12 MINIMAL LOWER LAYER PROTOCOL (4)

12.1 Introduction (4.1)

12.1.1 Background (4.1.1)

12.1.2 Goals and Assumptions (4.1.2)

12.1.3 Differences (4.1.3)

12.1.4 Notation Conventions (4.1.4)

12.2 Block Format (4.2)

dddd

=

Start Block character (1 byte)ASCII , i.e., <0x0B>. This should not be confused with the ASCII characters SOH or STX.

dddd =

Data (variable number of bytes)

This is the HL7 data content of the block. The data can contain any displayable ASCII characters and the carriage return character, .

=

End Block character (1 byte)ASCII , i.e., <0x1C>. This should not be confused with the ASCII characters ETX or EOT.

=

Carriage Return (1 byte)The ASCII carriage return character, i.e., <0x0D>.

12.3 Processing Rules (4.3)

13 HYBRID LOWER LAYER PROTOCOL (2)

13.1 Introduction (2.1)

13.1.1 Goals and Assumptions (2.1.1)

13.1.2 Notation Conventions (2.1.2)

13.2 Blocks (2.2)

'C' - character count wrong in previous data block received

'X' - checksum wrong in previous data block received

'B' - data too long for input buffer in previous block received

13.3 Processing Rules (2.3)

13.3.1 Optional Connection and Disconnection (2.3.1)

13.3.2 Initiating and Responding (2.3.2)

d)If the block is acceptable and has block type 'N', it is a negative acknowledgement. Resend the original block as many times as is specified in the NPT or return to the application with an indication of the error.

e)If the block is acceptable and has block type 'D' it is the response. Go to the next step.

f)If the initiating system detects an error in the data block from the responding system, it has the option of retransmitting the original data block. The decision of whether to retransmit the original block is application-specific. It depends on the type of message and the ability of the receiving system to detect duplicate messages.

13.4 Carriage Return Stuffing (2.4)

13.5 Flow-Through Processing (2.5)

13.5.1 Inititiating System Processing (2.5.1)

13.5.2 Responding System Processing (2.5.2)

13.6 Implementation, System and Site-Specific Issues (2.6)

13.6.1 Connect Retries (For optional transient virtual circuits) (2.6.1)

13.6.2 Receive Timeout Errors (2.6.2)

13.6.3 The Network Parameter Table (NPT) (2.6.3)

Connect Retry Count - the number of times to try to connect to a destination.

Connect Pause - the amount of time to wait between connect attempts.

Receive Timeout - the amount of time to wait for a response data block.

Send Retry Count - the number of times to resend a data block after receive errors.