2.2.14.3 Server Auto-Detect Request PDU
The Auto-Detect Request PDU is sent by server to the client 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 |
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mcsSDin (variable) |
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securityHeader (variable) |
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autoDetectReqPduData (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.
mcsSDin (variable): A variable-length PER-encoded MCS Domain PDU (DomainMCSPDU) that encapsulates an MCS Send Data Indication structure (SDin, choice 26 from DomainMCSPDU), as specified in [T125] section 11.33 (the ASN.1 structure definitions are given in [T125] section 7, parts 7 and 10). The userData field of the MCS Send Data Indication contains a Security Header and auto-detect request data.
securityHeader (variable): A security header. The 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). 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) or ENCRYPTION_LEVEL_LOW (1) and the embedded flags field does not contain the SEC_ENCRYPT (0x0008) flag.
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) and the embedded flags field contains the SEC_ENCRYPT (0x0008) flag.
FIPS Security Header (section 2.2.8.1.1.2.3) if the Encryption Method selected by the server is ENCRYPTION_METHOD_FIPS (0x00000010) and the embedded flags field contains the SEC_ENCRYPT (0x0008) flag.
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If the Encryption Level is set to ENCRYPTION_LEVEL_CLIENT_COMPATIBLE (2), ENCRYPTION_LEVEL_HIGH (3), or ENCRYPTION_LEVEL_FIPS (4) and the flags field of the security header does not contain the SEC_ENCRYPT (0x0008) flag (the PDU is not encrypted), then the field MUST contain a Basic Security Header.
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The flags field of the security header MUST contain the SEC_AUTODETECT_REQ (0x1000) flag (2.2.8.1.1.2.1).
autoDetectReqPduData (variable): A variable-length field that contains auto-detect request data, specifically one of the five messages described in sections 2.2.14.1.1, 2.2.14.1.2, 2.2.14.1.3, 2.2.14.1.4 and 2.2.14.1.5.