U-Boot has support for UDP over IP (but not TCP/IP). TFTP (Trivial File Transfer Protocol) was practically designed for this; it uses UDP/IP, and is supported by U-Boot. Is there a reason why you don't want to use TFTP?
TCP/IP requires quite a complex stack. Many of the implementations intended for embedded devices are quite restricted, for example to four TCP sockets total, with severe limitations on in-flight packets -- thus, very slow transfer rates. HTTP/1.1 is even more complex, especially if you want to communicate with arbitrary HTTP servers; in particular, the response may or may not be chunked. You can avoid most of those issues by using HTTP/1.0, but if the connection is via a proxy, further complications may occur. All it means is that the TCP/IP+HTTP stack is a complex beast, and definitely not suited in an embedded boot loader.
Last edited by Nominal Animal; 07-11-2011 at 04:33 AM.
Reason: A wild duplicate appears!