tcp pacing && bbr

本文探讨了BBR拥塞控制算法的工作原理及其在网络中的应用。对比了BBR与传统CUBIC算法在不同网络条件下的表现,指出BBR通过控制发送速率有效降低了网络延迟。
作者:tsetao
链接:https://www.zhihu.com/question/53559433/answer/136002384
来源:知乎
著作权归作者所有。商业转载请联系作者获得授权,非商业转载请注明出处。

在探讨这个问题之前,关于网络中的Bufferbloat问题需要了解,详细信息在这里(https://www.bufferbloat.net/projects/bloat/wiki/Introduction/),

的回答也说得比较清楚了。

在这里做一些补充吧。
流量控制分为两部分:
* 接收方的流量控制(即滑动窗口)-- 由接收方告知,只关注自身缓存情况,不关注网络,这里不讨论。
* 发送方的流量控制(即拥塞控制)
现在广泛使用的CUBIC/(new)Reno都是基于丢包的,在算法上重点输出拥塞窗口(cwnd);
而BBR输出cwndpacing_rate,且pacing_rate为主,cwnd为辅,参考(groups.google.com/d/msg)

什么是pacing?看下图:

<img src="https://pic3.zhimg.com/50/v2-033f904724e92977e6f6e13942e3981f_hd.jpg" data-rawwidth="981" data-rawheight="573" class="origin_image zh-lightbox-thumb" width="981" data-original="https://pic3.zhimg.com/v2-033f904724e92977e6f6e13942e3981f_r.jpg"> 图片引用来自 QUIC @ Google Developers Live, February 2014
也就是说早期的拥塞控制输出cwnd只是告诉tcp可以发多少数据,而没有说怎么发,恰好, BBR输出的pacing_rate就是告诉TCP怎么发


BBR对TCP的大胆改动:


<img src="https://pic2.zhimg.com/50/v2-b742e172ed1ae802bab8e0903f47f98c_hd.jpg" data-rawwidth="563" data-rawheight="328" class="origin_image zh-lightbox-thumb" width="563" data-original="https://pic2.zhimg.com/v2-b742e172ed1ae802bab8e0903f47f98c_r.jpg"> 红框中是BBR加入时添加的,这里很明显,BBR从TCP接管了充分的控制权。
之前的拥塞控制并不总是能起作用,换句话说就是会被夺权。TCP走进PRR算法( 参考论文:Proportional Rate Reduction for TCP)后,拥塞控制无能为力。
从工程实现的角度来看,BBR这个小小的修改把TCP的 可靠传输 / 拥塞控制 解耦了 —— TCP你专注于自己的可靠性(当然还有很多其它细节),我BBR总是会负责任地告诉你(TCP)现在可以发多少数据,以什么速度发出这些数据。

丢包对BBR有什么影响?
<img src="https://pic4.zhimg.com/50/v2-2fe40d036eae2f25045242ce9e6f8f86_hd.jpg" data-rawwidth="928" data-rawheight="481" class="origin_image zh-lightbox-thumb" width="928" data-original="https://pic4.zhimg.com/v2-2fe40d036eae2f25045242ce9e6f8f86_r.jpg">
图片来自 BBR-TCP-Opportunities
从算法上来讲,丢包对BBR的影响微乎其微。BBR只管告诉TCP cwnd/pacing_rate, 不管需要发送的包是重传的还是正常发送的。看上图,丢包率在20%的时候BBR的输出骤降,导致这个现象其实是从实现层面考虑设置的一个 阈值
/* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */
static const u32 bbr_lt_loss_thresh = 50;

这里还考虑了被限速的场景,不展开。

友好性测试
提到的友好性问题,google groups里有测试数据
groups.google.com/d/msg
----------------
10 Mbps link with 40ms RTT
带宽,RTT固定的情况下,测试不同Buffer大小的情况:
buf以n倍BDP表示,CUBIC/Vegas/BBR输出单位Mbps
(1) 1 CUBIC flow vs. 1 Vegas flow:
buf  CUBIC  Vegas
---- -----  -----
0.5   6.81   2.73
1     8.49   1.06
2     9.12   0.43
4     9.15   0.4

(2) 1 CUBIC flow vs. 1 BBR flow:
buf  CUBIC  BBR
---- -----  -----
0.5   1.74   7.67
1     1.71   7.7
2     4.79   4.72
4     6.12   3.43

说明:
Vegas是基于延迟的拥塞控制,现在几乎不用了,因为它们跟基于丢包的拥塞控制发生竞争时会处于几乎饿死的状态。
另外,关于Ledbat(基于延迟的)用于BT,是理所应当的(挂BT下载的急迫性一般是低于常规网络流量的,当有常规流量介入时,主动退避是符合常理的)。

v------------2016.12.20更新--------------v
bbr-dev邮件组中一组测试数据(

的回答中也提供了)引起了大家的关注。
最开始,Leo Zhang的回答所提到的测试报告我并未详细阅读。今天抽时间详细看了一下,感到意外。
比如出现BBR饿死CUBIC,BBR饿死同类。这和其它测试数据出入很大。

我第一反应就是环境不对,BBR挑环境。然而这方面却没找到说明,BBR相关的文档都没有提到专用场景。

接着,

抛出了另一个问题( 如何评价文章《令人躁动一时且令人不安的TCP BBR算法》?)。看过文章(该作者之前的文章也看了),写了简答,才发现自己似乎错过了什么,同时自己其实也对20%的丢包率阈值设置有疑问,偷懒的理解就是大量测试统计的结果吧。

这些天bbr-dev中关于BBR Report( groups.google.com/forum)这份精彩的邮件列表我错过了,赶紧补一下!
Neal Cardwell 说到:
We are actively working on reducing the buffer pressure exerted by BBR, which should help in the sorts of CUBIC vs BBR scenarios you describe (as well as BBR vs BBR scenarios).

这份刚刚诞生的拥塞控制的确还是存在不少缺陷,不过依然在持续改进中,期待美好的事情总会发生吧!
^-------------2016.12.20更新-------------^

根据

的回答中已经提到的实测延迟改善数据,我们可以看到目前互联网整体上Bufferbloat问题是比较严重的,即我们的网络请求延迟总体被拉高很多。
为了降低延迟,如果:
1、我们改用基于延迟的拥塞控制,因为不可能一时间全部更新,先替换的那部分网络体验会很糟糕;
2、逐步改用BBR这类拥塞控制,我们的网络高延迟问题将会逐渐得到改善。

以上并非说一定是BBR,但是BBR在拥塞控制上开辟了一条新的路(也许早就有人做过类似的尝试,但是因为工程实现,或者测试环境受限不能得到广泛验证,石沉大海),相信以后关于拥塞控制的研究改进更多会基于这条路去走。

最后,BBR是基于什么的拥塞控制?
根据论文,是基于拥塞的拥塞控制(Congestion-based Congestion Control),但是看起来感觉不好理解。
根据我的理解,我更倾向于称它为 基于带宽延迟的拥塞控制(BDP-based Congestion Control)。
因为,BBR总是在测量最小RTT(10s内),最大Bandwidth(10 Round Trips),并且尽量控制输出到网络的数据包(in-flight)靠近 BDP(without buffer),这样既能保证带宽利用率,又能避免Bufferbloat问题。

PS. BBR也已经被实现在QUIC协议中,参考(cs.chromium.org/chromiu)。

我也并非完全理解了BBR的实现细节,并且其中还牵扯到TCP的实现,也不熟悉。
如果以上理解有错,或者不到位,欢迎指正。

完。

---
XTao
Kconfig如下 开启哪些可以配置tcp_delack_min # # IP configuration # config IP_MULTICAST bool "IP: multicasting" help This is code for addressing several networked computers at once, enlarging your kernel by about 2 KB. You need multicasting if you intend to participate in the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. More information about the MBONE is on the WWW at <http://www.savetz.com/mbone/>. For most people, it's safe to say N. config IP_ADVANCED_ROUTER bool "IP: advanced router" ---help--- If you intend to run your Linux box mostly as a router, i.e. as a computer that forwards and redistributes network packets, say Y; you will then be presented with several options that allow more precise control about the routing process. The answer to this question won't directly affect the kernel: answering N will just cause the configurator to skip all the questions about advanced routing. Note that your box can only act as a router if you enable IP forwarding in your kernel; you can do that by saying Y to "/proc file system support" and "Sysctl support" below and executing the line echo "1" > /proc/sys/net/ipv4/ip_forward at boot time after the /proc file system has been mounted. If you turn on IP forwarding, you should consider the rp_filter, which automatically rejects incoming packets if the routing table entry for their source address doesn't match the network interface they're arriving on. This has security advantages because it prevents the so-called IP spoofing, however it can pose problems if you use asymmetric routing (packets from you to a host take a different path than packets from that host to you) or if you operate a non-routing host which has several IP addresses on different interfaces. To turn rp_filter on use: echo 1 > /proc/sys/net/ipv4/conf/<device>/rp_filter or echo 1 > /proc/sys/net/ipv4/conf/all/rp_filter Note that some distributions enable it in startup scripts. For details about rp_filter strict and loose mode read <file:Documentation/networking/ip-sysctl.txt>. If unsure, say N here. config IP_FIB_TRIE_STATS bool "FIB TRIE statistics" depends on IP_ADVANCED_ROUTER ---help--- Keep track of statistics on structure of FIB TRIE table. Useful for testing and measuring TRIE performance. config IP_MULTIPLE_TABLES bool "IP: policy routing" depends on IP_ADVANCED_ROUTER select FIB_RULES ---help--- Normally, a router decides what to do with a received packet based solely on the packet's final destination address. If you say Y here, the Linux router will also be able to take the packet's source address into account. Furthermore, the TOS (Type-Of-Service) field of the packet can be used for routing decisions as well. If you need more information, see the Linux Advanced Routing and Traffic Control documentation at <http://lartc.org/howto/lartc.rpdb.html> If unsure, say N. config IP_ROUTE_MULTIPATH bool "IP: equal cost multipath" depends on IP_ADVANCED_ROUTER help Normally, the routing tables specify a single action to be taken in a deterministic manner for a given packet. If you say Y here however, it becomes possible to attach several actions to a packet pattern, in effect specifying several alternative paths to travel for those packets. The router considers all these paths to be of equal "cost" and chooses one of them in a non-deterministic fashion if a matching packet arrives. config IP_ROUTE_VERBOSE bool "IP: verbose route monitoring" depends on IP_ADVANCED_ROUTER help If you say Y here, which is recommended, then the kernel will print verbose messages regarding the routing, for example warnings about received packets which look strange and could be evidence of an attack or a misconfigured system somewhere. The information is handled by the klogd daemon which is responsible for kernel messages ("man klogd"). config IP_ROUTE_CLASSID bool config IP_PNP bool "IP: kernel level autoconfiguration" help This enables automatic configuration of IP addresses of devices and of the routing table during kernel boot, based on either information supplied on the kernel command line or by BOOTP or RARP protocols. You need to say Y only for diskless machines requiring network access to boot (in which case you want to say Y to "Root file system on NFS" as well), because all other machines configure the network in their startup scripts. config IP_PNP_DHCP bool "IP: DHCP support" depends on IP_PNP ---help--- If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the DHCP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does DHCP itself, providing all necessary information on the kernel command line, you can say N here. If unsure, say Y. Note that if you want to use DHCP, a DHCP server must be operating on your network. Read <file:Documentation/filesystems/nfs/nfsroot.txt> for details. config IP_PNP_BOOTP bool "IP: BOOTP support" depends on IP_PNP ---help--- If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the BOOTP protocol (a special protocol designed for doing this job), say Y here. In case the boot ROM of your network card was designed for booting Linux and does BOOTP itself, providing all necessary information on the kernel command line, you can say N here. If unsure, say Y. Note that if you want to use BOOTP, a BOOTP server must be operating on your network. Read <file:Documentation/filesystems/nfs/nfsroot.txt> for details. config IP_PNP_RARP bool "IP: RARP support" depends on IP_PNP help If you want your Linux box to mount its whole root file system (the one containing the directory /) from some other computer over the net via NFS and you want the IP address of your computer to be discovered automatically at boot time using the RARP protocol (an older protocol which is being obsoleted by BOOTP and DHCP), say Y here. Note that if you want to use RARP, a RARP server must be operating on your network. Read <file:Documentation/filesystems/nfs/nfsroot.txt> for details. config NET_IPIP tristate "IP: tunneling" select INET_TUNNEL select NET_IP_TUNNEL ---help--- Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This particular tunneling driver implements encapsulation of IP within IP, which sounds kind of pointless, but can be useful if you want to make your (or some other) machine appear on a different network than it physically is, or to use mobile-IP facilities (allowing laptops to seamlessly move between networks without changing their IP addresses). Saying Y to this option will produce two modules ( = code which can be inserted in and removed from the running kernel whenever you want). Most people won't need this and can say N. config NET_IPGRE_DEMUX tristate "IP: GRE demultiplexer" help This is helper module to demultiplex GRE packets on GRE version field criteria. Required by ip_gre and pptp modules. config NET_IP_TUNNEL tristate select DST_CACHE select GRO_CELLS default n config NET_IPGRE tristate "IP: GRE tunnels over IP" depends on (IPV6 || IPV6=n) && NET_IPGRE_DEMUX select NET_IP_TUNNEL help Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This particular tunneling driver implements GRE (Generic Routing Encapsulation) and at this time allows encapsulating of IPv4 or IPv6 over existing IPv4 infrastructure. This driver is useful if the other endpoint is a Cisco router: Cisco likes GRE much better than the other Linux tunneling driver ("IP tunneling" above). In addition, GRE allows multicast redistribution through the tunnel. config NET_IPGRE_BROADCAST bool "IP: broadcast GRE over IP" depends on IP_MULTICAST && NET_IPGRE help One application of GRE/IP is to construct a broadcast WAN (Wide Area Network), which looks like a normal Ethernet LAN (Local Area Network), but can be distributed all over the Internet. If you want to do that, say Y here and to "IP multicast routing" below. config IP_MROUTE_COMMON bool depends on IP_MROUTE || IPV6_MROUTE config IP_MROUTE bool "IP: multicast routing" depends on IP_MULTICAST select IP_MROUTE_COMMON help This is used if you want your machine to act as a router for IP packets that have several destination addresses. It is needed on the MBONE, a high bandwidth network on top of the Internet which carries audio and video broadcasts. In order to do that, you would most likely run the program mrouted. If you haven't heard about it, you don't need it. config IP_MROUTE_MULTIPLE_TABLES bool "IP: multicast policy routing" depends on IP_MROUTE && IP_ADVANCED_ROUTER select FIB_RULES help Normally, a multicast router runs a userspace daemon and decides what to do with a multicast packet based on the source and destination addresses. If you say Y here, the multicast router will also be able to take interfaces and packet marks into account and run multiple instances of userspace daemons simultaneously, each one handling a single table. If unsure, say N. config IP_PIMSM_V1 bool "IP: PIM-SM version 1 support" depends on IP_MROUTE help Kernel side support for Sparse Mode PIM (Protocol Independent Multicast) version 1. This multicast routing protocol is used widely because Cisco supports it. You need special software to use it (pimd-v1). Please see <http://netweb.usc.edu/pim/> for more information about PIM. Say Y if you want to use PIM-SM v1. Note that you can say N here if you just want to use Dense Mode PIM. config IP_PIMSM_V2 bool "IP: PIM-SM version 2 support" depends on IP_MROUTE help Kernel side support for Sparse Mode PIM version 2. In order to use this, you need an experimental routing daemon supporting it (pimd or gated-5). This routing protocol is not used widely, so say N unless you want to play with it. config SYN_COOKIES bool "IP: TCP syncookie support" ---help--- Normal TCP/IP networking is open to an attack known as "SYN flooding". This denial-of-service attack prevents legitimate remote users from being able to connect to your computer during an ongoing attack and requires very little work from the attacker, who can operate from anywhere on the Internet. SYN cookies provide protection against this type of attack. If you say Y here, the TCP/IP stack will use a cryptographic challenge protocol known as "SYN cookies" to enable legitimate users to continue to connect, even when your machine is under attack. There is no need for the legitimate users to change their TCP/IP software; SYN cookies work transparently to them. For technical information about SYN cookies, check out <http://cr.yp.to/syncookies.html>. If you are SYN flooded, the source address reported by the kernel is likely to have been forged by the attacker; it is only reported as an aid in tracing the packets to their actual source and should not be taken as absolute truth. SYN cookies may prevent correct error reporting on clients when the server is really overloaded. If this happens frequently better turn them off. If you say Y here, you can disable SYN cookies at run time by saying Y to "/proc file system support" and "Sysctl support" below and executing the command echo 0 > /proc/sys/net/ipv4/tcp_syncookies after the /proc file system has been mounted. If unsure, say N. config NET_IPVTI tristate "Virtual (secure) IP: tunneling" depends on IPV6 || IPV6=n select INET_TUNNEL select NET_IP_TUNNEL depends on INET_XFRM_MODE_TUNNEL ---help--- Tunneling means encapsulating data of one protocol type within another protocol and sending it over a channel that understands the encapsulating protocol. This can be used with xfrm mode tunnel to give the notion of a secure tunnel for IPSEC and then use routing protocol on top. config NET_UDP_TUNNEL tristate select NET_IP_TUNNEL default n config NET_FOU tristate "IP: Foo (IP protocols) over UDP" select XFRM select NET_UDP_TUNNEL ---help--- Foo over UDP allows any IP protocol to be directly encapsulated over UDP include tunnels (IPIP, GRE, SIT). By encapsulating in UDP network mechanisms and optimizations for UDP (such as ECMP and RSS) can be leveraged to provide better service. config NET_FOU_IP_TUNNELS bool "IP: FOU encapsulation of IP tunnels" depends on NET_IPIP || NET_IPGRE || IPV6_SIT select NET_FOU ---help--- Allow configuration of FOU or GUE encapsulation for IP tunnels. When this option is enabled IP tunnels can be configured to use FOU or GUE encapsulation. config INET_AH tristate "IP: AH transformation" select XFRM_ALGO select CRYPTO select CRYPTO_HMAC select CRYPTO_MD5 select CRYPTO_SHA1 ---help--- Support for IPsec AH. If unsure, say Y. config INET_ESP tristate "IP: ESP transformation" select XFRM_ALGO select CRYPTO select CRYPTO_AUTHENC select CRYPTO_HMAC select CRYPTO_MD5 select CRYPTO_CBC select CRYPTO_SHA1 select CRYPTO_DES select CRYPTO_ECHAINIV ---help--- Support for IPsec ESP. If unsure, say Y. config INET_ESP_OFFLOAD tristate "IP: ESP transformation offload" depends on INET_ESP select XFRM_OFFLOAD default n ---help--- Support for ESP transformation offload. This makes sense only if this system really does IPsec and want to do it with high throughput. A typical desktop system does not need it, even if it does IPsec. If unsure, say N. config INET_IPCOMP tristate "IP: IPComp transformation" select INET_XFRM_TUNNEL select XFRM_IPCOMP ---help--- Support for IP Payload Compression Protocol (IPComp) (RFC3173), typically needed for IPsec. If unsure, say Y. config INET_TABLE_PERTURB_ORDER int "INET: Source port perturbation table size (as power of 2)" if EXPERT default 16 help Source port perturbation table size (as power of 2) for RFC 6056 3.3.4. Algorithm 4: Double-Hash Port Selection Algorithm. The default is almost always what you want. Only change this if you know what you are doing. config INET_XFRM_TUNNEL tristate select INET_TUNNEL default n config INET_TUNNEL tristate default n config INET_XFRM_MODE_TRANSPORT tristate "IP: IPsec transport mode" default y select XFRM ---help--- Support for IPsec transport mode. If unsure, say Y. config INET_XFRM_MODE_TUNNEL tristate "IP: IPsec tunnel mode" default y select XFRM ---help--- Support for IPsec tunnel mode. If unsure, say Y. config INET_XFRM_MODE_BEET tristate "IP: IPsec BEET mode" default y select XFRM ---help--- Support for IPsec BEET mode. If unsure, say Y. config INET_DIAG tristate "INET: socket monitoring interface" default y ---help--- Support for INET (TCP, DCCP, etc) socket monitoring interface used by native Linux tools such as ss. ss is included in iproute2, currently downloadable at: http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2 If unsure, say Y. config INET_TCP_DIAG depends on INET_DIAG def_tristate INET_DIAG config INET_UDP_DIAG tristate "UDP: socket monitoring interface" depends on INET_DIAG && (IPV6 || IPV6=n) default n ---help--- Support for UDP socket monitoring interface used by the ss tool. If unsure, say Y. config INET_RAW_DIAG tristate "RAW: socket monitoring interface" depends on INET_DIAG && (IPV6 || IPV6=n) default n ---help--- Support for RAW socket monitoring interface used by the ss tool. If unsure, say Y. config INET_DIAG_DESTROY bool "INET: allow privileged process to administratively close sockets" depends on INET_DIAG default n ---help--- Provides a SOCK_DESTROY operation that allows privileged processes (e.g., a connection manager or a network administration tool such as ss) to close sockets opened by other processes. Closing a socket in this way interrupts any blocking read/write/connect operations on the socket and causes future socket calls to behave as if the socket had been disconnected. If unsure, say N. menuconfig TCP_CONG_ADVANCED bool "TCP: advanced congestion control" ---help--- Support for selection of various TCP congestion control modules. Nearly all users can safely say no here, and a safe default selection will be made (CUBIC with new Reno as a fallback). If unsure, say N. if TCP_CONG_ADVANCED config TCP_CONG_BIC tristate "Binary Increase Congestion (BIC) control" default m ---help--- BIC-TCP is a sender-side only change that ensures a linear RTT fairness under large windows while offering both scalability and bounded TCP-friendliness. The protocol combines two schemes called additive increase and binary search increase. When the congestion window is large, additive increase with a large increment ensures linear RTT fairness as well as good scalability. Under small congestion windows, binary search increase provides TCP friendliness. See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/ config TCP_CONG_CUBIC tristate "CUBIC TCP" default y ---help--- This is version 2.0 of BIC-TCP which uses a cubic growth function among other techniques. See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf config TCP_CONG_WESTWOOD tristate "TCP Westwood+" default m ---help--- TCP Westwood+ is a sender-side only modification of the TCP Reno protocol stack that optimizes the performance of TCP congestion control. It is based on end-to-end bandwidth estimation to set congestion window and slow start threshold after a congestion episode. Using this estimation, TCP Westwood+ adaptively sets a slow start threshold and a congestion window which takes into account the bandwidth used at the time congestion is experienced. TCP Westwood+ significantly increases fairness wrt TCP Reno in wired networks and throughput over wireless links. config TCP_CONG_HTCP tristate "H-TCP" default m ---help--- H-TCP is a send-side only modifications of the TCP Reno protocol stack that optimizes the performance of TCP congestion control for high speed network links. It uses a modeswitch to change the alpha and beta parameters of TCP Reno based on network conditions and in a way so as to be fair with other Reno and H-TCP flows. config TCP_CONG_HSTCP tristate "High Speed TCP" default n ---help--- Sally Floyd's High Speed TCP (RFC 3649) congestion control. A modification to TCP's congestion control mechanism for use with large congestion windows. A table indicates how much to increase the congestion window by when an ACK is received. For more detail see http://www.icir.org/floyd/hstcp.html config TCP_CONG_HYBLA tristate "TCP-Hybla congestion control algorithm" default n ---help--- TCP-Hybla is a sender-side only change that eliminates penalization of long-RTT, large-bandwidth connections, like when satellite legs are involved, especially when sharing a common bottleneck with normal terrestrial connections. config TCP_CONG_VEGAS tristate "TCP Vegas" default n ---help--- TCP Vegas is a sender-side only change to TCP that anticipates the onset of congestion by estimating the bandwidth. TCP Vegas adjusts the sending rate by modifying the congestion window. TCP Vegas should provide less packet loss, but it is not as aggressive as TCP Reno. config TCP_CONG_NV tristate "TCP NV" default n ---help--- TCP NV is a follow up to TCP Vegas. It has been modified to deal with 10G networks, measurement noise introduced by LRO, GRO and interrupt coalescence. In addition, it will decrease its cwnd multiplicatively instead of linearly. Note that in general congestion avoidance (cwnd decreased when # packets queued grows) cannot coexist with congestion control (cwnd decreased only when there is packet loss) due to fairness issues. One scenario when they can coexist safely is when the CA flows have RTTs << CC flows RTTs. For further details see http://www.brakmo.org/networking/tcp-nv/ config TCP_CONG_SCALABLE tristate "Scalable TCP" default n ---help--- Scalable TCP is a sender-side only change to TCP which uses a MIMD congestion control algorithm which has some nice scaling properties, though is known to have fairness issues. See http://www.deneholme.net/tom/scalable/ config TCP_CONG_LP tristate "TCP Low Priority" default n ---help--- TCP Low Priority (TCP-LP), a distributed algorithm whose goal is to utilize only the excess network bandwidth as compared to the ``fair share`` of bandwidth as targeted by TCP. See http://www-ece.rice.edu/networks/TCP-LP/ config TCP_CONG_VENO tristate "TCP Veno" default n ---help--- TCP Veno is a sender-side only enhancement of TCP to obtain better throughput over wireless networks. TCP Veno makes use of state distinguishing to circumvent the difficult judgment of the packet loss type. TCP Veno cuts down less congestion window in response to random loss packets. See <http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1177186> config TCP_CONG_YEAH tristate "YeAH TCP" select TCP_CONG_VEGAS default n ---help--- YeAH-TCP is a sender-side high-speed enabled TCP congestion control algorithm, which uses a mixed loss/delay approach to compute the congestion window. It's design goals target high efficiency, internal, RTT and Reno fairness, resilience to link loss while keeping network elements load as low as possible. For further details look here: http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf config TCP_CONG_ILLINOIS tristate "TCP Illinois" default n ---help--- TCP-Illinois is a sender-side modification of TCP Reno for high speed long delay links. It uses round-trip-time to adjust the alpha and beta parameters to achieve a higher average throughput and maintain fairness. For further details see: http://www.ews.uiuc.edu/~shaoliu/tcpillinois/index.html config TCP_CONG_DCTCP tristate "DataCenter TCP (DCTCP)" default n ---help--- DCTCP leverages Explicit Congestion Notification (ECN) in the network to provide multi-bit feedback to the end hosts. It is designed to provide: - High burst tolerance (incast due to partition/aggregate), - Low latency (short flows, queries), - High throughput (continuous data updates, large file transfers) with commodity, shallow-buffered switches. All switches in the data center network running DCTCP must support ECN marking and be configured for marking when reaching defined switch buffer thresholds. The default ECN marking threshold heuristic for DCTCP on switches is 20 packets (30KB) at 1Gbps, and 65 packets (~100KB) at 10Gbps, but might need further careful tweaking. For further details see: http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf config TCP_CONG_CDG tristate "CAIA Delay-Gradient (CDG)" default n ---help--- CAIA Delay-Gradient (CDG) is a TCP congestion control that modifies the TCP sender in order to: o Use the delay gradient as a congestion signal. o Back off with an average probability that is independent of the RTT. o Coexist with flows that use loss-based congestion control. o Tolerate packet loss unrelated to congestion. For further details see: D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using delay gradients." In Networking 2011. Preprint: http://goo.gl/No3vdg config TCP_CONG_BBR tristate "BBR TCP" default n ---help--- BBR (Bottleneck Bandwidth and RTT) TCP congestion control aims to maximize network utilization and minimize queues. It builds an explicit model of the the bottleneck delivery rate and path round-trip propagation delay. It tolerates packet loss and delay unrelated to congestion. It can operate over LAN, WAN, cellular, wifi, or cable modem links. It can coexist with flows that use loss-based congestion control, and can operate with shallow buffers, deep buffers, bufferbloat, policers, or AQM schemes that do not provide a delay signal. It requires the fq ("Fair Queue") pacing packet scheduler. #if defined(CONFIG_BCM_KF_MPTCP) && defined(CONFIG_BCM_MPTCP) config TCP_CONG_LIA tristate "MPTCP Linked Increase" depends on MPTCP default n ---help--- MultiPath TCP Linked Increase Congestion Control To enable it, just put 'lia' in tcp_congestion_control config TCP_CONG_OLIA tristate "MPTCP Opportunistic Linked Increase" depends on MPTCP default n ---help--- MultiPath TCP Opportunistic Linked Increase Congestion Control To enable it, just put 'olia' in tcp_congestion_control config TCP_CONG_WVEGAS tristate "MPTCP WVEGAS CONGESTION CONTROL" depends on MPTCP default n ---help--- wVegas congestion control for MPTCP To enable it, just put 'wvegas' in tcp_congestion_control config TCP_CONG_BALIA tristate "MPTCP BALIA CONGESTION CONTROL" depends on MPTCP default n ---help--- Multipath TCP Balanced Linked Adaptation Congestion Control To enable it, just put 'balia' in tcp_congestion_control config TCP_CONG_MCTCPDESYNC tristate "DESYNCHRONIZED MCTCP CONGESTION CONTROL (EXPERIMENTAL)" depends on MPTCP default n ---help--- Desynchronized MultiChannel TCP Congestion Control. This is experimental code that only supports single path and must have set mptcp_ndiffports larger than one. To enable it, just put 'mctcpdesync' in tcp_congestion_control For further details see: http://ieeexplore.ieee.org/abstract/document/6911722/ https://doi.org/10.1016/j.comcom.2015.07.010 #endif choice prompt "Default TCP congestion control" default DEFAULT_CUBIC help Select the TCP congestion control that will be used by default for all connections. config DEFAULT_BIC bool "Bic" if TCP_CONG_BIC=y config DEFAULT_CUBIC bool "Cubic" if TCP_CONG_CUBIC=y config DEFAULT_HTCP bool "Htcp" if TCP_CONG_HTCP=y config DEFAULT_HYBLA bool "Hybla" if TCP_CONG_HYBLA=y config DEFAULT_VEGAS bool "Vegas" if TCP_CONG_VEGAS=y config DEFAULT_VENO bool "Veno" if TCP_CONG_VENO=y config DEFAULT_WESTWOOD bool "Westwood" if TCP_CONG_WESTWOOD=y config DEFAULT_DCTCP bool "DCTCP" if TCP_CONG_DCTCP=y config DEFAULT_CDG bool "CDG" if TCP_CONG_CDG=y config DEFAULT_BBR bool "BBR" if TCP_CONG_BBR=y #if defined(CONFIG_BCM_KF_MPTCP) && defined(CONFIG_BCM_MPTCP) config DEFAULT_LIA bool "Lia" if TCP_CONG_LIA=y config DEFAULT_OLIA bool "Olia" if TCP_CONG_OLIA=y config DEFAULT_WVEGAS bool "Wvegas" if TCP_CONG_WVEGAS=y config DEFAULT_BALIA bool "Balia" if TCP_CONG_BALIA=y config DEFAULT_MCTCPDESYNC bool "Mctcpdesync (EXPERIMENTAL)" if TCP_CONG_MCTCPDESYNC=y #endif config DEFAULT_RENO bool "Reno" endchoice endif config TCP_CONG_CUBIC tristate depends on !TCP_CONG_ADVANCED default y config DEFAULT_TCP_CONG string default "bic" if DEFAULT_BIC default "cubic" if DEFAULT_CUBIC default "htcp" if DEFAULT_HTCP default "hybla" if DEFAULT_HYBLA default "vegas" if DEFAULT_VEGAS default "westwood" if DEFAULT_WESTWOOD default "veno" if DEFAULT_VENO #if defined(CONFIG_BCM_KF_MPTCP) && defined(CONFIG_BCM_MPTCP) default "lia" if DEFAULT_LIA default "olia" if DEFAULT_OLIA default "wvegas" if DEFAULT_WVEGAS default "balia" if DEFAULT_BALIA #endif default "reno" if DEFAULT_RENO default "dctcp" if DEFAULT_DCTCP default "cdg" if DEFAULT_CDG default "bbr" if DEFAULT_BBR default "cubic" config TCP_MD5SIG bool "TCP: MD5 Signature Option support (RFC2385)" select CRYPTO select CRYPTO_MD5 ---help--- RFC2385 specifies a method of giving MD5 protection to TCP sessions. Its main (only?) use is to protect BGP sessions between core routers on the Internet. If unsure, say N.
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