net/dccp/ccids/Kconfig

menu "DCCP CCIDs Configuration (EXPERIMENTAL)"

config IP_DCCP_CCID2
	tristate "CCID2 (TCP-Like)"
	def_tristate IP_DCCP
	---help---
	  CCID 2, TCP-like Congestion Control, denotes Additive Increase,
	  Multiplicative Decrease (AIMD) congestion control with behavior
	  modelled directly on TCP, including congestion window, slow start,
	  timeouts, and so forth [RFC 2581].  CCID 2 achieves maximum
	  bandwidth over the long term, consistent with the use of end-to-end
	  congestion control, but halves its congestion window in response to
	  each congestion event.  This leads to the abrupt rate changes
	  typical of TCP.  Applications should use CCID 2 if they prefer
	  maximum bandwidth utilization to steadiness of rate.  This is often
	  the case for applications that are not playing their data directly
	  to the user.  For example, a hypothetical application that
	  transferred files over DCCP, using application-level retransmissions
	  for lost packets, would prefer CCID 2 to CCID 3.  On-line games may
	  also prefer CCID 2.  See RFC 4341 for further details.

	  CCID2 is the default CCID used by DCCP.

config IP_DCCP_CCID2_DEBUG
	  bool "CCID2 debugging messages"
	  depends on IP_DCCP_CCID2
	  ---help---
	    Enable CCID2-specific debugging messages.

	    When compiling CCID2 as a module, this debugging output can
	    additionally be toggled by setting the ccid2_debug module
	    parameter to 0 or 1.

	    If in doubt, say N.

config IP_DCCP_CCID3
	tristate "CCID3 (TCP-Friendly)"
	def_tristate IP_DCCP
	select IP_DCCP_TFRC_LIB
	---help---
	  CCID 3 denotes TCP-Friendly Rate Control (TFRC), an equation-based
	  rate-controlled congestion control mechanism.  TFRC is designed to
	  be reasonably fair when competing for bandwidth with TCP-like flows,
	  where a flow is "reasonably fair" if its sending rate is generally
	  within a factor of two of the sending rate of a TCP flow under the
	  same conditions.  However, TFRC has a much lower variation of
	  throughput over time compared with TCP, which makes CCID 3 more
	  suitable than CCID 2 for applications such streaming media where a
	  relatively smooth sending rate is of importance.

	  CCID 3 is further described in RFC 4342,
	  http://www.ietf.org/rfc/rfc4342.txt

	  The TFRC congestion control algorithms were initially described in
	  RFC 3448.

	  This text was extracted from RFC 4340 (sec. 10.2),
	  http://www.ietf.org/rfc/rfc4340.txt
	  
	  To compile this CCID as a module, choose M here: the module will be
	  called dccp_ccid3.

	  If in doubt, say M.

if IP_DCCP_CCID3
config IP_DCCP_CCID3_DEBUG
	  bool "CCID3 debugging messages"
	  ---help---
	    Enable CCID3-specific debugging messages.

	    When compiling CCID3 as a module, this debugging output can
	    additionally be toggled by setting the ccid3_debug module
	    parameter to 0 or 1.

	    If in doubt, say N.

choice
	  prompt "Select method for measuring the packet size s"
	  default IP_DCCP_CCID3_MEASURE_S_AS_MPS

config IP_DCCP_CCID3_MEASURE_S_AS_MPS
	  bool "Always use MPS in place of s"
	  ---help---
	    This use is recommended as it is consistent with the initialisation
	    of X and suggested when s varies (rfc3448bis, (1) in section 4.1).
config IP_DCCP_CCID3_MEASURE_S_AS_AVG
	  bool "Use moving average"
	  ---help---
	    An alternative way of tracking s, also supported by rfc3448bis.
	    This used to be the default for CCID-3 in previous kernels.
config IP_DCCP_CCID3_MEASURE_S_AS_MAX
	  bool "Track the maximum payload length"
	  ---help---
	    An experimental method based on tracking the maximum packet size.
endchoice

config IP_DCCP_CCID3_RTO
	  int "Use higher bound for nofeedback timer"
	  default 100
	  ---help---
	    Use higher lower bound for nofeedback timer expiration.

	    The TFRC nofeedback timer normally expires after the maximum of 4
	    RTTs and twice the current send interval (RFC 3448, 4.3). On LANs
	    with a small RTT this can mean a high processing load and reduced
	    performance, since then the nofeedback timer is triggered very
	    frequently.

	    This option enables to set a higher lower bound for the nofeedback
	    value. Values in units of milliseconds can be set here.

	    A value of 0 disables this feature by enforcing the value specified
	    in RFC 3448. The following values have been suggested as bounds for
	    experimental use:
	    	* 16-20ms to match the typical multimedia inter-frame interval
	    	* 100ms as a reasonable compromise [default]
	    	* 1000ms corresponds to the lower TCP RTO bound (RFC 2988, 2.4)

	    The default of 100ms is a compromise between a large value for
	    efficient DCCP implementations, and a small value to avoid disrupting
	    the network in times of congestion.

	    The purpose of the nofeedback timer is to slow DCCP down when there
	    is serious network congestion: experimenting with larger values should
	    therefore not be performed on WANs.
endif	# IP_DCCP_CCID3

config IP_DCCP_TFRC_LIB
	tristate
	default n

config IP_DCCP_TFRC_DEBUG
	bool
	depends on IP_DCCP_TFRC_LIB
	default y if IP_DCCP_CCID3_DEBUG

endmenu