On my site there are some digital files which can be downloaded through a PHP script. The script works fine for small files but large files i.e. 115MB cannot be downloaded successfully. The connection dies after around 15 minutes but it's not consistent - sometimes longer sometimes shorter.

I don't think it's a problem with the script timing out because the download time isn't consistent. Equally it doesn't seem like a memory limit problem because the amount downloaded varies each time.

Does anyone know of any Apache or PHP related settings which could cause this kind of problem?