def ctsnav(self, rts):
"""Overloaded to add RSH to NAV and apply rate adaptation..
:param rts: RTS packet.
:return: Integer; representing NAV value.
This method uses `DCF.ctsnav()`, `calcrate()`, and `duration()` to
calculate the new value of the CTS NAV.
"""
ctsnav = DCF.ctsnav(self, rts)
errmsg = "[RBAR]: Invalid RTS! No RAI found in ctsnav()!"
assert rts.haslayer(RAI), errmsg
errmsg = "[RBAR]: Cannot find 'phy-sinr' annotation in ctsnav()!"
assert rts.hasanno('phy-sinr'), errmsg
# calculate new rate from SINR
sinr = rts.getanno('phy-sinr')
newrate = self.calcrate(sinr)
# extract info from RTS+RAI
rai = rts[RAI]
oldrate, length = rai.rate, rai.length
# recompute NAV using length and new rate
dold = self.duration(length, oldrate)
dnew = self.duration(length, newrate)
nav = ctsnav - int(dold*1e6) + int(dnew*1e6)
return nav
