AL103 Revision 1.0
this case, the flow control option is recommended so when the frame buffer is full, incoming frames
will be backpressured. To prevent buffer starvation, half of the memory is reserved and allocated to
each port while the other half is shared.
The other option is to limit the number of frames that each output queue can store. This option is
selected by setting bit 00.15 to “1.” An output queue watermark can be set in System Configuration
Register I (Register 00, Bits 7:6) to keep the balance between utilization and fairness of buffer
sharing. This method prevents other ports from suffering performance reduction due to a single port
experiencing an extreme congestion. If severe congestion is experienced in a single port, only that
port will suffer from frame loss because the buffer is limited to its dedicated portion. Other ports
will not experience any frame loss due to congestion problem in other ports since all other ports
retain their own allocated buffer space.
When an output queue or multicast queue experiences a buffer full condition, the AL103 will
backpressure the incoming frames if flow control is enabled. A watermark for buffer full condition
can be selected in register 04.
3.10 Uplink Port
The uplink port provides a means to connect the switch with a repeater hub, a workgroup switch, a
router, or any type of interconnecting device compliance with IEEE 802.3 standards.
If flood control is enabled, the AL103 will send all frames with unmatched DA and multicast/
broadcast frames to the uplink port. It is very important that each port is assigned to an uplink port
via the Port Configuration Register (0D to1C), or data frames might be lost. The uplink port should
be configured to be within the same VLAN of the source port. If the uplink port is not a member of
the VLANs, the broadcast or multicast frames will not be forwarded to its designated uplink port.
Multiple VLANs can share the same uplink port.
The AL103 will direct the following frames to the uplink port:
•
Frames with a unicast destination address that doesn’t match with any MAC
address stored in the switch.
•
Frames with a broadcast/multicast destination address if the uplink port is in the
same VLAN.
Note: When configuring an uplink port, the uplink port should designate itself as the uplink port.
3.11 Port Monitoring
The AL103 supports port monitoring. This feature provides complete network monitoring
capability at 100 Mbit/s. A copy of egress (TX) data and ingress (RX) data of the monitored port is
sent to their respective snooping ports.
The monitored port is selected by register 30. The AL103 allows transmit and receive data to be
monitored by different snooping ports. The snooping ports are also selected by register 30.
9/00
Reference Only / Allayer Communications
27
ABC [ ABC Taiwan Electronics Corp ]
