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\LARGE ETX Link Cost Computation (OBSOLETE)
\\

\large
ETX will maintain smoothed probability ratings for receiving 
from and transmiting to each of it's peers.
The probability for receiving is computed as 
\begin{eqnarray} 
srxp_{0} &=& .5 \nonumber\\
srxp_{k} &=& h \cdot srxp_{k-1} + (1 - h) \cdot rx_{k} \nonumber\\
\end{eqnarray}
where $rx_{k}$ is 1 if a beacon has been received from 
the peer during the current interval, 0 if not.
The probability for transmitting is computed as
\begin{equation} 
stxp_{k} = 
    h \cdot stxp_{k-1} + (1 - h)
    \sum_{i=s_{p}}^{s_{c}} {h^{s_{c}-i-s_{p}}tx_{i-s_{p}}} 
    \nonumber\\
\end{equation}
where $s_{p}$ is the previous sequence number received, and 
$s_{c}$ is the sequence number currently received.
$tx_{i-s_{p}}$ is read from the bitfield of our address's
entry in the peer's beacon.  If no data is available 
because a beacon was not recieved or the {\tt ETX\_F\_INIT} flag 
is set and $i>{\tt eb\_seqno}$, $tx_{i}=\frac{1}{2}$.
The cost of the link is computed as
\begin{equation}
cost_{k} = \left( \frac{1}{srxp_{k}}-\frac{1}{stxp_{k}} \right)^{-1}
\end{equation}

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