This Recommendation describes in general terms the link access procedure on the D-channel, LAPD. Details are provided in ITU-T Q.921 [1]. The purpose of LAPD is to convey information between layer 3 entities across the ISDN user-network interface using the D-channel. This Recommendation has been amended in order to add a new Annex A to describe in general terms the link access procedure for use in a symmetrical application between two Private Integrated Network eXchanges (PINXs) at the Q reference point.