ECHO-BACK

Echo back. The practice where a partner re-attaches the original payload in their acknowledgement to prove faithful reception.

Definition

Echo back is an integration practice where the receiver of an EDI message re-includes part or all of the received payload in their return acknowledgement. The goal: provide cryptographic or application-level proof that the received content matches exactly what was sent, in addition to the AS2 MIC or the CONTRL/997 syntactic acknowledgement. Echo back can cover key identifiers (PO number, GTIN) or the entire payload.

Origin

Echo back is implicitly encoded in the AS2 MDN through MIC computation on the original payload bytes before decryption (RFC 4130). It is explicit in business acknowledgements like ORDRSP (Order Response) which re-includes the source order identifiers, or in CIH (Confirmation of Inbound Handling) acknowledgements of some PEPPOL hubs. The practice sharply reduces disputes about the actual nature of the received content.

Example in context

BGM+231+ORDRSP-2026-0042+9'
RFF+ON:PO-2026-0099'
DTM+171:20260514:102'

In this ORDRSP, the RFF+ON segment echoes back the original order reference (PO-2026-0099) received by the manufacturer. The buyer can thus reconcile the ORDRSP against their own PO unambiguously, and log in their application journal that the order was indeed received on 20260514.

Related terms

• MDN — AS2 acknowledgement that implements an implicit echo back via MIC.
• Functional Acknowledgement — 997/999 X12 echoes back ST and GS references.
• Idempotency — operational property complementary to echo back.