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A tool for converting tcp stream into kcp+udp stream, ⚡ download address⚡

kcptun is based on kcp-go

QuickStart 🍭

Server Side: ./server_linux_amd64 -t "127.0.0.1:1080" -l ":554" -mode fast2  // forwarding to local port 1080
Client Side: ./client_darwin_amd64 -r "SERVERIP:554" -l ":1080" -mode fast2  // listening on port 1080

Performance 🍭

* Speed tested with: https://fast.com * WAN Link Speed: 100M ADSL * WIFI: 5GHz TL-WDR3320

Usage 🍭

Applications 🍭

1. Real-time gaming.
2. Cross-ISP data exchange in PRC.
3. Other lossy network.

Parameters Recommended 🍭

Test Environment: China Telecom 100M ADSL(100mbps up/8mbps down)
SERVER:   -mtu 1400 -sndwnd 2048 -rcvwnd 2048 -mode fast2
CLIENT:   -mtu 1400 -sndwnd 256 -rcvwnd 2048 -mode fast2 -dscp 46

How to optimize：

Step 1：Increase client rcvwnd & server sndwnd simultaneously & gradually。
Step 2：Try download something and observer, if the bandwidth usage is close the limit then stop, otherwise goto step 1.

NOTICE: if too much retranmission happens, it's quite possible the windows are too large

Traffic Control 🍭

Intended audience : for those server's bandwidth is quite limited.

Example: To limit outgoing bandwidth to 32mbit/s on server.

root@kcptun:~# cat tc.sh
tc qdisc del dev eth0 root
tc qdisc add dev eth0 root handle 1: htb
tc class add dev eth0 parent 1: classid 1:1 htb rate 32mbit
tc filter add dev eth0 protocol ip parent 1:0 prio 1 handle 10 fw flowid 1:1
iptables -t mangle -A POSTROUTING -o eth0  -j MARK --set-mark 10
root@kcptun:~#

DSCP 🍭

Differentiated services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing quality of service (QoS) on modern IP networks. DiffServ can, for example, be used to provide low-latency to critical network traffic such as voice or streaming media while providing simple best-effort service to non-critical services such as web traffic or file transfers.

DiffServ uses a 6-bit differentiated services code point (DSCP) in the 8-bit differentiated services field (DS field) in the IP header for packet classification purposes. The DS field and ECN field replace the outdated IPv4 TOS field.[1]

setting each side with -dscp value.

Embeded Mode 🍭

Latency:
fast3 > [fast2] > fast > normal > default
Payload Ratio:
default > normal > fast > [fast2] > fast3
Parameters in middle is balanced for latency & payload ratio, the faster you get the more wasteful you are. Manual control is supported with hidden parameters, you must understand KCP protocol before doing this.

 -mode manual -nodelay 1 -resend 2 -nc 1 -interval 20

Forward Error Correction 🍭

In coding theory, the Reed–Solomon code belongs to the class of non-binary cyclic error-correcting codes. The Reed–Solomon code is based on univariate polynomials over finite fields.

It is able to detect and correct multiple symbol errors. By adding t check symbols to the data, a Reed–Solomon code can detect any combination of up to t erroneous symbols, or correct up to ⌊t/2⌋ symbols. As an erasure code, it can correct up to t known erasures, or it can detect and correct combinations of errors and erasures. Furthermore, Reed–Solomon codes are suitable as multiple-burst bit-error correcting codes, since a sequence of b + 1 consecutive bit errors can affect at most two symbols of size b. The choice of t is up to the designer of the code, and may be selected within wide limits.

Setting parameters of RS-Code with -datashard 10 -parityshard 3

Snappy Stream Compression 🍭

Snappy is a compression/decompression library. It does not aim for maximum compression, or compatibility with any other compression library; instead, it aims for very high speeds and reasonable compression. For instance, compared to the fastest mode of zlib, Snappy is an order of magnitude faster for most inputs, but the resulting compressed files are anywhere from 20% to 100% bigger.

Reference: http://google.github.io/snappy/

disable compression by setting -nocomp on both side.

Tips: Turning off compression may reduce latency.

SNMP 🍭

// Snmp defines network statistics indicator
type Snmp struct {
	BytesSent        uint64 // payload bytes sent
	BytesReceived    uint64
	MaxConn          uint64
	ActiveOpens      uint64
	PassiveOpens     uint64
	CurrEstab        uint64
	InErrs           uint64
	InCsumErrors     uint64 // checksum errors
	InSegs           uint64
	OutSegs          uint64
	OutBytes         uint64 // udp bytes sent
	RetransSegs      uint64
	FastRetransSegs  uint64
	EarlyRetransSegs uint64
	LostSegs         uint64
	RepeatSegs       uint64
	FECRecovered     uint64
	FECErrs          uint64
	FECSegs          uint64 // fec segments received
}

Sending a signal by kill -SIGUSR1 pid will give SNMP information for KCP，useful for fine-grained adjustment. Of which RetransSegs,FastRetransSegs,LostSegs,OutSegs is the most useful.

Donations 💵

All donations to this project will be used on the R&D of gonet/2.

References 📎

1. https://github.com/skywind3000/kcp -- KCP - A Fast and Reliable ARQ Protocol.
2. https://github.com/klauspost/reedsolomon -- Reed-Solomon Erasure Coding in Go.
3. https://en.wikipedia.org/wiki/Differentiated_services -- DSCP.
4. http://google.github.io/snappy/ -- A fast compressor/decompressor.
5. https://www.backblaze.com/blog/reed-solomon/ -- Reed-Solomon Explained.
6. http://www.qualcomm.cn/products/raptorq -- RaptorQ Forward Error Correction Scheme for Object Delivery.
7. https://en.wikipedia.org/wiki/PBKDF2 -- Key stretching.
8. http://blog.appcanary.com/2016/encrypt-or-compress.html -- Should you encrypt or compress first?
9. https://github.com/hashicorp/yamux -- Connection multiplexing library.
10. https://tools.ietf.org/html/rfc6937 -- Proportional Rate Reduction for TCP.
11. https://tools.ietf.org/html/rfc5827 -- Early Retransmit for TCP and Stream Control Transmission Protocol (SCTP).
12. http://http2.github.io/ -- What is HTTP/2?
13. http://www.lartc.org/ -- Linux Advanced Routing & Traffic Control