Configuring Congestion Management; Overview; Fifo - HP FlexNetwork MSR Series Configuration Manuals

Configuring congestion management

Overview

Congestion occurs on a link or node when traffic size exceeds the processing capability of the link or
node. It is typical of a statistical multiplexing network and can be caused by link failures, insufficient
resources, and various other causes.
Figure 14 Traffic congestion causes
100M
100M > 10M
(1)
Congestion can introduce the following negative results:
•
Increased delay and jitter during packet transmission.
•
Decreased network throughput and resource use efficiency.
•
Network resource (memory, in particular) exhaustion and system breakdown.
Congestion is unavoidable in switched networks or multiuser application environments. To improve
the service performance of your network, implement congestion management policies.
For example, congestion management defines a resource dispatching policy to prioritize packets for
forwarding when congestion occurs.
Congestion management involves queue creating, traffic classification, packet enqueuing, and
queue scheduling.
Queuing is a common congestion management technique. It classifies traffic into queues and picks
out packets from each queue by using an algorithm. Various queuing algorithms are available, and
each addresses a particular network traffic problem. Your choice of algorithm significantly affects
bandwidth assignment, delay, and jitter.
This section describes several common queue-scheduling mechanisms.

FIFO

As shown in
schedule queues. FIFO delivers packets in their arrival order. The packet that arrives earlier is
scheduled first. The only concern of FIFO is queue length, which affects delay and packet loss rate.
On a device, resources are assigned to packets depending on their arrival order and load status of
the device. The best-effort service model uses FIFO queuing.
FIFO does not address congestion problems. If only one FIFO output/input queue exists on a port,
you cannot ensure timely delivery of mission-critical or delay-sensitive traffic or smooth traffic jitter. If
malicious traffic occupies bandwidth aggressively, the problems increase. To control congestion and
prioritize forwarding of critical traffic, use other queue scheduling mechanisms, where multiple
queues can be configured. Within each queue, FIFO is still used.
100M
10M
10M
(100M + 10M + 50M) > 100M
Figure 15, the first in first out (FIFO) uses a single queue and does not classify traffic or
Figure 14 shows common congestion scenarios.
100M
50M
(2)
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