User`s manual

CLARION M10 SERIES STANDARDS
M10 SERIES USER’S MANUAL PAGE 33
6. COMPLIANCE WITH STANDARDS
6.1 MAU
While the M10 has been designed to appear electrically as a standard MAU,
it is executing a medium-access protocol appropriate for the wireless
medium. As a result, some of its behaviors are not reflected in a wired-
medium MAU, and the transparency to the wired-medium MAC in the
attached computer or bridging device cannot be absolute. MAUs for wired
networks have no internal storage; they operate with negligible delay
relative to the signals at the AUI/MAU interface.
Because the MAC software in the attached computer is executing a
protocol appropriate for the wired medium, and the M10 must employ a
protocol appropriate for the wireless medium, the M10 stores frames in
buffers in order to isolate the (wired and wireless) media.
This results in important differences from conventional 802.3 MAUs; these
include buffer delay as well as the need for RF re-transmissions and for
flow control.
6.1.1 BUFFER DELAY
The protocol operating over a M10 link must anticipate a delay of two
frames in each direction. When a frame is offered from the AUI port, first
it is saved in a buffer; subsequently the frame is transferred over the RF
channel to a receive buffer in the destination M10; only then is the frame
downloaded to the destination AUI port.
This need not limit throughput if the transport protocol properly anticipates
the delay. If the protocol waits for each frame to be acknowledged, then
the throughput achieved will be very low due to the excess delay.
However, if a burst mode is used, then the effect of the delay can be made
negligible. This effect can be readily demonstrated using, for example,
Perform 3®.
6.1.2 FLOW CONTROL
When no buffers are available for UPLOAD of AUI frames to the M10,
some action is required. The M10 may: