def reset(self):
self.metric = infinity
# P = prob. that will retransmit and use self path
# total = metric * (1-P) [this part is additive!]
# totalP = { rate : [total, P] }
self.totalP = {}
for rate in self.links.keys():
self.totalP[rate] = [wifi.packetTime(Node.PACKETSIZE, rate), 1.0]
self.rate = 0 # = Madwifi 802.11 bit-rate
self.totalP[0] = [0.0, 1.0]
self.P = 1.0 # = totalP[rate][1] [for load distribution]
self.usedlinks = None
self.loads = {} # = x_ik
self.load = 0.0 # = sumk x_ik
self.tx = -1.0 # = load / (1-P)
self.tt = 0.0 # = tx * packetTime(rate)
self.next = self # = argmax_k x_ik | next hop in ett
self.rx = 0.0 # = E[number of packets heard from teachers]
def computeLoadOpp(self, src):
""" Compute opportunistic load and best hop.
Process nodes in topological order and distribute loads.
Expected packet rate is computed by sending a flow from src
and forwarding at all those who receive and have better metric.
Complexity: O(n^2)
"""
nodes = self.nodes
for n in nodes:
n.load = n.tx = n.rx = 0.0
n.loads = {}
if(len(nodes) == 1): return # degenerate case
srcnode = nodes[-1]
assert(srcnode.id == src)
if(srcnode.rate == 0):
return
raise Exception("No route!")
if(srcnode.P == 1.0):
# need to compute P
self.computeP()
srcnode.load = 1.0
# Expected rate is computed by sending a flow from src
# and forwarding at all those who receive and have STRICTLY better metric
for i in range(len(nodes)-1, 0, -1):
ni = nodes[i]
if(ni.load == 0.0):
continue
P = ni.P
assert P < 1.0
pt = ni.usedlinks
# compute actual #tx from the load
ni.tx = ni.load / (1 - P)
P = 1.0
bestp = 0.0 # for next
for j in range(0, i):
if(nodes[j].metric == ni.metric): # we don't want equal metrics
break
puv = pt.get(nodes[j].id, 0)
if(puv == 0.0): continue
# compute the load on (u,v)
ld = ni.tx * puv * P
ni.loads[nodes[j].id] = ld
# add to total load of v
nodes[j].load += ld
if(P * puv > bestp):
bestp = P * puv
ni.next = nodes[j]
P *= (1 - puv)
#if(P == 0.0): # no point continuing
# break
# we have to continue to compute rx
nodes[j].rx += ni.tx * puv # used in unicast only
assert(P == ni.P)
# compute this node's tx time
ni.tt = ni.tx * wifi.packetTime(Node.PACKETSIZE, ni.rate)
