3Com 3036, Руководство по настройке

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680 C
HAPTER
49: C
ONGESTION
M
ANAGEMENT
Figure 217 Schematic diagram of the congested network
Congestion
Management Policy
Overview
When the congestion occurs, if not enough memory space is provided to buffer
the packets, some of the packets will be lost. The loss of the packets may cause
the host or router that is sending the packet to resend this packet because of
overtime, re-congesting and resending, and so on, thereby causing a vicious circle.
Therefore, some policies are used to manage network congestion. When
congestion occurs, the router takes some policies to dispatch the data packets,
deciding which data packets may be sent first and which ones may be discarded.
These policies are called the congestion management policy.
For the congestion management, the queuing mechanism is generally used. When
congestion occurs, the packet is queued at the router egress by a given policy.
During dispatching, the order for sending the packet out of the queue is decided
by a given policy.
FIFO Queuing In the FIFO mode, the concept of no communication priority and classification is
adopted. During the use of FIFO, the sending order of data packet from the
interface depends on the order in which the data packet arrives at this interface, at
this time, the queuing and de-queuing orders of the packet are the same.
FIFO provides the basic storage and transmission capabilities.
Priority Queuing In Priority Queueing (PQ) mode, you can flexibly specify the priority queues which
the packets enter according to the fields packet length, source address, and
destination address in the packets header and the interface into which the packets
will come. The packets belonging to a higher priority queue can be sent first. In
this way, the most important data can be handled first.
Custom Queuing In the Custom Queueing (CU) model, according to the user's requirements, the
traffic can be classified in terms of TCP/UDP port number, ACL and interface type.
Each type of traffic is allocated with a certain percent of bandwidth. When
network congestion occurs, the traffic that has high demands on delay (such as
voice) can obtain reliable service. If a type of traffic cannot occupy all the reserved
bandwidth, other types of traffic will occupy the reserved bandwidth
automatically, thus making full use of the resource.
DDN/FR/ISDN/PSTN
Quidway
Router
Ethernet
Server
Ethernet
Server
Company LAN1
10 M
100 M
Occurrence of
congestion
P
C
P
C
Company LAN2
RouterA
RouterB