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Collaboration, Voice & AV · Advanced

Traversal Using Relays around NAT (TURN)

A protocol (RFC 8656) in which a server relays media for endpoints that cannot connect directly through NAT or firewalls.

Definition

A TURN client allocates a relay address on a TURN server, and peers send media to that address, which the server forwards. TURN works through symmetric NATs and restrictive firewalls but consumes server bandwidth and adds latency. Cisco Expressway-E can act as a TURN server for ICE media in MRA and B2B calls, and Teams uses TURN relays in the Microsoft network.

Example

A Jabber client behind a hotel firewall sends media via the TURN relay on Expressway-E on UDP 3478.

Exam tip

TURN is the last resort in ICE because it always relays media; default TURN port is 3478.

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