"No NAS-Port seen"

Dears, I have freeradius installed on CentOS, and i am very interested in Simultaneous-use attribute to limit the number of logins per user. Anyway my nas seems to not sending NAS-Port attribute to freeradius which causes realm radutmp not to work. i looked all over the internet but i conuldnt find a solution, please help me to find a workaround to solve this problem. these are the two lines i keep seeing as an output from the debugging command radiusd -X : rlm_radutmp: No NAS-Port seen. Cannot do anything. rlm_radumtp: WARNING: checkrad will probably not work! its very urgent. thanks in advance.