. .21 .21- .
HDLC , .25/3.
. , (IEEE Institute of Electrical and Electronics Engineers).
IEEE 802 , (ISO) . :
802.1 ;
802.2 (LLC);
802.3 (CSMA/CD Carrier Sense Multiple Access with Collision Detection );
802.4 ;
802.5 ;
802.6 .
. 6.18. , .
. . , . , , . .
. 6.18.