In one network there were 5 NEs out of which 4 were ASON and one was non-ASON. TE links were normal and up between all ASON NEs and Virtual TE links were normal and up between ASON and non-ASON NE. All the connectivities were of STM-16 level. But in one TE link 'Bandwidth Usage' was 0.3% out of maximum 16VC4s. But no service was configured on it.
After analysis missmatch was located due to VC4 reserved function. One VC4 was reserved in between link on both NEs due to which it was showing "Bandwidth Usage" 0.3%. After that VC4 was get free problem was resolved and link usage was 0%.
There may be following reasons:
1) Make sure there should no residual service in any link
2) Query all NEs and Cross connections from NE Topology Management
3) Maybe some VC4 are used for reserverd purpose
Make sure in the above case reserve VC4 is not used on any VC4 out of whole link.