CAC On Voice Gateway/CME part 2

To read part 1 , click here

To read part 2 , click here

To read part 3 , click here

To read part 4 , click here

Local Voice Busy Out : (LVBO)

In the figure below, the legacy PBX is connected directly to the PSTN via E1 , it is also connected via E1 to a Cisco voice Gateway , the PBX give the priority to go out through the voice Gateway to reach the SIP provider via the WAN interface of this Gateway.

what will happen if the WAN interface is down ? the PBX will keep sending calls to the voice Gateway because it is not aware of the WAN status !

The solution is to use LVBO , it will monitor the WAN status , and whenever it is down , it will cause the E1 to give busy tone , in this case the legacy PBX will use its secondary method via the PSTN.


Cisco2821(config)#voice-port 0/0/0
Cisco2821(config-voiceport)#busyout monitor ?
BRI ISDN Basic Rate Interface
GigabitEthernet GigabitEthernet IEEE 802.3z
Loopback Loopback interface
Port-channel Ethernet Channel of interfaces
backhaul Busyout when backhaul L3 connectivity is lost
gatekeeper Busyout when lost connectivity to gatekeeper
keepalive Busyout when SIP keepalive mechanism fails
probe busyout on probe results to the specified IP address

Notice that we can use keepalive to detect the SIP keepalive mechanism fails

Cisco2821(config-voiceport)#busyout monitor gigabitEthernet 0/1

So now , whenever the Wan interface is down , the E1 port will give busy out , allowing the PBX to switch to the PSTN

find blow and example of the router message that activate the LVBO for a BRI card


*Jul 24 05:59:50.243: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed state to down
*Jul 24 05:59:50.243: %HTSP-5-VPM_BUSYOUT: voice port Basic Rate Interface 0/0/0: activate busyout
*Jul 24 05:59:50.243: %ISDN-4-ISDN_UNEXPECTED_EVENT: NOT PRI: Occurred at ../isdn/isdnif_event.c:663
*Jul 24 05:59:50.243: %ISDN-4-ISDN_UNEXPECTED_EVENT: NOT PRI: Occurred at ../isdn/isdnif_event.c:663
*Jul 24 05:59:50.771: %ISDN-6-LAYER2DOWN: Layer 2 for Interface BR0/0/1, TEI 64 changed to down
*Jul 24 05:59:50.823: %LINK-3-UPDOWN: Interface BRI0/0/1, changed state to down

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3 Responses to CAC On Voice Gateway/CME part 2

  1. Pingback: CAC On Voice Gateway/CME part 3 | elhallak

  2. Pingback: CAC On Voice Gateway/CME part 4 | elhallak

  3. Pingback: CAC On Voice Gateway/CME part 1 | elhallak

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