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H.255 is also used in VOIP and is the part of H.323 used for call setup

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Posted by HamidAliKhan

H.225 is basically used for call setup & its a part of H.323.

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Posted by Hash007

H.225 protocol is a part of H.323 ITU-T Standard. Protocol itself consists of 2 parts Call Signalling and RAS(Registration ,Admission and Status).
Call Signalling is used to setup the connection between two H.323 Endpoint phones or between H.323 Endpoint and a Gatekeeper.

H.225 RAS works between H.323 Endpoints and a Gatekeeper . It is the first channel which is opened for communications prior to any other channel.

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Posted by insidesol