Flow Control; Disable Address Learning - Alcatel-Lucent 9500 MXC User Manual

Chapter 2. 9500 MXC Terminals

Flow Control

Disable Address Learning

Vol. II-2-18
• 802.1p provides prioritization based on the three-bit priority field of the 802.1p
VLAN tag. Each of the possible eight tag priority values are mapped into a
four-level (2-bit) priority level. If packets are not tagged, then the Port Default
prioritization will apply to these packets.
• DiffServ provides prioritization based on the six bits of the IP packet DiffServ
or Type of Service byte. Each of the possible 63 levels are mapped into a
four-level (2-bit) priority level. If packets are not tagged, then the Port Default
prioritization will apply to these packets.
• 802.1p-then-DiffServ provides prioritization based first on the 802.1p VLAN
tag, and then on the DiffServ or Type of Service byte. If packets are not tagged,
then the Port Default prioritization will apply to these packets.
• DiffServ-then-802.1p provides prioritization based first on the IP packet
DiffServ or Type of Service byte, then on the 802.1p VLAN tag. If packets are
not tagged, then the Port Default prioritization will apply to these packets.
Flow Control is an option for full-duplex links only. It is implemented through
use of IEEE 802.3x PAUSE frames, which tell the remote node to stop or restart
transmission to ensure that the amount of data in the receive buffer does not
exceed a 'high water mark'. The receiver will signal to the transmitter to stop
transmitting until sufficient data has been read from the buffer, triggered by a
'low water mark', at which point the receiver signals to the transmitter to resume
transmission. To be effective, flow control must be established from the
originating source through to the end point, and vice versa, which means the
equipment connected to the IDU ES ports and beyond should also be enabled for
flow control.
Address Learning is default implemented to support efficient management of
Ethernet traffic in multi-host situations. The option to disable Address Learning
is for use in a ring network where protection for Ethernet traffic is provided by an
external RSTP switch. To avoid conflict between the self-learning function
within IDU ES and the external RSTP switch during path failure situations, the
IDU ES capability must be switched off. Failure to do means that in the event of
an Ethernet path failure, and subsequent re-direction of Ethernet traffic by the
external switch to the alternate path, the IDU ES will prevent re-direction of
current/recent traffic until its address register matures and deletes unused/
un-responsive destination addresses, which may take up to 5 minutes.
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