Once you understand what EDI documents need to be exchanged, the next question is: how do they actually travel between your system and your trading partner's? The answer depends on which transport protocol your partner uses — and the three dominant options (AS2, SFTP, and VAN) work very differently from each other. Here is what each one means, when it is used, and how to decide which setup you need.
AS2 — Applicability Statement 2
AS2 is a real-time, internet-based transport protocol specifically designed for secure EDI transmission. It is the preferred method for most major retailers — Walmart, Target, Home Depot, Costco, and many others specify AS2 in their vendor compliance guides.
How it works:
- Documents are encrypted and digitally signed using SSL/TLS certificates
- The document is sent directly from the sender's AS2 server to the receiver's AS2 server over HTTPS
- The receiver sends back an MDN (Message Disposition Notification) — a signed digital receipt confirming the document arrived and was verified
- Transmission is synchronous and near-real-time — acknowledgment within seconds
AS2 requires both parties to have AS2 server software (or a hosted AS2 service), exchange certificates in advance, and configure connection parameters including each partner's AS2 ID and endpoint URL. Setup has more moving parts than SFTP, but the result is the most secure and verifiable transport available.
SFTP — Secure File Transfer Protocol
SFTP is the simpler, widely-supported alternative. Instead of a direct server-to-server connection, EDI documents are deposited as files in an agreed-upon folder on a secure FTP server. The receiving party picks up the files on a schedule — typically every few minutes to every hour.
SFTP is favoured by smaller trading partners, regional distributors, and 3PLs that lack the infrastructure to run an AS2 server. It is also commonly used for bulk file transfers where real-time delivery is less critical.
The main limitations compared to AS2:
- No built-in delivery confirmation — you deposit the file but cannot verify it was received without checking the partner's pickup logs
- Latency — the pickup schedule means documents are not truly real-time, which can cause issues with trading partners requiring fast acknowledgments
- File management — without a good platform, SFTP-based EDI can devolve into manual folder monitoring
VAN — Value Added Network
A VAN is a third-party intermediary service that routes EDI documents between trading partners. Instead of connecting directly to each partner, you connect once to the VAN. The VAN handles routing to every other company on the network, manages mailboxes, and provides transmission logging.
VANs were the dominant EDI infrastructure through the 1980s and 1990s, and they remain in use today — particularly in industries with complex many-to-many trading partner networks. Major VANs include SPS Commerce, TrueCommerce, and Sterling Commerce.
The tradeoffs:
- Pro: Simplifies connectivity — one VAN connection reaches all partners on that network
- Pro: Managed service with transmission tracking and archiving
- Con: Per-transaction fees charged by the VAN add up at volume
- Con: Documents transit an intermediary, adding latency compared to AS2
Which One Do You Need?
The answer is almost always determined by your trading partner, not by your preference. Check your partner's EDI specification sheet or vendor guide — it will specify which transport method they support and often which they prefer. Large retailers typically require AS2. Smaller distributors may only support SFTP or VAN.
Managing Multiple Protocols Across Partners
As your trading partner network grows, you will likely end up with a mix: some partners on AS2, some on SFTP, some on a VAN. The right EDI platform abstracts this complexity — you manage documents at the business level, and the platform handles which protocol each partner requires. That is the approach that scales.