Howto:Tweak SIP Response Code to Q.931 Cause Code Mapping
Applies To
This information applies to
- innovaphone SIP implementations
Build V9 Hotfix 2 (90600.02) and later.
More Information
Problem Details
Telephony protocols traditionally in use such as e.g. ISDN, SS7 and H.323 convey detailed information about failure reasons in so-called cause code information elements. SIP however relies on so-called Response Codes. When interworking calls between those protocols, cause codes must be mapped to response codes and vice versa. Unfortunately, the details of this mapping are not clearly defined. Many mappings are straight forward, but some are not. It might thus be necessary to override innovaphone's default mapping table in certain interworking scenarios. Each SIP implementation (SIP, TSIP and SIPS) has its own mapping table. Each of them can (and must) be overridden separately.
There is no clear understanding of how this mapping should look like in detail. RFC 3398 contains recommendations for most of the call codes, but it is not followed in all implementations. It may though help as a reference.
System Requirements
Available from V9 Hotfix 2, build 90600.02. Keep in mind that the setting is effective globally on the box. It is thus not possible to have a SIP connection of a specific type (SIP, TSIP or SIPS) to have a different mapping than another connection of the same type on the same box.
Configuration
The settings can be examined and altered using a hidden UI on the boxes. This is available under the following URLs, depending on the type of SIP connection:
| Protocol | URL for Mapping UI |
|---|---|
| SIP | http://x.x.x.x/SIP/mod_cmd.xml?xsl=sip.xsl |
| TSIP | http://x.x.x.x/TSIP/mod_cmd.xml?xsl=sip.xsl |
| SIP | http://x.x.x.x/SIPS/mod_cmd.xml?xsl=sip.xsl |
All values for cause codes and response codes found in the table are decimal.
The left table defines the mapping from Q.931 cause codes to SIP response codes. For example, an entry like 17 -> 486 specifies that an ISDN User busy (17) cause code will be translated to an Busy Here (486) cause code when translating a message from SIP/TSIP/SIPS to e.g. H.323. If there is no mapping defined for the cause code to be translated, then the default SIP response code Decline (603) will be used.
The table on the right side defines the reverse mappings from SIP response codes to Q.931 cause codes. If there is no mapping defined for the SIP response code to be translated, then no cause code will be generated (that is, e.g. an resulting H.323 message will have no cause code information element).
Resetting to defaults
The table will be populated with the current defaults (as defined by the firmware build you are using). When you make any changes to the mappings, these will be stored as /q931-maps and /sip-maps in the config change SIP, config change TSIP and config change SIPS config lines. To restore the defaults, you would e.g. issue the commands
config rem SIP /q931-maps
config rem SIP /SIP-maps
for SIP.
Known Problems
There is an issue in V9 hotfix 2 builds which destroys the mapping tables when changes are done to it. The feature thus is available but must not be used.
As of V9 hotfix 2, a user defined table replaces the standard settings entirely (taking the current defaults as a base). This is somewhat unfortunate, as in the event that there are changes in the standard mappings in later firmware releases, these will not be effective as there is a user defined table with only the old mappings in place.
Reference:ISDN_Cause_Codes
http://en.wikipedia.org/wiki/Q.931
http://en.wikipedia.org/wiki/List_of_SIP_response_codes