Advantages/Disadvantages of AS3 (Compared to AS1 and AS2)
AS3 was developed to add ASx file transfer capabilities to the well-established FTP/SSL ("FTPS") protocol. Also, using FTP as a transport rather than HTTP seemed to address the "no standard regarding username/password" limitation of AS2: most FTP servers already require username/password. The AS3 protocol is generally recognized by various industries as the "next" ASx protocol, but movement toward AS3 from established AS2 users has not been rapid.
Advantage: If you have an AS3 client and access to an FTP server, you can send and receive AS3 transmissions. You do not need to control or host the FTP server participating in an AS3 transmission, so AS3 ranks just behind AS1 in terms of easiest ASx protocols to install and configure as long as firewall issues are not much of a concern.
Disadvantage: AS3 has frequent firewall issues. AS3 is built on the FTP/SSL protocol, one of the most firewall-unfriendly protocols in use today. Some of the common issues involving FTP/SSL involve NAT translation, multiple data ports and improper translation of FTP commands by intervening firewalls. (Some people look for SSH and/or HTTP file transfer solutions specifically to avoid reoccurring FTP/SSL firewall issues; MOVEit products offer several tactical solutions for various FTP/SSL issues in terms of features and support.)
Disadvantage: No AS3 transmission mode is as fast as AS2 "synchronous MDN" transfers. This is likely the issue that keeps established many ASx players from moving from AS2 to AS3. When AS2 senders request on-the-fly "synchronous MDNs" for their small file transfers (such as part orders), AS2 is by far the fastest ASx protocol. The AS3 protocol does not support similar MDN-on-the-fly capabilities.
