This object is used to represent the VT (sonet Virtual
Tributary) counting.
standard - standard counting (based on Bellcore TR253)
titan - TITAN5500 counting (based on Tellabs TITAN 5500)
Note: 'titan' is valid only if sonet line medium type
(sonetMediumType of SONET-MIB) is 'sonet' and
sonet path payload type (cspSonetPathPayload of
CISCO-SONET-MIB) is 'vt15vc11'.