C H A P T E R 2 Intel
®
Express 530T Switch Users Guide
14
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 Express 530T switch.
Spanning Tree Protocol
Spanning Tree helps 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 from working.
Spanning Tree prevents loops by allowing only one active path between
any two network devices at a time. However, you can also use this
behavior to establish redundant links between devices which can take
over in the event the primary link fails.
The 530T supports one instance of Spanning Tree per switch (or per
stack of switches).
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, traffic is sent over the
backup path automatically.
Path: 3
Cost: 100
Path: 2
Cost: 200
Path: 1
Cost: 100
Switch A
Switch C
Server B
PC Client A
Switch B
530-Chapter2.fm Page 14 Monday, September 11, 2000 4:14 PM
