The IMG 2020 can monitor the status of multiple external SIP gateways by sending periodic SIP OPTIONS messages. If the gateway does not respond to one OPTIONS message the gateway will be considered down or unreachable and attempt to re-route the call to a different gateway. Once the gateway is down or considered unreachable it will take the configured amount of responses to show the gateway as UP or Reachable. SIP Options Keep Alive - Gateway Busy Out follows RFC 3261 SIP: Session Initiation Protocol, Section 11.
Configuration
The procedure below explains how to configure the IMG 2020 to transmit SIP Options messages to a specific gateway to see if it is still alive. Before configuring, the IMG 2020 must have an initial configuration created on it. Follow the procedure before proceeding. Once all initial steps have been executed the IMG 2020 can be configured for the Gateway Busy Out feature. Follow steps below:
If the Options Keep Alive property is enabled, disable it before changing other Properties in the SIP External Gateway object. Then, re-enable it once the other changes have been made. This sequence will ensure the IMG 2020 is configured correctly.
Create SIP Profile (SGP) and SIP Options Keep Alive
Right click on the Profiles object and select New SIP Profiles. The SIP Profiles object is a parent or container object. No configuration is needed here. Refer to the SIP Profiles topic for more information on this object.
Right click on the SIP Profiles object and select New SIP Profile. The first profile that gets created is a Default SIP Profile and cannot be modified. Disregard this profile.
Right click on the SIP Profiles object and select New SIP Profile again. In the SIP Profile object that appears, either enter a name that identifies this SIP Profile or accept the default name already entered. In this example the SIP Profile was labeled SIP_Options_KeepAlive_Profile.
Right click on the SIP Profile object just created and select New Options KeepAlive. Modify the fields as required.
Number of Responses - Number of responses received before marking the gateway as reachable. Drop down menu has selections from 1 to 10 (Default 3).
Up Timer (s) - Timer to define the interval the IMG 2020 will send the OPTIONS message to the gateway when the gateway up and responsive. Timer is in seconds (Default=120 seconds)
Down Timer (s) - Timer to define the interval the IMG 2020 will send the OPTIONS message to the gateway when the gateway is down or non responsive. Timer is in seconds (Default=30 seconds)
Refer to SIP Profile - Options Method - Busy Out-Keep Alive for more information.
Create Remote Gateway
Create an external network element. To associate the SIP profile created with a remote SIP gateway, an external network element must be created. Follow procedure below to communicate with a remote gateway.
Right click on the Dialogic object and select New External Network Elements. The External Network Elements object is a parent or container object and no configuration is needed here. Refer to External Network Elements topic for more information.
Right click on External Network Elements and select New External Gateways. The External Gateways object is a parent or container object also and no configuration is needed here. Refer to External Gateways for more information.
Right click on External Gateways and select New External Gateway. Enter a name that identifies the gateway being configured. In this example the gateway was labeled SIP_Options_GW.
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Refer to External Gateway topic for more information.
Configure SIP Signaling
The configuration above displays how to configure the SIP Profile and External SIP Gateway so that the SIP Options-Busy Out/Keep Alive functionality is configured. The next step is to configure the SIP signaling stack and SIP Channel Groups. Refer to the Configure SIP (Single SIP IP) topic for a procedure on how to configure the SIP functionality.
Call Tracing
Call Tracing will capture the sending/reception of the OPTIONS method and indicate that re-routing has taken place because the gateway is down. See example trace below.
Example Call Trace
21:24:03.305 SIP (W)
<--- [10.129.43.154, 5060 <- 10.129.43.23, 5060]
OPTIONS sip:10.129.43.154:5060;ttl=0 SIP/2.0
Via: SIP/2.0/UDP 10.129.43.23:5060; rport;branch=z9hG4bK-6df4-1156281802-19999-423
Call-ID: 5aa9-1e61-7222006212322-chiloe-0@10.129.43.23CSeq: 1 OPTIONS
Max-Forwards: 70
To: <sip:10.129.43.154;ttl=0>
From: <sip:10.129.43.23>;tag=95ffcd055e0f78f7d5d397020e89288db5f2
User-Agent: Dialogic-SIP/10.3.2.57 chiloe 0
Contact: <sip:10.129.43.23:5060>
Accept: application/ sdp
Content-Length: 0
Example entry in Call Trace
13:12:48.804 CALL(GCL) (01:00003:01) WARNING: Channel Group [Lap_PC],GWIP [10.129.51.137] DOWN, trying next one
Additional Information
The SIP Options message being sent is supported on UDP only. When SIP Options Keep Alive is configured, verify the Default Transport type within the SIP Signaling object is set to UDP.
When sending a 200 OK to an OPTIONS request the IMG 2020 will not include SDP information.
If an OPTIONS message is not answered the corresponding gateway will be marked as down or unreachable.
When a call is attempted to an unreachable gateway, the IMG 2020 will automatically trigger the re-attempt logic if the gateway is part of a route list.
A gateway will only be marked as reachable when the number of sequential responses meet the configured value. (SIP Options Keep Alive Pane = Profiles/SIP SGP/SIP Options Keep Alive Pane)
The IMG 2020 will keep sending OPTIONS request at a configured rate. (SIP Options Keep Alive Pane = Profiles/SIP SGP/SIP Options Keep Alive Pane)