The problems and their solutions when using SIP in NAT environment

Abstract

As the number of Internet users increases rapidly, IPv4 address shortage has been developing.The shortage can be completely solved by using IPv6, but it takes too much time to replace all the equipments in the world.Therefore, NAT is used as a temporally solution. NAT reduces the use of address by connecting a local address to a public address only when it is necessary, which can be a good solution for server-client models, but causes NAT-Traversal problem in peer-to-peer communication such as VoIP using SIP in NAT environment. STUN and TURN are used to solve NAT-Traversal problem.This document explains how STUN and TURN are applied to SIP to solve problems when using NAT and points out problems that STUN and TURN cause, and suggests a way to improve.