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Knowledge Base

The POS service of NE40 is normal, but the link light is not bright.

Publication Date:  2019-07-12  |   Views:  223  |   Downloads:  0  |   Author:  Li Gonggui  |   Document ID:  EKB0000115775


Issue Description

As NE40 connects with the router of Vendor C via 155M interface POS along the transmission network, the service is normal, but the LINK light is not bright.

Alarm Information

display pos interface pos 9/1/0 

detect C2-mismatch alarm.

Handling Process

1.check if the C2 configuration of those two routers is consistent?
2.check SDH, enable it in overhead transmissionmode, that means router A sends out C2,transfer it to the router B unchangeably;
3.if want to maintain the SDH configuration, we can configure the C2 character of the POS interface to 2,consistent with the default value of SDH;
if the above method does not work, check the C2 character received by NE80 directly.
under the diagnose mode, use the Command  display lpu register slot_number  ADDR 1 
slot_number is the slot number, ADDR is the address corresponding to the register,
after executing Command, the character displayed is the C2 character received by NE80 actually. Change the C2 configuration of POS to this character, the alarm that C2 does not match must disappear.

POS2/0/0  =>   display lpu register 2 ffe20337 1
POS2/0/1  =>   display lpu register 2 ffe20237 1
POS2/0/2  =>   display lpu register 2 ffe20137 1
POS2/0/3  =>   display lpu register 2 ffe20037 1
POS2/1/0  =>   display lpu register 2 ffe00337 1
POS2/1/1  =>   display lpu register 2 ffe00337 1
POS2/1/2  =>   display lpu register 2 ffe00337 1
POS2/1/3  =>   display lpu register 2 ffe00337 1

the modification method for C2:
enter into interface POS FLAG C2 2, the configuration can be saved.

Root Cause

The service is normal, the links are correct.
via Command "display pos interface pos 9/1/0"
detect the C2-mismatch alarm.
The relative information
:C2 is one overhead byte in frame SDH, SDH tells other devices via this byte which kind of data it sends out. RFC suggestion, if one device sends PPP packets, C2 byte must be 0x16(=22). if it is the HDLC serviceC2 byte is 0xcf(=207).if it sends out the ATM service,C2 must be 0x11. if it is voice service (TUG), C2 is 2. C2 is only to identify, not affect the service. Though not match, the service is still normal.
generally, there are two reasons

1.SDH device has no the correct configuration
the general SDH network runs the voice service, so by default, the C2 of SDH is 2
it is different with the default configuration of NE80,so there is the unmatching alarm, and the LINK light is not bright. The deploying engineers have made an experiment, change C2 of NE80 to 2, the alarm disappears immediately, and the light is bright. connecting with the vendor’s device, not modify the default configuration
The default configuration of various router vendor is various. Such as  by default, the interface POS155 runs under the HDLC mode
C2 byte is 0xCF; by default, NE80 runs under the PPP mode,C2 is 0x16. If not do any modification, the C2 byte does not match.