H.323 VS MGCP



Using H.323 as the call control protocol to a gateway has the following advantages:

•	H.323 provides integrated access. Data and voice channels can be placed on the same T1. 
For example, for a service provider like AT&T, FR and PRI can be placed on the same T1.
•	H.323 provides support for fractional PRI. 
•	Gateways support caller ID on FXO ports. Callmanager does not support caller ID on FXO ports from MGCP gateways.
•	Many more TDM interface types and signaling protocols—for example, analog-Direct 
Inward Dialed (DID), receive and transmit (E&M), T1 Feature Group-D (FGD), and E1
R2—can be used.
•	H.323 drops DSP’s on hairpinned calls to enable capabilities like ISDN video switching. 
•	Gateway resident applications like Toolkit Command Language (TCL) and voice 
Extensible markup language (VXML) can be used. TCL and VXML applications provide
IVR features and call control functionality such as call forwarding, conference calling, and
Voice mail.
•	CAC network design with H.323 gatekeepers is often necessary when voice and video 
Coexist in a network and Cisco CallManager is not the only call controller in the network.
•	There are no release dependencies between gateways and Cisco CallManager for 
supporting new voice hardware. New hardware cards on Cisco IOS gateways become
Immediately available for use with all existing Cisco CallManager releases.
•	H.323 enables a much easier migration architecture to SIP because the fundamental 
Concepts of H.323 and SIP—for example, distributed control with dial-peer Configurations—are the same.
•	Calls from IP phones through an H323 gateway are dropped on a CallManager failover 
Unless SRST mode is enabled. With SRST enabled, the calls are preserved.

Using MGCP as the call control protocol to a gateway has the following advantages:

•	Centralized configuration, control, and download from Cisco CallManager 
•	Better feature interaction with capabilities like caller ID and name display 
•	Easy, centralized dial-plan management 
•	Gateway voice security features (voice encryption) as of Cisco IOS Software Release 
12.3.(5th)T
•	Q Signaling (QSIG) supplementary services as supported by Cisco CallManager: 
o	— Cisco CallManager interconnects to a QSIG network using an MGCP gateway and T1 or E1 PRI connections to a private integrated services network (PISN). The MGCP gateway establishes the call connections. Using the PRI backhaul
Mechanism, the gateway passes the QSIG messages to the Cisco CallManager to    setup QSIG calls and send QSIG messages to control features.
o	— When a PBX is connected to a gateway that is using QSIG via H.323, calls that are made between phones on the PBX and IP phones attached to the Cisco CallManager can have only basic PRI functionality. The gateway that terminates the QSIG protocol provides only the calling line ID (CLID) and DID number, instead of Cisco CallManager providing that information.
•	Enhanced call survivability: 
o	— Calls from IP phones through an MGCP gateway are preserved on a CallManager failover. This feature avoids dropped calls when applying the monthly operating system service release on the Cisco CallManagers
o	— In SRST mode, calls from IP phones through an MGCP gateway are preserved on MGCP fallback for calls on analog or CAS circuits. Calls on ISDN circuits are dropped on fallback.