Local / Remote cause code 34 in Reason Header
Before the introduction of feature F-5761, if there were no resources
available the IMG would send out a 503 Service Unavailable message to
the incoming SIP network informing the SIP entity that there were no resources
available. The 503 message sent would not give any indication as to whether
the IMG itself was out of resources
or whether the SS7 network on the outgoing side was out
of resources. With the introduction of this feature, a user can
distinguish whether the release “503 Service Unavailable” sent by IMG
to the SIP entity was caused due to the IMG being out of resources or
the outgoing SS7 network is out of resources. This feature will be disabled
by default.
Call Flow
With the feature set to Enabled
the next two examples display the functionality of the feature.
Example 1
The call flow below displays when the IMG is out of resources and the
feature is enabled. In a SIP to SS7 call, when IMG detects no channel
at the outgoing side, it shall send “503 Service Unavailable” to the SIP
side with Reason-header having the following details: “Reason: Q.850;
cause=34; text=”No Circuit/Channel Available, Local”

Example 2
The call flow below displays what is sent back to the SIP network when
the SS7 network is out of resources and a cause code of 34 is sent to
the IMG. In a SIP to SS7 call, when IMG receives REL with cause code 34
from the SS7 network side, it shall send “503 Service Unavailable” to
the SIP side with Reason-header having the following details: “Reason:
Q.850; cause=34; text=”No Circuit/Channel Available”

Call Trace
The call trace below is the call trace from Example
1 above where the resources on the IMG are unavailable
17:04:16.083 CALL(L4) (00:00018:00)
SENT Route Control Rej to SIP
17:04:16.083 CALL(SIP)
(00:00018:00) RCVD Route Control Rej from L4
17:04:16.083 CALL(SIP)
(00:00018:00) NO CHANNEL AVAILABLE!!!
17:04:16.083 CALL(SIP)
(00:00018:00) Reason Hdr: "No circuit/channel available,Local"
17:04:16.083 CALL(SIP)
(00:00018:00) Channel query rejected
17:04:16.083 CALL(SIP)
(00:00018:00) SENT 503 Service Unavailable to 10.129.39.
101:8000
Cseq:1
17:04:16.083 CALL(SIP)
(00:00018:00)
<---
[10.129.39.101, 8000 <- 10.129.39.51, 5060]
SIP/2.0
503 Service Unavailable [Channel query rejected]
\r\n
Via:
SIP/2.0/UDP 10.129.39.101:8000;received=10.129.39.101\r\n
Call-ID:
1-8464@10.129.39.101\r\n
From:
"1111" <sip:anonymous@10.129.39.101:8000>;tag=1\r\n
To:
3333 <sip:3333@10.129.39.51:5060>;tag=a94c095b773be1
dd6e8d668a785a9c842326ff21\r\n
Contact:
<sip:3333@10.129.39.51:5060>\r\n
CSeq:
1 INVITE\r\n
Server:
Dialogic-SIP/10.5.3.83 img51 0\r\n
Reason: Q.850 ;cause=34 ;text="No
circuit/channel available,Local"\r\n
Content-Length:
0\r\n
\r\n
Configuration
Below are instructions
on how to configure the IMG to send a Reason Header to the incoming SIP
entity displaying whether the call failed because resources were not available
on the IMG or not available in the SS7 network.
Configure these initial
objects before proceeding to the procedure below.
Create SIP Profile and SIP Headers object.
- Right click on the Profiles object and select New
SIP SGP. Modify the SIP Profile Id field so the
ID is something other than ID:0. Once ID:0 is changed then the rest
of the fields can be modified. Refer to the SIP
Profile - 10.5.3 topic for more information on configuring this
object.
Note:
Profile Id:0 is a default ID and the fields cannot be modified while the
ID is left as ID:0.
- Right click on the SIP Profile created and select New
SIP Headers. To enable the feature, select Enable
in the drop down menu of the Reason-Header
Local field. See screen capture below.

Create SIP Channel Group
- Right click on the Routing Configuration object and select New Channel Groups. The Channel
Groups object is a container object for multiple channel group objects.
Refer to the Channel Groups object
for more information.
- Right click on Channel Groups object and select New
Channel Group. Set the Signaling
Type field to SIP and enter a name for this channel group.
Refer to Channel Group topic for more
information on configuring a SIP Channel Group.
Create External SIP Gateway
- Right click on IMG EMS and select New
External Network Elements. No configuration is accomplished
here. The External Network Element pane is a parent object to multiple
external entities in the network. Refer to External
Network Elements topic for more information.
- Right click on the External Network Elements object and select
New External Gateways. Again,
no configuration is accomplished here. Refer to External
Gateways object for more information.
- Right click on External Gateways object and select New
External Gateway. Enter a name to identify this gateway, modify
the Gateway Signaling Protocol field to display SIP, and enter an
IP address in the Gateway IP Address field. Refer to the External
Gateway topic for more information on configuring the gateway
object.
- In the SIP Profile field, select from the drop down menu, the SIP
Profile created earlier . Within the SIP Profile field select the
SIP SGP created above for the Local/Remote cause code feature. See
screen capture below.

Right click on the SIP channel group
created earlier and select New IP
Network Element. Select the gateway created above that has
the Generic Notification SIP SGP associated with it.
At this point the feature has been configured.
Routing and translations can now be accomplished.
Additional Information
This feature is applicable only when the IMG outgoing side (SS7
CICs) are out of resources. No reason header is sent in ‘503 Service
Unavailable’ when the IMG incoming side (IP channels) is out of resources.
This feature is applicable for only Release reason 34 and SIP
to SS7 calls.