Rejected Outbound ISDN calls
Symptom:
Outbound ISDN calls are rejected by the switch due to a missing IE (3.1 Extension Bit/Interface Identifier). This behavior is seen with 4ESS ISDN configuration after upgrading to SR5.1.1 SU125 or higher.
Reason for the problem:
According to AT&T Telco Specifications (TR41459) octet 3.1 (Extension Bit/Interface Id) can be omitted when the "interface identifier present" field in octet 3 indicates "interface implicity identified".
In Service Update 125, corrections was made to the springware firmware, NOT to send octet 3.1information element, if a board was NOT configured in an NFAS group. On earlier SUs, the springware firmware would always set the Interface ID Present and send octet 3.1 even in Non-NFAS configurations. Some switches are configured to require this octet for both configurations and may reject the ISDN call if the setup is missing IE (octet 3.1, Extension Bit/Interface Identifier).
Here's a partial layer 2 trace (D-channel trace log) of the setup message of 2 calls from 2 different SUs.
[Partial Setup from SR5.1.1 SU98. You can see the Interface ID is present and the Extension Bit octet is present by default]
1: CHANNEL ID(0x18)
2: IE Length(0x04)
3: 1------- Extension Bit
-1------ Interface ID Present
--1----- Interface Type
---0---- Spare
----1--- Preferred/Exclusive
-----0-- D-Channel Indicator
------01 Info. Channel Sel.
3.1: 1------- Extension Bit
-0000000 Interface Identifier 3.2: 1------- Extension Bit
-00----- Coding Standard
---0---- Number Map
----0011 Channel/Map Element
[Partial Setup from SR5.1.1 SU125. You can see the setup is compliant according to AT&T's specification, where the Interface ID is not set and extension Bit octet is NOT present by default]
1: CHANNEL ID(0x18)
2: IE Length(0x03)
3: 1------- Extension Bit
-0------ Interface ID Present
--1----- Interface Type
---0---- Spare
----1--- Preferred/Exclusive
-----0-- D-Channel Indicator
------01 Info. Channel Sel.
3.2: 1------- Extension Bit
-00----- Coding Standard
---0---- Number Map
----0011 Channel/Map Element
Fix / Solution:
Try to get the switch Engineer to make the appropriate changes on the switch. If the changes cannot made refer to work around solution below.
Workaround:
If the switch requires octet 3.1 to be present for non-NFAS configurations, perform the following configuration changes:
Step 1. Modify the nfas.cfg file so that each span is in its own NFAS group.
#NFAS group 1
# Board ID Interface ID Channel board ID NFAS group ID
1 0 1 1
2 1 2 2
3 2 3 3
Step 2. Do not modify parameter 0016 in the isdn parmeter file (4ess.prm) for each span as you normally would within an NFAS environment. Instead, leave the D-channel as enabled:
;---
;--- ENABLE/DISABLE the D channel (Parameter type 16H)
;--- Used only when the protocol type (Parameter number 13H) is
PRI ISDN
;--- for NFAS configuration.
;--- Possible values for the data are as follows:
;--- 00H = Undefined.
;--- 01H = Enable the D channel.
;--- 02H = Disable the D channel.
0016 01
Step 3. Restart the drivers for the changes to take affect.
Product List
- D/240JCT-T1
- D/480JCT-2T1
Glossary of Acronyms / Terms
SU = Service Update
Related Documentation
SPRINGWARE:
9.3. Editing NFAS Configuration Files
http://resource.intel.com/telecom/support/documentation/unix/rel2_openserver/htmlfiles/install/0948-03-48.html
ISDN NFAS Setup On Windows* NT
http://resource.intel.com/telecom/support/tnotes/tnbyos/winnt/tn177.htm
First published: 06-Apr-2008
Open access: Product rule: ; Page rule: Auto
