Table of Contents

FRITZ!Box

Status: ✅ verified against a live device (manual). Registration, dialing, two-way audio and DTMF were exercised by hand against a real AVM FRITZ!Box, and several SDK hardening fixes came directly out of that test (advertised media-address resolution, static payload types without rtpmap, codec preference). This is a manual verification against real hardware, not an automated CI test.

Set up an IP phone on the FRITZ!Box

  1. In the FRITZ!Box UI: Telephony → Telephony Devices → Configure New Device → Telephone (LAN/DECT) and choose a LAN/WLAN (IP telephone).
  2. Note the username and password the FRITZ!Box assigns.
  3. The registrar is the FRITZ!Box IP (commonly fritz.box / 192.168.178.1).

Connect from the SDK

var connect = await client.ConnectAsync(new SipAccount
{
    Username  = "620",                 // the IP-phone user from the FRITZ!Box
    Password  = "your-device-password",
    SipServer = "fritz.box"            // or the box IP
});

Dial internal numbers (e.g. **9 for a broadcast, or another registered device) or external numbers per your FRITZ!Box dialing rules.

Notes from the interop test

  • Codec — FRITZ!Box favours G.711 (PCMA/PCMU). If you also enable Opus, keep G.711 in your PreferredAudioCodecs list as a fallback.
  • Media address — the SDK advertises a routable LAN address (not loopback) so audio flows both ways on the local network. This was one of the fixes surfaced here.
  • DTMF — RFC 4733 telephone-events work; verify tone detection on your target IVR.

If audio is one-way

Enable the SIP wire trace and check the c=/m= lines in the offered/answered SDP against the actual device address. See NAT and SIP trunks.

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