A CES Service Was Unavailable

Networking: BSC----NE1 (SDH equipment)----NE2 (PTN 3900)----NE3 (PTN 950)----BTS The BSC connected to a 155M optical port on NE1, which connected to the CO1 board of NE2. An attempt to provision a 2M CES service from the BSC failed after the service was configured on the SDH and PTN sides. Version information: U2000: V100R002C01SPC004 PTN 950: V100R002C00SPC300(5.65.02.13) PTN 3900: V100R002C01SPH505
Possible causes include:
a. The tunnel on the PTN side was unavailable. b. The service was incorrectly configured on SDH equipment. c. The service was incorrectly configured on PTN equipment. d. The service timeslot was inconsistently configured for the optical ports of NE1 and the BSC, or those of NE1 and NE2. e. The optical port on NE1 was faulty. f. The CO1 board on NE2 was faulty. g. The ML1 board on NE3 was faulty.
Huawei completed the following steps to diagnose the problem: 1. Tested the tunnel on the Huawei PTN side. The tunnel was available. 2. Performed an inloop at the 2M port of the ML1 board on NE3. The problem persisted according to BSC-side engineers. 3. Performed a loopback of the service timeslot on NE1 at its optical port connected to BSC (a loopback on VC-12 timeslots was not supported by NE1). The service was available according to BSC-side engineers, indicating that a fault existed between NE1 and NE3. 4. Created another CES service using another timeslot, and performed an inloop on the 2M port of the ML1 board on NE3 (a loopback on VC-12 timeslots was not supported by the CO1 board of NE2). The problem persisted according to BSC-side engineers, indicating that the service timeslot was correctly interconnected between NE1 and NE2. 5. Configured another CES service for another port on the ML1 board of NE3, and and performed an inloop on the 2M port. The problem persisted according to BSC-side engineers. 6. Performed an inloop on the 2M port of the ML1 board on NE3, and started a PRBS test on the service timeslot at the optical port of the CO1 board on NE2. Bit errors were found. 7. Re-configured the CES service on another ML1 board on NE3, and started a PRBS test. No bit error was found. 8. Performed an inloop on the 2M port of the new ML2 board on NE3. The service was available according to BSC-side engineers. 9. Replaced the faulty ML1 board on NE3. The ML1 board on NE3 was faulty. Replace the faulty ML1 board. If a CES service is unavailable, perform the following: 1. Test tunnel connectivity. 2. Configure the service on another timeslot or port and check whether the service is available. 3. Used PRBS tests to check for bit errors.
4. Configure the service on another tributary PTN 950 board or another NE and check whether the service is available.