I summarize the functionality of an X.25 logical channel here as I understand it. I suppress X.25 details that are hidden by our proposed Gnosis abstraction. This abstraction does not diminish the function of the logical channel beyond preventing the abstraction user from doing things that the X.25 recommendation says he "shouldn't" do.
The functions of the X.25 logical channel are separated into two categories so that access to a logical channel may be granted to a user only for the duration of a "virtual call" called ... a "session" here.
Some packets are "qualified". The sender determines this and the receiver may choose to sense it.
An interrupt is a signal carrying from 1 to 32 bytes of "Interrupt user data".
m, q and d are each either zero or one.
If d is zero the operation will complete as soon as the packet can be accepted for delivery. Otherwise the operation completes only after the packet has been delivered across the network and the peer has accepted it.
If q is 1 the packet is qualified, otherwise not.
If m is one then this is not a complete packet and following packet is to be concatenated to this (recursively). The q of the next packet must be the same as this one. d for this packet must be 0.
If the preceeding inbound packet required delivery confirmation and it has been not yet been confirmed it will be confirmed. This operation with l=0 has the effect of confirming such a delivery as well as providing a preview of bits d, m and q for the next inbound packet.