D-Link DI-1750 Reference Manual page 387

synchronization of TCP hosts can occur as multiple TCP hosts reduce their transmission rates. The
congestion clears, and the TCP hosts increase their transmissions rates, resulting in waves of
congestion followed by periods where the transmission link is not fully used.
RED reduces the chances of tail drop by selectively dropping packets when the output interface begins
to show signs of congestion. By dropping some packets early rather than waiting until the buffer is full,
RED avoids dropping large numbers of packets at once and minimizes the chances of global
synchronization. Thus, RED allows the transmission line to be used fully at all times.
In addition, RED statistically drops more packets from large users than small. Therefore, traffic sources
that generate the most traffic are more likely to be slowed down than traffic sources that generate little
traffic.
WRED provides separate thresholds and weights for different IP precedences, allowing you to provide
different qualities of service for different traffic. Standard traffic may be dropped more frequently than
premium traffic during periods of congestion.
See the WRED Configuration for concrete configuration.
♦ Custom Queueing
When CQ is enabled on an interface, the system maintains 17 output queues for that interface. You
can specify queues 1 through 16. Associated with each output queue is a configurable byte count,
which specifies how many bytes of data the system should deliver from the current queue before it
moves on to the next queue.
Queue number 0 is a system queue; it is emptied before any of the queues numbered 1 through 16
are processed. The system queues high priority packets, such as keepalive packets and signalling
packets, to this queue. Other traffic cannot be configured to use this queue.
For queue numbers 1 through 16, the system cycles through the queues sequentially (in a
round-robin fashion), dequeueing the configured byte count from each queue in each cycle,
delivering packets in the current queue before moving on to the next one. When a particular queue
is being processed, packets are sent until the number of bytes sent exceeds the queue byte count
or the queue is empty. Bandwidth used by a particular queue can only be indirectly specified in
terms of byte count and queue length. Like PQ, CQ is statically configured and does not
automatically adapt to changing network conditions
See the " CQ Configuration" for concrete configuration.
♦ Priority Queueing
PQ define 4 class of communication priority(high,middle,normal,low). During transmission, PQ
gives priority queues absolute preferential treatment over low priority queues; important traffic,
given the highest priority, always takes precedence over less important traffic.
Packets are classified based on user-specified criteria and placed into one of the four output
queues—high, medium, normal, and low—based on the assigned priority. Packets that are not
classified by priority fall into the normal queue. When a packet is to be sent out an interface, the
priority queues on that interface are scanned for packets in descending command of priority. The
high priority queue is scanned first, then the medium priority queue, and so on. The packet at the
head of the highest queue is chosen for transmission. This procedure is repeated every time a
packet is to be sent.
See thePQ Configuration for concrete configuration.
9.1.2 QoS Signalling
The Router QoS signalling provides a way for an end station or network node to signal its neighbors to
request special handling of certain traffic. QoS signalling is useful for coordinating the traffic handling
techniques provided by other QoS features. It plays a key role in configuring successful overall
end-to-end QoS service across your network. QoS signalling takes advantage of IP. Either in-band (IP
Precedence, 802.1p) or out-of-band (RSVP) signalling is used to indicate that a particular QoS service
is desired for a particular traffic classification. Together, IP Precedence and RSVP provide a robust
combination for end-to-end QoS signalling: IP Precedence signals for differentiated QoS and RSVP for
guaranteed QoS.
For more complete conceptual information, see the chapter " Resource Reservation Protocol (RSVP)"
Model Name
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