The concept of a zone is used to define the group of H.323 devices that an individual gatekeeper controls. That is, the devices that belong to the zone register with the controlling gatekeeper. Zones can cross subnets, and a gatekeeper can manage devices in one or more subnets. Up to 100 zones can be registered to an individual gatekeeper.
Prior to H.323 Version 2, only one gatekeeper could be active in a zone at a time. H.323 Version 2 introduced the concept of alternate gatekeepers. Implementing the alternate gatekeeper feature allows multiple gatekeepers to control one zone. This helps to provide redundancy and load sharing for large installations. The gateway must also support the alternate gatekeeper to use this feature.
Figure 16-1 is an example of two gatekeepers controlling devices in two separate zones. Notice that communication and signaling can cross between the zones.
Figure 16-1. Multiple Gatekeepers and Zones
The following are services for voice calls that the gatekeeper can provide:
The gatekeeper can track bandwidth that active calls use both within and between zones. You can configure the maximum bandwidth available. When you place a call, the bandwidth used is subtracted from the maximum. If bandwidth is insufficient to place the call, the call is rejected. When a call terminates, the bandwidth for that call is returned to the available pool.
Part I: Voice Gateways and Gatekeepers
Gateways and Gatekeepers
Part II: Gateways
Media Gateway Control Protocol
Session Initiation Protocol
Connecting to the PSTN
Connecting to PBXs
Connecting to an IP WAN
Influencing Path Selection
Configuring Class of Restrictions
SRST and MGCP Gateway Fallback
Using Tcl Scripts and VoiceXML
Part III: Gatekeepers
Part IV: IP-to-IP Gateways
Cisco Multiservice IP-to-IP Gateway
Appendix A. Answers to Chapter-Ending Review Questions