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DUA1840-0AAA01
Switch Operation and Features
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Intelligent Flow Management
Intelligent Flow Management
(IFM)
is a congestion control mechanism
built into the Switch 1005. Congestion is caused by one or more
devices sending traffic to a Switch port which is already busy. The
Switch 1005 contains both input and output packet buffers and while
congestion is rare, IFM is designed to alleviate problems during those
moments when packet buffers in the Switch 1005 are full. IFM will
prevent packet loss by inhibiting the transmitting device from sending
any further packets until the port is no longer congested.
If a packet arrives at a conventional switch that does not operate IFM,
and that port is congested, the transmitting device is unaware of this
until it times out and decides that the receiving station is not going to
respond to the message. This can take as long as 30 seconds, and
depending on the protocol you are running, may not happen until
many packets have been sent. The transmitting device then has to
retransmit the packets, effectively wasting bandwidth.
Switch
modules
implementing IFM are aware of congestion, and
prevent packet loss by inhibiting the transmitting device from
transmitting the packet in the first place. It does this by forcing the
device to retransmit the packet later. This “back-off” and retransmission
happens very quickly (typically less than one second) and is much
faster than waiting for the transmitting device to time-out. There are
two benefits:
■
the packet is transmitted quickly and successfully
■
the packet is only transmitted once, thereby saving bandwidth.
IFM is designed to be enabled on ports connected to a single network
device. If IFM is enabled on a port connected to multiple devices
through a repeater, packet congestion within the Switch 1005 could
result in packet transmission between two devices connected to the
repeater being inhibited.