Alcatel-Lucent 9500 MXC User Manual page 144

Chapter 3. 9500 MXC Nodes
Flow Control
Disable Address Learning
Maximum Frame Size
Vol. II-3-50
• 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 applies 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 applies 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 applies 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 applies 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 terminal 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 signals 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 DAC 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 primarily for use in a ring network where protection for the Ethernet traffic is
provided by an external RSTP switch. To avoid conflict between the self-learning
functions within the DAC ES and the external RSTP switch during path failure
situations, the DAC 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 DAC 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.
Maximum Frame Size sets the largest size frame for the interface, which
determines the largest datagram than can be transmitted without it being broken
down into smaller units (fragmented). Although CT indicates settable frame sizes
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