As we have already seen it before , if the voice gateway is unable to match an inbound leg for the call , your call will take the properties of the PVID0 .
Don’t forget that you can’t update any properties if the PVID0 is hitted .
Let’s review then the specificities of this default dial-peer:
For POTS dial-peer
- No IVR applications possible
For VOIP dial-peer
- Any codec
- fax-rate voice
- ip precedence 0
- No Resource Reservation Protocol ( RSVP)
- VAD enabled
As seen with the inbound dial-peer matching , outbound matching is much easier as the dial-peer matches on the destination-pattern expression.
Then the outbound will be selected with the port if you have a POTS dial-peer or will take the session-target in you have a VOIP dial-peer
When a voice gateway receive a call , you can divide your call in an inbound and outbound leg.
Let’s see how the inbound priority matching .
- incoming-called-number (called number “DNIS” information used)
- answer-address (calling number “ANI” information used)
- destination-pattern (calling number “ANI” information used)
- voice-port (that has dial port configured)
During WAN failure , we can observe that H323 will not preserve absolutely the call when the failover occurs as there is no more any signal from the CUCM.
An unofficial workaround is to use the command h225 timeout to suppress the keepalive between the Call Manager and the gateway.
no h225 timeout keepalive
RTP ports are used on top of UDP to carry on the voice payload/traffic.
The common range of ports are 16384 and 32767 .
Depending the Layer 2 technology that you use , the header can change :
- Ethernet Frame => 18 bytes
- Frame Relay/FRF.12 => 6 bytes
- MLP => 6 bytes 13 bytes
- ATM => 5 bytes
- MLP over Frame Relay => 14 bytes
For Layer 3 , you can use the following values
- IP Header = 20 bytes
- UDP Header = 8 bytes
- RTP Header = 12 bytes
So it gives you the following amount
- IP+TCP+UDP Header => 40 bytes
With CRTP enabled, you can then benefit of a huge saving of compression of this payload.
Indeed , from 40 bytes , you can decrease this payload from 2 up 4 bytes.