2.2.3.1 TS_FRAME_ACKNOWLEDGE_PDU
The TS_FRAME_ACKNOWLEDGE_PDU structure is a client-to-server PDU sent to the server whenever the client receives a Frame Marker Command ([MS-RDPBCGR] section 2.2.9.2.3) with the frameAction field set to SURFACECMD_FRAMEACTION_END (0x0001) and it has finished processing this particular frame (that is, the surface bits have been rendered on the screen). The server uses this acknowledgment to throttle the rate at which it generates frames of data to avoid overloading the client with too many updates. The server SHOULD NOT wait for an acknowledgment for each frame before sending the next frame. Instead, the server SHOULD have a "window" mechanism where it allows multiple frames to be unacknowledged before it slows down its frame rate (or stops completely).
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tpktHeader |
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x224Data |
mcsSDrq (variable) |
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securityHeader (variable) |
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shareDataHeader (18 bytes) |
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frameID |
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tpktHeader (4 bytes): A TPKT Header as specified in [T123] section 8.
x224Data (3 bytes): An X.224 Class 0 Data TPDU, as specified in [X224] section 13.7.
mcsSDrq (variable): Variable-length PER-encoded MCS Domain PDU (DomainMCSPDU) that encapsulates an MCS Send Data Request structure (SDrq, choice 25 from DomainMCSPDU). This is as specified in [T125] section 11.32, and the ASN.1 structure definitions are specified in [T125] section 7, parts 7 and 10. The userData field of the MCS Send Data Request PDU contains a Security Header, Share Data Header, and a frame ID.
securityHeader (variable): Optional security header. The presence and format of the security header depend on the Encryption Level and Encryption Method selected by the server ([MS-RDPBCGR] sections 5.3.2 and 2.2.1.4.3). If the Encryption Level selected by the server is greater than ENCRYPTION_LEVEL_NONE (0) and the Encryption Method selected by the server is greater than ENCRYPTION_METHOD_NONE (0), this field MUST contain one of the following headers:
Non-FIPS Security Header ([MS-RDPBCGR] section 2.2.8.1.1.2.2) if the Encryption Method selected by the server is ENCRYPTION_METHOD_40BIT (0x00000001), ENCRYPTION_METHOD_56BIT (0x00000008), or ENCRYPTION_METHOD_128BIT (0x00000002).
FIPS Security Header ([MS-RDPBCGR] section 2.2.8.1.1.2.3) if the Encryption Level selected by the server is ENCRYPTION_METHOD_FIPS (0x00000010).
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If the Encryption Level selected by the server is ENCRYPTION_LEVEL_NONE (0) and the Encryption Method selected by the server is ENCRYPTION_METHOD_NONE (0), this header MUST NOT be included in the PDU.
shareDataHeader (18 bytes): Share Data Header ([MS-RDPBCGR] section 2.2.8.1.1.1.2) containing information about the packet. The type subfield of the pduType field of the Share Control Header ([MS-RDPBCGR] section 2.2.8.1.1.1.1) within the Share Data Header MUST be set to PDUTYPE_DATAPDU (0x0007). The pduType2 field of the Share Data Header MUST be set to PDUTYPE2_FRAME_ACKNOWLEDGE (0x38).
frameID (4 bytes): A 32-bit unsigned integer. This field specifies the 32-bit identifier of the frame that was sent to the client using a Frame Marker Command and is being acknowledged as delivered. The frameID field MUST be populated with the value of the frameID field that was specified in the Frame Marker Command associated with the frame being acknowledged. If the frameID field is set to the value 0xFFFFFFFF, the server SHOULD<5> assume that all in-flight frames have been acknowledged.