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Small-scale UDP Fast Transmission Protocol

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The SUFT (Small-scale UDP Fast Transmission) Protocol is an application layer transmission protocol based on UDP and implemented in Golang. It has lower latency than TCP and provides reliable and ordered delivery of a stream of octets under plain congestion control.

The protocol seeks for maximized throughput and minimizes impact of lost packets on throughput. It is only for small/medium-scale communication or some situations where TCP is not applicable.

Goals & Features

  • Transmitting model has predictable performance.
  • Fast retransmission mode does better on lossy link.
  • Minimum retransmission mode doesn't waste traffic.
  • No resource consumption while the connection is idle.
  • Special modes for certain situations.

Protocol APIs

SUFT implements the Golang: net.Conn and net.Listener interfaces completely.

import ""

e, err := suft.NewEndpoint(p *suft.Params) // for server conn := e.Listen() // or e.Accept() // for client conn, err := e.Dial(rAddr string) // your business ... conn.Close() e.Close()

Basic Theories

scnt(sender: the count of unique data packets) and dups(sender: retransmission counter)

Lose Rate = dups/(scnt + dups)

Retransmit Rate = dups/scnt

latency, window and traffic speed

Speed = (1000 / latency) * mss * win


GPL version 3 or any later version

SUFT Protocol
Copyright (C) 2016  spance, l2dy

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http:.

Tool Usage

"suft-nc" package include a tool for testing, similar to netcat (nc).

Build with

go get -u -v
./suft-nc [-l addr:port] [-r addr:port] [-s] [-b 10] [-fr] < [send_file] > [recv_file]

-l: local bind address, e.g. localhost:9090 or :8080 -r: remote address (for client), e.g. or -b: max bandwidth of sending in mbps (be careful, see Notes#2) -s: for server -fr: enable fast retransmission (useful for lossy link) -ft: flat traffic (slow down bursty traffic, useful when sender has more bandwidth than receiver)


// send my_file to remote in 10mbps
remote# ./suft-nc -l :9090 -s > recv_file
local# ./suft-nc -r remote:9090 -b 10 -fr < my_file
// recv my_file from remote in 50mbps
remote# ./suft-nc -l :9090 -s -b 50 -fr < my_file
local# ./suft-nc -r remote:9090 > recv_file
// simple chat room
remote# ./suft-nc -l :9090 -s
local# ./suft-nc -r remote:9090


  1. The target to be connected shouldn't be behind NAT (or should use port mapping).
  2. Use improper bandwidth(-b) may waste huge bandwidth and may be suspected of carrying out flood attack.

How to test?

// remote, send 100MB stream in 50mbps (your bandwidth bottleneck)
remote# dd if=/dev/zero bs=1M count=100 status=none | ./suft-nc -s -l :9090 -b 50 -fr -ft
// status=none or status=noxfer

// local console#1, monitor traffic(for simplicity, we can use bmon) local# bmon -p eth0 // local console#2, recv stream local# ./suft-nc -r remote:9090 > /dev/null

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