单项选择题 Which timing mode is most appropriate for an ONS 15454 that has lost its BITS-1 and optical references?（）

单项选择题 You are provisioning a DS-1 circuit on an ONS 15454 2F-BLSR with a XC-10G card. Each VT1.5 connection must also terminate via the STS matrix. On the originating circuit node, how many STS ports are now available for VT1.5 circuits?（）

单项选择题 A customer has 2 DS1s to add between adjacent nodes in a UPSR ring. What type of circuit should you recommend?（）