Nortel Networks 350 Choosing a High Speed Flow Control Mode, Field Description Preferred Phy

Using the BayStack 350 10/100/1000 Series Switch

Table 3-13.	High Speed Flow Control Configuration Screen Fields (continued)
Field		Description
		Note: The following two fields only appear when a (single MAC) MDA with a
Preferred Phy		separate redundant Phy port is installed.
		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.

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 350 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 frames is received. Both devices on the link must support this mode when it is selected.

Asymmetric

This mode allows the link partner to send flow control pause frames to the gigabit MDA port. When a pause frame is received, the receiving port suspends transmission of frames for a number of slot times specified in the control frame or until a pause-release control frames is received. In this mode the gigabit MDA port is disabled from transmitting pause frames to its link partner. This mode can be used if the gigabit MDA port is connected to a buffered repeater device.

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