/ Blog /TURN Server - Everything You Need To Know
November 10, 20234 min read
A TURN (Traversal Using Relays around NAT) server is a network entity used to facilitate communication between two devices or clients located behind Network Address Translation (NAT) systems or firewalls. The TURN server acts as a relay for network traffic, allowing devices that may not be able to establish a direct connection due to NAT or firewall restrictions to communicate with each other. Rerouting traffic through the TURN server ensures that data can be exchanged even in complex network environments where peer-to-peer communication would otherwise be impossible.
Imagine you're in a busy café trying to talk to your friend across the room. Your first attempt to wave or use a mirror to reflect light to catch their attention represents a STUN server's attempt to establish a direct connection.
If your friend can't see your signals due to obstacles (people walking by, pillars), you turn to another friend who's moving around the café. You ask them to deliver your message to your friend. This friend acts like a TURN server, relaying messages when direct line-of-sight communication (STUN) fails due to obstructions.
Before the establishment of TURN, STUN (Session Traversal Utilities for NAT) was the primary solution employed to address the challenges posed by NAT (Network Address Translation). NAT devices allow multiple endpoints (like personal computers) in a local network to share a single public IP address for accessing resources on the Internet.
STUN is a protocol that aids in the discovery of a device's public IP address and port as seen from the outside of its local network. It operates by querying a STUN server on the Internet, which then provides the device with its public-facing IP address and port number.
While STUN worked effectively in many scenarios, it faced challenges, especially with specific NAT types:
To address the limitations of STUN, TURN (Traversal Using Relays around NAT) was developed. Here's how TURN overcomes the above challenges:
TURN servers come into play when other methods, like STUN (Session Traversal Utilities for NAT), fail. STUN is typically the first line of approach, where devices attempt to discover their public-facing IP addresses and ports, allowing for direct communication if possible. However, in more complex network environments, such as those involving symmetric NATs or restrictive firewalls that alter the source port of outbound packets, STUN is insufficient.
This is where TURN servers are employed. These servers act as intermediaries, relaying data between devices when direct connections are not feasible. In practical terms, all traffic between the communicating devices is routed through the TURN server. While ensuring data delivery, this approach introduces added latency due to the additional hop in data transmission.
From a software development perspective, integrating TURN servers into RTC applications involves several key considerations:
Developers typically use a combination of STUN and TURN in their applications. STUN is used to establish direct connections wherever possible, with TURN serving as a reliable fallback for scenarios where direct communication is blocked. Tools like Coturn, which provide both STUN and TURN functionalities, are popular among developers for streamlining the implementation of these protocols in RTC applications.
STUN (Session Traversal Utilities for NAT) servers help devices discover their public IP addresses and ports to facilitate direct communication, typically in simpler network configurations. TURN (Traversal Using Relays around NAT) servers, on the other hand, act as intermediaries, relaying data between devices when direct communication is obstructed by complex NATs or firewalls. While STUN attempts direct connection with minimal overhead, TURN is a fallback that ensures connectivity through data relay but with added latency and resource usage.
TURN servers typically use port 3478 for both TCP and UDP traffic, and they may also use port 5349 for secured traffic over TLS. Additionally, TURN servers can be configured to use other ports as required by network policies or specific deployment needs.
TURN servers can use both TCP and UDP protocols for relaying traffic. UDP is often preferred for real-time applications due to lower latency, but TCP is used when UDP is restricted or unreliable in certain network environments. This flexibility allows TURN to operate effectively across diverse network conditions.
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