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.
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no h225 timeout keepalive
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MGCP is Master/Slave protocol and MGCP endpoints are controlled by the Control Agent ( Most of the case , it will be the CUCM)
MGCP uses the UDP/2427 for its communication between the CUCM and the GW. It is also a text-based master/slave protocol used by a media gateway controller (MGC) and Call Agent to control media gateways. However , TCP/2428 is used to exchange keepalives between endpoints and Call Agent, as well for MGCP PRI/BRI backhaul.
MGCP MGCs and MGs can be described as follows:
- MGC/Call Agent: this element possesses call control intelligence and controls MGs (example : Call Manager)
- MG: This device provides translation between data packet and audio signals reveived over VoIP networks and other networks such as the PSTN ( example: IOS gateway)
As defined for SIP , here are the transport layers used by Skinny/SCCP Protocol:
- TCP Connection with CUCM
- UDP Connection between the endpoints
SCCP is a Cisco proprietary protocol master/slave protocol that Call Manager and other call agents can use to communicate with devices and endpoints as Cisco IP Phones.
SCCP uses port TCP/2000 and TCP/2443 for SCCPS
SIP is a text-based, application-Layer control signaling protocol that is used for setting up, modifying and tearing down multimedia sessions between participants and takes advantages of elements of HTPP, SMTP and SDP.
SIP Protocol can use TCP or UDP at the transport layer. The port used is then TCP/UDP/5060 but is TCP/5061 for TLS over TCP
It can use as well multicast as well unicast communication or a combination of the both.
Here are the mandatory functions that a GK must observe:
- Admission Control
- Address Translation
- Bandwidth Control
- Zone Management