Which three functions are associated with MGCP? (Choose three.)
A.
Control is implemented by a series of plain-text commands that are sent over UDP port 2427
between Cisco Unified Communications Manager and the gateway.
B.
A PRI backhaul channel forwards PRI Layer 2 (Q.921) signaling information via a TCP
connection from the gateway to the call agent.
C.
MGCP uses a separate channel for backhauling signaling information between the call agent
and the gateway.
D.
The gateway maintains a separate dial plan for redundancy in case the call agent fails.
E.
Users query the call agent to determine the location of the call recipient.
F.
A call agent uses control messages to direct its gateways and their operational behavior.
Explanation:
MGCP is a plain-text protocol used by call-control devices to manage IP Telephony
gateways. MGCP is a master/slave protocol that allows a call control device to take control of a
specific port on a gateway. With this protocol, the Cisco CallManager knows and controls the state
of each individual port on the gateway. It allows complete control of the dial plan from Cisco
CallManager, and gives CallManager per-port control of connections to the PSTN, legacy PBX,
voice mail systems, POTS phones and so forth. This is implemented with the use of a series of
plain-text commands sent over User Datagram Protocol (UDP) port 2427 between the Cisco
CallManager and the gateway.
Another concept relevant to the MGCP implementation with Cisco CallManager is PRI Backhaul.
This occurs when Cisco CallManager takes control of the Q.931 signaling data used on an ISDN
PRI. The one thing that distinguishes a PRI from other interfaces is the fact that the data that is
received from the PSTN on the D-channel and needs to be carried in its raw form back to the
Cisco CallManager to be processed. The gateway does not process or change this signaling data,
it simply passes it onto the Cisco CallManager through TCP port 2428. The gateway is still
responsible for the termination of the Layer 2 data. That means that all the Q.921 data-link layer
connection protocols are terminated on the gateway, but everything above that (Q.931 network
layer data and beyond) is passed onto the Cisco CallManager. This also means that the gateway
does not bring up the D-channel unless it can communicate with Cisco CallManager to backhaul
the Q.931 messages contained in the D-channel.http://www.cisco.com/en/US/tech/tk1077/technologies_tech_note09186a00801da84e.shtml