The filter group index, from the set signaled at DOCSIS Registration. Provides a referenceable entry to which diffServClfrElementSpecific points. A packet matches this classifier entry if the packet's cable modem registered this index value as one of its four filter groups, and if the packet direction and MAC address select the use of this index among the four. Because this is the only field in this table, it is read-only, contrary to the usual SMI custom of making indices not-accessible. Note that although zero may be signaled (or defaulted) at DOCSIS Registration to indicate a default filtering group, no such entry appears in this table, as diffServClfrElementSpecific will use a zeroDotZero pointer for that classification.