Which SIP transport to use, and why TLS solves most registration problems.
VOIP.SO accepts all three SIP transports on the same hostname. The difference matters more than it looks.
UDP on port 5060
The default, and the fastest to set up. It is also the transport most aggressively handled by consumer routers, which rewrite SIP packets in ways that break call setup. If registrations drop every few minutes, this is usually why.
TCP on port 5060
Keeps a connection open, which survives NAT timeouts better than UDP. A reasonable middle ground on networks you do not control.
TLS on port 5061
Encrypts SIP signalling. Two benefits: your call metadata is private in transit, and the traffic is indistinguishable from other TLS to intermediate equipment, so routers stop interfering with it. Pair it with SRTP to encrypt the audio as well.
Our recommendation
Use TLS with SRTP set to optional. If a specific device does not support it, fall back to TCP before UDP.
Last updated 12 Sep 2026. Something wrong or missing here? Tell us — we would rather fix the page than answer the same ticket twice.