E1 Service Interruption Caused by Different Timeslot Numbering Schemes (ITU-T G.707 and ITU-T G.709)

When different devices or networks are interconnected with each other to provide services, part of the services are interrupted if different timeslot numbering schemes are adopted. After a timeslot numbering scheme is adopted, the fault is rectified.

Product

OptiX OSN 7500, OSN3500, OSN 2500

Fault Type

• Configuration problem
• Device interconnection failure
• Service interruption

Symptom

Two transmission devices from different vendors are interconnected with each other, and 20 timeslots of one STM-1 are adopted to transmit E1 services. When the services are configured, it is found that seven E1 services of timeslots 1, 4, 7, 10, 13, 16 and 19 are normal, and 13 E1 services of timeslots 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, 18 and 20 are interrupted.

Cause Analysis

Company A uses a Huawei device, which adopts the ITU-T G.707 timeslot numbering scheme. Company B uses the device of a competitor, which adopts the ITU-T G.709 timeslot numbering scheme.

 NOTE:

The sequences of timeslots 1, 4, 7, 10, 13, 16, and 19 in the two timeslot numbering schemes (ITU-T G.707 and ITU-T G.709) are the same, but the sequences of timeslots 2, 3, 5, 6, 8, 9, 11, 12, 14, 15, 17, 18 and 20 in the two timeslot numbering schemes are different, thus causing the service interruption.

Procedure

1. According to the timeslot sequence from 1 to 20, configure the E1 services on the device of company A.
2. Configure the services on the device of company B. Table 1 shows the mapping of timeslot numbers.

   Table 1Mapping of timeslot numbers between the devices of companies A and B
   Company	Timeslot Number
   A	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20
   B	1	22	43	4	25	46	7	28	49	10	31	52	13	24	55	16	37	58	19	40

    NOTE:

   You can configure the E1 services on the device of company A, and then according to the timeslot mapping, configure the services for corresponding timeslots on the device of company B. For the corresponding timeslots, see Table 1.

Reference Information

• The ITU-T G.707 timeslot numbering scheme adopts the sequential mode, which is also called Huawei mode, as shown in Figure 1. The numbering scheme is as follows: VC-12 number = TUG-3 number + (TUG-2 number - 1) x 3 + (TU-12 number - 1) x 21.
• The ITU-T G.709 timeslot numbering scheme adopts the interleaved mode, which is also called Lucent mode, as shown in Figure 1. The numbering scheme is as follows: VC-12 number = (TUG-3 number - 1) x 21 + (TUG-2 number - 1) x 3 + TU-12 number.

Figure 1 ITU-T G.707 timeslot numbering

Figure 2 ITU-T G.709 timeslot numbering

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