little confusion while studying l1l2 interface via sercomm

in layer23 apps we open local unix socket in layer23 app and one in osmocon another socket to communicate in between. now in layer23 we just send (write) or receive (read) msg. but we handle actual communication with phone is handled in osmocon. now flow of functions is main ->register_tool_server->tool_accept->un_tool_read->hdlc_send_to_phone->sercomm_sendmsg then sercomm handles all transmission in details then layer1 accept all data via so i wanted to ask that how does rssi firmware is sending data directly to l1 -l2 and i would also like to ask what is actual protocol used in communication between l1 and l2 -- Akib Sayyed Matrix-Shell akibsayyed(a)gmail.com akibsayyed(a)matrixshell.com Mob:- +91-966-514-2243