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The Packet Loss Occurs During SHLQ Test Because the E1 Mode of the Modem Is Incorrect

Publication Date:  2012-07-25 Views:  31 Downloads:  0
Issue Description
The user uses the single-line high speed digital subscriber line (SHDSL) to perform a test. The SHDSL standard is formulated by the ITU-T and the SHDSL can provide high speed and symmetric rates of transmitting and receiving data on one pair of copper lines. The networking is as follows:
Router A<->SHDSL modem<-Frame E1->M1000 SHLQ board<-->M1000 SP1D<---->router B
The model of the modem is X3207D. Router A is connected to the modem through the SHDSL. Router B is connected to the SP1D board through the 2M line.
The modem is configured according to the preceding description and the M1000 SHLQ board guide. It is found that two routers can be successfully pinged, with many packets lost. 
 
Alarm Information
No alarm information on the OptiX Metro 1000 equipment 
Handling Process
1. Check the configuration of the OptiX Metro 1000 equipment. The configuration is correct.
2. Query the performance event. No bit error is found. Therefore, the OptiX Metro 1000 equipment is normal.
3. Connect two routers. No packet is lost.
4. It is inferred that the problem results from the incorrect connection of the modem to the router.
5. Check the modem guide. It is found that the modem and the router can be connected in several modes:
"0.fas only": Frame Alignment Sequence
"1.fas+crc4": FAS+CRC4
"2.fas+cas": FAS + Channel Associated Signaling
"3.fas+crc4+cas ": FAS+CAS+CRC4
"4.unframe E1": Unframe E1 mode
According to the OptiX Metro 1000 guide, only the second working mode is selected. Through the discussion with datacom engineers, the CRC mode is recommended for the test. The test is normal and no packet is lost.
Therefore, mode 1 is used for the interconnection. The problem is solved. 
 
Root Cause
The possible causes are as follows:
1.The configuration is incorrect.
2.The board hardware is faulty.
3.The grounding is incorrect. 
 
Suggestions
In the SHLQ guide, the meanings of the five modes are not described. In addition, the default mode (the second mode) is recommended for field engineers. As a result, the field fault location is wrongly guided. It is recommended that the SHQL guide should be modified and the meanings of each mode should be described.
The meanings of the five modes are as follows:
The E1 has five frame structures: FRAME E1 (four types) and UNFRAME E1 (one type).
1.PCM31 ("0.fas only"): Except timeslot 0, other 31 timeslots transmit services.
2.PCM31C ("1.fas+crc4"): Except timeslot 0, other 31 timeslots transmit services, with the CRC4 function.
3.PCM30 ("2.fas+cas"): Except timeslot 0, timeslot 16 transmits the channel associated signaling (CAS) and other 30 timeslots transmit services.
4.PCM30C ("3.fas+crc4+cas "): Except timeslot 0, timeslot 16 transmits the CAS and other 30 timeslots transmit services, with the CRC4 function.
5.UNFRAME E1 ("4.unframe E1"): All the 32 timeslots transmit services. 
 

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