ITU-T Recommendations

Recommendation ITU-T H.248.39 describes the principles used to identify a single session description protocol (SDP) sub-field and how to apply wildcarding to that sub-field. The sub-field may be fully specified, wildcarded (CHOOSE "$" or ALL "*") or not significant "-". Being able to identify a single sub-field is of use when requesting the media gateway (MG) to choose a parameter, specifying a range or for the purposes of auditing. Further specification of how SDP can be wildcarded will assist in interoperation between a media gateway controller (MGC) and an MG.
This revision incorporates guidelines for the wildcarding of source-specific media attributes. It also includes a package to indicate MG support for advanced wildcarding procedures that allow a MGC to request multiple SDP parameter values and/or multiple SDP lines to be returned in response to a CHOOSE request. Additionally, it allows the linking of multiple CHOOSE wildcards so that they return the same value. Furthermore, a new maintain value wildcard is introduced to allow the retention of a previously set value to avoid repetition of redundant information.