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X12 segment reference
ISA — Interchange Control Header
Understand the X12 ISA segment: envelope delimiters, sender/receiver IDs, and interchange control numbers for every EDI document.
ISA segment facts
- ISA is always the first segment in an X12 interchange and defines element and segment terminators for the entire file.
- ISA06 and ISA08 must match the IDs your trading partner enrolled — padded width errors are a common silent parse failure.
- ISA13 interchange control numbers must stay unique per partner relationship to avoid duplicate-interchange rejections.
- ISA13 is a 9-digit interchange control number (000000001–999999999) and must equal IEA02 in the IEA trailer, or the interchange is rejected.
What the ISA segment does
The ISA segment opens every X12 interchange. It declares element and segment separators, identifies the sender and receiver, and assigns the interchange control number partners use for correlation.
Key elements
| Element | Name | Description |
|---|---|---|
| ISA01 | Authorization qualifier | Usually 00 (no authorization) or 03 (additional data). |
| ISA06 | Interchange sender ID | Your ISA ID as the partner expects it — often padded to 15 characters. |
| ISA08 | Interchange receiver ID | Partner ISA ID; mismatches here are a top cause of rejected interchanges. |
| ISA13 | Interchange control number | Must be unique per partner; reused numbers can trigger duplicate detection. |
Example ISA segment
ISA*00* *00* *ZZ*SENDER *ZZ*RECEIVER *250609*1200*U*00501*000000001*0*P*>~
Parse and validate samples with the free EDI validator or send JSON via the JSON→X12 mapping guide.
Common ISA errors
- Sender ID width off by one character (shifts all downstream parsing)
- Reused ISA13 control number on the same partner lane
- ISA13 does not match IEA02 in the closing IEA trailer (interchange control number mismatch rejects the whole interchange)
Related reference
FAQ
Frequently asked questions
Yes. ISA is the outer envelope for ANSI X12. EDIFACT uses UNB instead.
ISA defines delimiters. A malformed ISA mis-splits every following segment.
ISA13 is the interchange control number: a fixed 9-digit value (valid range 000000001–999999999, zero-padded) that uniquely identifies one X12 interchange. It must be unique per trading-partner lane and must match IEA02 in the closing IEA trailer. A mismatch between ISA13 and IEA02 — or a reused control number — is a common reason the interchange is rejected.
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