On Sep 29, 2009, at 5:59 AM, ph3arconf@xxxxxxxxx wrote:
I have searched a bit, but I couldn't find what (RA) located next to
destination MAC address stands for?
Recipient Address.
802.11 is not like Ethernet (802.3), where a packet is always sent
directly from the link-layer sender to the link-layer recipient; if
you're on a network with an access point, packets are sent to the
access point, which relays them to the recipient.
For data frames, this means that the frame might have a "destination
address", which is the intended final link-layer recipient of the
frame, and a "recipient address", which is the machine that will be
receiving the frame as sent. A frame sent from a host (station) to an
access point has tthe recipient address (RA) set to the MAC address of
the access point and the destination address (DA) set to the MAC
address of the ultimate recipient. When that frame is then sent by
the access point to the ultimate recipient, the same field will be
used for the recipient address and the destination address, and that
field will be set to the MAC address of the ultimate recipient.
See, for example, IEEE Std 802.11-2007:
http://standards.ieee.org/getieee802/download/802.11-2007.pdf
section 7, and see earlier sections for a description of the concepts
involved, although reading the 802.11 standard is probably a bit like
taking a drink from a fire hose; you might want to search for an
online 802.11 tutorial - Googling for
802.11 tutorial
found, for example:
http://sss-mag.com/pdf/802_11tut.pdf
