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	stand-
       ing/persistent  queue delay. This minimum delay is identified by track-
       ing 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  end-
       points 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)