Tracking request / response packets

Hi all, Wondering please, does FreeRADIUS use only the packet identifier number to match request / response packets together? Or a combination of things - to further decrease the likelihood of mixing up two packets with matching identifier numbers? If the server is busy, 256 concurrent packets doesn't feel like a lot. I wondered if it might use a combo of packet code + identifier, or something like that, to help keep track of which client a request came from. Hope that makes sense? Thanks in advance for your time and consideration!