MGCP and H.323 Features in Cisco Unified Communications Manager

This document will cover some of the comparison differences when integrating either MGCP or H.323 gateway protocols. The last blog entry compared the survivability differences of the two gateway protocols. Analog FXO gateway voice ports using MGCP did not support the Caller-ID service. Caller ID and Automatic Number Identification (ANI) services have been supported over MGCP controlled T1-CAS (Channel Associated Signaling) and T1 PRI (ISDN Primary Rate Interface) voice ports for a long time. Cisco IOS 12.4(15T) code has the caller ID service, but earlier versions of IOS do not. The 12.4(15T) code features are in the XJ code train as well [e.g. 12.4(15T)]. H.323 gateway interfaces support the NFAS (Non-Facility Associated Signaling) feature, while MGCP gateways do not. The NFAS feature allows one Q.931 D channel in a PRI to carry voice signaling for up to 20 PRIs. NFAS will allow more B channels in a PRI to accommodate additional phone calls. MGCP gateways do not support fractional PRIs, while H.323 does. If MGCP is statically configured, fractional PRI support can be accommodated, but is not officially supported. Cisco’s recommended MGCP gateway deployment configuration uses the automated ccm-manager config and ccm-manager config server commands covered in a previous blog. When these automated configuration commands are used, CUCM registers all 24 channels of the PRI with the MGCP call agent. If a fractional PRI of less than 23 channels is desired, the H.323 protocol is recommended. MGCP support Q.SiG features in Call Manager 4.x, while H.323 did not. Cisco Unified Communications Manager (CUCM) 5.0 introduced the Q.SIG feature . Q.SiG feature support enables multi-vendor interoperability which will not work over the standard Q.931 signaling capabilities of an ISDN circuit. Q.SiG leverages the information elements (IEs) of Q.931 Factility messages to exchange supplementary services such as message waiting indication (MWI) messages between different vendors MGCP has supported gateway encryption via secure Real-Time Protocol (SRTP) since Call Manager 4.0, while encrypted voice call support was not integrated into H.323 gateways until Cisco Unified Communications Manager 5.0. Check the Cisco feature navigator at www.cisco.com/go/fn to determine the IOS requirement of the gateway router to support the SRTP feature. Feel free to share any MGCP, H.323, and SIP feature differences. There are many features that I have not mentioned in this blog. The next blog entry will cover the RFC2833 DTMF-Relay Feature.

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