Nortel Networks 24T manual Choosing a High Speed Flow Control Mode

Using the BayStack 410-24T 10BASE-T Switch

Table 3-20.	High Speed Flow Control Configuration Screen Fields (continued)
Field		Description
Flow Control		Allows you to control traffic and avoid congestion on the gigabit MDA port. Two
		modes are available (see “Choosing a High Speed Flow Control Mode” on
		page 3-56 for details about the two modes). Autonegotiation must be disabled
		for this port when using this feature.
		Default Value	Disabled
		Range	Disabled, Symmetric, Asymmetric
		Note: The following two fields only appear when a (single MAC) MDA with a
		separate redundant Phy port is installed.
Preferred Phy
		Allows you to choose the preferred Phy port; the other Phy port reverts to
		backup.
		Default Value	Right
		Range	Right, Left
Active Phy		Indicates the operational Phy port.
		Default Value:	None
		Range:	None, Right, Left

Choosing a High Speed Flow Control Mode

The High Speed Flow Control feature allows you to control traffic and avoid congestion on the gigabit full-duplex link. If the receive port buffer becomes full, the BayStack 410-24T switch issues a flow-control signal to the device at the other end of the link to suspend transmission. When the receive buffer is no longer full, the switch issues a signal to resume the transmission. You can choose Symmetric or Asymmetric flow-control mode:

Symmetric Mode

This mode allows both the gigabit MDA port and its link partner to send flow-control pause frames to each other. When a pause frame is received (by either the gigabit MDA port or its link partner), the port suspends transmission of frames for a number of slot times specified in the control frame or until a pause-release control frame is received. Both devices on the link must support this mode when it is selected.

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