Speed mismatches are the most typical cause of congestion Possibly persistent when going from LAN to WAN Usually transient when going from LAN to LAN

Speed mismatches are the most typical cause of congestion in a network.

Speed mismatches are most common when traffic moves from a high-speed LAN environment (1000 Mbps or higher) to lower-speed WAN links (1 or 2 Mbps). Speed mismatches are also common in LAN-to-LAN environments when, for example, a 1000-Mbps link feeds into a 100-Mbps link.

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The most common site of congestion is at points of aggregation in a network.

Typical points of aggregation occur in WANs when multiple remote sites feed back into a central services site.

In a LAN environment, congestion resulting from aggregation often occurs at the distribution layer of networks, where the different access layer devices feed traffic to the distribution-level switches.

Queuing Algorithms

This topic describes the different queuing algorithms.

This topic describes the different queuing algorithms.

Key queuing algorithms include the following:

■ FIFO: The simplest algorithm

■ Priority queuing (PQ): Allows certain traffic to be strictly-prioritized

■ Round robin: Allows several traffic flows to share bandwidth

■ Weighted round robin (WRR): Allows sharing of bandwidth with preferential treatment

■ Deficit round robin (DRR): Resolves problem with some WRR implementations

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