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The transport section configures the underlying protocol used for communication between client and server. Currently, paqet only supports the KCP protocol.

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Transport Protocol

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transport.protocol
string
default:"kcp"
Transport protocol to use. Currently only "kcp" is supported.

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Connection Settings

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transport.conn
integer
default:"1"
Number of parallel connections (1-256). Multiple connections can improve throughput on high-latency networks.Client restriction: If the client port is explicitly set (non-zero) in network.ipv4.addr, only 1 connection is allowed.
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transport.tcpbuf
integer
default:"8192"
TCP buffer size in bytes
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transport.udpbuf
integer
default:"4096"
UDP buffer size in bytes

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KCP Protocol Configuration

KCP is a fast and reliable ARQ protocol that can achieve higher throughput and lower latency than TCP, especially on lossy or high-latency networks.

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KCP Modes

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transport.kcp.mode
string
default:"fast"
Predefined KCP mode preset. Choose based on your network conditions and performance requirements:
  • normal: Conservative TCP-like behavior with congestion control
  • fast: Balanced mode for general use (recommended)
  • fast2: More aggressive mode for better performance
  • fast3: Most aggressive mode for maximum speed
  • manual: Use custom parameters defined below
Each mode configures the underlying KCP parameters differently:
ModenodelayintervalresendnocongestionUse Case
normal04020Stable networks, TCP-like behavior
fast13021General use, balanced performance
fast212021Low-latency networks
fast311021Maximum performance, high bandwidth
manualcustomcustomcustomcustomFull control over all parameters

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Manual Mode Parameters

When mode is set to "manual", you can configure individual KCP parameters:
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transport.kcp.nodelay
integer
Enable or disable nodelay mode:
  • 0: Disable (TCP-like conservative behavior)
  • 1: Enable (lower latency and aggressive retransmission)
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transport.kcp.interval
integer
Internal update timer interval in milliseconds (10-5000ms).Lower values increase responsiveness but raise CPU usage. Typical values:
  • 10ms: Maximum responsiveness, higher CPU
  • 20ms: Good balance
  • 40ms: Conservative, lower CPU
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transport.kcp.resend
integer
Fast retransmit trigger (0-2):
  • 0: Disabled (wait for timeout only)
  • 1: Most aggressive (retransmit after 1 ACK skip)
  • 2: Aggressive (retransmit after 2 ACK skips)
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transport.kcp.nocongestion
integer
Congestion control setting:
  • 0: Enable TCP-like fair congestion control (slow start, congestion avoidance)
  • 1: Disable congestion control for maximum speed
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transport.kcp.wdelay
boolean
Write batching behavior:
  • false: Flush immediately (low latency, recommended for real-time applications)
  • true: Batch writes until next update interval (higher throughput)
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transport.kcp.acknodelay
boolean
ACK sending behavior:
  • true: Send ACKs immediately when packets are received (lower latency)
  • false: Batch ACKs (more bandwidth efficient)

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MTU and Window Settings

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transport.kcp.mtu
integer
default:"1350"
Maximum transmission unit in bytes (50-1500).
Default is 1350 to avoid fragmentation. Only increase if you’re certain your network path supports larger MTUs.
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transport.kcp.rcvwnd
integer
default:"512 (client) / 1024 (server)"
Receive window size (1-32768).Controls how many packets can be in flight. Larger windows improve throughput on high-latency networks.
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transport.kcp.sndwnd
integer
default:"512 (client) / 1024 (server)"
Send window size (1-32768).Controls how many packets can be sent before waiting for ACKs. Larger windows improve throughput.

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Buffer Settings

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transport.kcp.smuxbuf
integer
default:"4194304"
SMUX multiplexing buffer size in bytes (minimum 1024). Default is 4MB.
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transport.kcp.streambuf
integer
default:"2097152"
Stream buffer size in bytes (minimum 1024). Default is 2MB.

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Keepalive Settings

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transport.kcp.smuxkalive
integer
default:"2"
SMUX keepalive interval in seconds. How often to send keepalive probes.
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transport.kcp.smuxktimeout
integer
default:"8"
SMUX keepalive timeout in seconds. Connection is considered dead after this timeout.

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Encryption

Encryption is configured within the KCP section. See Encryption Configuration for details.
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transport.kcp.block
string
default:"aes"
Encryption algorithm to use. See Encryption Configuration for available options.
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transport.kcp.key
string
required
Encryption key. Must match between client and server. Generate using paqet secret.

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Forward Error Correction (FEC)

FEC is currently disabled in paqet. The parameters below are reserved for future use.
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transport.kcp.dshard
integer
Data shards for FEC (currently disabled)
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transport.kcp.pshard
integer
Parity shards for FEC (currently disabled)

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Configuration Examples

transport:
  protocol: "kcp"
  conn: 1
  kcp:
    mode: "fast"
    key: "your-secret-key-here"

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Manual Mode for Low-Latency

transport:
  protocol: "kcp"
  conn: 1
  kcp:
    mode: "manual"
    nodelay: 1
    interval: 10
    resend: 2
    nocongestion: 1
    wdelay: false
    acknodelay: true
    mtu: 1350
    rcvwnd: 512
    sndwnd: 512
    key: "your-secret-key-here"

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Multiple Connections for High-Latency Networks

transport:
  protocol: "kcp"
  conn: 4  # Use 4 parallel connections
  kcp:
    mode: "fast2"
    rcvwnd: 1024
    sndwnd: 1024
    key: "your-secret-key-here"

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Performance Tuning

  • Use mode: "fast2" or mode: "fast3"
  • Increase window sizes: rcvwnd: 1024, sndwnd: 1024
  • Consider multiple connections: conn: 2 or conn: 4
  • Increase buffers: smuxbuf: 8388608, streambuf: 4194304
  • Use mode: "fast" (default)
  • Keep default window sizes
  • Single connection is usually sufficient: conn: 1
  • Lower interval for responsiveness: interval: 10 (manual mode)
  • Use mode: "fast2" or mode: "fast3"
  • Increase retransmission: resend: 2 (manual mode)
  • Enable aggressive ACKs: acknodelay: true (manual mode)
  • Consider FEC when it becomes available
  • Use mode: "normal" or mode: "fast"
  • Increase interval: interval: 40 (manual mode)
  • Reduce connections: conn: 1
  • Enable write batching: wdelay: true (manual mode)

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See Also

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