[ns] What's the meaning of "rate_" in ErrorModel?

[Bai David <ns_uofa@yahoo.com>]

Hi,
   I use ns to simulate a Multicast protocol. I want
to create the loss scenario on all the multicast tree
links. I used the ErrorModel and set "rate" to 0.1. I
want ot have the effect to lose 1 pkt out of 10 pkts
passing a link. However, it seems that nearly 80% pkts
are lost from the view of receivers. What cause this
problem? Is my understanding of "rate_" wrong  or it
is just the total effect of loss on different links?
For example, the packet from source to a receiver need
pass 10 links. Because every link has 10% packet loss.
Then the final effect on the receiver is nearly 70% 
(1 - (1 - 0.1)^10 )packet loss?
  
    Thanks very much

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