Weighted Random Early Detection Mechanism

DE.

Weighted Random Early Detection (WRED) is just a congestion avoidance mechanism.

WRED drops packets selectively based on IP precedence.

Edge routers assign IP precedences to packets as they enter the network.

When a packet arrives, the following events occur: 1

The average queue size is calculated.

2

If the average is less than the minimum queue threshold, the arriving packet is queued.

3

If the average is between the minimum queue threshold for that type of traffic and the maximum threshold for the interface, the packet is either dropped or queued, depending on the packet drop probability for that type of traffic.

4

If the average queue size is greater than the maximum threshold, the packet is dropped.

WRED reduces the chances of tail drop (when the queue is full, the packet is dropped) by selectively dropping packets when the output interface begins to show signs of congestion (thus it can mitigate congestion by preventing the queue from filling up)

By dropping some packets early rather than waiting until the queue is full, WRED avoids dropping large numbers of packets at once and minimizes the chances of global synchronization.

Thus, WRED allows the transmission line to be used fully at all times.

WRED generally drops packets selectively based on IP precedence.

Packets with a higher IP precedence are less likely to be dropped than packets with a lower precedence.

Thus, the higher the priority of a packet, the higher the probability that the packet will be delivered.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_conavd/configuration/15-mt/qos-conavd-15-mt-book/qos-conavd-cfg-wred.html

The Weighted Random Early Detection (WRED) mechanism is used to manage network congestion in a more efficient way. It is typically used in routers and switches to manage packet queues when the incoming traffic exceeds the device's capacity to handle it. WRED mechanism can mitigate congestion by selectively dropping packets based on their priority.

The two actions performed by the Weighted Random Early Detection mechanism are:

1. Mitigate congestion by preventing the queue from filling up: WRED mechanism manages the packet queue by monitoring the queue depth and selectively dropping packets before the queue becomes full. By dropping packets early, WRED can prevent congestion from occurring in the first place.

2. Drop lower-priority packets before it drops higher-priority packets: WRED mechanism can be configured to prioritize packets based on their importance or priority. When the packet queue begins to fill up, the WRED mechanism can drop packets based on their priority. Lower-priority packets are dropped before higher-priority packets, ensuring that high-priority packets are delivered first.

Therefore, the correct options are D and E. Option A is incorrect because WRED does not support protocol discovery. Option B is incorrect because WRED does not guarantee the delivery of high-priority packets, but it prioritizes them over lower-priority packets. Option C is incorrect because although WRED can identify different flows, it is not known for providing a high level of granularity in this regard.