Flow Control; Spanning Tree Protocol - Intel 470F - NetStructure Switch User Manual

C H A P T E
470T Ch2.p65
R 2 Using the Intel® NetStructure™ 470T and 470F Switches

Flow Control

During times of heavy network activity, the switch's port buffers can
receive too much traffic and fill up faster than the switch can send the
information. In cases like this, the switch tells the transmitting device to
wait so the information in the buffer can be sent. This traffic control
mechanism is called flow control.
The method of flow control depends on whether the port is set to full- or
half-duplex. If a port is operating at half-duplex, the switch sends a collision
(also called backpressure) which causes the transmitting device to wait. If
the port operates at full-duplex, the switch sends out an IEEE 802.3x
PAUSE frame. You can enable or disable flow control for each port on the
470 switches.

Spanning Tree Protocol

Spanning Tree Protocol, as referenced in the IEEE 802.1D specification, is a
protocol designed to prevent any loops within the network topology. A loop
can occur if there is more than one path for information to travel between
devices. The Spanning Tree Protocol works by determining the "cost" of a
connection. For example, if two devices are connected by two links,
Spanning Tree uses the connection with the lowest cost and blocks the
second connection.
Spanning Tree prevents loops by allowing only one active path between any
two network devices at a time. However, you can also use this protocol to
establish redundant links between devices which can take over in the event
the primary link fails.
Backup Path from Client A to Server B:
Switch A –> Switch B –> Switch C
Primary Path from Client A to Server B: Switch A –> Switch C
In this example, Client A can communicate with Server B over two different
paths. The primary path is Path 1 because the cost of the connection between
switches A and C is lower than the cost between switches A, B and C. If the
primary path fails, then traffic is automatically sent over the backup path.
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