which standard is used for SES and UAS thresholds.
bellcore_tr_nwt_253_1991 -
refers to Bellcore TR-NWT-000253, 1991 or ANSI
T1M1.3/93-005R2,1993
ansi_t1231_1993 -
refers to ANSI T1.231, 1993 or Bellcore GR-253-CORE,
Issue 2, 1995
itu_g826_1995 -
refers to ITU recommendation G.826, 1995