for no the table 130 shows that for firm failures the known protection mechanisms are able to account for all combinations of hf time and wtr time with either revertive or non revertive protection the table also shows that short time failures are only able to be accounted for with non revertive protection which uses a hf time with revertive protection which uses a hf time but not a wtr time and with revertive protection which uses a hf time and a wtr time furthermore the table also shows that the known protection mechanisms are not able to handle blinking failures with non revertive protection which uses a hf time or revertive protection which uses a hf time but not a wtr time or with revertive protection which uses a hf time and a wtr time shown at 132 fig9 shows a table summarising how a protection mechanism according to an embodiment of the invention handles failures generally designated 140 similar notation to the table 130 of fig8 is used in the table 140 in fig9 the table 140 shows the various cases for revertive rev and non revertive nrev protection mechanisms which use a time period t p of the method of fig3 and or a wtr time according to the itu g 841 standard the table 140 shows that the protection mechanisms according to an embodiment of the invention are able to handle blinking failures with non revertive protection which uses a time period t p and revertive.