H.225.0

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H.225.0 is a substandard of H.323 .

The main concern of H.225 is the definition of messages:

  • Call signaling : Establishing, controlling and ending an H.323 call. The call signaling of H.225 is based on the ISDN call procedures, standard Q.931 .
  • RAS signaling function : Perform registration, access, bandwidth changes, status and logout procedures between endpoints and an H.323 gatekeeper. This amount of messages is called RAS (Registration Admission and Status). The RAS signaling function uses a separate channel.

The messages are encoded using the Q.931 user-to-user information element. The messages themselves are encoded according to the Packed Encoding Rules (PER) of ASN.1 .