3Com 10014299 manual Comparison of Several Congestion Management Policies

682CHAPTER 49: CONGESTION MANAGEMENT

Table 719 Comparison of Several Congestion Management Policies

	Number of
	queues	Advantage	Disadvantage
FIFO	1	1. It does not need to be	1. No matter how urgent they are,
		configured and is easy to use.	all the packets, voice or data, will
		2. The processing is simple with	enter the FIFO (First In, First Out)
			queue. The bandwidth used for
		small delay.
			sending packets, delay time, drop
			rate are decided by the arrival
			sequence of the packets.
			2. It has no restriction on the
			uncoordinated data sources (such as
			the packet transmission of UDP), and
			the unmatched data sources will
			cause the damage of the
			coordinated data source bandwidth
			(such as the TCP packet
			transmission).
			3. The delay of the real time
			application sensitive to time (such as
			VolP) cannot be guaranteed.
PQ	4	The absolute priority can be	1. It needs to be configured, and the
		provided to various service data,	processing speed is slow.
		and the delay of the real time	2. If the bandwidth of the packet
		application sensitive to time
			with high priority is not restricted, it
		(such as VolP) can be
			will cause that the packet with low
		guaranteed. The bandwidth
			priority cannot obtain the
		occupation of the packet with
			bandwidth.
		the priority service may have the
		absolute priority.
CQ	1	1. The packets of various services	It needs to be configured, and the
		may be allocated with the	processing speed is slow.
		bandwidths based on the
		bandwidth proportion.
		2. When there is no packet, the
		available bandwidth occupied by
		the existing types of packets can
		be automatically increased.
WFQ	It is decided	1. It is easily configured.	The processing speed is slower than
	by users	2. The bandwidth of the	FIFO.
	(256 by	coordinated (interactive) data
	default)	source (such as the TCP packet
		transmission) can be protected.
		3. The delayed jitter can be
		reduced.
		4. The small packet has priority.
		5. The flows with various priority
		levels may be allocated with
		different bandwidths.
		6. When the traffic is reduced,
		the available bandwidth
		occupied by the existing flows
		may be automatically increased.

Operating Principle of For congestion management, queuing technology is used. When congestion

the Congestion occurs, the data packet is queued at the router by a policy. When dispatching, the Management Policies order for sending the data packet is decided by the policy.