ame that: Is not properly bounded by two flags (e.g., a frame abort). Has fewer than three octets between the address field and the closing flag. Does not consist of an integral number of octets prior to zero bit insertion or following zero bit extraction. Contains a frame check sequence error. Contains a single octet address field. Contains a data-link connection identifier (DLCI) that is not supported by the receiver. Invalid frames are discarded without notification to the sender, with no further action. 12.5.4.1 Address Field Variables 12.5.4.1.1 Address Field Extension Bit (EA). The address field range is extended by reserving the first transmitted bit of the address field octets to indicate the final octet of the address field. If there is a 0 in this bit position, it indicates that another octet of the address field follows this one. If there is a 1 in the first bit position, it indicates that this octet is the final octet of the address field. As an example, for a two-octet address field, bit one of the first octet is set to 0 and bit one of the second octet is set to 1. It should be understood that a two-octet address field is specified by ANSI. It is a user's option whether a three- or four-octet field is desired. 12.5.4.1.2 Command/Response Bit (C/R). The C/R bit is not used by the ANSI protocol, and the bit is conveyed transparently. 12.5.4.1.3 Forward Explicit Congestion Notification (FECN) Bit. This bit may be set by a congested network to notify the user that congestion avoidance procedures should be initiated, where applicable, for traffic in the direction of the frame carrying the FECN indication. This bit is set to 1 to indicate to the receiving end-system that the frames it receives have encountered congested resources. The bit may be used to adjust the rate of destination-controlled transmitters. While setting this bit by the network or user is optional, no network shall ever clear this bit (i.e., set to 0). Networks that do not provide FECN shall pass this bit unchanged. 12.5 SPEEDING UP THE 