Subject: AW: Question on nonpersistant vs. p-persistant

From: Lott Matthias <[email-masked]>
Date: Mon, 3 Dec 2001 10:59:47 +0100

Dear Yang,
p-persistent and nonpersistent CSMA perform very similar (depending on the selected p and the backoff strategy applied). You can find respective investigations in
 
        Dynamic Tuning of the IEEE802.11 Protocol to Achieve a Theoretical Throughput Limit 
        Transactions on Networking  December 2000
        Frederico Calì, Marco Conti, and Enrico Gregori 

For p-persistent CSMA the value of p is the problem. It should be varied depending on the load. This is the problem, so nonpersistent CSMA is the first choice.
Regards,
Matthias
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  Matthias Lott
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> -----Ursprüngliche Nachricht-----
> Von: Yang Xiao [mailto:[email-masked]]
> Gesendet: Freitag, 30. November 2001 19:02
> An: [email-masked]
> Cc: [email-masked]
> Betreff: Question on nonpersistant vs. p-persistant
> 
> 
> Normally, we refer CSMA as 1-persistent CSMA. There are also
> p-persistent CSMA (0<p<1) and Nonpersistant CSMA.
> 
> A CSMA with backoff algorithm is called Nonpersistent-CSMA. Therefore,
> we can call Ethernet or 802.3 as Nonpersistant-CSMA/CD. Similarly, we
> can call IEEE 802.11 MAC 's DCF basic mode as Nonpersistant-CSMA/CA.
> When I read a lot of papers which provide performance analysis of
> either 802.11 MAC 's DCF or 802.3, most of them make a asumption that
> there exists a transmission probability (p) which is the same for each
> station. Such an asumption claim that a Nonpersistant CSMA can be
> approximated by a special case of p-persistant CSMA. If such an
> assumption is accurate, why 802.3 adopted a Nonpersistant-CSMA/CD
> instead of p-persistant-CSMA/CD, and why 802.11 adopted a
> Nonpersistant-CSMA/CD instead of p-persistant-CSMA/CA ? What's the
> drawback of p-persistant? Any paper to compare Nonpersistant vs.
> p-persistant?
> 
> Any comment is appreciated.
> 
> Yang