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Monday, 4 June 2018

Tcsplitter

Tunnel TCP or UDP over multiple TCP connections.

An end to end "tunnel" that demuxes a tcp connection into multiple connections each one having a predefined size. You could say each connection carries a datagram...eh!
Inbound data traffic is also initialized by the client for classic out-of-nat reach.

Quickstart

Use scripts in utils/, put the binary tcsplitter in the same folder.
## server side
./tcs-server.sh

## client side
./tcs-client.sh
start a local service on 127.0.0.1:6003 connect the client on 127.0.0.1:6000

Configuration

Important arguments are tick tock and buffer.
Tick determines how frequently one end of the tunnel is read.
Tock determines how frequently a payload is scheduled to be sent to the other end of the tunnel.
Buffer determines the frequency of forwarding data to the client or service once it has been received through the tunnel, can be important to avoid chockings/hiccups and keep a stable data stream.
Note that to keep the tunnel interactive (i.e. ssh session) the tock of one end should be the same of the buffer of the other end. This should not be a requirement if the second paramater of buffer, that is the number of payloads to buffer, would merge payloads, so that it could be tweaked to be equal to the number of connections received, since each connection carries a payload.
There are a couple of config file to be used on linux (sysctl -p sysctl.dirty) to test different setups, dirty means to saturate connections/sockets, clean to use as little as possible.
Note: for long data streams on slow networks, the server might need a buffer time lower than the client (0.5<bt<1) to avoid falling behind the stream, this happens because the data is forwarded according to the value of bt but since payloads might be late, steps might be skipped but there is no fast-forward (intentionally), this to make stable video data streams with less buffering spikes. Adding a catchup version for forwarding is also trivial.

Other options

Most other options are not effectively functional at the moment.

fec

As in datashards:parityshards like 10:3, to be considered when using a lot of connections resulting in ack timeouts and whatnot.

dup

Controls the direction of communication between tunnel ends.
  • fling (default), connections from client to server are used both for incoming and outgoing data in an asynchronous manner, meaning that connections which are always running timeout if no payloads are provided and new ones are established.
  • lasso, same as fling but lasso connections are used, this means the priority of the traffic is in favor of incoming data, server -> client
  • both, full duplex, fling and lasso mode together, for high interaction for both outgoing and incoming data.
  • none, simplex, connections only send data in one direction and are promptly closed afterwards.

protocol

Tunnel TCP or UDP over TCP, currently only TCP effectively working.

after

Warm up time in ms at the start of a connection, to complete handshakes and still being able to use high buffer times.

frags

As in payloadSize:MTU, how much data each connection carries in bytes. MTU not currently used.

conns/lassoes

How many fling connections and lasso connections to keep open at any given time.

retries

As in on/off:skippingRate, the first value controls whether there should be attempts at retrasmitting lost payloads. This is best used in simplex mode (dup none) so that one end of the connection is used for acks. Otherwise the sync comm channel would be used to send retry requests. The skippingRate is instead best used with fec or when data integrity is not important in general as it simply skips over not available payloads after the specified number of attempts.

listen

The target where data is sent to, i.e. client/service.

lFling, rFling, lLasso, rLasso, lSync, rSync, lFlingR, rFlingR

Respectively the addresses in form IPv4:PORT of the local and remote endpoints for flings, lassoes, clients status/data synchronizations and retries.

burst

This is hardcoded off by default. In this mode there should a fixed based number of connections, plus room to ramp up the number when the payloads queue gets long.

Stuff left to try, polishing, optimizations

See issues.

Flow

Kind of outdated at this point.
flow

Dependencies


from https://github.com/untoreh/tcsplitter

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