Polycom Version 2.0.3B manual Behavior When the Primary Server Connection Fails

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Technical Bulletin

SoundPoint ® IP, SIP 2.1

Behavior When the Primary Server Connection Fails

For Outgoing Calls (INVITE Fallback)

When the user initiates a call, the phone will go through the following steps to connect the call:

1.Try to make the call using the working server.

2.If the working server does not respond correctly to the INVITE, then try and make a call using the next server in the list (even if there is no current registration with these servers). This could be the case if the Internet connection has gone down, but the registration to the working server has not yet expired.

3.If the second server is also unavailable, the phone will try all possible servers (even those not currently registered) until it either succeeds in making a call or exhausts the list at which point the call will fail.

At the start of a call, server availability is determined by SIP signaling failure. SIP signaling failure depends on the SIP protocol being used as described below.

If TCP is used, then the signaling fails if the connection fails or the Send fails.

If UDP is used, then the signaling fails if ICMP is detected or if the signal times out. If the signaling has been attempted with all servers in the list and this is the last server then the signaling fails after the complete UDP timeout defined in RFC 3261. If it is not the last server in the list, the maximum number of retries using the configurable retry timeout is used. For more information, refer to Server <server/> on page 95 and Registration <reg/> on page 149 of the SIP 2.0 Administrator's Guide.

Warning If DNS is used to resolve the address for Servers, the DNS server is unavailable, and the TTL for the DNS records has expired, the phone will attempt to contact the DNS server to resolve the address of all servers in its list before initiating a call. These attempts will timeout, but the timeout mechanism can cause long delays (for example, two minutes) before the phone call proceeds “using the working server”. To mitigate this issue, long TTLs should be used. It is strongly recommended that an on-site DNS server is deployed as part of the redundancy solution.

For Incoming Calls (Incoming Call Fallback)

The primary call server can use mechanisms for detecting that the Internet connection is down and route incoming calls through the PSTN link to the back-up gateway/router on-site. Since the phone is simultaneously registered to both servers, it will receive calls through the gateway even if the primary registration has not expired. This is a key advantage of the new behavior introduced in SIP 2.1.

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Contents SIP 2.0 Administrator’s Guide SoundPoint/SoundStation IP SIP Polycom, Inc Configurable Feature Keys Attribute DefaultHandset, Headset, and Speakerphone LCD Backlight Attribute Permitted Default Interpretation ValuesPermitted Attribute Values Default Interpretation DefaultExpanded Memory and Expanded Flash Memory RAM Disk ramdisk Default Interpretation MicroBrowserPermitted Values Attribute Values 6 G.722 Audio CodecAttribute Default Receive rxEq USB Diagnostics Administrator’s Guide SoundPoint IP / SoundStation IP Digit Map Billing CodeSyslog Supported Platforms Unsupported Platforms Server RedundancyDaylight Saving Time Changes for Disable Message Waiting Indicator by RegistrationDST Platform Key IDs 9.1 sip.cfg Miscellaneous Configuration File ChangesPorted on SoundPoint IP Attribute Permitted Default Interpretation Values Phone1.cfg Device Parameter Central Configuration File ChangesBoot server Sip.cfg IntroductionDial Plan in Application Configuration File Attribute Permitted Default Interpretation ValuesLocal Permitted Attribute Values Default Interpretation Attribute Permitted Values Default Interpretation Dial Plan in Per-Phone Configuration FileDial Plan in Application To Digit Map digitmap/ on Dialplan.x.digitmap is Trademark InformationBilling Code Entry on SoundPoint IP Phones with Sylantro Billing Code EntryTrademark Information Syslog on SoundPoint IP Phones Name Possible Values Description Network Configuration ChangesName Possible Values Description Flash Parameter ConfigurationSIP Server Fallback Enhancements on SoundPoint IP Phones Terminology SIP 2.0 Administrators GuideExample Deployment SIP 2.1 Server Fallback ImplementationReg.1.server.2.address=172.23.0.1 Behavior When the Primary Server Connection Fails Recommended Practices for Server Fallback Deployments Changes From Previous Phone Behavior Releases Before SIPBefore SIP Boot server Protocol in Application Configuration FileReferences Trademark Information Registration in Per-Phone Configuration File