MTU [B]
Defines maximum transmission unit (MTU) frame size allowed to be received or transmitted from
or to a given physical port. This implies that a Jumbo frame may be allowed to be received from a
given input port but may or may not be allowed to be transmitted out of a port or ports.
The possible values are 1522, 2048 and 10240 Bytes.
Note
The definition of frame size is counting the frame bytes from MAC_DA through Layer2
CRC of the frame.
Flow control send/receive (previously TX/RX)
It is the mechanism for temporarily stopping the transmission of data on an Ethernet network, so
that the receiving node is not overwhelmed with data from transmitting node. It works according
IEEE 802.3x standard. If allowed, speed of data receive in to the switch (from the connected device)
is regulated by the switch sending out flow control pause frames (according parameter 'Pause
limit out') to the connected device. If allowed, speed of data transmission out from the switch (to
the connected device) is regulated by processing received in flow control pause frames (according
parameter 'Pause limit in') sent by the connected device.
Enabling flow control allows use of buffers of connected active network elements for leveling uneven
flow of user data. For correct operation it is necessary to also enable Flow control on the connected
device. Flow control is handled by sending Pause frames to the connected device. Possible values:
• off — Flow control is disabled.
• on — Flow control is enabled (forced to be active).
• auto — Sending pause packets is advertised and depends on result on the auto-negotiation
process. Auto-Negotiation has to be supported and enabled on the port to take effect.
Important
For optimal utilization of Ethernet switch buffers and maximal operational speed of the link
it is recommended to upgrade unit to the latest FW version and apply its defaults to ensure
optimal buffers cooperation. Optimal performance may require playing a bit with Pause
limit parameters to optimize the communication with the switch or router connected to the
MW unit.
Note
Additional link performance and better utilization of all available buffers in transmitting
network could be typically achieved by configuring Flow Control between the MW unit and
the nearest switches feeding the link by data. Important for incoming data are parameters
'Flow Control send' on ports 'Eth1(p1)' and/or 'Eth2(p10)', which needs to be set to values
'auto' or 'on' (the value to use depends on the switch).
FW versions 1.0.16.0 and earlier require RX Flow Control for port 'Air (p9)' on both units
to be set to 'on'. The only exception is FW version 1.0.14.0 with activated 'Unit 24S com-
patibility' (for more info see 'Setting up a link between RAy3-24S and other hardware variant
of RAy3-24' in Chapter 8, Troubleshooting).
Pause limit in [frame]
Value limits the number of continuous Pause refresh frames that can be received on this port (if
full-duplex) or the number of 16 consecutive collisions (if half-duplex). Pause limit in [frame] When
a port has flow control enabled, this parameter can be used to limit how long this port can be Paused
or Back Pressured off to prevent a port stall through jamming.
The Flow Control on the port is (temporarily) disabled when the Pause refresh frames count exceeds
the value of this parameter.
Setting this parameter to 0 will allow continuous jamming to be received on this port.
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