AL103 Revision 1.0
3.2.2 Frame Transmission
The AL103 transmits all frames in accordance to IEEE 802.3 standard. The AL103 will send the
frames with a guaranteed minimum IPG (Inter Packet/Frame Gap) of 96BT even if the received
frames have an IPG less than the minimum requirement. The AL103 also supports transmission of
frames with an IPG of 64BT (optional). This option can be selected in System Register III, Bit 8,
Register 02.
3.2.3 Frame Generation
During a transmit process the frame data is read from the memory buffer and forwarded to the
destination port’s PHY device in di-bits. Seven bytes of preamble signal (10101010) will be
generated first before the SFD (10101011). Frame data is sent after the SFD along with four-bytes
of FCS at the end.
3.3 Half Duplex Mode Operation
For half-duplex operation, the MAC logic will abort the transmit-process if collision is detected.
Re-transmission of the frame is scheduled in accordance to IEEE 802.3’s truncated binary
exponential back-off algorithm. If the transmit process has encountered 16 consecutive collisions,
an excessive collision error is reported and AL103 will not try to re-transmit the frame unless the
retry-on-excessive-collision (REC) option in System Register III (register 02) is enabled. When
REC is enabled, the number of collisions are reset to zero and transmission is started as soon as 96
bit time of inter packet gap is passed after the last collision. If a collision is detected after 512 BT of
the transmission, a late collision error will be reported but the frame will still be retransmitted after
proper back-off time.
The AL103 also provides an option for an aggressive back-off in the System Configuration Register
II (SuperMAC). This option allows the MAC to back-off only three slots. This will create a more
aggressive channel capture behavior than the standard IEEE back-off algorithm.
3.4 Secure Mode Operation
The AL103 provides security support on a per port basis. Whenever the secure mode is enabled, the
port will stop learning new addresses. The address table of each port will remain unchanged. In this
mode of operation, the address lookup table will freeze and no additional new address will be
learned.
The AL103 provides two levels of security protection. The most severe intrusion protection is
disabling a port if intrusion is experienced. The security management (SecMgmt bit in register 01)
will disable a port if a frame with unlearned source address (SA) is received from a secured port
(security violation). An alternative is to enable security at the local port level without the security
management. When the AL103 is configured this way, the device will only discard frames that have
security violations, which prevents intruders from accessing the network.
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Reference Only / Allayer Communications
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