 an ANSI initiative. There is also the Frame Relay Forum, consisting of manufacturers of frame relay equipment, that many feel is leading this imag- inative initiative. So when we discuss frame relay, we must consider what specifications a certain system is designed around: ANSI, based on ANSI specifications and their publication dates Frame Relay Forum with publication dates ITU-T organization and its most current recommendations There are also equivalent ANSI specifications directly derived from ITU-T recommen- dations such as ANSI T1.617-1991 (Ref. 15). We will see the term core aspects of ISDN 4 LAPD stands for link access protocol D-channel. ENTERPRISE NETWORKS II: WIDE AREA NETWORKS LAPD or DL-CORE. This refers to a reduced subset of LAPD found in Annex A of ITU- T Rec. Q.922 (Ref. 16). The basic body of Q.922 presents CCITT/ITU-T specification for frame relay. This derivative is called LAPF rather than LAPD. The material found in ANSI T1.618-1991 (Ref. 17) is identical for all intents and purposes with Annex A of Q.922. To properly describe frame relay from our perspective, we will briefly give an overview of the ANSI T1.618-1991 (Ref. 17) and T1.606-1990 (Ref. 18). This will be followed by some fairly well identified variants. 12.5.3 Introduction to Frame Relay Operation Frame relay may be considered a cost-effective outgrowth of ISDN, meeting high data rate (e.g., 2 Mbps) and low delay data communications requirements. Frame relay encapsulates data files. These may be considered "packets," although they are called frames. Thus frame relay is compared to CCITT Rec. X.25 packet service. Frame relay was designed for current transmission capabilities of the network with its relatively wider bandwidths5 and excellent error performance (e.g., BER better than 1 X 10-7). The incisive reader will note the use of the term bandwidth. It is used synonymously with bit rate. If we were to admit at first approximation 1 bit per hertz of bandwidth, such use is acceptable. We are mapping frame relay bits into bearer chan