2.2.14.4 Client Auto-Detect Response PDU

The Auto-Detect Response PDU is sent by the client to the server and is used to detect network characteristics such as bandwidth and round-trip time.

This PDU MUST only be sent over the MCS message channel. The ID of the message channel is specified in the Server Message Channel Data (section 2.2.1.4.5).


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tpktHeader

x224Data

mcsSDrq (variable)

...

securityHeader (variable)

...

autoDetectRspPduData (variable)

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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): A variable-length PER-encoded MCS Domain PDU (DomainMCSPDU) that encapsulates an MCS Send Data Request structure (SDrq, choice 25 from DomainMCSPDU), as specified in [T125] section 11.32 (the ASN.1 structure definitions are given in [T125] section 7, parts 7 and 10). The userData field of the MCS Send Data Request contains a Security Header and auto-detect response data.

securityHeader (variable): An 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 following headers:

  • Basic Security Header (section 2.2.8.1.1.2.1) if the Encryption Level selected by the server is ENCRYPTION_LEVEL_NONE (0).

  • 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).

  • FIPS Security Header (section 2.2.8.1.1.2.3) if the Encryption Method selected by the server is ENCRYPTION_METHOD_FIPS (0x00000010).

The flags field of the security header MUST contain the SEC_AUTODETECT_RSP (0x2000) flag (2.2.8.1.1.2.1).

autoDetectRspPduData (variable): A variable-length field that contains auto-detect response data, specifically one of the three messages described in sections 2.2.14.2.1, 2.2.14.2.2 and 2.2.14.2.3.

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