Some Emergency Service provider's phone systems do not send the Connect message to establish the call fully end to end, even after the operator answers the call. If the call originates from a SIP device or a Skype client it will result in one way audio. This Best Practice describes how to configure the Ribbon SBC 1000/2000 to force the originating device to open the voice path in both directions in situations where the Connect message is not received from the terminating carrier.

The instructions below assume you are logged into the WebUI and connected to the applicable Ribbon SBC 1000/2000.

Prerequisite: Verify if Emergency Services Configuration is Required

There are two options to verify if 911 emergency services configuration is required for establishing calls: Verify through WebUI Monitor or Verify through Logs.

For Digital, this procedure applies to CAS and ISDN calls.

For Analog, this procedure applies to FXS devices, such as an Overhead pager.

Verify through WebUI Monitor

  1. From the WebUI, access the Monitor tab.
  2. View the channels used for PSTN connection to the Emergency call route (for both Analog and Digital routes).
    1. If the channels show in Alerting state but the other side answered the call, the emergency call was not connected. See Step c.
    2. If the channels show in normal state, and the emergency call connected, no other configuration is required.
    3. Configure the SBC for Emergency Services.

Verify through Logs

This example applies to SBC 2000 system logs; the same process applies to obtaining SBC 1000 system logs.

  1. From the WebUI, access Logs. See Working with Logging.
  2. Ensure the log level is set to Trace (see Managing Subsystems Logging).
    1. For CAS: Set to CAS TRACE level.
    2. For ISDN: Set to ISDN TRACE level.
  3. View the logs. The connect message data (noted in the red lines below) should be present in the logs for 911 calls. These messages indicate the PSTN is sending the connect message to the SBC. If these lines are not present, you must configure the SBC for emergency services.
  4. Configure the SBC for Emergency Services.

Verify Connect Message through Logs - For SBC 2000

This example is a Trace Level System log, which applies to SBC 2000 with CAS E&M Signaling.

Configure the SBC for Emergency Services

Step 1: Configure Message Mapping Table

This step is different depending on whether the calls are CAS (Digital or Analog) or ISDN. See below.

For CAS calls (Digital or Analog)

  1. Access Settings> Telephone Mappings Table.
  2. Create and configure a Message Translation table (i.e., Alerting to Connect). See Creating and Modifying Entries to Message Translation Tables).
  3. Configure Message Type as Alerting/180 Ringing.
  4. Apply changes.


For ISDN calls

  1. Access Settings> Telephone Mappings Table.
  2. Create and configure a Message Translation table (i.e. Proceeding to Connect). See Creating and Modifying Entries to Message Translation Tables.
  3. Configure Message Type as Proceeding (ISDN only).
  4. Apply changes.


Step 2: Create Transformation Table

The steps below apply to Digital (CAS or ISDN) or Analog (FXS) calls.

For 911 Calls

This example applies only if the call has originated from Skype, and Skype is configured to prepend the '+' sign.

This configuration is for 911 calls going from Skype→T1→ 911.

  1. Access Settings> Transformation.
  2. Create a call Transformation Table for 911 calls (i.e., SkypeToT1-911). See Creating and Modifying Entries to Transformation Tables.
  3. Configure per parameters below.
  4. Apply changes.


For all Other Call Destinations

This configuration is applicable for regular calls (non 911) going from Skype to the T1 carrier.

  1. Access Settings> Transformation.
  2. Create a call Transformation Table for all other call destinations except 911 (i.e., Skype to T1). See Creating and Modifying Entries to Transformation Tables).
  3. Configure per parameters below.
  4. Apply changes.


Step 3: Add Transformation Table to the Call Route Table

For 911 calls

Add the Transformation table (SkypeToT1-911) to the Routing table used for routing IP calls (911) to the T1 carrier.

  1. Access Settings > Call Routing Table.
  2. Create a Call Route for 911 calls (i.e., Emergency Calls).
  3. Select the Number/Name Transformation Table that includes 911 specifications (i.e, SkypeToT1-911 calls).
  4. (For CAS only) Select the Message Translation table that includes Alerting/180 Ringing (i.e., Alerting To Connect).
  5. (For ISDN calls only) Select the Message Translation table that includes Proceeding (ISDN only) (i.e., Proceeding To Connect).


For all other IP calls

Add a Transformation table (SkypeToT1) to the Routing table used for routing IP calls to the T1 carrier.

  1. Access Settings > Call Routing Table.
  2. Create a Call Route for all IP calls (not 911).
  3. Select the Number/Name Transformation Table created for all IP calls (i.e, SkypeToT1 calls).