Type: String
Identifies class or source of the UnderlyingSecurityAltID (458) value. Required if UnderlyingSecurityAltID is specified.
Valid values:
Same valid values as the SecurityIDSource (22) field
Added in protocol FIX.4.3
See in: FIX.4.3, FIX.4.4, FIX.5.0, FIX.5.0SP1, FIX.5.0SP2 EP240.