From: Rosalia Tungaraza (rltungar@u.washington.edu)
Date: Mon Nov 22 2004 - 01:07:03 PST
This paper is about the MACAW protocol, which is a modification of the
MACA (Multiple Access with Collision Avoidance) protocol. MACAW extends
MACA by adding features that are essential for wireless local area
networks to function properly.
One such feature is how a sender manages to access the receiver and send
its data over the wireless network without colliding with another node's
data. While in the MACA protocol this was achieved by the source node
sending an RTS (request to send) message to the destination host, the
destination host upon receiving that message sends a CTS (clear to send)
message back to the source. After receiving the CTS, the source node sends
the required data. In the MACAW protocol the receiver sends an ACK to
acknowledge receipt of data. During the time when the data is transmitted
all nodes within the wireless that hear the CTS cannot transmit any data
until they hear an ACK transmitted to the source.
Another success of this paper/protocol is that MACAW incorporates a
30-byte Data-Sending packet (DS) right after the RTS-CTS between two nodes
has successfully been executed. This again, lets every node that can hear
the DS know that data is being transmitted and that they should refrain
from doing so until an ACK is heard.
I think the MACAW protocol is an improvement to wireless technology. The
way it works though reminds me a lot about virtual circuits because within
a given wireless network when one node is transmitting data the rest can't
do so. It is sort of like establishing a dedicated link until transmission
is done (i.e. from RTS to CTS to DS to ACK). This makes me wonder how much
loss of efficiency MACAW causes compared to say an Ethernet based LAN. I
think the authors should have talked a little about how their protocol
compares to other wired networks.
A possible future work as the authors suggest is to explore various
service models for wireless networks e.g. synchronous and asynchronous
service as applied to MACAW.
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