Advent Instruments - Caller ID and Telephony Equipment

Caller ID Signal Levels (Part 2: Standards)

Caller ID Signal Levels (Part 3: Standards)

Introduction:

The Caller ID levels stated in various standards vary significantly in how they are defined. Along with the use of different units, these standards may specify unique termination conditions. The following table provides a summary of signal level definitions for three common Caller ID standards. These being Telecordia (Bellcore) SR-3004, Telecommunication Industry Association (TIA) TIA-716 & TIA-777, and European Telecommunications Standards Institute (ETSI) ETS 300 778-1 & ETS 300 778-2.

Summary of Level Definitions:

	CPE State
Standard	On-Hook	Off-Hook
Telecordia (Bellcore)	Document: SR-3004 Units: dBm (referenced to 600 ohms) Source Impedance: 900 ohms Load Impedance: 600 ohms	Document: SR-3004 Units: dBm (referenced into 600 ohms) Source Impedance: 900 ohms Load Impedance: 600 ohms
	Setup: Levels are measured across tip and ring with the line terminated by a 600 ohm resistor. When performing the tests, replace the 600 ohm resistor by the CPE.	Setup: Levels are measured across tip and ring with the line terminated by a 600 ohm resistor. When performing the tests, replace the 600 ohm resistor by the CPE.
	Example: Sending a FSK signal level of -13.5 dBm requires a CO voltage source level of -5.54 dBm (0.409 Vrms). The level across tip and ring during testing is also -5.54 dBm (0.409 Vrms).	Example: Sending a FSK signal level of -13.5 dBm requires a CO voltage source level of -5.54 dBm (0.409 Vrms). The level across tip and ring during testing will depend on the CPE’s off-hook impedance. Since this is normally close to 600 ohms, the level will be approximately -13.5 dBm (0.163 Vrms).
TIA	Document: TIA/EIA-716 Units: mVrms Source Impedance: 900 ohms Load Impedance: open circuit	Document: TIA/EIA-777 Units: mVrms Source Impedance: 900 ohms Load Impedance: 600 ohms
	Setup: Levels are measured across tip and ring with the line open circuit. When performing the tests, connect the CPE to the telephone line.	Setup: Levels are measured across tip and ring with the line terminated by a 600 ohm resistor. When performing the tests, replace the 600 ohm resistor by the CPE.
	Example: Sending a FSK signal level of 120 mVrms requires a CO voltage source level of 120 mVrms. The level across tip and ring during testing is also 120 mVrms.	Example: Sending a FSK signal level of 120 mVrms requires a CO voltage source level of 300 mVrms. The level across tip and ring during testing will depend on the CPE’s off-hook impedance. Since this is normally close to 600 ohms, the level will be approximately 120 mVrms.
ETSI	Document: ETS 300 778-1 Units: dBV Source Impedance: not specified Load Impedance: the CPE’s AC termination can be either: a) greater than 8 kohms b) impedance of 820 ohms in series with a parallel combination of 360 ohms and 180 nF.	Document: ETS 300 778-2 Units: dBV Source Impedance: not specified Load Impedance: CPE’s AC termination requirements depend on additional national standards
	Setup: Levels are measured across tip and ring with the CPE connected in the on-hook state (off-line).	Setup: Levels are measured across tip and ring with the CPE connected in the off-hook state (on-line).
	Example: Sending a FSK signal level of -20 dBV requires adjusting the CO voltage source until the level across tip and ring is -20 dBV. The actual CO sending level depends on the CPE’s AC termination and the source impedance of the test setup.	Example: Sending a FSK signal level of -20 dBV requires adjusting the CO voltage source until the level across tip and ring is -20 dBV. The actual CO sending level depends on the CPE’s AC termination and the source impedance of the test setup.