>From what I can tell, both of these are transfer protocols. How are they different? Why use one over the other? There is almost so much information available that I'm having a hard time sifting through it all to get to the basics.

Renoir, I have no idea about SOAP, but I can help briefly with the idea of "protocol layering".

(References to "Layers" refer to the 7-layer OSI reference model.)

Briefly, at the local network, some "Layer 2" protocol will be used, usually Ethernet (or some WAN technology for other parts of the network).

Layer 2 does not have the information required to connect different networks (or subnets); that's where Layer 3 comes in. This would usually be the IP protocol. The IP data packets have a source and a destination address (this is precisely the famous IP address), which has enough information to connect remote networks. The Layer 3 packet is encapsulated into a Layer 2 "packet", (which in this case is actually called "frame"). This is like putting a letter into an envelope, then putting the envelope into a larger envelope.

Layer 3 lacks the mechanisms for a reliable connection; this is where Layer 4 does its work. This is usually TCP. The data stream (e.g., an e-mail) is divided into pieces (called "segments" at this level), and each segment is numbered, e.g. "Byte 1", "Byte 1001", etc. (assuming each segment carries 1000 bytes of data). (The segments are then encapsulated within IP packets - a third level of "envelopes"). TCP provides the mechanisms for requesting that a missing or corrupted segment be sent again - or have the sender resend it automatically, if no confirmation is received within a certain time.

Now, the key point is that nearly all network communication uses one of the two Layer 4 protocols - either TCP or (if speed is more important than reliability, as in voice over IP) - UDP.

So, higher-level protocols, like FTP and HTTP (and pressumably SOAP) will make use of TCP, which in turn uses IP, which in turn uses Ethernet or whatever Layer 2 protocol is used within a single LAN or WAN.