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CCNA Collaboration CIVND 210-065 Official Cert Guide by Jason Ball, Brian Morgan

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Call Processing with H.323

The H.323 call process is a lot chattier than the SIP call process. Because the Cisco VCS is the only H.323 gatekeeper Cisco has, this explanation references the VCS. When a device, whether it is an endpoint, multipoint control unit (MCU), or a gateway, registers with a gatekeeper, that device is completely subservient to the gatekeeper. Therefore, it must have permission before it can do anything. So, if an endpoint wants to place a call to another endpoint registered to the same VCS, the source endpoint must first send an Admission Request (ARQ) to the VCS to request permission to call. This message is sent when the source endpoint dials the destination alias. When the VCS receives the ARQ message, it responds with ...

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