ZyXEL MAX208M2W User Guide - Page 169
The VoIP Account Screens, WiMAX Device Configuration User's Guide
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Chapter 10 The VoIP Account Screens Table 76 SIP Call Progression (continued) A P 13. UPDATE SE: 3600 14. UPDATE SE:3600 16. OK SE: 3600 17. BYE B 15. OK SE: 3600 18. OK 1 A sends a SIP INVITE request. This message is an invitation for B to participate in a SIP telephone call. A's INVITE specifies a SE of 60 seconds. 2 A's request arrives at P but is below the minimum allowed value of 3600, so it is rejected with a 422 message, which contains the MSE of 3600. 3 A sends an ACK to acknowledge the message was received. 4 A retries the INVITE request with SE of 3600 and MSE of 3600. 5 The SE in the new INVITE is acceptable so P forwards it to B. 6 B receives the INVITE. 7 B responds with an OK message which includes the SE of 3600. 8 P forwards the OK message to A. 9 A receives the OK. 10 A then sends an ACK message to acknowledge that the call is established completely. 11 The proxy server forwards the ACK message to B. 12 Now A and B exchange voice media (talk). 13 After around half of the SE time period is reached, or 1800 seconds in this case, A sends an UPDATE request to refresh the session. WiMAX Device Configuration User's Guide 169