Review "MACAW: A Media Access Protocol for Wireless LAN’s"

       MACAW: A Media Access Protocol for Wireless LAN’s

This paper presents some amendments to basic MACA (Multiple Access
Collission Avoidance) protocol for packet exchange in wireless
networks and names it MACAW. The purpose of this design is to improve
throughput and fairness for all the nodes of a wireless network.

Paper states two main amendments in MACAW over MACA. The first
amendment is in the Backoff algorithm. Binary exponential backoff
(BEB) does not provide an adequate level of fairness even in very
simple scenarios. MACAW suggests copying the value of backoff counter
using a field in the packet header field. In this scheme, when a
station hears a packet, it copies its backoff counter’s value to its
own counter. As a result, after each successful transmission, the
backoff counters of all stations are set to minimum, and this results
in fairness.

In a revision, paper suggests Per-destination backoff algorithm
instead of Single backoff to rectify problems such as noise next to
the sender or receiver and leakage of backoff values between two
cells. In Per-destination backoff algorithm, there is a separate
backoff value for each station, and backoff values of both ends are
inserted in the packet header.

The second amendment is in signaling. The first step is to add ACK
after receiver receives data. In fact, this signaling in link layer
works in place of transport layer and speeds up the retransmit
process. Next step is adding DS to previous algorithm to obtain
RTS-CTS-DS-DATA-ACK. DS is sent before data transmission to inform
hidden terminals that a successful RTS-CTS has taken place. The other
change is to add RRTS (Request for Request to Send).This packet is
sent whenever a station receives RTS but cannot reply(due to deferral)
to inform the sender that it is ready for communication now.

Preliminary evaluations shows that throughput in MACAW has a decrease
of 8% due to overhead of extra packets. However, this overhead is
compensated by superior performance in the presence of congestion and
noise.
Received on Mon Sep 25 2006 - 23:23:36 EDT