3Com Router User Manual

Physical Interface Line Rate677
Shape all the flows on Ethernet interface 1.
[Router] interface ethernet1
[Router-Ethernet1] qos gts any cir 45000000 cbs 5800000 ebs 5800000
Physical Interface Line 
RateBy using the physical interface line rate (LR), the total rate for sending packets 
(including the emergency packet) on a physical interface can be limited.
LR also uses the token bucket to perform the traffic control. If LR is configured in 
an interface of the router, the LR token bucket first processes...

678CHAPTER 48: TRAFFIC POLICING, TRAFFIC SHAPING AND LINE RATE
Displaying and 
Debugging LRTa b l e 718   Display and Debug LR
OperationCommand
Display the LR configuration conditions 
and statistic information of the interfacedisplay qos lr [ interface type 
number ] 

49
CONGESTION MANAGEMENT
This chapter covers the following topics:
■What is Congestion?
■Congestion Management Policy Overview
■Selecting Congestion Management Policies
■Operating Principle of the Congestion Management Policies
■Configuring Congestion Management
■Congestion Management Configuration Examples
What is Congestion?For a network unit, when the speed of the data packet is faster than the speed at 
which this interface sends the data packet, congestion occurs on the interface. If 
not enough...

680CHAPTER 49: CONGESTION MANAGEMENT
Figure 217   Schematic diagram of the congested network
Congestion 
Management Policy 
OverviewWhen 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...

Selecting Congestion Management Policies681
For the interface with the lower rate, customizing the queue for it can guarantee 
that the data flows passing through this interface may also obtain the network 
services to certain extent.
Weighted Fair QueuingWeighted Fair Queuing (WFQ) provides a dynamic and fair queuing mode, which 
distinguishes the traffic based on the priority/weight and decides the bandwidth 
size of each session according to the session situation. Thus, it guarantees that all...

682CHAPTER 49: CONGESTION MANAGEMENT
Ta b l e 719   Comparison of Several Congestion Management Policies
Operating Principle of 
the Congestion 
Management PoliciesFor congestion management, queuing technology is used. When congestion 
occurs, the data packet is queued at the router by a policy. When dispatching, the 
order for sending the data packet is decided by the policy.
Number of 
queues
AdvantageDisadvantage
FIFO11. It does not need to be 
configured and is easy to use.
2. The processing is...

Operating Principle of the Congestion Management Policies683
Figure 218   Schematic diagram of the first in first out queue
First-In, First-Out (FIFO) 
QueuingAs shown in Figure 218, the data packets are input to the first-in, first-out (FIFO) 
queue according to the priority order of their arrivals. Data packets that first arrive 
are first transmitted, and the data packets that later arrive are transmitted later. All 
the packets that will be transmitted from the interface are input to the end of the...

684CHAPTER 49: CONGESTION MANAGEMENT
rate and throughput rate can be guaranteed to a certain extent in case of network 
congestion.
The key service (such as ERP) data packets may be put into the higher priority 
queue, while the non-key service (such as E-Mail) data packets are put into the 
lower priority queue, so that the data packets of the non-key service are 
transmitted in the idle intervals during the processing of the key service data. In 
this way, the priority of the key service is guaranteed...

Operating Principle of the Congestion Management Policies685
In the network shown in Figure 217, it is assumed that the server of LAN 1 
transmits the data of the key service to the server of LAN 2, and the PC of LAN 1 
transmits the data of the non-key service to PC of LAN 2. If the serial interface to 
be connected with the WAN is configured for congestion management with CQ, 
and the data flows of the key services between the servers are input to queue A, 
while the data flows of the non-key services...

686CHAPTER 49: CONGESTION MANAGEMENT
occupied by each traffic is (each priority + 1)/ the sum of each priority plus 1, that 
is, 1/15, 2/15, 3/15, 4/15 and 5/15.
For example, there are total 4 flows currently, and the priority levels of three of 
them are 4, and that of one of them is 5, and then the total number of the 
allocated bandwidth is:
(4 + 1) x 3 + (5 + 1) = 21
Then, the bandwidths of the three flows with the priority levels of 4 are 5/21, and 
the bandwidth of the flows with the priority level...