TRAVERSAL METHOD FOR ICMP-SENSITIVE NAT

摘要

In SIP network environment, a general NAT traversal method will become invalid when an NAT with ICMP (Internet Control Message Protocol) is met. The present invention provides four sessions for SIP, i.e. Login Session, Port Prediction Session, Synchronization Session and Media Session, and the SIP network environment includes a first Internet telephone, a second Internet telephone, a first symmetric NAT, a second symmetric NAT and an SIP proxy server. The first symmetric NAT and the second symmetric NAT are ICMP-sensitive. In the Synchronization Session, the first Internet telephone and the second Internet telephone are designed to transmit packets synchronously to avoid port locking.

主权项

1. A traversal method for ICMP-sensitive NAT, a registration session, a communication port prediction session, a synchronous session and a media session are set up for SIP, and an Internet environment for SIP comprises a first Internet telephone, a second Internet telephone, a first symmetric NAT, a second symmetric NAT, and an SIP proxy server; the first Internet telephone is under the first symmetric NAT, the second Internet telephone is under the second symmetric NAT; both the first symmetric NAT and the second symmetric NAT are ICMP-sensitive; the traversal method comprises:
a. the first Internet telephone and the second Internet telephone register on the SIP proxy server firstly to accomplish the registration session; b. the first Internet telephone conducts a plurality of detection procedure to the first symmetric NAT for detecting the regular rule of allocating communication port by the first symmetric NAT; the second Internet telephone conducts a plurality of detection procedure to the second symmetric NAT for detecting the regular rule of allocating communication port by the second symmetric NAT; so as to accomplish the communication port prediction session; c. thereafter the synchronous session is entered, the first Internet telephone passes a test packet to the SIP proxy server through T1 time, then the SIP proxy server returns the test packet to the first Internet telephone through T2 time; (T1+T2)/2 is therefore the average time T3 that the first Internet telephone sends a packet to the SIP proxy server; then the first Internet telephone sends a packet including T3 information to the SIP proxy server for being kept by the SIP proxy server; d. similarly, the second Internet telephone passes a test packet to the SIP proxy server through T4 time, then the SIP proxy server returns the test packet to the second Internet telephone through T5 time; (T4+T5)/2 is therefore the average time T6 that the second Internet telephone sends a packet to the SIP proxy server; then the second Internet telephone sends a packet including T6 information to the SIP proxy server for being kept by the SIP proxy server; e. after the SIP proxy server receives the packets including time information from both sides, the SIP proxy server will then exchange the time information to the opposite side simultaneously, the first Internet telephone will receive the packet including T6 information sent from the second Internet telephone; the second Internet telephone will receive the packet including T3 information sent from the first Internet telephone; f. if T6>T3, then after the second Internet telephone receives the packet including T3 information, the second Internet telephone enters the media session immediately to send speech packets directly to the first Internet telephone without going through the SIP proxy server; while the first Internet telephone has to wait T6−T3 time after receiving the packet including T6 information, and then enter the media session to send speech packets directly to the second Internet telephone without going through the SIP proxy server; therefore both sides have entered the media session to send speech packets with each other synchronously; g. if T3>T6, then after the first Internet telephone receives the packet including T6 information, the first Internet telephone enters the media session immediately to send speech packets directly to the second Internet telephone without going through the SIP proxy server; while the second Internet telephone has to wait T3−T6 time after receiving the packet including T3 information, and then enter the media session to send speech packets directly to the first Internet telephone without going through the SIP proxy server; therefore both sides have entered the media session to send speech packets with each other synchronously.