Subject: Re: about ns-2

From: Martin Haenggi <[email-masked]>
Date: Wed, 16 Jan 2002 10:44:09 -0500 (EST)

Li-Peng,

>In the ns-2 simulator with CMU wireless extension,
>the document said that the implementation is based on IEEE 802.11.
>It's clearly to know that the PHYSICAL layer is FHSS, but in this module,
>the PHY layer is DSSS.
>We know that the PHY layer will infect the transmission rate like
>IEEE 802.11   -> FHSS ->  2Mbps
>IEEE 802.11b -> DSSS -> 11Mbps
>So, why in the CMU wireless extension, the implementation is DSSS, but
>the transmission rate is still limited in 2Mbps ?

802.11 defines three PHY layers: DSSS, FHSS, and infrared,
all at 1Mbps or 2Mbps depending on the modulation.
So, DSSS does not imply that it's 802.11b.
802.11b is restricted to DSSS, but it's implemented
differently than 802.11 DSSS, and that's why it
achieves higher troughput.

Martin