User`s manual

CLARION M10 SERIES STRUCTURE
M10 SERIES USER’S MANUAL PAGE 9
• Detection of any collision condition for avoiding collision of the
Download to the Upload and signaling of such to the AUI
interface and to the CPU.
2.3.3 BUFFER MEMORY
A data transfer is called an Upload when the Ethernet device conveys a
frame to the buffer memory, and a Download when a frame is conveyed
from the buffer memory to the Ethernet device. The buffer memory is
organized as 16 2-Kbytes FIFOs, each FIFO being independently employed
and capable of storing a maximum-length Ethernet frame of 1518-bytes.
When all buffers are consumed, a Collision signal is generated to force the
Ethernet card into its exponential back-off algorithm for flow control. If
generation of the Collision is not selected, then no Collision is generated
but Upload(s) are ignored.
2.3.4 FORWARD ERROR CORRECTION (FEC)
The nominal transmission mode (uncoded mode) employs modulation
without FEC. The enhanced-robustness mode (coded mode) employs FEC
to overcome irreducible errors due to multi-path propagation condition.
The coded mode and/or selection of a diversity antenna can be selected by
the RF-MAC-level re-transmission protocol.
2.3.5 RE-TRANSMISSION
A re-transmission protocol at the RF MAC layer provides enhanced
reliability. The 32-bit CRC, checked by the 802.3 MAC layer to provide
ultimate data reliability, is also used to support the re-transmission protocol.
Figure 2.3.5 shows a conceptual signal flow diagram of the re-transmission.
The use of MAC-level re-transmission protocol, recommended by 802.11
draft standard, is important for high throughput. Re-transmission via the
level-four transport protocol must be avoided because of the long time-out
typically employed.