RTP no-anchoring

What is "RTP no-anchoring?"

RTP no-anchoring is a variant of low-delay media relay where the RTP packets are not "anchored" to the SBC (not going through the SBC).

Instead the RTP path is established directly between the two legs of a call (which send RTP to each other).

This greatly reduces the IP bandwidth required by the SBC, while the SBC continues to be involved in SIP signaling and call routing.

When should "RTP no-anchoring" be enabled?

Make sure to enable this option only on profiles used for calls that can reach each other directly, otherwise RTP packets will be lost and users won't hear each other. For example, it may not work if call legs are behind NATs, or if call legs are on separate networks.

We recommend to configure "no-anchoring" per route (each route may override the NAP's default profile). Profiles with "RTP no-anchoring" enabled should only be used on routes that are known to bridge call legs that can directly send RTP to each other.

Will "RTP no-anchoring" always be used when enabled in a profile?

Not all calls with no-anchoring mode enabled will actually use it.

In fact, RTP no-anchoring mode is possible if

  • both call legs of a call have the "RTP no-anchoring" option enabled in their assigned profile.
  • The call does not require IVR functionalities (play file, record to file, tone detection or tone generation).

TelcoBridges SBCs can dynamically change, during a call, from no-anchoring mode, to transcoding (IVR) mode. When changing mode, a SIP re-invite is used on both call legs (to change the RTP path so it goes or not through the SBC)

Synonyms of "RTP no-anchoring"

"RTP no-anchoring" is also sometimes called "Media no-anchoring", "Media pass-around" or "media bypass".