TR-41.3.8-04-11-005
STANDARDS PROJECT
PN-3-4350.230-RV3
TITLE
Dial Pulse Criteria Considerations
SOURCE
VTech Communications
2 Shannon Ct
Howell, NJ 07731
CONTACT
Stephen R Whitesell
Phone 732 751 1079
Fax
732 751 0095
Email swhitesell@vtech.ca
DATE
November 8, 2004
DISTRIBUTION
TR-41.3.8
Abstract
The dial pulse criteria in the T1.401 network interface standard are specified for the Customer Installation
(CI), not for an individual piece of Customer Premises Equipment (CPE). The CI consists of all the CPE
and wiring on the customer side of the Network Interface (NI). Since the bridged ringers of other CPE
connected to the line can have an effect on the dial pulse shape, they need to be taken into account when
specifying the requirements in PN-3-4350.230-RV3.
The relative number of telephone customers using pulse dialing compared to those using tone dialing is
certainly decreasing, and the incidence of dial pulse customers with large numbers of CPE connected to
their line is arguably quite small. So while the possibility of bridged ringers needs to be taken into
account, the expected number of such bridged ringers also needs to be considered. TIA-470.210-C has
set a precedence of establishing mandatory on-hook resistance and impedance criteria based on an
assumption of 3 CPE connected to the customer side of the NI. The same assumption seems valid here.
Thus, changes are proposed to require the Equipment Under Test (EUT) to meet the dial pulse criteria
with any combination of up to two additional electromechanical or electronic tone ringers bridged to the
line.
In addition, one of the critical parameters in Addendum A to the T1.401 network interface standard is to
ensure the dial pulse exceeds 21.4 mA during the make interval on a minimum current loop. The tests
currently specified in PN-3-4350.230-RV3 only address typical loop current conditions. An additional test
needs to be added for the minimum loop current condition.
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Disclaimer:
This contribution has been prepared by VTech Communications (VTech) to assist the TIA TR-41 Engineering
Committee or one of its sub-elements as noted above. It is offered as a basis for discussion and is not to be
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Intellectual Property Statement:
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of which may be essential to the practice of all or part of this contribution when incorporated into a TIA Publication.
2
T1.401-2000 and T1.401a-2001 Requirements
Dial pulse requirements for the CI are given in T1.401-2000, Network to Customer Installation Interfaces
– Analog Voicegrade Switched Access Lines Using Loop-Start and Ground-Start Signaling, and in its
T1.401a-2001 addendum.
Clause 8.1.1 of T1.401-2000 places requirements on the network to accept dial pulses having specified
pulse rate and percent break criteria “with the equivalent of up to 5 C4A type ringers bridged between the
tip and ring conductors at the NI.” A footnote provides information for simulating a C4A ringer with an
RLC series circuit. Note however that the mention of “up to 5 C4A type ringers” is a requirement on the
network, not on the CI.
Clause 8.2.1 provides requirements on the CI and identifies several criteria, including a template for dial
pulse shape, that the CI must meet when tested into a specified resistive termination. However, the
composition of the CI is not discussed in clause 8.2.1, or anywhere else in the document except in the
scope (clause 1.1) and the definitions (clause 3.1.12). Clause 1.1 reads, in relevant part: “. . . the
customer premises cabling and equipment is referred to as the Customer Installation (CI).” The definition
in clause 3.1.12 reads as follows: “Customer Installation (CI): All telecommunication equipment and wiring
on the customer side of the network demarcation point.” To be sure, there are several other places in the
document where requirements are given for the CI, but there is nowhere that the number of pieces of
equipment and the amount of wiring that may be used are specified.
Figure 15 of T1.401-2000 shows the CI being tested using a circuit consisting of 50 Vdc in series with a
resistance that can be adjusted from 400 to 1900 Ω. The current that the CI can draw during the make
interval of the dial pulse is determined by its own resistance and the above parameters. To allow for up
to 430 Ω CIs (400 Ω for the CPE plus 30 Ω for the wiring), the minimum allowed current during the make
interval was revised from 22.4 to 21.4 mA in Figure 16 of T1.401a-2001. [Note: 50V / 2330Ω = 21.46 mA]
Discussion
While a CI with up to 5 C4A ringers may have been envisioned when the T1.401 dial pulse criteria were
originally established, the likelihood of encountering such a CI today is quite remote for at least two
reasons. First of all, nearly every telephone product being manufactured today uses an electronic tone
ringer, not an electromechanical ringer like the C4A. So in the vast majority of cases where the CI
includes more than one CPE, most of the additional CPE are going to have electronic tone ringers.
Secondly, dual tone multi-frequency (DTMF or tone dialing) service is almost universally available, and a
strong argument can be made that CIs with several CPE are much more likely to have DTMF than dial
pulse service. In fact, many CPE being sold in the marketplace today only support DTMF service. Thus,
while the dial pulse criteria in PN-3-4350.230-RV3 needs to take into account the possibility of additional
CPE with bridged ringers, the criteria need to be set with a realistic expectation of the number of such
bridged ringers likely to be connected to a dial pulse line.
In TIA-470.210-C we have established mandatory on-hook resistance and impedance criteria based on 3
CPE being connected to the line, with support for 5 CPE being desirable. There is certainly justification
for defining both mandatory and desirable criteria for on-hook resistance and impedance because of the
expectation that a significant percentage of CIs exceed 3 CPE in the general case. However, based on
the arguments given above, we probably need only consider a mandatory criteria involving 3 CPE for the
dial pulse case.
This then leaves the question of how to simulate the additional bridged ringers. As noted above, T1.4012000 provides a footnote describing how an electromechanical C4A ringer may be simulated. The text of
the footnote is as follows:
A C4A ringer may be simulated by a 110-henry inductor having a resistance of 3650 Ω in series
with a 0.45 µF capacitor. The tolerance of the components may vary ± 10%. The inductance shall
be essentially constant for dc current up to 10 mA, measured by observing the exponential
buildup of current during the application of a 36.5 Vdc voltage across the inductor without the
series capacitor.
3
An electronic tone ringer can be simulated by a series RC combination. A resistance of 8200 Ω in series
with a 0.56 µF capacitor gives an A-type REN of 0.4 at 20 Hz and a B-type REN with a maximum value of
0.9 at 68 Hz. Other RC combinations are possible, but one set of component values needs to be agreed
upon for the purpose of dial pulse testing in this standard.
The test circuit shown in Figure 1 of PN-3-4350.210-RV3 uses 1000 Ω in series with 50 Vdc. This is
suitable for dial pulse testing under typical use conditions, but does not properly check that the CPE will
comply with the 21.4 mA minimum current requirement during the make interval of the dial pulse when on
a long loop. An additional test needs to be made using 1930 Ω in series with 50 Vdc. The ± 2 V
tolerance on the battery voltage also needs to be tightened considerably for this measurement. In
addition, the voltmeters V1 and V2 shown in the figure are inappropriate for measuring the transient
nature of dial pulse characteristics. Furthermore, no mention of them is made in the test procedures.
What is needed is an oscilloscope across the 1000 Ω resistor to monitor the current waveform.
Proposed Changes to Draft 5 of PN-3-4350.210-RV3
1. Replace Figure 1 and its associated note with the following figure and notes:
930 Ω
Scope
S
T
1000 Ω
50 V
Bridged
Ringers
(Note 2)
CPE
R
Notes:
1. Voltage and resistance tolerances for circuit components are ±1%.
2. Up to 2 electronic tone ringers or C4A electromechanical ringers may be bridged across tip
and ring. See test procedures for details.
a. Electronic tone ringers may be simulated by a resistance of 8200 Ω in series with a
capacitance of 0.56 µF.
b. C4A electromechanical ringers may be simulated by a 110 H inductor having a winding
resistance of 3650 Ω in series with a 0.45 µF capacitor. The inductance shall be
essentially constant for dc currents up to 10 mA, as measured by observing the
exponential buildup of current during the application of a 36.5 Vdc potential across the
inductor without the series capacitor.
c. Tolerances on components simulating either type of ringer may be ±10%.
2. Add the following to the paragraph in clause 4.3 that is above Figure 1:
Unless indicated otherwise, switch S shall be set to by-pass the 930 Ω resistor and no additional
ringers shall be bridged across tip and ring.
3. Add the following additional steps to clause 4.3.4.2:
4. Position switch S to include the 930 Ω resistor in the test circuit and repeat steps 2 and 3.
4
5. Leaving switch S set to include the 930 Ω resistor in the test circuit, bridge two simulated
electronic tone ringers across tip and ring and repeat steps 2 and 3.
6. Leaving switch S set to include the 930 Ω resistor in the test circuit, replace the two simulated
electronic tone ringers bridged across tip and ring with two C4A electromechanical ringers
(real or simulated) and repeat steps 2 and 3.