Telephones in VoIP networks: Sensitivity to RING signal and Calling Number Display

Background:

Due to reports on difficulties to make certain telephones ring we have investigated the required RING voltage for a number of specific telephones. The used test setup is shown in Figure 1 below.
VAC Lbcke R52-260T 230 VAC 50 Hz Vario Trafo 10 kohm

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48VDC DC Bias Network
Figure 1 Test setup for measuring RING sensitivity.
The RING signal is applied for approximately 1 second, and the telephones reaction or lack of reaction is observed. Please note: The test is carried out using a 50 Hz AC signal. Normally 25 Hz ringing signal frequency is used on the PSTN network. We ASSUME that this is without significance.

Results:

Make B&O B&O B&O CBRA CBRA CBRA CBRA Doro Doro Facit GNT Jysk Telefon Kirk Kirk KTAS Philips Type Beocom 4 Beocom 2000 Beocom 6000 Z101 Z303 Z305 Z306 Afti 45 Congress 200 FT820 Danmark2 DK80 FUGA Delta Trio Anthene luxe Dect I212S/I21 Required RING voltage 20 ~ 25 VAC 22 ~ 24 VAC 20 ~ 22 VAC 15 ~ 20 VAC 10 ~ 15 VAC 5 ~ 7 VAC 20 ~ 25 VAC 20 ~ 25 VAC 20 ~ 25 VAC 27 ~ 29 VAC 22 ~ 25 VAC 23 ~ 25 VAC 30 ~ 35 VAC 20 ~ 22 VAC 30 ~ 33 VAC 5 ~ 7 VAC
Visipia ApS Herstedvang 8 DK-2620 Albertslund Denmark
The tested telephones are all within the standard PSTN requirements, i.e. 35 V sensitivity (Europe) and 40 V (USA). It is noted that this test is not related to Caller ID = calling number display.
Calling Number display and Answering Machines
The telephones listed above have been tested for calling number display in a setup where they are connected to our CPE, attached to ComX Networks VoIP telephone service. The test has been carried out by connecting the telephone/answering machine under test to a TRP1G CPE (fiber terminal) and make 2 incoming calls to the unit and observe if the unit displays the calling nummer (Asubscriber) correctly. No problems have been observed with any of the tested models with number display. GNT Danmark2 and Beocom 2000 do not have calling number display function. Their display is entirely intended to show called number, i.e. for outgoing calls. B&O BeoTalk 1100 is a stand-alone telephone answering machine with display. Test: The DUT is connected to a TRP1G, and a total of 5 calls to the DUT from a mobile telephone and POTS telephones on the same and another CPE. Both number display, call browsing, and return calls work well.
KNOWN ISSUES: Remote operation of answering machines requires passing of DTMF signals from the calling telephone. This function is supported by the Visipia CPEs. Number Display by call forwarding When a call from subscriber A is made to subscriber B, who forwards the call to C, then the number displayed at C may be changed to subscriber Bs number. I.e. Cs telephone displays Bs number in stead of As number. This is due to the operation of the telephone system, i.e. in some systems the number information passed along with the call used for display is also used for call charging.

Load Test

Visipias CPEs are designed for a load o fup to 4 REN on each of the two FXS (POTS) ports. In order to check the CPEs RING drive capability in a practical setup, we have however undertaken the test outlined in Figure 2 with 8 telephones connected to the SAME port. Port 2 was left unused in this test setup.
Figure 2 Test setup, CPE with 8 telephones and an answering machine connected.
The telephones connected to the CPEs port 1 by simple parallel connection. Port 2 is unconnected. The connected units in this test are: Beocom 2000, Beocom 6000, Doro Congress 200, Facit FT820 , GNT Danmark2, Jysk Telefon DK80, Kirk Delta Trio, and a Beocom 1100 answering machine. Results: Number display works well on telephones with number display function as well as the Beocom 1100 answering machine. The Beocom 1100 shows the digits of outgoing calls as they are entered. Incoming call: All connected telephones are ringing in a stable way. The RING voltage is recorded at 42,8 V. The CPE thus complies with relevante PSTN standards in spite of the large number of connected telephones in this test. Quality of the connection: The connection was checked for interruptions, i.e. drop outs in the signal during 15 minutes of music playback. No interruptions, and no dropouts of noticeable length were observed.
Please note that the maximum specified load is 4 REN per FXS port. More telephones can be connected as long as the total load does not exceed 4 REN per port. Telephones of more recent development are typically well below 1 REN.
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