Subject: [manet] question in IEEE 802.11 std

From: [email-masked]
Date: Wed, 2 Feb 2005 10:27:56 +0530 (IST)

What is "post backoff"? (I have found something about it in "IEEE 802.11e
Wireless LAN for Quality of Service", Stefan Mangold etal., Proc. European
Wireless (EW 2002))
Does 802.11 standard mention something about "post-backoff"? If so where?
Also does NS2.27 implement "post-backoff"? What will happen if there is 
two backoffs (post-backoff and a pre-backoff)? i.e. If a node has already
finished post-backoff and a packet arrives into its empty queue from 
higher layer and this packet finds the channel idle, then should it do 
another backoff before transmitting the packet OR should it transmit the 
packets without any backkoff ?

Vinod Kumar
M.E. Telecommunication
IISc

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From: Yue Fang <[email-masked]>
Date: Wed, 2 Feb 2005 11:11:14 -0500 (EST)

Hello, Vinod:

In my understanding, there is just one backoff scheme in the standard and
Ns2.27 do imprlent it. Ppl refer it to "post backoff" as the backoff after
a packet has been transmitted in order to avoid the capture of the
channel. while "pre backoff" refers to the backoff a node execute when it
has packet to send but find channel is not idle.

For the case you described, when the node find that the backoff counter is
0 and the channel is idle for DIFS, it can transmit immediately.

Hope this helps

Regards

-----------------------------------
Yue Fang
227 Egan Research Building
Dept. of Electrical & Computer Eng.
Northeastern University
Boston, MA, 02115
(tel) 617-373-3009
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