Single Line Telephones

Connect analog devices such as single line telephones and fax machines to the system.
Programming for this Feature
Programming Single Line Telephones


The system is compatible with 500 type (dial pulse) and 2500 type (DTMF) analog telephone devices. This includes on-premises single line telephones (SLTs), fax machines, and modems.

In DSX-40, SLTs connect to analog ports in the main equipment cabinet. In DSX-80/160, SLTs connect to SLIU PCBs. Each analog port provides power and ring voltage for the connected SLT. The analog ports use DTMF receivers. Each system provides 10 DTMF receivers that are shared by all connected analog ports.

Message Waiting

Both DSX-40 and DSX-80/160 support FSK Message Waiting lamps. DSX-80/160 also provides support for high voltage Message Waiting lamps – while DSX-40 does not.

Ringing For Incoming Calls

Single line extensions ring according to the settings in 2132-[01-64]: Line Ringing Stations: Config: Ring Assign: Line Ringing (2132): Ring Assignment]. It is not necessary to assign single line sets to Ring Groups to make them ring for incoming calls; they follow Key Ring instead.
  • In DSX-80/160 by default, the first 16 extensions (300-315) ring (option 2) for lines 1-12 and flash (option 1) for lines 13-64. All other extensions have lamp only (no ringing) for all lines.
  • In DSX-40 by default, all extensions (including single line sets) have immediate ring for all lines.

Ringer Equivalence Number (REN) Considerations


Single line telephones assigned to Key Ring or the same Ring Group will ring simultaneously. This is also true for single line telephones connected to the same port. Since the Ringer Equivalence Numbers of connected single line telephones are cumulative, you must do the following:
  • Add up the RENs of all connected single line telephones.
  • Be sure the total REN does not exceed 4 on any single port or system-wide.

Note that a REN of 1 is normal for an industry standard 2500 set with electromechanical ringer. Many phones with electronic ringers have significantly lower RENs. Check the label on the bottom of each single line telephone for the REN value.


Single line telephones assigned to Key Ring or the same Ring Group ring in pairs according to their SLIU PCB port assignment. For example, ports 1 and 2 ring together, followed by 3 and 4, 5 and 6, and finally 7 and 8. If the system has more than one SLIU PCB installed, the respective port pairs ring simultaneously on each card (e.g., ports 1 and 2 ring simultaneously on each PCB). The SLIU provides the capability to support this ringing arrangement, and REN calculations are not required. In DSX-80/160, there is not a REN limitation.

Conditions and Defaults


  • Dial Pulse (500 type) single line telephones cannot access any features that require the user to dial # or *.
  • The system provides a pool of 10 DTMF receivers that are dynamically allocated as required.

Default Setting

  • See Description above.

Other Related Features


  • Background Music
    • Background Music is not available to single line telephones.
  • Conference
    • Single line telephones can use Conference.
  • Do Not Disturb
    • Single line telephones cannot use DND.
  • Flash
    • The Class of Service option 1403-01: Flash for Single Line Set (page 635) allows you to enable or disable hookflash for analog single line extensions.
  • Handsfree and Handsfree Answerback
    • Single line telephones do not have Handsfree and Handsfree Answerback capability.
  • Headset Compatibility
    • Single line telephones do not have headset capability.
  • Intercom
    • All Intercom calls to single line telephones ring.
  • Last Number Redial
    • Last Number Redial is not available at single line telephones.
  • Paging
    • Single line telephones can make Paging announcements, but cannot receive Paging announcements.
  • Prime Line Preference
    • Single line telephones can use Prime Line Preference.
  • Save Number Dialed
    • Save Number Dialed is not available to single line telephones.

IntraMail Features

  • None.