You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
226 lines
7.8 KiB
226 lines
7.8 KiB
// WLAN PROTOCOL (two stations)
|
|
// discrete time model
|
|
// gxn/jzs 20/02/02
|
|
|
|
mdp
|
|
|
|
// COLLISIONS
|
|
const int COL; // maximum number of collisions
|
|
|
|
// 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 either 2 or 3 which is modelled by a non-deterministic choice
|
|
const int VULN = 1; // due to scaling can be either 0 or 1 which is modelled by a non-deterministic choice
|
|
const int TRANS_TIME_MAX; // scaling up
|
|
const int TRANS_TIME_MIN = 4; // scaling down
|
|
const int ACK_TO = 6;
|
|
const int ACK = 4; // due to scaling can be either 3 or 4 which is modelled by a non-deterministic choice
|
|
const int SIFS = 1; // due to scaling can be either 0 or 1 which is modelled by a non-deterministic choice
|
|
// maximum constant used in timing constraints + 1
|
|
const int TIME_MAX = max(ACK_TO,TRANS_TIME_MAX)+1;
|
|
|
|
// CONTENTION WINDOW
|
|
// CWMIN =15 & CWMAX =63
|
|
// this means that MAX_BACKOFF IS 2
|
|
const int MAX_BACKOFF = 2;
|
|
|
|
//-----------------------------------------------------------------//
|
|
// THE MEDIUM/CHANNEL
|
|
|
|
// FORMULAE FOR THE CHANNEL
|
|
// channel is busy
|
|
formula busy = c1>0 | c2>0;
|
|
// channel is free
|
|
formula free = c1=0 & c2=0;
|
|
|
|
module medium
|
|
|
|
// number of collisions
|
|
col : [0..COL];
|
|
|
|
// 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,COL));
|
|
[send2] c2=0 & c1>0 -> (c1'=2) & (c2'=2) & (col'=min(col+1,COL));
|
|
|
|
// 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..3];
|
|
backoff1 : [0..15];
|
|
|
|
// BACKOFF COUNTER
|
|
bc1 : [0..MAX_BACKOFF];
|
|
// SENSE
|
|
// let time pass
|
|
[time] s1=1 & x1<DIFS & free -> (x1'=min(x1+1,TIME_MAX));
|
|
// ready to transmit
|
|
[] 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,MAX_BACKOFF));
|
|
// backoff counter 1
|
|
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=1 -> 1/2 : (s1'=4) & (x1'=0) & (slot1'=0) & (bc1'=min(bc1+1,MAX_BACKOFF))
|
|
+ 1/2 : (s1'=4) & (x1'=0) & (slot1'=1) & (bc1'=min(bc1+1,MAX_BACKOFF));
|
|
// backoff counter 2
|
|
[] s1=3 & (x1=DIFS | x1=DIFS-1) & bc1=2 -> 1/4 : (s1'=4) & (x1'=0) & (slot1'=0) & (bc1'=min(bc1+1,MAX_BACKOFF))
|
|
+ 1/4 : (s1'=4) & (x1'=0) & (slot1'=1) & (bc1'=min(bc1+1,MAX_BACKOFF))
|
|
+ 1/4 : (s1'=4) & (x1'=0) & (slot1'=2) & (bc1'=min(bc1+1,MAX_BACKOFF))
|
|
+ 1/4 : (s1'=4) & (x1'=0) & (slot1'=3) & (bc1'=min(bc1+1,MAX_BACKOFF));
|
|
// 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);
|
|
// check channel and free: let time pass
|
|
[time] s1=10 & c1=0 & x1=0 & free -> (x1'=min(x1+1,TIME_MAX));
|
|
// let time pass
|
|
// following guard is always false as SIFS=1
|
|
// [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
|
|
// ---------------------------------------------------------------------------- //
|
|
|
|
label "twoCollisions" = col=2;
|
|
label "fourCollisions" = col=4;
|
|
label "sixCollisions" = col=6;
|