In the different packets types of X.25 can you please tell me what does M D Q and X stand for? Also what is P(S) and P(R)?
Crikey, this is going back a bit :)
P(S) and P(R) were the send and receive sequence numbers, used to handle transmit and receive windows (how many data packets at L3 could be outstanding in either direction i.e flow control) If a receiver wasn't able to accept any more packets it would send an RNR back, when the congestion had cleared it would send an RR
M bit set denotes a data packet is full D bit set denotes only the far end should confirm receipt (i.e. delivery)
Don't recall the other two, you might need to get your google foo working