METRODATA LTD
WCM1100 / WCM3100 / WCM-Serial
User Manual
76-02-082 Rev J
49 of 140
5.2.3 Flow Control
The WCM supports IEEE 802.3x pause frame based flow control on all auto negotiating
ports. Flow control may be globally enabled or disabled for the device.
If flow control is enabled, then any port will advertise flow control during auto negotiation
and if required generate pause frames to throttle a port to prevent packet loss.
In practice, flow control will normally be disabled as it interferes with priority based
queueing as it acts per port and shuts it down for all traffic meaning high priority is blocked
as well. With priority queueing enabled, when congestion is encountered the higher
priority traffic will keep passing, whilst the lower priority traffic will be buffered and
eventually discarded.
5.2.4 Max Frame Size
The Max Frame size setting globally defines the MTU for the WCM unit. The options are
as below
2048
Frames upto 2048 bytes will be accepted, this will allow for multiple layers
of MPLS or QinQ tagging
1522
This is the standard MAC MTU size as defined by IEEE 802.3 and
supports 1518 bytes untagged, or 1522 bytes with a single VLAN Tag
applied.
