TWAMP

A minimal TWAMP Light implementation in Go for active round-trip time (RTT) measurement over UDP. It follows the TWAMP-Test packet format from RFC 5357 §4.1.2 and uses NTP-style 64-bit timestamps.

Features

• Sends and receives TWAMP-Test packets over UDP
• NTP-based timestamps for accurate RTT
• Summary statistics including packet loss, min/max/avg RTT, and jitter
• Simple Sender and Reflector interfaces
• Optional Prometheus metrics instrumentation
• Configurable padding for packet size control
• Unit tests and fuzz testing

Example

Reflector (Listener)

go func() {
    listener, _ := twamp.NewListener(":9000", 512, nil, nil)
    _ = listener.Run()
}()

Sender (Client)

sender, _ := twamp.NewSender(":0", "127.0.0.1:9000", time.Second, nil, nil)
res, _ := sender.SendProbe()
fmt.Printf("RTT = %v (seq %d)\n", res.RTT, res.Seq)

Packet Flow Diagram (TWAMP Light)

+---------+                                 +------------+
| Sender  | -- TWAMP-Test packet (UDP) -->  | Reflector  |
|         |                                 |            |
|         | <-- echoed with timestamp ----- |            |
+---------+                                 +------------+

Interfaces

type Sender interface {
	SendProbe() (*ProbeResult, error)
	SendProbeWithPadding(paddingLen int) (*ProbeResult, error)
	Summary() *ProbeSummary
	Close() error
}

type Reflector interface {
    HandleProbe(msg []byte, from net.Addr) ([]byte, error)
}

type Listener interface {
    Run() error
    Close() error
    LocalAddr() net.Addr
}

TWAMP-Test Packet Format

This library uses the minimal TWAMP-Test format (RFC 5357 §4.1.2):

Field	Offset	Size (bytes)
Sequence Number	0	4
Timestamp (seconds)	4	4
Timestamp (fraction)	8	4
Error Estimate	12	2
MBZ (reserved)	14	2
Reflector TS (sec)	16	4
Reflector TS (frac)	20	4
Padding	24	variable

Timestamps follow NTP 64-bit format: 32 bits for seconds, 32 bits for fractional seconds since Jan 1, 1900 UTC.

Output Example

RTT = 212.400µs (seq 4)

Limitations (Not Yet Implemented)

This library implements the essentials of TWAMP Light. Some features are not yet included:

• DSCP / TOS field configuration
• Don't Fragment (DF) bit
• CLI tools (twamp-client, twamp-reflector)