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Outbound calls out to PSTN gateways fail with cause code "i = 0x84EF - Protocol error unspecified"

Core Issue

If an outbound call fails to local numbers or any other number out of the Public Switched Telephone Network (PSTN) gateway, it can be because the gateway sends a bearer capability with Unrestricted Digital. For example:

Bearer Capability i = 0x8890A3
Standard = CCITT
Transfer Capability = Unrestricted Digital
Transfer Mode = Circuit
Transfer Rate = 64 kbit/s
Channel ID i = 0xA9839F
Exclusive, Channel 31

Telco disconnects with the Cause i = 0x84EF - Protocol error; unspecified error message.

This capability is sent when the IP phone has video capability enabled. If Telco does not support this capability, the call is rejected.


In order to resolve this issue, complete this configuration on the primary rate interface (PRI) voice-port, on the PSTN gateway:

voice-port x/y:z  bearer-cap 3100Hz

This changes the bearer capability in the setup message to 3100Hz (for voice).

Refer to IP Phone Call Failure with VT Advantage - Bearer Capability for more information on this issue.

Community Member

Here is the solution..

!--- This is an example of how to configure the bearer cap parameter 
!--- on a Cisco AS5300.

esc-5300-2(config)#voice-port 0:D
esc-5300-2(config-voiceport)#bearer-cap ?
  3100hz   enable 3100hz
  speech   enable speech
esc-5300-2(config-voiceport)#bearer-cap speech

!--- Sample output of the IOS configuration
!--- <some output omitted>.

voice-port 0:D
 bearer-cap Speech