read radius response

Hi all, I suppose to send radius request as well as accounting start request. I can do this both successfully . Now In radius response packet It returns me some values including " acct-session-id" now I want to read this packet and send this parameter with " acct start request . using rc_avpair_add or rc_avpair_get like commands.. can anyone help me ? how can I read that packet and get this data ? Thanks in advance.