The current system for fetching images from the servers goes through the simulator using UDP.
This system is not well documented and will be replaced by the HTTP Image Pipeline
HTTP Image Pipeline
Load From Cache* Load any Image data from the local cache
Compare the cached data with the requested discard level. If no additional data is required, skip to Decode Image
Request URL Request a URL for the image from the simulator (Note: URL requests are batched)
Wait for URL Idle until the URL Response is received
Request Image Request the Image data from the server using the URL provided
Wait for Image Idle until the Image Response is received
Decode Image* Decode the Image
Cache Image* Cache the Image
* Note: These steps are actually implemented using an asynchronous request / response pattern, but because this is internal to the client, that is not illustrated here.