```// WLAN PROTOCOL (two stations)
// discrete time model
// gxn/jzs 20/02/02

mdp

// TIMING CONSTRAINTS
// we have used the FHSS parameters
// then scaled by the value of ASLOTTIME
const int ASLOTTIME = 1;
const int DIFS = 3; // due to scaling can be non-deterministically either 2 or 3
const int VULN = 1; // due to scaling can be non-deterministically either 0 or 1
const int TRANS_TIME_MAX = 315; // scaling up
const int TRANS_TIME_MIN = 4; // scaling down
const int ACK_TO = 6;
const int ACK = 4; // due to scaling can be non-deterministically either 3 or 4
const int SIFS = 1; // due to scaling can be non-deterministically either 0 or 1
const int TIME_MAX = 315; // maximum constant used in timing constraints + 1
const int BOFF = 6; // max backoff (since contention window is [15,1023])

// THE MEDIUM/CHANNEL

formula busy = c1>0 | c2>0; // channel is busy
formula free = c1=0 & c2=0; // channel is free

module medium

col : [0..8]; // number of collisions
// medium status
c1 : [0..2];
c2 : [0..2];
// ci corresponds to messages associated with station i
// 0 nothing being sent
// 1 being sent correctly
// 2 being sent garbled

// begin sending message and nothing else currently being sent
[send1] c1=0 & c2=0 -> (c1'=1);
[send2] c2=0 & c1=0 -> (c2'=1);
// begin sending message and  something is already being sent
// in this case both messages become garbled
[send1] c1=0 & c2>0 -> (c1'=2) & (c2'=2) & col'=min(col+1,8);
[send2] c2=0 & c1>0 -> (c1'=2) & (c2'=2) & col'=min(col+1,8);
// finish sending message
[finish1] c1>0 -> (c1'=0);
[finish2] c2>0 -> (c2'=0);

endmodule

// STATION 1
module station1
// clock for station 1
x1 : [0..TIME_MAX];

// local state
s1 : [1..12];
// 1 sense
// 2 wait until free before setting backoff
// 3 wait for DIFS then set slot
// 4 set backoff
// 5 backoff
// 6 wait until free in backoff
// 7 wait for DIFS then resume backoff
// 8 vulnerable
// 9 transmit
// 11 wait for SIFS and then ACK
// 10 wait for ACT_TO
// 12 done
// BACKOFF
// separate into slots
slot1 : [0..63];
backoff1 : [0..15];

// BACKOFF COUNTER
bc1 : [0..BOFF];
// SENSE
// let time pass
[time] s1=1 & x1<DIFS & free -> (x1'=min(x1+1,TIME_MAX));
[] s1=1 & (x1=DIFS | x1=DIFS-1) -> (s1'=8) & (x1'=0);
// found channel busy so wait until free
[] s1=1 & busy -> (s1'=2) & (x1'=0);
// WAIT UNTIL FREE BEFORE SETTING BACKOFF
// let time pass (no need for the clock x1 to change)
[time] s1=2 & busy -> (s1'=2);
// find that channel is free so check its free for DIFS before setting backoff
[] s1=2 & free -> (s1'=3);
// WAIT FOR DIFS THEN SET BACKOFF
// let time pass
[time] s1=3 & x1<DIFS & free -> (x1'=min(x1+1,TIME_MAX));
// found channel busy so wait until free
[] s1=3 & busy -> (s1'=2) & (x1'=0);
// start backoff  first uniformly choose slot
// backoff counter 0
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=0 ->
(s1'=4) & (x1'=0) & (slot1'=0) & (bc1'=min(bc1+1,BOFF));
// backoff counter 1
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=1 ->
1/2 : (s1'=4) & (x1'=0) & (slot1'=0) & (bc1'=min(bc1+1,BOFF))
+ 1/2 : (s1'=4) & (x1'=0) & (slot1'=1) & (bc1'=min(bc1+1,BOFF));
// backoff counter 2
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=2 ->
1/4 : (s1'=4) & (x1'=0) & (slot1'=0) & (bc1'=min(bc1+1,BOFF))
+ 1/4 : (s1'=4) & (x1'=0) & (slot1'=1) & (bc1'=min(bc1+1,BOFF))
+ 1/4 : (s1'=4) & (x1'=0) & (slot1'=2) & (bc1'=min(bc1+1,BOFF))
+ 1/4 : (s1'=4) & (x1'=0) & (slot1'=3) & (bc1'=min(bc1+1,BOFF));
// backoff counter 3
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=3 ->
1/8 : (s1'=4) & (x1'=0) & (slot1'=0) & (bc1'=min(bc1+1,BOFF))
+ 1/8 : (s1'=4) & (x1'=0) & (slot1'=1) & (bc1'=min(bc1+1,BOFF))
+ 1/8 : (s1'=4) & (x1'=0) & (slot1'=2) & (bc1'=min(bc1+1,BOFF))
+ 1/8 : (s1'=4) & (x1'=0) & (slot1'=3) & (bc1'=min(bc1+1,BOFF))
+ 1/8 : (s1'=4) & (x1'=0) & (slot1'=4) & (bc1'=min(bc1+1,BOFF))
+ 1/8 : (s1'=4) & (x1'=0) & (slot1'=5) & (bc1'=min(bc1+1,BOFF))
+ 1/8 : (s1'=4) & (x1'=0) & (slot1'=6) & (bc1'=min(bc1+1,BOFF))
+ 1/8 : (s1'=4) & (x1'=0) & (slot1'=7) & (bc1'=min(bc1+1,BOFF));
// backoff counter 4
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=4 ->
1/16 : (s1'=4) & (x1'=0) & (slot1'=0 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=1 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=2 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=3 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=4 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=5 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=6 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=7 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=8 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=9 ) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=10) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=11) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=12) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=13) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=14) & (bc1'=min(bc1+1,BOFF))
+ 1/16 : (s1'=4) & (x1'=0) & (slot1'=15) & (bc1'=min(bc1+1,BOFF));
// backoff counter 5
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=5 ->
1/32 : (s1'=4) & (x1'=0) & (slot1'=0 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=1 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=2 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=3 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=4 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=5 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=6 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=7 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=8 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=9 ) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=10) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=11) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=12) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=13) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=14) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=15) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=16) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=17) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=18) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=19) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=20) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=21) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=22) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=23) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=24) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=25) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=26) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=27) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=28) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=29) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=30) & (bc1'=min(bc1+1,BOFF))
+ 1/32 : (s1'=4) & (x1'=0) & (slot1'=31) & (bc1'=min(bc1+1,BOFF));
// backoff counter 6
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=6 ->
1/64 : (s1'=4) & (x1'=0) & (slot1'=0 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=1 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=2 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=3 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=4 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=5 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=6 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=7 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=8 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=9 ) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=10) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=11) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=12) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=13) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=14) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=15) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=16) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=17) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=18) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=19) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=20) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=21) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=22) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=23) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=24) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=25) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=26) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=27) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=28) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=29) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=30) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=31) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=32) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=33) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=34) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=35) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=36) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=37) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=38) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=39) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=40) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=41) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=42) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=43) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=44) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=45) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=46) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=47) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=48) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=49) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=50) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=51) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=52) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=53) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=54) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=55) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=56) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=57) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=58) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=59) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=60) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=61) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=62) & (bc1'=min(bc1+1,BOFF))
+ 1/64 : (s1'=4) & (x1'=0) & (slot1'=63) & (bc1'=min(bc1+1,BOFF));
// SET BACKOFF (no time can pass)
// chosen slot now set backoff
[] s1=4 -> 1/16 : (s1'=5) & (backoff1'=0)
+ 1/16 : (s1'=5) & (backoff1'=1)
+ 1/16 : (s1'=5) & (backoff1'=2)
+ 1/16 : (s1'=5) & (backoff1'=3)
+ 1/16 : (s1'=5) & (backoff1'=4)
+ 1/16 : (s1'=5) & (backoff1'=5)
+ 1/16 : (s1'=5) & (backoff1'=6)
+ 1/16 : (s1'=5) & (backoff1'=7)
+ 1/16 : (s1'=5) & (backoff1'=8)
+ 1/16 : (s1'=5) & (backoff1'=9)
+ 1/16 : (s1'=5) & (backoff1'=10)
+ 1/16 : (s1'=5) & (backoff1'=11)
+ 1/16 : (s1'=5) & (backoff1'=12)
+ 1/16 : (s1'=5) & (backoff1'=13)
+ 1/16 : (s1'=5) & (backoff1'=14)
+ 1/16 : (s1'=5) & (backoff1'=15);
// BACKOFF
// let time pass
[time] s1=5 & x1<ASLOTTIME & free -> (x1'=min(x1+1,TIME_MAX));
// decrement backoff
[] s1=5 & x1=ASLOTTIME & backoff1>0 -> (s1'=5) & (x1'=0) & (backoff1'=backoff1-1);
[] s1=5 & x1=ASLOTTIME & backoff1=0 & slot1>0 ->
(s1'=5) & (x1'=0) & (backoff1'=15) & (slot1'=slot1-1);
// finish backoff
[] s1=5 & x1=ASLOTTIME & backoff1=0 & slot1=0 -> (s1'=8) & (x1'=0);
// found channel busy
[] s1=5 & busy -> (s1'=6) & (x1'=0);
// WAIT UNTIL FREE IN BACKOFF
// let time pass (no need for the clock x1 to change)
[time] s1=6 & busy -> (s1'=6);
// find that channel is free
[] s1=6 & free -> (s1'=7);

// WAIT FOR DIFS THEN RESUME BACKOFF
// let time pass
[time] s1=7 & x1<DIFS & free -> (x1'=min(x1+1,TIME_MAX));
// resume backoff (start again from previous backoff)
[] s1=7 & (x1=DIFS | x1=DIFS-1) -> (s1'=5) & (x1'=0);
// found channel busy
[] s1=7 & busy -> (s1'=6) & (x1'=0);

// VULNERABLE
// let time pass
[time] s1=8 & x1<VULN -> (x1'=min(x1+1,TIME_MAX));
// move to transmit
[send1] s1=8 & (x1=VULN | x1=VULN-1) -> (s1'=9) & (x1'=0);
// TRANSMIT
// let time pass
[time] s1=9 & x1<TRANS_TIME_MAX -> (x1'=min(x1+1,TIME_MAX));
// finish transmission successful
[finish1] s1=9 & x1>=TRANS_TIME_MIN & c1=1 -> (s1'=10) & (x1'=0);
// finish transmission garbled
[finish1] s1=9 & x1>=TRANS_TIME_MIN & c1=2 -> (s1'=11) & (x1'=0);
// WAIT FOR SIFS THEN WAIT FOR ACK

// WAIT FOR SIFS i.e. c1=0
// check channel and busy: go into backoff
[] s1=10 & c1=0 & x1=0 & busy -> (s1'=2);
// chack channel and free: let time pass
[time] s1=10 & c1=0 & x1=0 & free -> (x1'=min(x1+1,TIME_MAX));
// let time pass
[time] s1=10 & c1=0 & x1>0 & x1<SIFS -> (x1'=min(x1+1,TIME_MAX));
// ack is sent after SIFS (since SIFS-1=0 add condition that channel is free)
[send1] s1=10 & c1=0 & (x1=SIFS | (x1=SIFS-1 & free)) -> (s1'=10) & (x1'=0);

// WAIT FOR ACK i.e. c1=1
// let time pass
[time] s1=10 & c1=1 & x1<ACK -> (x1'=min(x1+1,TIME_MAX));
// get acknowledgement so packet sent correctly and move to done
[finish1] s1=10 & c1=1 & (x1=ACK | x1=ACK-1) -> (s1'=12) & (x1'=0) & (bc1'=0);

// WAIT FOR ACK_TO
// check channel and busy: go into backoff
[] s1=11 & x1=0 & busy -> (s1'=2);
// check channel and free: let time pass
[time] s1=11 & x1=0 & free -> (x1'=min(x1+1,TIME_MAX));
// let time pass
[time] s1=11 & x1>0 & x1<ACK_TO -> (x1'=min(x1+1,TIME_MAX));
// no acknowledgement (go to backoff waiting DIFS first)
[] s1=11 & x1=ACK_TO -> (s1'=3) & (x1'=0);

// DONE
[time] s1=12 -> (s1'=12);

endmodule

// STATION 2 (rename STATION 1)
module station2=station1[x1=x2,
s1=s2,
s2=s1,
c1=c2,
c2=c1,
slot1=slot2,
backoff1=backoff2,
bc1=bc2,
send1=send2,
finish1=finish2]
endmodule

// reward structure for expected number of collisions
rewards "collisions"
[send1] c1=0 & c2>0 : 1; // station one starts transmitting and station two is already transmitting
[send2] c2=0 & c1>0 : 1; // station two starts transmitting and station one is already transmitting
endrewards

// reward structure for expected time
// recall one time unit equals ASLOT(=50μs)
rewards "time"
[time] true : 50;
endrewards

// reward strcuture for expected cost
// cost (per time unit) is set to:
// 1 in locations where the channel is free,
// 10 in locations where the channel is in use and a message is being sent correctly
// 1000 in locations where a station is sending a garbled message
// 2000 in locations where both stations are sending garbled messages
rewards	"cost"
[time] c1=0 & c2=0 : 50;
[time] c1=1 & c2=0 : 50*10;
[time] c1=0 & c2=1 : 50*10;
[time] c1=1 & c2=1 : 50*20;
[time] c1=0 & c2=2 & bc1=0 & bc2=0 : 50*10;
[time] c1=2 & c2=0 & bc1=0 & bc2=0 : 50*10;
[time] c1=2 & c2=2 & bc1=0 & bc2=0 : 50*20;
[time] c1=0 & c2=2 & (bc1>0 | bc2>0) : 50*1000;
[time] c1=2 & c2=0 & (bc1>0 | bc2>0) : 50*1000;
[time] c1=2 & c2=2 & (bc1>0 | bc2>0) : 50*2000;
endrewards
```