FQ_CoDel(8)							       Linux							       FQ_CoDel(8)

NAME

       CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel)

SYNOPSIS

       tc qdisc ... fq_codel [ limit PACKETS ] [ flows NUMBER ] [ target TIME ] [ interval TIME ] [ quantum BYTES ] [ ecn | noecn ]

DESCRIPTION

       FQ_Codel  (Fair	Queuing Controlled Delay) is queuing discipline that combines Fair Queuing with the CoDel AQM scheme. FQ_Codel uses a sto-
       chastic model to classify incoming packets into different flows and is used to provide a fair share of the bandwidth to all the flows using
       the  queue.  Each  such	flow is managed by the CoDel queuing discipline. Reordering within a flow is avoided since Codel internally uses a
       FIFO queue.

PARAMETERS

   limit
       has the same semantics as codel and is the hard limit on the real queue size.  When this limit is reached, incoming  packets  are  dropped.
       Default is 10240 packets.

   flows
       is  the	number of flows into which the incoming packets are classified. Due to the stochastic nature of hashing, multiple flows may end up
       being hashed into the same slot. Newer flows have priority over older ones. This parameter can be set only at load time since memory has to
       be allocated for the hash table.  Default value is 1024.

   target
       has the same semantics as codel and is the acceptable minimum standing/persistent queue delay. This minimum delay is identified by tracking
       the local minimum queue delay that packets experience. Default value is 5ms.

   interval
       has the same semantics as codel and is used to ensure that the measured minimum delay does not become too stale.  The minimum delay must be
       experienced  in	the  last epoch of length .B interval.	It should be set on the order of the worst-case RTT through the bottleneck to give
       endpoints sufficient time to react. Default value is 100ms.

   quantum
       is the number of bytes used as 'deficit' in the fair queuing algorithm. Default is set to 1514 bytes which corresponds to the Ethernet  MTU
       plus the hardware header length of 14 bytes.

   ecn | noecn
       has  the  same  semantics  as codel and can be used to mark packets instead of dropping them. If ecn has been enabled, noecn can be used to
       turn it off and vice-a-versa. Unlike codel, ecn is turned on by default.

EXAMPLES

       #tc qdisc add   dev eth0 root fq_codel
       #tc -s qdisc show
       qdisc fq_codel 8002: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514
	target 5.0ms interval 100.0ms ecn
	  Sent 428514 bytes 2269 pkt (dropped 0, overlimits 0 requeues 0)
	  backlog 0b 0p requeues 0
	   maxpacket 256 drop_overlimit 0 new_flow_count 0 ecn_mark 0
	   new_flows_len 0 old_flows_len 0

       #tc qdisc add dev eth0 root fq_codel limit 2000 target 3ms interval 40ms noecn
       #tc -s qdisc show
       qdisc fq_codel 8003: dev eth0 root refcnt 2 limit 2000p flows 1024 quantum 1514 target 3.0ms interval 40.0ms
	Sent 2588985006 bytes 1783629 pkt (dropped 0, overlimits 0 requeues 34869)
	backlog 0b 0p requeues 34869
	 maxpacket 65226 drop_overlimit 0 new_flow_count 73 ecn_mark 0
	 new_flows_len 1 old_flows_len 3

SEE ALSO

       tc(8), tc-codel(8), tc-red(8)

AUTHORS

       FQ_CoDel was implemented by Eric Dumazet. This manpage was written by Vijay Subramanian. Please report corrections to the Linux	Networking
       mailing list <netdev@vger.kernel.org>.

iproute2							    4 June 2012 						       FQ_CoDel(8)