- REGISTER sip: 124.40 . 120.188 : 5060 SIP / 2.0
- Via: SIP/ 2.0 / UDP 124.42 . 4.203 : 15500 ;branch = z9hG4bK - d8754z -1049ed261d2e643d - 1 --- d8754z -;rport
- Max - Forwards: 70
- Contact: < sip: 19988888888 @ 192.168 . 2.65 : 12344 ;rinstance =7cd1c532e92fdb0e > ;expires =
- To: " 19988888888 " < sip: 19988888888 @ 124.40 . 120.188 : 5060 >
- From: " 19988888888 " < sip: 19988888888 @ 124.40 . 120.188 : 5060 >;tag =203ba359
- Call -ID: Yzc4N2IwMzY5OWU4MTdkMzY0NWY4OWU3NjMzNmJiM2U.
- CSeq: 1 REGISTER
- Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO
- User - Agent: eyeBeam release 1105a stamp 56793
- Content- Length:
2. 發(fā)送到的服務器支持rport機制，它看到請求中的rport后，將通過分析UDP包信息得到的的NAT的公網地址（124.42.4.203）和端口信息（15500）分別作為received和rport屬性帶給客戶端：
- SIP / 2.0 200 OK
- Via: SIP / 2.0 / UDP 124.42 . 4.203 : 15500 ;branch = z9hG4bK - d8754z -1049ed261d2e643d - 1 --- d8754z - ;rport = 15500 ;received = 124.42. 4.203
- From: " 19988888888 " < sip: 19988888888 @ 124.40 . 120.188 : 5060 >;tag = 203ba359
- To: " 19988888888 " < sip: 19988888888 @ 124.40 . 120.188 : 5060 > ;tag= 0005 - 058 - 7d6dc90516ae2e21
- Call - ID: Yzc4N2IwMzY5OWU4MTdkMzY0NWY4OWU3NjMzNmJiM2U.
- CSeq: 4 REGISTER
- Allow: INVITE,ACK,OPTIONS,BYE,CANCEL,REGISTER,INFO,UPDATE,PRACK,REFER,SUBSCRIBE,NOTIFY,MESSAGE
- Contact: < sip: 124.40 . 120.188 : 5060 >
- Content - Length:
3. 客戶端在得到響應信息后，知道了所使用的公網地址和端口，在之后定期重發(fā)的REGISTER信息中，Contact變換成124.42.4.203: 15500，例如新發(fā)的REGISTER信息變?yōu)椋?/div>
- REGISTER sip: 124.40 . 120.188 : 5060 SIP / 2.0
- Via: SIP / 2.0 / UDP 124.42 . 4.203 : 15500 ;branch = z9hG4bK - d8754z -1049ed261d2e643d - 1 --- d8754z - ;rport
- Max - Forwards: 70
- Contact: < sip: 19988888888 @ 124.42 . 4.203 : 15500 ;rinstance =7cd1c532e92fdb0e > ;expires =
- To: " 19988888888 " < sip: 19988888888 @ 124.40 . 120.188 : 5060 >
- From: " 19988888888 " < sip: 19988888888 @ 124.40 . 120.188 : 5060 >;tag = 203ba359
- Call - ID: Yzc4N2IwMzY5OWU4MTdkMzY0NWY4OWU3NjMzNmJiM2U.
- CSeq: 2 REGISTER
- Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO
- User - Agent: eyeBeam release 1105a stamp 56793
- Content - Length:
這樣IPPBX（或者SIP Proxy）知道了怎么將消息，發(fā)送給放在Nat后面的SIP終端，實現(xiàn)了NAT穿透。
備注：
- 若使用freeswitch服務器，rport機制沒有生效時，看下freeswithc的sip profile里面的NDLB-force-rport參數(shù)，設為 NDLB-force-rport=safe ， 重啟該profile 生效
- 若是分機的contact地址是私網的，導致無法送呼叫到分機，
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