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Background: Know: Recognize: 

Anticipates: ASN.1

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H.245 uses ASN.1Edit

H.245 is the protocol of control signaling in H.323 multimedia communication system. The main purpose is that information exchange between different terminals. Moreover, H.245 adopts ASN.1 (Abstract Syntax Notation 1) to define its information structure, where ASN.1 is a language for defining data types.

Here is an example for resolution of video encoding.

First, define a structure and setting parameters for terminal capability by using "sequence" sentence.

TerminalCapabilitySet ::=SEQUENCE {
    sequenceNumber SequenceNumber,
    protocolIdentifier OBJECT IDENTIFIER,
    multiplexCapability MultiplexCapability OPTIONAL,
    capabilityTable SET SIZE(1...256) OF CapabilityTableEntry
    OPTIONAL,
...
}

Second, it is necessary to define the capability table entry.

CapabilityTableEntry ::=SEQUENCE{
    capabilityTableEntryNumber CapabilityTableEntryNumber,
    capability Capability OPTIONAL}

Then, choosing the type of capability, whereas, the choice type is video capability.

Capability ::CHOICE{
    nonStandard NonStandardParameter,
    receiveVideoCapability VideoCapability,
    transmitVideoCapability VideoCapability,
  ...
    receiveAudioCapability AudioCapability,
    transmitAudioCapability AudioCapability,
  ...
}

The following step is choosing the type of video capability which is H261 video capability.

VideoCapability ::=CHOICE{
    nonStandard NonStandardParameter,
    h261VideoCapability H261VideoCapability,
    h262VideoCapability H262VideoCapability,
  ...
}

Last, defining H261 video capability.

H261VideoCapability ::=SEQUENCE{
    qcifMPI INTEGER(1..4)OPTIONAL,
    cifMPI INTEGER(1..4)OPTIONAL,
    temporalSpatialTradeOffCapability BOOLEAN,
    maxBitRate INTEGER(1..19200),
  ...
}


See alsoEdit

Corresponding TELE9752 lecture slide