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3. Functional Description
3.1 PHY Monitoring and Port Mode Set-up
It is a major task of the software to continuously monitor the PHYs in order to set up the
switch ports according to whether the link is down or up and in the latter case what the
current speed, duplex mode and pause capabilities are.
PHYs are being polled every 100 ms.
3.2 Flow Control
In the 24-port switch flow control (back pressure) is also supported in half duplex.
Flow control can be enabled or disabled on a per-port basis from the command line
interface.
If flow control is enabled for a port the associated PHY will be set to advertise support of
“Symmetric Pause”, but not “Asymmetric Pause”. If the station connected to the port also
supports “Symmetric Pause”, flow control will be enabled on the switch port.
3.3 Ageing
To prevent that an automatically learned MAC address of a station that has been
detached will remain in the MAC address table permanently, the ageing function in the
switch is activated on a regular basis. The period for doing the ageing function is
determined by the ageing time parameter. The ageing time parameter can be set from
the command line interface. Default value is 300 seconds. Setting the ageing time
parameter to 0 disables the ageing function.
3.4 VLAN
The device supports 802.1Q tag based VLAN. With tagging to the header of packets, the
network can be segmented in groups to reduce the collisions from widely broadcasting. A
maximum of 16(16-ports) /24(24-ports) VLANs can be stored in EEPROM.
