What is AS2? The EDI Transport Explained

Retailer requirement documents say things like "we trade EDI via AS2" and assume you know what that means. Here it is, minus the acronym fog.

The transport layer, not the content

EDI has two layers people constantly blur. The content is X12: the 850 purchase orders and 856 ship notices this blog spends most of its time on. The transport is how those documents physically move between you and your partner. AS2 is a transport — the dominant one in North American retail.

AS2 (Applicability Statement 2) moves documents directly between trading partners over the internet, using HTTPS. No intermediary network, no mailbox provider — your AS2 endpoint talks straight to Walmart's. Three mechanisms make that safe enough for commerce:

1. Encryption. The payload is encrypted with the receiver's public certificate; only the receiver's private key opens it.
2. Digital signatures. The sender signs each transmission, proving origin and that nothing changed in transit.
3. MDNs — Message Disposition Notifications. The receiver returns a signed receipt confirming the message arrived and decrypted intact. In legal terms, non-repudiation; in operational terms, proof of delivery.

Note what an MDN is not: it isn't the 997 functional acknowledgment. The MDN says "your transmission arrived intact." The 997 says "and the EDI inside it parsed." Two layers, two receipts — a healthy document exchange produces both, minutes apart.

AS2 versus the alternatives

Versus a VAN. Value-added networks are the legacy answer: both parties connect to a network that stores and forwards documents — and bills per kilocharacter. AS2 removes the intermediary and the metered pricing; that's why Walmart pushed the industry onto it two decades ago. VANs persist where partners still require them (Costco and McLane among them), typically via interconnects.

Versus SFTP. Secure file drop: you put files in a partner's directory, they pick them up. Simpler than AS2 — no MDNs, no certificate exchange ceremony — but also no delivery receipts, so lost files announce themselves only by their consequences. Target trades over SFTP; plenty of partners do.

Versus APIs. Modern programs (Amazon among them) increasingly run REST APIs alongside EDI. The trend is real but slow; X12 over AS2/SFTP remains the retail backbone in 2026.

The practical takeaway: you don't choose the transport — your partner does. A supplier with six retailers might run AS2 to three, SFTP to two, and a VAN interconnect to one. Multi-transport is the normal case, not the exception.

What operating AS2 actually involves

Running your own AS2 endpoint means: server software (or a cloud service), a certificate for yourself, your partners' certificates, and ongoing care — certificate rotation chief among them. Certificates expire; a partner rotates theirs, you miss the memo, and transmissions fail at 2 a.m. until someone updates a keystore. Add MDN monitoring, retry handling, and endpoint changes, and AS2 becomes a small standing IT function.

This is precisely the layer EDISQ absorbs. Enable a partner and the platform maintains the AS2 connection — certificates, MDNs, monitoring, rotation — or the SFTP session, or the VAN interconnect, whichever that partner demands. The partner directory shows each partner's transport; your per-document price already includes it. No AS2 surcharge, no VAN kilocharacter pass-through, no certificate calendar on your wall.

Transport should be plumbing. If you're thinking about it, something's leaking.

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