?? npcsma.m
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% Program 6-8
% npcsma.m
%
% non-persistent CSMA System
%
% Input argument
% now_time : now time but, now_time<0 initializes the access terminals
%
% Output argument
% next_time : next state change time
%
% Programmed by M.Okita
% Checked by H.Harada
%
function [next_time] = npcsma(now_time)
global STANDBY TRANSMIT COLLISION % definition of the global variable
global Srate Plen
global Mnum Mplen Mstime Mstate
global Tint Rint
global Spnum Splen Tplen Wtime
persistent mgtime mtime % definition of the static variable
if now_time < 0 % initialize access terminals
rand('state',sum(100*clock)); % resetting of the random table
mgtime = -Tint * log(1-rand(1,Mnum)); % packet generation time
Mstime = zeros(1,Mnum) - inf; % packet transmitting time
mtime = mgtime; % state change time
Mstate = zeros(1,Mnum);
Mplen(1:Mnum) = Plen;
next_time = min(mtime);
return
end
idx = find(mtime==now_time & Mstate==TRANSMIT); % finding of the terminal which transmission succeeded
if length(idx) > 0
Spnum = Spnum + 1;
Splen = Splen + Mplen(idx);
Wtime = Wtime + now_time - mgtime(idx);
Mstate(idx) = STANDBY;
mgtime(idx) = now_time - Tint * log(1-rand); % next packet generation time
mtime(idx) = mgtime(idx); % next packet transmitting time
end
idx = find(mtime==now_time & Mstate==COLLISION); % finding of the terminal which transmission failed
if length(idx) > 0
Mstate(idx) = STANDBY;
mtime(idx) = now_time - Rint * log(1-rand(1,length(idx))); % resending time
end
idx = find(mtime==now_time & Mstate==STANDBY); % finding of the terminal which carrier sensing
if length(idx) > 0
Tplen = Tplen + sum(Mplen(idx));
for ii=1:length(idx)
jj = idx(ii);
if carriersense(jj,now_time) == 0 % channel is idle
Mstate(jj) = TRANSMIT; % packet transmitting
Mstime(jj) = now_time; % start time of transmitting
mtime(jj) = now_time + Mplen(jj) / Srate; % end time of transmitting
else % channel is busy
mtime(jj) = now_time - Rint * log(1-rand); % waiting time
end
end
end
next_time = min(mtime); % next state change time
%%%%%%%%%%%%%%%%%%%%%% end of file %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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