Information Technology Reference
In-Depth Information
Next, the CUCM sends a
NotificationRequest
to request (R) that the gateway inform it when an on-hook (hu) event occurs and
request that the gateway collect digits 0 to 9, *, and #. The CUCM also sends a signaling request (S) asking the gateway to use the
line package (L) and play a dial tone (dl).
The gateway then informs the CUCM of an observed event (O); the digit 1 has been pressed.
The CUCM now sends another
NotificationRequest
to request that the gateway again inform it when an on-hook (hu) event occurs,
collect digits 0 to 9, *, and #, and turn off the dial tone.
The gateway informs the CUCM that the digit 2 has been pressed.
The CUCM sends a
CreateConnection
(CRCX) message to the gateway to ask it to create a connection and turn on the ring tone.
The gateway then sends an acknowledgment message to inform the CUCM that the CRCX was completed and to inform the CUCM
of the gateway's local RTP IP address and port.
Finally, the CUCM sends a
ModifyConnection
(MDCX) to inform the gateway of the remote peer's RTP IP address and port.
Note that the signaling between the CUCM and the remote peer (such as an SCCP phone) is not shown in
Figure 3-2.
MGCP messages are sent on UDP port 2427. However, TCP port 2428 is used to exchange keepalives between an MG and CUCM,
and for MGCP PRI/BRI backhaul between a media gateway and CUCM.
MGCP PRI/BRI backhaul is used to transport ISDN Q.931 (D channel) signaling information from the gateway to the call agent
(CUCM). ISDN Q.921 signaling is terminated on the gateway and is not backhauled to the call agent (only Q.931 is).
