H.323 Architecture 2357H.323 Architecture An H.323 network consists of terminals, voice gateways, an optional gatekeeper,and multipoint control units (MCUs). If a gatekeeper is present in an H.323network, the terminals, gateways, and MCUs registered with the gatekeeper forma zone. In this zone, the gatekeeper provides the following functions for H.323terminals, gateways, or MCUs:■ Address translation■ Admission control■ Bandwidth control■ Zone administration and security control■ Call control signaling and call management■ Routing control and accountingFigure 681 shows a simple H.323 network. For all calls, a gatekeeper is the callservice control and central control unit in its administrative zone.Gateway entities are usually deployed on routers. You may configure the IP voicegateway function on the router at command line interface (CLI). They interact withgatekeepers by sending H.225.0 RAS messages.In the current implementation, gatekeepers are usually deployed on SUN stationsor servers while gateways are deployed on routers. For reliability sake, a backupmechanism is provided for gatekeepers. In case the communication with a primarygatekeeper is abnormal (for example, timeout occurs) or the primary gatekeeperbecomes unavailable, gateways can turn to a secondary gatekeeper forregistration.Call disengage DRQ (Disengage_Request)DCF (Disengage_Confirm)DRJ (Disengage_Reject)Status information IRQ (Information_Request)IRR (Information_Request_Response)IACK (Info_Request_Acknowledge)INAK (Info_Request_Neg_Acknowledge)Bandwidth control BRQ (Bandwidth_Request)BCF (Bandwidth_Confirm)BRJ (Bandwidth_Reject)Gateway resource availability RAI (Resource Availability Indicator)RAC (Resource Availability Confirm)RAS timer modification RIPTable 89 Major RAS messagesCategory Message
