I have webserver running on my board. I am requesting image (4500 bytes approx) from the board through webpage after every 200ms. Most of times (99%) its works fine but rest of the times the request from TCP layer doesn reach http layer. I am testing it in a very low traffic environment hence no chances for packet loss. Can anyone help me on this?

You do not say which mico or stack you are using.  I would guess that you were running out of connections and this could be fixed by one of the configuration constants.

I am using STR912 microcontroller and LWIP stack. I am having only one connection established. Ethernet Switch has my webserver (STR9 board) and PC Client attached.

How do you understand that request doesn’t reach to Http layer? Which api are you using in lwIP?