D-Link 3250TG Product Manual - Page 78

QOS Quality of Service

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D-Link DES-3250TG Standalone Layer 2 Switch Admin State Max Learning Addr.(0-10) Lock Address Mode Allows the selected port(s) dynamic MAC address learning to be locked such that new source MAC addresses cannot be entered into the MAC address table for the locked port or group of ports. It can be changed by toggling between Disabled and Enabled. Select the maximum number of addresses that may be learned for the port. The port can be restricted to 10 or less MAC addresses that are allowed for dynamically learned MAC addresses in the forwarding table. Select Delete On Timeout to clear dynamic entries for the ports on timeout of the Forwarding Data Base (FDB). Specify Delete On Reset to delete all FDB entries, including static entries upon system reset or rebooting. QOS (Quality of Service) The DES-3250TG switch supports 802.1p priority queuing. The switch has four priority queues. These priority queues are numbered from 0 - the lowest priority queue - to 3 - the highest priority queue. The eight priority queues specified in IEEE 802.1p (Q0 to Q7) are mapped to the switch's priority queues as follows: Q2 and Q1 are assigned to the switch's Q0 queue. Q3 and Q0 are assigned to the switch's Q1 queue. Q5 and Q4 are assigned to the switch's Q2 queue. Q7 and Q6 are assigned to the switch's Q3 queue. The switch's four priority queues are emptied in a round-robin fashion-beginning with the highest priority queue, and proceeding to the lowest priority queue before returning to the highest priority queue. For strict priority-based scheduling, any packets residing in the higher priority queues are transmitted first. Only when these queues are empty, are packets of lower priority transmitted. The weighted-priority based scheduling alleviates the main disadvantage of strict priority-based scheduling − in that lower priority queues get starved of bandwidth − by providing a minimum bandwidth to all queues for transmission. This is accomplished by configuring the maximum number of packets allowed to be transmitted from a given priority queue and the maximum amount of time a given priority queue will have to wait before being allowed to transmit its accumulated packets. This establishes a Class of Service (CoS) for each of the switch's four hardware priority queues. The possible range for maximum packets is: 0 to 255 packets. The possible range for maximum latency is: 0 to 255 (in increments of 16 microseconds each). 70

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D-Link DES-3250TG Standalone Layer 2 Switch
Admin State
<
Disabled
>
Allows the selected port(s) dynamic
MAC address learning to be locked
such that new source MAC addresses
cannot be entered into the MAC
address table for the locked port or
group of ports. It can be changed by
toggling
between
Disabled
and
Enabled
.
Max Learning
Addr.(0-10) <
1
>
Select
the
maximum
number
of
addresses that may be learned for the
port. The port can be restricted to 10
or less MAC addresses that are allowed
for
dynamically
learned
MAC
addresses in the forwarding table.
Lock Address
Mode
<Delete On Reset>
Select
Delete On Timeout
to clear
dynamic entries for the ports on
timeout of the Forwarding Data Base
(FDB). Specify
Delete On Reset
to delete
all FDB entries, including static entries
upon system reset or rebooting.
QOS (Quality of Service)
The DES-3250TG switch supports 802.1p priority queuing. The switch has four priority queues. These
priority queues are numbered from 0 — the lowest priority queue — to 3 — the highest priority queue.
The eight priority queues specified in IEEE 802.1p (Q0 to Q7) are mapped to the switch’s priority
queues as follows:
Q2 and Q1 are assigned to the switch’s Q0 queue.
Q3 and Q0 are assigned to the switch’s Q1 queue.
Q5 and Q4 are assigned to the switch’s Q2 queue.
Q7 and Q6 are assigned to the switch’s Q3 queue.
The switch’s four priority queues are emptied in a round-robin fashion—beginning with the highest
priority queue, and proceeding to the lowest priority queue before returning to the highest priority
queue.
For strict priority-based scheduling, any packets residing in the higher priority queues are transmitted
first. Only when these queues are empty, are packets of lower priority transmitted.
The weighted-priority based scheduling alleviates the main disadvantage of strict priority-based
scheduling
−
in that lower priority queues get starved of bandwidth
−
by providing a minimum
bandwidth to all queues for transmission. This is accomplished by configuring the maximum number of
packets allowed to be transmitted from a given priority queue and the maximum amount of time a given
priority queue will have to wait before being allowed to transmit its accumulated packets.
This
establishes a Class of Service (CoS) for each of the switch’s four hardware priority queues.
The possible range for maximum packets is: 0 to 255 packets.
The possible range for maximum latency is: 0 to 255 (in increments of 16 microseconds each).
70