In country M of project M, RTN900V1R1 is utilized to be the last mile solution. The solution is such that each end site will connect to a fiber collection point (GPON
ONT) using RTN900V1R1 microwave radio. For example in Figure 1, ALBA is an end site Node-B connecting to CHEB (GPON ONT) over only one hop of microwave radio.
Figure 1. Basic topology of transmission network
During the commissioning and testing stage for one of the link, we have detected BER error in the CES services. The CES was using SAToP mode with unframed
mode. During the observation, the E1 is experiencing BER every 30 minutes or 1 hour for a very short period of time. The 24- hour BER result is shown in Figure 2.
Figure 2. BER result of CES service
We suspected the BER was due to clock tracing. Hence we have configured the clock for the link like in Figure 3. For NE at Fiber Site, we trace the clock from E1 or
Ethernet interface (Synchronous Ethernet). While for NE at End Site, we trace the clock from IF interface.
Figure 3. Clock tracing
Figure 4 shows the snapshot after configuration of clock priority for NE at Fiber Site. The link was configured to trace clock from 1st E1 to 4th E1 and all Ethernet
interfaces. The figure shows that the NE has successfully locked to clock extracted from 1st E1.
Figure 4. Clock tracing for Fiber Site over E1 or Synchronous Ethernet
Figure 4 shows the snapshot after configuration of clock priority for NE at End Site. The link was configured to trace clock from IF interfaces. The figure shows that
the NE has successfully locked to clock extracted from IF interfaces.
Figure 5. Clock tracing for End Site over IF
The BER test was performed again for 24 hours on 1st E1. The test result shows that there’s no error and the problem was solved for all the links experiencing BER.
During the BER test, we have simultaneously run RFC2544 Ethernet test using a SUNRISE tester. The Ethernet test results show that there was no packet loss.
Furthermore, there was no abnormal alarm for the radio. The link was aligned to its designed RSL with fade margin of 35dB. We suspected it was due to quality of
BNC connector connection. The error still persist even we have replaced with new BNC connector. Simultaneously all other links installed was experiencing the
same problem. We suspected it is due to the clock tracing problem of the link as there’s no clock source ready and the radio clock was at free-running mode.
It general it is a requirement to perform clock tracing for transmission equipment. Nevertheless, in many cases the microwave equipment can work error free without
tracing clock in TDM mode with electrical E1 interfaces such as RTN600 series equipment and RTN900R1V2 equipment. However, for packet microwave radio such
as RTN900V1R1, it has become a strict requirement to perform clock tracing to avoid BER.