1991. Table A.~.~.3.! also lists references on ~SL. Asymmetnc Digital Subscriber Line (ADSL) is a recent high speed digital subscriber link Tat is motivated by the telephone industry's desire to provide "video-on-demand" to home subscribers. Capabilities provided are: Up to 4 DS-Is, 6.536 Mbps one direction (downstream); UD to 640 kbos asYmmetnc the other direction (upstream); UD to 12.000 over a single 24 AWG-TWP win no repeaters; and Permits analog voice over same TWP. Like HDSL, ADSL is intended for minimum installation design and installation on exposing telephone company loops. ADSL, would appear ideal for low-cost backbone communication hub to camera equipment cabinets in llS-related systems. Longer distances are possible on higher quality loop plants than are achievable on new TWP loop designs and in many existing ITS-related installations. ISDN basic (B RI) rate provides a full duplex 2B ~ D; or 2 bearer, DS-O (64 kbps) channels, plus one data (16 kbps) channel over a single TWP (2 wire) link up to about 18,000 feet on existing telephone company loop plants. ISDN is a switched subscriber digital service Nat includes the L\NCHR~PhaS~rP ~NCHRP3-51~ PhaSe2F=a1RePO ~A1-43

above BR! full duplex at 160 kbps and the primary ISDN (PRI) at DS-1, 1,544 Mbps, rate. PRI uses repeatered T1 camer circuits or HDSL for subscriber links. Table A.~.~.3-2 presents a summary of high data rate circuits that are available to support ITS- related requirements. The above him speed digital circuits must accommodate certain common impairments: . Attenuation, dB/ft, dB/km, etc.; · Near-end crosstalk (NEXT); · Far-end crosstalk (FEXI); · Amplitude and delay distortion; and ~ Noise. Cable plant design must account for these impairments and design methodologies are available. Careful consideration must be given to NEXT and FEXr when multiple circuits, consisting of Be same or different type canters, are included with multiple pair TWP cable. A.~.~.4 T] Digital Hierarchy and Digitized Voice Section A.1.2.3 discusses SONET which is a modern extension of the T1 hierarchy. Section A.2.6. 1 discusses the applicability of the T1 and SONET hierarchy to ITS applications. Origin, Funefiona/ify, end elements The ong~ns of the Digital Hierarchy, or T-Carrier Systems (or TI), were the result in New York City (NYC) of subscriber growth to He extent that analog Twisted Wire Pair (TWP) required for a single analog voice was growing beyond the capacity of existing and expandable conduit space for new installations. As a solution, early implementations of the digital hierarchy were conceived that digitized up to 24 analog voice signals into 24 digital voice signals at ~ bits~sample and 8,000 samples/sec to create a DS-O digital signal at 64,000 bps. The analog voice signal is filtered to limit He bandwidth to less than 3100-3500 Hz. These 24 DS-O digital voice signals are then Time Division Multiplexed (TDM) into a 1.544 Mbps digital signal. ~:mCHRP\Phase2 rip NCHRP 3-51 · Phase 2 Fmal Report A1-44

- o c~ u) . Q $ a, ca ~ 0 O ~ => ° o ' ·= E ~ · · · · · ~ mo , o ~o o~ °=, C~ o° ~ ~ ~ o O) ~ w Q ~ CtJ · ~ . O O _ _ C ~ _ o~ o~ E E D a · · ·_ - .C~ I as ~ ~._ ~ a) - ~._ a, 0 .~. ~E <, ,= = a' ~ I cn ~ Cl) _ CD a' .> ~ o =O 0 .= .C a,._ cn ~ .0 _ a) O ~ ~ {D ~ cn 0° =' .= CO o o o C~ Q _ CO ~ C] _ · · · · · · · _ - w C~ F a) ~0 Ct Q U' a ~c ~._ O ~ a, Q Cl' CD - - _ .~ O ~ ~C S ~ E-~ o ~ ~ CO ._ ~n ~n 0 - C~ o~ d. o c~ o o 0 ~ -C`i Q t5, o ~r Ul m . .~0 X |5 - ._ ._ C~ cn s C ~ CO _ _ o · _ _ ~ _ ~ ~cn CD ~: CO C,8 Q Q Q Q CO Q ~ O ~ ~ +~O 0 m 1l 1l - ._ ~_ - m - a) - CO ._ U) CO m z CO r - CO a' .~ C, - CO C] 8 :s -

The concept is illustrated in Figure A.1.1.4-1. This TDM was found to be cheaper Han popular alternative Frequency Division Multiplexing (FDM) alternatives of the 1950s era. Thus, the 24 TWP for analog signals could be reduced to 2 TWP (full duplex, one for each direction). The equipment that interfaces to analog voice TWP is a channel bank and usually includes the standard telephone BORSCHT functions: Battery (normally 48 Vdc) Overvoltage Protection (lightning, etc.) Ringing (Voltage) Supervision (i.e. Dial Tone, On/Off Hook Detection, etc.) Coding (A/D, D/A Analog/Digital Conversions) Hybrid (i.e., 2 wire to 4 wire for fills duplex) Test There are several altemative channel bank options that can be selected depending on He application. The multiplexed digital signal consists of 24 DS-0 digital signals at 64 kbps and one frame bit for a total of 1.544 Mbps. This signal can be transmitted on TWP using 16 to 26 gauge cable to support repeaterIess distances of 6000 feet, the common telephone industry manhole spacing. Greater IMP repeater spacing distance and data rates are supportable with careful system design including cable plant design. The DS-! (often incorrectly used synonymously as TI) was very successful alla has expanded into He Digital TDM Hierarchy presented in Figure A.~.~.4-2 to accommodate greater multiplexing and higher data rates. The figure includes: The composite serial bit rate. Defined standard multiplexing between the venous digital signal levels. · The number of 64 kbps DS-0 (64 kbps) channels multiplexed at each digital signal level. · The typical transmission media. :\NCHRP\Phase:.rp ~NCHRP 3-51 · Phase 2 Final Report A1-46

. ~ cr) o <( cn ~ c: o > a) - he ~ ~7 I m ' if ~ L' tiL] m mu o (A Lo - ~ 0 1 0 ~cn 0 CY Lo _ a) a) Q in - o 1 en ~ m J a) l _ ~7 u) Q D :~ en Q V = - ~ in ~7 x J ~ 1 ~ o in _ (A ~ 7 tTI] ,JF Z Y Z Z I m A 1 U. 1 ~ ~ 1 Lo x L-I in in 0 Z ~ 0 Lo > Z Z 0 T ~ u) ~o - o ~n z ~ o z ~ - o ~ ~ - `' I Z O ~m X Q J z o Cl) s - C! - ~n o^>~ Z °[ ~ c.) ~ N > 0J

- - cO E ol D 0= 0 stop= ¢~3 on s 3-'T's s 0~~0= ~ b ~ ~ , c , ~ , ~ ~ o c~ ~ ~ X ~ X ~ X ~ ~ X ~ ~ ~ ~ Idol '~o° i o to oo~<T ! ~ I (D | on | ~| cot ~I 1 1 1 1 1 1 ~ a~ : ~' Z 1 | ~_ ~ N | . ~-~1 I ~0 0 1 I ~' ~ ~ ~ | ~ ~ ~ colt ~ ~ ~ ~_ ~ ~ ~ ~_c~ ~ ~ Q C > J

As He cost of electronics decreased, the telephone industry developed cost-effective digital Central office (CO) switches so that most cans (local and L.D.) are maintained In digital form from the CO of the calling subscriber Trough all intermediate transmission, multiplexing, and switching facilities to He CO of He caned subscnber. The concept is illustrated in Figure A.1.1.4-3. Except for PBX requirements, a switching capability or CO is usually not required for ITS and over private network infrastructure requirements; however, He transmission, multiplexing, and cross-connect equipment provides excellent capabilities. Of significance to ITS applications is He availability of high volume cost- effective, equipment for ITS communications infrastructure development. The cross-connect depicted in Figure A.~.~.4-3 is an important element of modern networks. A cross-connect historically has been an electromechanical panel of jacks, plugs, and jumpers for He purpose of reconfiguring DS-O, DS-l, DS-IC, and DS-2 connections. With these panels and jumpers, the following useful system manual functions can be performed: · Restoration of a failed circuit by using a spare. · Rerouting for systems reconfiguration. · Looping for testing during installation and maintenance. More recently, electronic cross-connects have been developed that operate at rates up to DS-3 and add significant advantage to digital transmission systems and networks by performing some of He following functions: Speed rearrangement of digital channels and circuits. · Hubb~ng, grooming, and consolidation of channels and circuits. Fast rerouting of circuit, based on routine tune-of-day, or temporary requirements. · Restore failed circuits quickly by rerouting if necessary. · Increased flexibility by rapid electronic control. ~ Network management and centralized testing; integrated network management. . L.\NCHRP\Ph~c2.rpt NCHRP 3-51 · Phase 2 Fmal Report A1-49

1 cn c: cn LLJ o z cy z c: o by is ~ 1 ' . o 1 ~ En LO o llJ z En llJ I ~n O o CY llJ X X ~ I X LLJ X u) ~ - , I t o Z Z o o I ~ ~) C) I 1 * ~ I Z W' o- 3: <1: <( \ 1 \ C) ~LLJ m C~ m \ o J <r z \ / Q z o z J \ O T i <1: ~ C) c ~ =1 , ~ CY m m~ Q cn ~ 0 0 0 Z Z cn ~ z y o 3 z z o s ~: ,_ - CY o~ 1 O ~ | 1 :\ 1 \ \ ~.° ~ 1 * ,, CO o ~ - 3 cn o .~ , _ O Q a) \ r LL CD 11

Electronics cross-connects are referred to as digital access and cross-connect systems (DACS). Thus, the electromechanical DSX designators (see Figure A.~.~.4-2) become DCS. Subrate Mu/fip/exing The digital hierarchy provides standards for bit rates from 64 kbps (DS-O) to 274.176 Mbps (DISC. ITS has applications for bit rates below the DS-! and DS-O circuits. These are addressed by TI subrates to DS-1 or DS-O as depicted in Figure A.~.~.4-4 with common rates. Standards exist for subrate multiplexing, but are not as widely and consistently embraced by industry. Many non-standard, often proprietary, implementations are deployed. Of particular importance to ITS are the ELA-232 bit rates that are multiplexed in a DS-O frame. The bit rates supported are: 2.4 kbps 4.8 kbps 9.6 kbps 19.2 kbps 28.8 kbps · 38.4 kbps Commercial services are available from telephone companies Mat support these DS-O subrates, typically under the name of digital data service (DDS) or subrate digital loop (SDRL). It should be noted that 56 kbps is a common available bit rate compared to the standard 64 kbps, DS-O bit rate. This lower rate is actually a DS-O frame, but with a "robbed bit" used for traditional signal functions (onion hook status). The bit rate 03R) is: Bit Rate = 7 bits~sample x 8,000 samples/sec = 56 kbps Many commercial services are available at 56 kbps, although Me modern trend is a fills "clear" 64 kbps, DS-O channel. ~:`NCHR~Phasc2 rpr NCHRP 3-51 · Phase 2 Fmal Report A1-5 1

~At, ~m > 0 ~ D D D D ~ of =~0= · <4 ~ ~ a' ~ D D D CD 00 In (D Cot ~ _ l 1 \ C) \ ~ \ I to 1 in 7 1 in Q o CO US 1 ~ / D 0 CM - 7 Q. LLI X Ill Y o ... z in Q 1 / ~ ~ ~ ~ ~ ~ ~ X ~ Q: / I Q T D ; l l o U) 1 Q / D _ CD 00 US Cat l 1 O O7 A 1 it X - al ~ c~ m ~n ~. Cl: 1~ OQ=~m' ~ ~m >c, D D D ~ D > C) 3 ~JC) ~ a, C£) 0 ~

T! Digifa/ Hierarchy Standards ant/ References The complete list of starboards for TI, Digital Hierarchy would be long. Below is an abbreviated list covering important topics. Expanded references are ~ncludecl in these documents. The U.S. T] digital hierarchy standards include: Amencan National Starboard for Telecommun~cabons. Digital Hierarchy-Formats Specifications. ANSITI.107-1988. Access Specification for High Capacity (DS]/DS3J Dedicated Digital Services. AT&T Technical Reference TR62415, June 1989. Available from AT&T Corporate Mailings. High Capacity Digital Service (] 544 Mb/sJ Interface Generic Requirements for End Users BeNcore Technical Reference TR-NPL-000054, Apn! 1989. Available from BeRcore Customer Service. Digroup Terminal and Digital Interface Frame Technical Reference and Compatibility Specification AT&T Compatibility Bulled 123, Aug. 1981. Available from AT&T Cotporate Mailings. Digital Channel Bank Requirements and! Objectives Bell System Transmission Engineenng, BeDcore Technical Reference TR4380l, Nov. 1982. Available from Beacon Customer Service. Amencan National Standard for Telecommun~cadons. Carrier-to-Customer Installation, DS] Metallic Interface ANST TI.403-1989. Requirements for Interfacing Digital Terminal Equipment to Services Employing the Exte~uled! Superframe Format AT&T Technical Reference TR54016, Sept. 1989. Available from AT&T Corporate Mailings. Data Communication Networks: Services and Facilities Interfaces Recommendations X.1- X.32. CCll-l Blue Book, Vol. VIII, Fascicle VIII.2, Geneva, 1989. Available from NITS. General Aspects of Digital Transmission Systems; Terminal Equipments Recommendations G.700-G.772. CCrrT Blue Book, Vol. m, Fascicle m.4, Geneva, 1989. Integrated Digital Loop Carrier System Generic Requirements, Objectives, and] Interface Belicore Technical Reference TR-TSY-000303, Sept. 1986, revision 4, Aug. 1991. :`NCHRP`Phase~rp' NCHRP 3-51 · Phase 2 Final Report A1-53

American National Standard for Telecommun~cabons. Integrated Services Digital Network (ISDN): Basic Access Interface for Use on MelaRic Loopsfor Application on the Network Side of the NT Player 1 SpecificationJ. A~ST Tl.601-1988. Digital Networks, Digital Sections and Digital Line Systems. CC~ Blue Book, vol. m, Fascicle m.s, Geneva, 1989. Available from NTIS, Order No. PBg9-143895. American National Standatd for Telecommun~cabons. Digital Hierarchy: Supplement to Formats Specifications (Synchronous Digital Data FormatJ. ANST TI.107b-1991. Generic Requirements for High-Bit-Rate Digital Subscriber Lines. Bedcore Technical Advisory TA-NWT-001210, act. 1991. Available from BeUc ore Customer Service. Amencan national Standard for Telecommun~cabons. Digital Hierarchy: Electrical Interfaces. ANST TI.102-1987. The subrate standards include: Subrate Data Multiplexing, A Service Function of DATAPHONE@' Digital Service. AT&T Technical Reference TR54075, Nov. 19SS. Secondary Channel in the Digital Data System: Channel Interface Requirements. BelIcore Technical Reference TR-NPL-000157, BelIcore, April 1986. Available from BeDcore Customer Service. Digital Data System Channel Interface Specifications. AT&T Technical Reference PUB 41021, March 1987. Available from AT&T Corporate Mailings. Digital Data System Channel Interface Specification. AT&T Technical Reference PIJB 62310, Nov. 1987; Addendum I, Jan. 19S8; Addendum 2, Oct. 1989; Addendum 3, Dec. 1989. Available from AT&T Corporate Mailings. D3 and D4 Subrate Dataport Channel Unit Technical Reference and Compatibility Specification. AT&T Compatibility Bulletin No. 126, April 1981. Available from AT&T Corporate Mailings. D3 and D4 56 KB Dataport Channel Unit Technical Reference and! Compatibility Specification. AT&T Compatibility Bulletin No. 141, April 1981. Available from AT&T Corporate Mailings. Digital Channel Banks: Requirements for Dataport Channel Unit Functions. Bellcore Technical Advisory TA-TSY-000077, 1986. Available from Bellcore Documents Registrar. ~:WCHRP`Phase:.rp' NCHRP3-51. Phase2FmalReport A1-54

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