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This Best Practice describes how the Sonus SBC 1000/2000 handles

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 (SBC)  handles incoming calls when the Server server is down or unreachable. The Sonus SBC routes the calls according to general configuration guidelines. The information below includes expected behavior for call routing when there is a problem reaching the server (i.e, registration fails, wrong configuration, etc.).

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This Best Practice assumes the following: Incoming call is based on Federated IP/Signaling Group listen port/transport protocol. Incoming call is one of the following: ISDN, SIP, or CAS.

Call Survivability when SIP Server is down - How calls are routed with PSTN Backup (SIP Survivability)

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A call route to the PSTN must be created in order for calls to be re-routed to the PSTN as a backup mechanism if the SIP Server is unavailable. See Managing SIP Server Tables and Managing Call Routing Tables.

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• Incoming call is allowed. Since the server is down, the Signaling Group's Server Status is set as Down. Instead of attempting to send calls to the server, the call proceeds to the next Destination Signaling Group (if configured based on the routing policy, which must include the PSTN). See Managing Signaling Groups.
• Based on routing configuration, incoming calls are made without any post dial delay to the configured SIP or ISDN trunk.

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Basic Call Mode with Agent Type as "Back-to-Back User Agent" Configuration - How Incoming Calls

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Are Handled

Below are the components of a basic configuration

• Endpoint is registered with the SBC 1000/2000 (see Creating and Modifying Entries in Contact Registrant Tables).
• SBC's Signaling Group is configured to send requests to a server (see Creating and Modifying Entries in SIP Server Tables).

Scenario 1: Registration to server fails; Monitor using SIP Options for the corresponding SIP Server is incorrectly configured.

The Sonus SBC handles the calls as follows:

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Scenario 2: Registration to server is not configured; Monitor using SIP Options for SIP Server fail

The Sonus SBC handles the calls as follows:

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When a very high registration expires (Global Time to Live TTL) interval is configured (configuration available through the Contact Registrant Table), ensure it is sent more frequently. For example, set the registration interval less than the time set for the Registration to expire.

The Sonus SBC handles the calls as follows: 

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Scenario 4: Registration to server fails; Monitor using SIP Options for SIP Server are successful

The Sonus SBC handles the calls as follows:

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Scenario 5: Both Registration and Monitor using SIP Options for SIP Server fail

The Sonus SBC handles the calls as follows:

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Scenario 6: Receiving a 3xx/4xx/5xx/6xx response to Register with a Retry after header

The Sonus SBC handles the calls as follows:

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Scenario 7: Receiving final 5xx/6xx (without Retry after header) failure responses to Register

The Sonus SBC handles the calls as follows:

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Scenario 8: Receiving 3xx/4xx (without Retry after header) response to Register

The Sonus SBC handles the calls as follows:

• The corresponding session is up.
• Invite requests are routed to the corresponding Signaling Group (the status is set to Up).

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Forward Register after Local Processing Mode - How Incoming Calls

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Are Handled in the

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SBC

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Below are the components of a configuration that includes Forward Register after Local Processing Mode (configured through the SIP Signaling Group).

• Endpoint is registerd with the Sonus SBC.
• SBC has a Signaling Group configured to send requests to a Server.
• Signaling Group is configured with Fwd Register After Local Processing as the SIP Mode.
• A signaling group is assocated with both call origination and termination device.

Scenario 1: Registration fails; Fwd Register Option not configured

The Sonus SBC handles the calls as follows:

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Scenario 2: Fwd Register Option fails; Registration not configured

The Sonus SBC handles the calls as follows:

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Scenario 3: Registration fails; Fwd Register Option succeeds

The Sonus SBC handles the calls as follows:

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Scenario 4: Registration succeeds; Fwd Register Option fails

The Sonus SBC handles the calls as follows:

• Normal call flow for incoming call. In case the Server is down, there may be post dial delay in attempting to call the Server.

 

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Troubleshoot Configuration for

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Connection to a Server

To troubleshoot a server failure due to configuration, verify the current Registration and SIP Server Options configured on the Sonus SBC 1000/2000.

Verify Signaling Group

In the Signaling Group screen, the selections available in the SIP Server Table drop down list are derived from the entries configured in the SIP Server Table. This signaling group is used in the SIP Server Table and corresponds to the Server being contacted.

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1. In the WebUI, click the Settings tab.
2. In the left navigation pane, go to Signaling Groups.
3. Click on the desired SIP Signaling Group.
4. In the SIP Channels and Routing portion, verify the SIP Server Table selected.
   
5. Change or update as necessary. See Creating and Modifying SIP Signaling Groups.

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Caption 0 Figure 1 Verify Signaling Group Image Modified

 

Verify Registration/Monitor for SIP Options (for SIP Server)

Through the SIP Server Table, you choose the Contact Registrant table that will be used by a Signaling Group to register one or more contacts to a registrar. Contact Registrant Tables are used to manage contacts that are registered to a SIP server. When Monitor using SIP options is selected, an Options message is sent to the server with more detailed information, such as how often the Sonus SBC 1000/2000 queries the server with an Options message to determine the server's availability.

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1. In the WebUI, click the Settings tab.
2. In the left navigation pane, go to SIP > SIP Server Table.
3. Select the desired SIP Server table that corresponds to the Server being contacted.

4. Click the Contact Registrant Table drop down box. All available registration tables listed in the Contact Registrant Tables are displayed. 

   Note
   When a challenge (401/407) is issued by the server, the table selected from the Remote Authorization drop down list is used by a SIP Server Table.

5. From the Monitor drop down list, select SIP options.
6. Verify the configuration and adjust, if necessary. See Creating and Modifying Entries in SIP Server Tables.

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Caption 0 Figure 1 Verify Registration/Monitor for SIP Options Image Modified

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Verify Configuration for Contact Registrant

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1. In the WebUI, click the Settings tab.
2. In the left navigation pane, go to SIP > Contact Registrant Table.
3. Click the table that corresponds to the Server.
4. Verify the configuration (i.e. Global Time to Live) and adjust, if necessary. See Creating and Modifying Entries in Contact Registrant Tables.

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Caption 0 Figure 1 Verify Configuration for Contact Registrant Image Modified

 

Verify Forward Register Option

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1. In the WebUI, click the Settings tab.
2. In the left navigation pane, go to Signaling Groups.
3. Click on the desired Signaling group that corresponds to the Server.
4. From the SIP Mode drop down list, select Fwd Reg. after Local Processing.

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Caption 0 Figure 1 Verify Forward Register Option Image Modified

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