2.2.2.4 S20_DATA
The S20_DATA packet is used by a host or client to send data to an application-sharing session.
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Version/Type |
user |
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Correlator |
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ackID |
stream |
dataLength |
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datatype |
compressionType |
compressedLength |
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data (variable) |
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... |
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Version/Type (2 bytes): MUST be set to 0x0037.
user (2 bytes): The local identifier of the user, which is obtained from the Multipoint Communication Service (MCS) [T122] layer. For more information about the MCS user ID, see [T122] section 3 (Definitions) in the ITU-T Recommendation.
Correlator (4 bytes): The unique identifier for the new session. The first two bytes are the MCS user identifier (above) followed by a monotonically increasing 2-byte sequence number that starts at zero.
ackID (1 byte): Reserved. SHOULD be set to zero when sent and SHOULD be ignored on receipt.
stream (1 byte): The type of stream message being transmitted.
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Value
Meaning
STREAM_UPDATES
0x01
Sends window update information.
STREAM_MISC
0x02
Sends cursor update information.
STREAM_UNUSED
0x00
Reserved. MUST be set to zero when sent and MUST be ignored on receipt.
STREAM_INPUT
0x04
Sends mouse movement update information.
dataLength (2 bytes): The combined uncompressed size, in bytes, of the following data fields: datatype, compressionType, and compressedLength.
datatype (1 byte): The following values indicate the contents of the data field.
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Value
Meaning
DT_AWC
0x17
An ActiveWindowPDU packet.
DT_CA
0x14
A Control Order for Application Sharing packet. This type of packet will be sent if CAPS_VERSION_20 is set in the version field in the PROTCAPS_GENERAL structure.
DT_CA30
0x15
A Control Order for Application Sharing Enhanced packet. This type of packet will be sent if CAPS_VERSION_30 is set from the version field in the PROTCAPS_GENERAL structure.
DT_CM
0x1B
A Cursor Management Order packet.
DT_CPC
0x20
A Screen Capabilities Update packet.
DT_FH
0x0B
A Font List packet.
DT_HET30
0x16
For a Host Tracking packet.
DT_HET
0x19
For a Microsoft NetMeeting 2 compatible Host Tracking packet.
DT_IM
0x1C
An Input PDU packet.
DT_SNI
0x1F
A Synchronization Order packet.
DT_SWL
0x18
A Shared Window List packet.
DT_UP
0x02
An Update Order packet.
compressionType (1 byte): The following values indicate the type of compression that is used for the data field:
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Value
Meaning
0x00
Uncompressed.
CT_NO_DICTIONARY
0x01
Uses compression without a persistent dictionary.
CT_PERSIST_DICTIONARY
0x02
Uses compression with a persistent dictionary for each type of S20_DATA message.
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Compression is applied to the S20_DATA packet payloads that are larger than or equal to 4,096 bytes. For more information, see [RFC1951].
compressedLength (2 bytes): The combined size, in bytes, of data when it is compressed, datatype, compressionType, and compressedLength.
data (variable): One of the data structures that are appropriate to the value of the datatype field.