The Sinch SDK will use P2P for the voice stream when possible. The ICE protocol is used for NAT traversal. If a P2P channel is not possible (for example when both sides are behind a symmetric NATs) the voice channel will fall back to Sinch media proxies. Approximately 70-75% of the calls made with the SDK can be expected to go over P2P, while approximately 25-30% of the calls can be expected to go through servers. This is due to firewall restrictions.
Visit the In-App Voice Calling product page to learn more about Sinch’s In-App Voice calling products.