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SRST Configuration: Dual and Octo Line Phones

Welcome to Part 6 in the SRST configuration series.  We'll look at what dual line and octo line configurations provide for your IP phones while they are in SRST mode.

Part 1: Basic SRST Configuration
Part 2: SRST Configuration:  IP Phone Clock, Date, and Time Formats
Part 3: SRST Configuration:  IP Phone Language Display
Part 4: SRST Configuration:  IP Phone Customized System Messages
Part 5: SRST Configuration:  Secondary Dial-Tone
Part 6: SRST Configuration:  Dual and Octo Line Phones 


Dual-line IP phones require the max-dn command to enable dual-line mode during Cisco Unified Communications Manager fallback.  They have one voice port with two channels and can handle two separate calls. As a result, they following features are available:  call waiting, call transfer, and conference functions.  Consultative transfer requires further configuration, consult the Cisco Unified SRST System Administrator's Guide.

When one of the dual-line channels is used on a specific phone, other phones that share the ephone-dn will be unable to use the secondary channel. The secondary channel will be reserved for use with the primary dual-line channel. 


From the Cisco SRST Admin Guide,
The octo-line feature supports up to eight active calls, both incoming and outgoing, on a single button. Eight incoming calls to an octo-line directory number ring simultaneously. After an incoming call is answered, the ringing stops and the remaining seven incoming calls hear a call waiting tone.

After an incoming call on an octo-line directory number is answered, the answering phone is in the connected state. Other phones that share the directory number are in the "remoteMultiline" state. A subsequent incoming call sends the call waiting tone to the phone connected to the call, and sends the ringing tone to the other phones that are in the "remoteMultiline" state. All phones sharing the directory number can pick up any of the incoming unanswered calls.

When multiple incoming calls ring on an octo-line directory number that is shared among multiple phones, the ringing tone stops on the phone that answers the call, and the call waiting tone is heard for other unanswered calls. The multiple instances of the ringing calls is displayed on other ephones sharing the directory number. After a connected call on an octo-line directory number is put on-hold, any phone that shares this directory number can pick up the held call. If a phone is in the process of transferring a call or creating a conference, other phones that share the octo-line directory number cannot steal the call.

As new calls come in on an octo-line, the system searches for the next available idle line using the huntstop chan tag command, where tag is a number from 1 to 8. An idle channel is selected from the lowest number to the highest. When the highest number of allowed calls is received, the system stops hunting for available channels. Use this command to limit the number of incoming calls on an octo-line directory number and reserve channels for outgoing calls or features such as call transfer or conference calls.

Octo-Line Limitations
  • Octo-line directory numbers are not supported by the Cisco Unified IP Phone 7902, 7920, or 7931, or by analog phones connected to Cisco ATA or Cisco VG224. 
  • The maximum number of directory numbers must be equal to or greater than the total of all line combinations. 
  • SIP endpoints are not supported on H.323 trunks. SIP endpoints are supported on SIP trunks only.

Sample Configuration

The following example sets the maximum number of virtual voice-ports that can be supported by the router to 20, and activates dual-line mode for all IP Phones registered to the router due to fallback mode.

Router(config)# call-manager-fallback
Router(config-cm-fallback)# max-dn 20 dual-line

The following example sets the maximum number of virtual voice-ports (DNs) that can be supported by the router to 24, and activates octo-line mode for up to 12 IP Phones registered to the router due to fallback mode.  The hunstop channel command specifies that only 4 channels to be available for incoming calls.

Router(config)# call-manager-fallback
Router(config-cm-fallback)# max-dn 24 octo-line 12
Router(config-cm-fallback)# huntstop channel 4

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