Voice Gatekeeper is an H323 device that provides the following major functions:
1) Address lookup and resolution, and translation between E.164 and IP addresses. This same function can be provided by voice gateway but the gatekeeper is used to simplify the configuration of the dial plans: instead of having every H323 to be knowledgable about every other device (meshed network) these devices will only need to know the address of the gatekeeper which will resolve the E.164 or H323 ID to the destination IP address.
2) Cisco voice gatekeeper provides the ability to authenticate and authorize the h323 endpoints (including voice gateways) and originating users.
3) Cisco gatekeeper also can be used to provide CDRs for accounting.
4) Cisco gatekeeper uses the principle of zones to control dial plan and provide bandwidth managements (for call admission control).
5) Cisco voice gatekeeper can connect to 3rd party applications using GKTMP to provide more routing capabilities.
6) Cisco gatekeeper can be designed and configured in hierarchical way using Directory gatekeepers to simply the configuration when you have many gatekeeper interworking with each other.
Voice Gateway is a device that connect telephony devices (phones, PBXs, PSTN switches) to the IP networks. The gateway provides the ability to make telephony phone, fax and modem calls over IP based networks using different compression techniques and it provides the required QoS.
Below links provides you with the first steps to understand and configure Cisco voice gatekeepers and gateways:
http://www.cisco.com/en/US/partner/tech/tk652/tk701/technologies_tech_note09186a00800c5e0d.shtml
http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080080b60.html
http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080080afd.html
http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080080aec.html
http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080080a66.html
http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a0080080a52.html
Thanks.
Najeeb
