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2.2.6.1 Virtual Channel PDU

The Virtual Channel PDU is sent from client to server or from server to client and is used to transport data between static virtual channel endpoints.


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tpktHeader

x224Data

mcsPdu (variable)

...

securityHeader (variable)

...

channelPduHeader

...

virtualChannelData (variable)

...

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.

mcsPdu (variable): If the PDU is being sent from client to server, this field MUST contain a variable-length, PER-encoded MCS Domain PDU (DomainMCSPDU) which encapsulates an MCS Send Data Request structure (SDrq, choice 25 from DomainMCSPDU), as specified in [T125] section 11.32 (the ASN.1 structure definition is given in [T125] section 7, parts 7 and 10). The userData field of the MCS Send Data Request contains a Security Header and the static virtual channel data.

If the PDU is being sent from server to client, this field MUST contain a variable-length, PER-encoded MCS Domain PDU (DomainMCSPDU) which encapsulates an MCS Send Data Indication structure (SDin, choice 26 from DomainMCSPDU), as specified in [T125] section 11.33 (the ASN.1 structure definition is given in [T125] section 7, parts 7 and 10). The userData field of the MCS Send Data Indication contains a Security Header and the static virtual channel data.

securityHeader (variable): Optional security header. The presence and format of the security header depends on the Encryption Level and Encryption Method selected by the server (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), then this field MUST contain one of the security headers described in section 2.2.8.1.1.2.

If the PDU is being sent from client to server:

  • The securityHeader field MUST contain a Non-FIPS Security Header (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).

If the PDU is being sent from server to client:

  • The securityHeader field MUST contain a Basic Security Header (section 2.2.8.1.1.2.1) if the Encryption Level selected by the server is ENCRYPTION_LEVEL_LOW (1).

  • The securityHeader field MUST contain a Non-FIPS Security Header (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).

If the Encryption Method selected by the server is ENCRYPTION_METHOD_FIPS (0x00000010) the securityHeader field MUST contain a FIPS Security Header (section 2.2.8.1.1.2.3).

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), then this header MUST NOT be included in the PDU.

channelPduHeader (8 bytes): A Channel PDU Header (section 2.2.6.1.1) structure, which contains control flags and describes the size of the opaque channel data.

virtualChannelData (variable): Variable-length data to be processed by the static virtual channel protocol handler. This field MUST NOT be larger than CHANNEL_CHUNK_LENGTH (1600) bytes in size unless the maximum virtual channel chunk size is specified in the optional VCChunkSize field of the Virtual Channel Capability Set (section 2.2.7.1.10).

 
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