Congestion Management Overview; Congestion Management Policies - 3Com MSR 50 Series Configuration Manual

86
Congestion
Management
Overview
Congestion
Management Policies
C
ONGESTION
As to a network device, congestion will occur on the interface where the arrival
rate of packets is faster than the sending rate. If there is no enough buffer capacity
to store those packets and then a part of them will be lost, which may cause the
packet retransmission from the device because of timeout, and lead to a vicious
circle.
The key to congestion management is how to define a dispatching policy for
resources to decide the forwarding order of packets when congestion occurs.
In general, congestion management adopts queuing technology. The system
classifies traffics using a kind of queuing algorithm, and then it will send out them
with a certain preference algorithm. Each queuing algorithm is used to handle a
particular network traffic problem and has great impacts on bandwidth resource
assignment, delay, and jitter.
We will introduce several common queue-scheduling mechanisms here.
FIFO (First In, First Out) queuing
Figure 464 FIFO queuing
As shown in above figure, FIFO designs the forwarding order of packets
depending upon their arrival time. On a device, the resources assigned for data
traffic of users are based on the arrival time of packets and the current load status
of the network. Best-Effort services use FIFO queuing policy.
If there is only one FIFO-based output/input queue on device's interface, malicious
applications may occupy all network resources and seriously affect mission-critical
data.
Within each queue, the sending (sequence) of packets is defaulted as FIFO.
M
ANAGEMENT