Magnum 4K220 Switches Installation and User Guide (10/04)
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4.6
Flow-control, IEEE 802.3x standard
Magnum 4K- Series Switches incorporate a flow-control mechanism for Full-
Duplex mode. The purpose of flow-control is to reduce the risk of data loss if a long
burst of activity causes the switch to save frames until its buffer memory is full. This is
most likely to occur when data is moving from a 100Mb port to a 10 Mb port, and the
speed difference makes the 10Mb port unable to keep up. It can also occur when
multiple 100Mb ports are attempting to transmit to one 100Mb port, and in other
protracted heavy traffic situations.
Magnum 4K-Series Switches implement the 802.3x flow control (non-
blocking) on Full-Duplex ports, which provides for a “PAUSE” packet to be transmitted
to the sender when the packet buffer is nearly filled and there is danger of lost packets.
The transmitting device is commanded to stop transmitting into the switched port for
sufficient time to let the Switch reduce the buffer space used. When the available free-
buffer queue increases, the Switch will send a “RESUME" packet to indicate the
transmitter to start sending the packets. Of course, the transmitting device must also
support the 802.3x flow control standard in order to communicate properly during
normal operation.
Note:
When in Half-Duplex mode, the 4K220-switch implements a
back-pressure algorithm
on 10/100 Mb ports for flow control. That is, the
switch prevents frames from entering the device by forcing a collision
indication on the half-duplex ports that are receiving. This temporary
“collision” delay allows the available buffer space to improve, as the switch
catches up with the traffic flow.
5.0 TROUBLESHOOTING
All Magnum Ethernet products are designed to provide reliability and
consistently high performance in all network environments. The installation of
Magnum 4K220 Series Switches is a straightforward procedure (see INSTALLATION,
Section 2.6); the operation is also straightforward and is discussed in Section 4.
Should problems develop during installation or operation, this section is
intended to help locate, identify and correct these types of problems. Please follow the
suggestions listed below prior to contacting your supplier. However, if you are unsure
of the procedures described in this section or if the Magnum 4K220 Series Switch is not
performing as expected, do not attempt to repair the unit; instead contact your supplier
for assistance or contact GarrettCom Customer Support.
