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4. Functional Description
4.1 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.
4.2 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.
4.3 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.
4.4 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 24 VLAN
groups can be stored in EEPROM. The VLAN look up is based on full 24-bit vlaue of packet VID or
Port PVID. It also provides egress tagging mode setting for each port.
4.5 Link Aggregation
Link aggregation groups (or channels) can be defined statically. LACP (Link Aggregation Control
Protocol) is not supported.
Maximum number of aggregation groups is 8.
The software will automatically detect that a link has gone down and then reassign packet distribution
on the other links in the group.
4.6 Quality of Service
Various classifications and prioritization such as TOS, Egress rate control, Ingress rate control and
Storm are supported in order to enable Quality of Service for real time applications such as VoIP
(Voice over IP).
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