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Precautions for CPOS Interface Configuration When the NE40Es Replace Cisco Devices

Publication Date:  2019-07-03 Views:  314 Downloads:  0

Issue Description

On a network of Carrier A, C suplier devices are used as core devices and connect to C suplier routers in other cities through CPOS E1 channels. Huawei's NE40E is used to replace C 7507. During the link test, it is found that traffic forwarding fails on the CPOS E1 channel after the original configuration of the 7507 is compiled to the NE40E. 

Handling Process

1. Check the link. No error packet is received on the interface, and the receive and transmit optical power are normal.

2. Check the board. The board registration is normal, no alarm is generated, and no board reset record is displayed in the hidden view.

3. Check the device configuration at both ends. All the interconnection parameters are correct.

4. It is suspected that the problem is caused by inconsistent timeslots on both ends. In this case, you need to check timeslot mapping during transmission.

Huawei's devices are used for intermediate transmission. Huawei's transmission devices adopt the sequential coding structure, whereas devices of C suplier , Lucent, FiberHome, ZTE, and Alcatel use timeslot coding mode. When all devices on the live network are from C suplier, the timeslots on both ends can be mapped. However, when the NE40E is used as the core device, its timeslot sequence needs to be changed to ensure interconnection with other vendors' devices on the city network.

Because CPOS interfaces adopt byte interleaved multiplexing, the lower-order VCs in a higher-order VC are not arranged in sequence. To facilitate user configuration, the following takes the CPOS E1 channel adopting AU-4 multiplexing course as an example to introduce the method of calculating TU numbers.
When the AU-4 multiplexing course is adopted, the 2 Mbit/s multiplexing structure is 3-7-3. The following formula shows how to calculate the numbers of TU-12s located in different positions in a VC-4.
VC-12 number = TUG-3 number + (TUG-2 number – 1) x 3 + (TU-12 number – 1) x 21
In a VC-4, all TUG-3s are numbered the same, and all TUG-2s are numbered the same. The two TU-12s with a difference of 1 in number are adjacent.

The original configuration of the NE40E:
controller Cpos6/0/0
clock master
frame-format sdh
multiplex mode au-4
e1 1 unframed
e1 2 unframed
e1 3 unframed
e1 4 unframed
e1 5 unframed
e1 6 unframed
e1 62 unframed
e1 63 unframed

The configuration of the NE40E is changed as follows:
controller Cpos6/0/0
clock master
frame-format sdh
multiplex mode au-4
e1 1 unframed
e1 22 unframed
e1 43 unframed
e1 4 unframed
e1 25 unframed
e1 46 unframed
e1 7 unframed
e1 28 unframed
e1 49 unframed
e1 10 unframed
e1 31 unframed
e1 52 unframed
e1 13 unframed
e1 34 unframed
e1 55 unframed
e1 16 unframed
e1 37 unframed
e1 58 unframed
e1 19 unframed
e1 40 unframed
e1 61 unframed
e1 2 unframed
e1 23 unframed
e1 44 unframed
e1 5 unframed
e1 26 unframed
e1 47 unframed
e1 8 unframed
e1 29 unframed
e1 50 unframed
e1 11 unframed
e1 32 unframed
e1 53 unframed
e1 14 unframed
e1 35 unframed
e1 56 unframed
e1 17 unframed
e1 38 unframed
e1 59 unframed
e1 20 unframed
e1 41 unframed
e1 62 unframed
e1 3 unframed
e1 24 unframed
e1 45 unframed
e1 6 unframed
e1 27 unframed
e1 48 unframed
e1 9 unframed
e1 30 unframed
e1 51 unframed
e1 12 unframed
e1 33 unframed
e1 54 unframed
e1 15 unframed
e1 36 unframed
e1 57 unframed
e1 18 unframed
e1 39 unframed
e1 60 unframed
e1 21 unframed
e1 42 unframed
e1 63 unframed

The interface serial 6 also needs to be configured according to the E1 timeslot sequence.
interface Serial6/0/0/1:0
link-protocol hdlc
ip address X.X.6.145
ospf authentication-mode md5 1 cipher XXXX
mpls ldp
interface Serial6/0/0/22:0
link-protocol hdlc
  ip address X.X.6.149
ospf authentication-mode md5 1 cipher XXXX
mpls ldp
interface Serial6/0/0/43:0
link-protocol hdlc 
ip address X.X.6.153
ospf authentication-mode md5 1 cipher XXXX
mpls ldp

Root Cause

1. The link is faulty.

2. The board is faulty.

3. Port negotiation between the NE40E and vendor C's devices is abnormal.

4. The timeslot division of the E1 channel is incorrect (the intermediate transmission devices need to be considered).


The timeslot coding mechanism of Huawei differs from that of peer vendors. Therefore, check whether the timeslot coding sequence is correct when interconnection through CPOS interfaces fails.