Avaya Configuring Ethernet, FDDI, and Token Ring Services Manual de usuario descargar pdf (Pagina 38)

Configuring Ethernet, FDDI, and Token Ring Services

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308623-14.00 Rev 00

Enabling Ethernet Flow Control

Ethernet flow control allows you to temporarily stop a remote station from

sending packets to prevent packet loss in a congested system. Ethernet flow

control is supported on BN platforms for the following boards:

• Quad 100BASE-TX

• Quad 100BASE-FX

• Gigabit Ethernet-SX

• Gigabit Ethernet-LX

The Nortel Networks implementation of flow control uses MAC control frames.

These frames have a unique value of 8808H in the length/type field. They differ

from typical Ethernet packets in that the data field consists of an opcode field and

a parameter field. The opcode field contains the opcode command Pause; the

parameter field defines the pause time. When the receive station detects a MAC

control frame with a Pause opcode, the remote transmitter pauses for a time

interval equal to the pause time * 512 bit times. The value 512 bit times converts

to 51.2 microseconds (ms) for 10 Mb/s, 5.12 ms for 100 Mb/s, and 512

nanoseconds (ns) for Gigabit.

When a transmitter receives a MAC control frame, it stops sending packets for the

specified time. You can configure the congested receiver (the sender of the MAC

control frame) to transmit a pause frame with a pause time of 0 when the receiver

is no longer congested, thereby causing the remote transmitter to resume sending

packets. You do this by setting the Transmit Pause Zero Enable (Site Manager)

parameter or the pause-zero-enable (BCC) parameter to Enable.

The following sections describe how to use the BCC and Site Manager to enable

Ethernet flow control.

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Avaya Configuring Ethernet, FDDI, and Token Ring Services Manual de usuario Pagina 38