------------------ ------------------- ------------------- |UA1 | |SIP proxy | |UA2 | |IP:192.168.100.1|-----|IP: 192.168.100.2 |--------|IP: 192.168.100.3 | |Port: 1111 | |Port: 2222 | |Port: 3333 | ------------------ -------------------- -------------------
If UA1 makes call to UA2, UA1 should send the following message to the SIP proxy: =============================================================== IP: Src: 192.168.100.1 Dst: 192.168.100.2 =============================================================== UDP: Src port: 1111 Dst port: 2222 ! =============================================================== SIP: INVITE sip:[EMAIL PROTECTED]:2222 SIP/2.0 ! Via: SIP/2.0/UDP 192.168.100.1:1111; =============================================================== Then SIP proxy sends the following message to UA2: =============================================================== IP: Src: 192.168.100.2 Dst: 192.168.100.3 =============================================================== UDP: Src port: 2222 Dst port: 3333 ! =============================================================== SIP: INVITE sip:[EMAIL PROTECTED]:3333 SIP/2.0 ! Via: SIP/2.0/UDP 192.168.100.2:2222; Via: SIP/2.0/UDP 192.168.100.1:1111; =============================================================== UAC(UA1) does not know the port of UAS(UA2). All the UAC needs to know is the proxy's port. And the proxy knows all the ports of UAs under it (UAs tell proxy when register). Therefore, the proxy does not care the port number in the received "Invite" request-linen (because the port number is proxy itself) Therefore, the port number in the "Invite" request-line is always same with the port number in the lower layer UDP. Why we insert redundant information? How about we drop this redundant and confusing port number in the URL? Please correct me if I am wrong. Thanks. Best regards Yuantao Zhang -----Original Message----- From: Paul Kyzivat [mailto:[EMAIL PROTECTED] Sent: 2008年6月6日 19:55 To: Yuantao Zhang Cc: Attila Sipos; [email protected]; [EMAIL PROTECTED] Subject: Re: [Sip] What is the port number in "Invite" request-line? Thanks The URI typically exists before the message is constructed. Then a message is constructed and the URI included in it. The URI specifies where the message is *intended* to go. And it might not go there immediately. Instead it may first go to a proxy. When it gets there the proxy needs to consult the R-URI to know where the message is intended to go. When the last hop to the final destination is made it is true that the port number, and the ip address, may be redundant. But we don't expect the intermediate nodes to remove the information. The recipient may do as it wishes if it receives a request with addressing that is inconsistent with where it is received. Paul Yuantao Zhang wrote: > Dear all > > Thanks for your reply. Please let me ask my question in another way. > > =============================================================== > > UDP: > > Src port: 5060 > > Dst port: 5555 *ß------------ > > =============================================================== > > SIP: > > INVITE sip:[EMAIL PROTECTED]:5555 SIP/2.0 *ß------------ > > Via: SIP/2.0/UDP 192.168.100.3:5060;rport;branch=z9hG4bK27195 > > From: <sip:[EMAIL PROTECTED]>;tag=27266 > > To: <sip:[EMAIL PROTECTED]:5555> > > Call-ID: [EMAIL PROTECTED] > > CSeq: 20 INVITE > > Contact: <sip:[EMAIL PROTECTED]:5060> > > =============================================================== > > The above "Invite" message is over UDP. In the UDP part (Transport > layer), the Destination port is 5555. In the SIP part (application > layer), the port in the "Invite" request-line URL is 5555 too. Both of > them are same. In which case the port in "Invite" request-line URL is > different from the Destination port in lower layer UDP? Furthermore, if > they are always same why we include redundant information (the port > number) in "Invite" request-line URL? What happens if the port in > "Invite" request-line URL is different from the Destination port in > lower layer UDP? > > Thank you very much > > Best Regards > > Yuantao >
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