Traffic control
Basic - L3P
Release
3.1
06/07
8.5
Flow control
149
8.5 Flow control
8.5.1 Description Flow control
Flow control is a mechanism which acts as an overload protection. During
periods of heavy traffic it holds off additional traffic.
In the example (see fig. 41) the functioning of flow control is displayed gra-
phically. Workstations 1, 2 and 3 want to simultaneously transmit a large
amount of data to Workstation 4. The combined bandwidth of Workstations
1, 2 and 3 is larger than the bandwidth of Workstation 4 to the Switch. This
leads to an overflow of the send queue of Port 4. The left-hand funnel sym
-
bolizes this status.
If the flow control function at Ports 1, 2 and 3 of the Switch is turned on, the
Switch reacts before the funnel overflows. Ports 1, 2 and 3 send a message
to the conected devices that no data may be received at present.
Fig. 41: Example of flow control
Switch
Port 3Port 2
Port 1 Port 4
Workstation 1 Workstation 2 Workstation 3 Workstation 4
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