e333b3edc4
This patch addresses the following problems:
1. DCCP relies for its proper functioning on having at least one CCID module
enabled (as in TCP plugable congestion control). Currently it is possible to
disable both CCIDs and thus leave the DCCP module in a compiled, but entirely
non-functional state: no sockets can be created when no CCID is available.
Furthermore, the protocol is (again like TCP) not intended to be used without
CCIDs. Last, a non-empty CCID list is needed for doing CCID feature negotiation.
2. Internally the default CCID that is advertised by the Linux host is set to CCID2
(DCCPF_INITIAL_CCID in include/linux/dccp.h). Disabling CCID2 in the Kconfig
menu without changing the defaults leads to a failure `module not found' when
trying to load the dccp module (which internally tries to load the default CCID).
3. The specification (RFC 4340, sec. 10) treats CCID2 somewhat like a
`minimum common denominator'; the specification says that:
* "New connections start with CCID 2 for both endpoints"
* "A DCCP implementation intended for general use, such as an implementation in a
general-purpose operating system kernel, SHOULD implement at least CCID 2.
The intent is to make CCID 2 broadly available for interoperability [...]"
Providing CCID2 as minimum-required CCID (like Reno/Cubic in TCP) thus seems reasonable.
Hence this patch automatically selects CCID2 when DCCP is enabled. Documentation also added.
Discussions with Ian McDonald on this subject are gratefully acknowledged.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
116 lines
4.4 KiB
Text
116 lines
4.4 KiB
Text
menu "DCCP CCIDs Configuration (EXPERIMENTAL)"
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depends on IP_DCCP && EXPERIMENTAL
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config IP_DCCP_CCID2
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tristate "CCID2 (TCP-Like) (EXPERIMENTAL)"
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depends on IP_DCCP
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def_tristate IP_DCCP
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select IP_DCCP_ACKVEC
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---help---
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CCID 2, TCP-like Congestion Control, denotes Additive Increase,
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Multiplicative Decrease (AIMD) congestion control with behavior
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modelled directly on TCP, including congestion window, slow start,
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timeouts, and so forth [RFC 2581]. CCID 2 achieves maximum
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bandwidth over the long term, consistent with the use of end-to-end
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congestion control, but halves its congestion window in response to
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each congestion event. This leads to the abrupt rate changes
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typical of TCP. Applications should use CCID 2 if they prefer
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maximum bandwidth utilization to steadiness of rate. This is often
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the case for applications that are not playing their data directly
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to the user. For example, a hypothetical application that
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transferred files over DCCP, using application-level retransmissions
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for lost packets, would prefer CCID 2 to CCID 3. On-line games may
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also prefer CCID 2. See RFC 4341 for further details.
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CCID2 is the default CCID used by DCCP.
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config IP_DCCP_CCID2_DEBUG
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bool "CCID2 debugging messages"
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depends on IP_DCCP_CCID2
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---help---
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Enable CCID2-specific debugging messages.
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When compiling CCID2 as a module, this debugging output can
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additionally be toggled by setting the ccid2_debug module
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parameter to 0 or 1.
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If in doubt, say N.
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config IP_DCCP_CCID3
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tristate "CCID3 (TCP-Friendly) (EXPERIMENTAL)"
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depends on IP_DCCP
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def_tristate IP_DCCP
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---help---
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CCID 3 denotes TCP-Friendly Rate Control (TFRC), an equation-based
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rate-controlled congestion control mechanism. TFRC is designed to
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be reasonably fair when competing for bandwidth with TCP-like flows,
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where a flow is "reasonably fair" if its sending rate is generally
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within a factor of two of the sending rate of a TCP flow under the
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same conditions. However, TFRC has a much lower variation of
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throughput over time compared with TCP, which makes CCID 3 more
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suitable than CCID 2 for applications such streaming media where a
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relatively smooth sending rate is of importance.
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CCID 3 is further described in RFC 4342,
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http://www.ietf.org/rfc/rfc4342.txt
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The TFRC congestion control algorithms were initially described in
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RFC 3448.
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This text was extracted from RFC 4340 (sec. 10.2),
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http://www.ietf.org/rfc/rfc4340.txt
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To compile this CCID as a module, choose M here: the module will be
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called dccp_ccid3.
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If in doubt, say M.
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config IP_DCCP_TFRC_LIB
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depends on IP_DCCP_CCID3
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def_tristate IP_DCCP_CCID3
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config IP_DCCP_CCID3_DEBUG
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bool "CCID3 debugging messages"
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depends on IP_DCCP_CCID3
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---help---
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Enable CCID3-specific debugging messages.
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When compiling CCID3 as a module, this debugging output can
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additionally be toggled by setting the ccid3_debug module
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parameter to 0 or 1.
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If in doubt, say N.
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config IP_DCCP_CCID3_RTO
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int "Use higher bound for nofeedback timer"
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default 100
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depends on IP_DCCP_CCID3 && EXPERIMENTAL
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---help---
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Use higher lower bound for nofeedback timer expiration.
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The TFRC nofeedback timer normally expires after the maximum of 4
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RTTs and twice the current send interval (RFC 3448, 4.3). On LANs
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with a small RTT this can mean a high processing load and reduced
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performance, since then the nofeedback timer is triggered very
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frequently.
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This option enables to set a higher lower bound for the nofeedback
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value. Values in units of milliseconds can be set here.
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A value of 0 disables this feature by enforcing the value specified
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in RFC 3448. The following values have been suggested as bounds for
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experimental use:
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* 16-20ms to match the typical multimedia inter-frame interval
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* 100ms as a reasonable compromise [default]
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* 1000ms corresponds to the lower TCP RTO bound (RFC 2988, 2.4)
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The default of 100ms is a compromise between a large value for
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efficient DCCP implementations, and a small value to avoid disrupting
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the network in times of congestion.
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The purpose of the nofeedback timer is to slow DCCP down when there
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is serious network congestion: experimenting with larger values should
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therefore not be performed on WANs.
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endmenu
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