&xep0231; is designed for small media, i.e. less than 8 KB in size, that is hosted server-side and transferred Base64 encoded in-band of an existing XMPP stream. Example use-cases are custom emoticons that are referenced in &xep0071; img-tags, or thumbnails for &xep0234;.
&xep0231; describes a peer-to-peer protocol for synchronous file-transfer between two XMPP entities. It attempts a direct transmission, followed by a proxied transmission, via &xep0260;. If neither works it will fallback to &xep0261; which will transfer the data inband of the exsiting XMPP stream.
+&xep0234; describes a peer-to-peer protocol for synchronous file-transfer between two XMPP entities. It attempts a direct transmission, followed by a proxied transmission, via &xep0260;. If neither works it will fallback to &xep0261; which will transfer the data inband of the exsiting XMPP stream.
&xep0363; was designed as a simpler to implement alternative to &xep0231;. This is achieved by reusing the HTTP APIs in todays mobile and language SDKs. It requires a server component where clients can request HTTP URLs to upload data to and share the corresponding download URL as part of plain text in a conversation.