The calculations performed here follow the requirements developed by Committee T1E1

Users agree to provide attribution to Telcordia for the use of any output of the Telcordia Spectral Compatibility Computer, by stating "this calculation was made using the Telcordia Spectral Compatibility Computer from Telcordia Technologies, Inc." or a reasonable variation thereof. The calculations here are subject to change in form and numerical value after more study. Telcordia specifically reserves the right to add to, amend, or withdraw the statements and calculation procedures contained herein. In no event will Telcordia be liable for any damages arising from the use of the Telcordia Spectral Compatibility Computer.

What are the calculations here for?

The calculations performed here follow the methodologies developed by Committee T1E1.4 as stated in the American National Standard for Telecommunications — Spectrum Management for Loop Transmission Systems, T1.417-2003. The calculations follow "method B" as defined in Annex A of T1.417-2003. See www.t1.org, technical subcommittee T1E1.4, or the White Paper for more information. These calculations are for spectrum management purposes and may be somewhat more optimistic than some actual DSL equipment performances. Performance of actual ADSL and VDSL modems may be about 3 dB lower than calculated here with the same worst-case crosstalk, requiring about 9 dB margin instead of 6 dB.

The calculations determine the performance of digital subscriber line (DSL) systems and loop transmission technologies in the presence of crosstalk from other systems. The calculations here can help determine spectral compatibility with all basis systems: ADSL, G.lite, SDSL, ISDN, HDSL, HDSL2, DDS, voicegrade, and Enhanced Business Services (Nortel P-Phone^TM) The user can enter any number of crosstalk disturbers of many types of technologies, and/or any number of the defined spectrum management (SM) classes (SM1-SM9). SM class crosstalk comes from the power spectral density (PSD) template of that class. These PSDs are illustrated in the "Help" section. The user can also enter the PSD (in Hz, dBm/Hz) of a new technology. There should be at most a total of 49 crosstalk disturbers, although the user can enter more if desired. Multiple types of crosstalk are combined with the FSAN crosstalk summation method.

If the calculated performance of the basis system with crosstalk from a technology is as good as the levels defined in the Spectrum Management Standard, then the technology is spectrally compatible with the basis system. To prove spectral compatibility, typically two crosstalk scenarios must pass: 24 new technology crosstalkers, and 12 new technology crosstalkers plus 12 reference crosstalkers for compatibility with ADSL and VDSL; or 49 new technology crosstalkers, and 24 new technology crosstalkers plus 24 reference crosstalkers for compatibility with other basis systems. SNR margins must be within delta (dB) (typically 0 to 1 dB) of the margins with 24 or 49 reference crosstalkers. If the evaluation initially fails, then loop lengths of both the crosstalkers and the basis system may be decreased until it passes. Evaluations are performed separately for each basis system, and the deployment guideline is the minimum loop length for which all evaluations pass.

All cases of upstream and downstream basis system performance, for all homogeneous and mixed crosstalk cases, must pass all basis system tests to be spectrally compatible. The tests are defined in detail in the Spectrum Management Standard. Loop lengths are in equivalent working length (EWL), a length of 26 gauge cable with attenuation approximately equal to that of the loop: EWL = L26 + (0.75)L24 + (0.60)L22 + (0.40)L19, where L26, L24, L22, and L19 are the working lengths of 26-, 24-, 22-, and 19-gauge cable in the loop. The longest EWL that is compatible with all basis systems is the "deployment guideline" of the technology.

General Hints

Your browser must have cookies enabled. Login and password are case sensitive. Loop lengths and disturber numbers must be entered as non-negative integers. Instead of re-entering data, use the Back button of your web browser and edit previous entries. When a user enters a User-entered PSD or a loop make-up, that data is stored in a persistent file, and this file will remain unless it is over-written. The files are not accessible by other users. The loop make-up file is overwritten if the user enters starting and ending loop lengths.

The bit rate of the SDSL and G.shdsl for which performance is calculated is entered in the basis bit rate field, and the bit rate of crosstalk from SDSL and G.shdsl are entered in a separate field. SDSL and G.shdsl can have any bit rate up to 2320000 bps. Worst case SDSL or G.shdsl crosstalk is generally self-NEXT at the same bit rate. Maximum compatible single carrier loop length calculations require many iterations and may take a few minutes.

All distances are integer feet equivalent working length (EWL ) 26 gauge, except if the user enters and uses a particular loop make-up. The performance of basis systems deployed from a central office (CO) are calculated. The cable make-up of the crosstalkers is the same as that of the basis system, and the crosstalkers terminate at the same location as the basis system (TU-Rs collocated). Crosstalk is same binder. The bottom part of the input form may be entered with a value Y > 0, then crosstalk from RT or repeatered lines is calculated, see "What about a remote terminal (RT) or repeater?" below. Otherwise, Z-Y = Z = loop length and crosstalk is CO-based.

The user can now also perform spectral compatibility calculations for cases where the disturbing TU-R and the basis TU-R are not collocated by entering non-zero values in the fields for variable B at the very bottom of the the loop input form. Note, however, that T1.417 calls for all CO-based systems to be evaluated with collocated TU-Rs and B should generally equal zero.

Loop length calculations that determine a maximum compatible distance equal to the maximum evaluation loop length of a basis system (defined in T1.417) passed all tests and are compatible with that basis system at all loop lengths. (i.e., if its determined that loop length compatible with ADSL is 15.5 kft, then compatible on all non-loaded loops). It is a good idea to cross-check calculated compatible loop lengths by running some bit rate and margin calculations.

For convenience, users can enter the "Number of reference disturbers" and the system automatically calculates and uses the type of reference disturbers for that basis system, rate or loop length. The reference disturbers are CO-based and are added to other specified disturbers. Both homogeneous and mixed crosstalk cases must pass to be spectrally compatible.

There are multiple different reference disturbers for HDSL2, so if the number of reference disturbers is positive in the HDSL2 compatible loop length calculation, then that number is replaced by running all mixed crosstalk calculations (2 X 24 and 12 + 12 reference) defined in T1.417 and all mixed crosstalk cases pass in upstream and downstream up to the displayed distance.

What Basis System Performance Calculations are Here?

All calculations determine the performance of CO-based basis systems. Requirements are only outlined here to be informative, and they are subject to change. See the latest version of T1.417 spectrum management standard for the actual current requirements.

VDSL

Calculate bit rate of VDSL, or maximum loop length compatible with VDSL. Follows the methodology defined in T1.417-2003, a channel capacity bit-rate calculation of band-plan 998 VDSL. Downstream VDSL and SM6 PSDs equal the SM6 PSD template limitied to be at most -50 dBm/Hz. Upstream VDSL and SM6 use M2 noise F power back-off (PBO). VDSL is CO-based and uses PBO for a loop of length Z. SM6 can be RT-based if Y > 0, and then it uses PBO for a loop of length Z-Y. Repeatered SM6 currently uses PBO for a loop of length Z-Y on both spans, which isn't correct unless Z-Y = Y.

ADSL

Discrete multitone (DMT)-based signals, basis systems: Full-rate ADSL (T1.413-1998 ITU G.992.1), and G.lite (ITU G.992.2, T1.419).

Calculate bit rate, SNR margin, or maximum loop length compatible with ADSL or G.lite.

The calculated ADSL and G.lite bit rates with the proper number of crosstalkers must be no less than those defined in the spectrum management standard to be spectrally compatible.

G.lite tests are defined in T1.417-2003, G.lite uses downstream tones up to 127 (ADSL uses up to tone 255), and G.lite downstream basis rates are lower than those of ADSL.

Single-carrier

Pulse amplitude modulated (PAM) signals with decision feedback equalizer (DFE) receivers, basis systems: 2B1Q ISDN BRI, HDSL, HDSL2, 2B1Q SDSL, and possibly G.shdsl.

Calculate SNR margin, and maximum loop length compatible with the basis system.

The relative SNR margins with the proper number of crosstalkers must be no less than the values of "delta (dB)" defined in the spectrum management standard (typically delta is close to 0 dB) to be spectrally compatible.

Can also calculate the maximum bit rate achieved by SDSL or G.shdsl with a given margin, crosstalk, and loop (not part of T1.417).

Legacy

Linear-equalization based signals, basis system: DDS.

Calculate SNR margin.

The relative SNR margins with the proper number of crosstalkers must be non-negative to be spectrally compatible.

Crosstalk power integration, basis system: Voicegrade. Calculate the integral of the crosstalk power from 200 Hz to 4 kHz. Must be no greater than -75 dBm to be spectrally compatible with V.90, and no greater than -66 dBm to be spectrally compatible with other voicegrade services.

Maximum crosstalk power, basis system: Enhanced Business Services (Nortel P-Phone^TM). Calculate the maximum crosstalk power in the 6 - 10 kHz band. Must be no greater than -96 dBm/Hz. Must also be compatible with voicegrade to be spectrally compatible.

Other Utilities

The frequency response of a loop can be calculated, a particular loop make-up can be entered, a user can enter a crosstalker PSD, a user can check the user-entered PSD, and help resources are available

Power back-off (PBO)

The crosstalk from G.shdsl and user-entered PSDs (upsd) may be lowered by a flat level of power back-off (PBO) in dB. The entered number of dB is subtracted from both upstream and downstream PSDs, the same at all frequencies. Some calculations also allow the G.shdsl transmit signal to be lowered by PBO that may be different from the crosstalking G.shdsl PBO. Self-crosstalk from G.shdsl has the same PBO level as entered for the G.shdsl signal. The G.shdsl noise floor is not changed by the PBO.

What are relative SNR margins and reference margins?

Calculations of single-carrier and DDS performance output relative signal to noise ratio (SNR) margins in dB. The relative SNR margin equals the calculated SNR minus the SNR margin with the reference crosstalk. The relative SNR margin must at least equal some value of "delta" (dB) in order for spectral compatibility to be demonstrated. Delta (dB) is defined in the spectrum management standard for each basis system, and typically delta (dB) is either equal to zero or is a small number less than about 1 dB. The SNR calculated with the reference crosstalk is the reference SNR margin, and was found to be equal to:

ISDN reference SNR margin = 8.8 dB with 49 SM1 at 17.5 kft.

HDSL reference SNR margin = 7.0 dB with 49 SM3 at 9 kft.

HDSL2 reference margin upstream = 5.1 dB with 24 SM3 + 24 SM5 at 9 kft, and HDSL2 reference margin downstream = 5.7 dB with 24 T1 + 24 SM4 at 9 kft.

400 kbps SDSL reference SNR margin = 5.1 dB, with 49 SM2 at 13.5 kft.

1040 kbps SDSL reference margin = 5.0 dB, with 49 SM8 at 8.5 kft.

1568 kbps SDSL reference margin = 4.2 dB; with 49 SM7 at 7 kft

G.shdsl has Many relative margins

9.6 kbps DDS reference margin = 19.2 dB with 49 SM1 at 27 kft.

64 kbps, 72 kHz DDS reference margin = 13.5 dB with 49 SM1 at 13 kft.

What about a remote terminal (RT) or repeater?

COMPATIBILITY WITH RT CROSSTALK IS NOT FULLY SPECIFIED IN T1.417.

Some DSLs are deployed from a remote terminal (RT) or with repeaters in the mid span of a loop, with transceivers called intermediate transmission units (TU-I). The user can calculate the effect of crosstalk from systems with TU-Is on CO-based basis systems. Calculations are as defined in informative Annex L of T1.417, and use the short-coupling length NEXT model in T1.417-2003. Crosstalk is made to be from a TU-I by entering a positive value of distance Y from CO to crosstalking TU-Is (feet 26 gauge EWL). Then the "loop length" is the distance Z-Y from the crosstalking TU-Is to the TU-Rs. The basis system transmits from the CO over a distance Z. While the basis system TU-R is usually collocated with the crosstalking TU-Rs at Z, the crosstalking TU-R can be on a loop that is defined to be B feet longer than the basis system loop, by entering non-zero values for B in the fields at the end of the loop input form. If B is less than zero, then the crosstalking TU-R is closer to the CO than the basis TU-R. Pictorially:

Basis TU-C <- Y ft-> intermediate TU-I <- loop length Z-Y ft -> basis TU-R <- B ft -> disturbing TU-R

Default is the TU-I is an RT, and crosstalk comes from the TU-I and TU-R. If crosstalk is specified to be from a repeatered line, then it comes from the C0 transmitter, the repeater at Y, and the TU-R at Z (there is one repeater at Y).

If Y>0, then by default all crosstalk is from remote terminals or repeatered lines. If Y>0, then a crosstalk type may be designated as being from a CO-based system; the other crosstalk is then from remote terminals or repeatered lines. If a number of reference disturbers is entered, then the reference crosstalk is CO-based. By designating a CO-based crosstalk type and a positive number of reference disturbers, there can be two different CO-based crosstalk types as well as the remote terminal or repeatered line crosstalk.

If the user-entered loop make-up is used, then this loop is from the TU-I to the TU-Rs (Z-Y), and the loop from the CO to the TU-I is Y kft 26 gauge.

What is spectrum management?

Spectrum management is the administration of the loop plant in a way that provides spectral compatibility for services and technologies that use pairs in the same cable. In order to achieve spectral compatibility, the ingress energy that transfers into a loop pair, from services and transmission system technologies on other pairs in the same cable, must not cause an unacceptable degradation of performance. In addition, the egress energy from a particular loop pair must not transfer into other pairs in a manner that causes an unacceptable degradation in the performance of services and technologies on those pairs.

Detailed margin calculations are required to demonstrate spectral compatibility. These calculations are here for each basis system. Because some technologies are spectrally asymmetric, that is, use a different transmit spectrum in each direction, evaluations must often be performed in both the upstream and downstream directions.

The calculations here apply to digital subscriber line systems operating on insulated solid copper conductor twisted-pair cables used in the North American subscriber loop environment.

Credits
Dr. Kenneth J. Kerpez, Senior Scientist
Abdullah Al Salem Ahmed, Java Guru
Sagor Hoque, Graphics Designer