单项选择题
A. SDH circuit over a SONET network delivering it as an SDH signal
B. SDH circuit over a SONET network delivering it as a SONET signal
C. SONET circuit over an SDH network delivering it as an SDH signal
D. SONET circuit over an SDH network delivering it as a SONET signal
单项选择题 In order to avoid misconnections due to a failed node in a Bidirectional Line Switched Ring (BLSR), Alarm Indication Signals (AISs) are sent on every channel normally terminating in that node. What is the name of this process?（）
单项选择题 How is UPSR and BLSR traffic rerouted during a protection switch when a complete fiber cable cut occurs?（）
单项选择题 What protection method is used in 4F BLSR networks?（）