Nortel Networks 3500, NTRN10AN manual OC-12 Protection switching, Optical receive, +1 linear

Hardware feature descriptions 3-73

Optical receive

The OC-12 interface receives an optical OC-12 signal on the optical receive channel. The OC-12 optical signal is converted into an STS-12 or STS-12c signal. The STS-12 or STS-12c signal is transmitted to the STX and VTX-series circuit packs.

Since different optical reaches are supported on OC-12, optical link budgets need to be calculated to determine if VOAs are required on a particular link.

Equipping rules

The OC-12 optical interface circuit pack can be installed in slots 3 through 12. See Table 3-3 on page 3-6for operational temperature ranges.

Note: For support of the OC-12 line rate in slots 11 and 12, your shelf must be equipped with the VTX-48e circuit pack (NTN414AB or NTN414AH).

1+1 linear

A protected linear system operating an OC-12 line rate requires two OC-12 circuit packs in each shelf. An unprotected linear system requires only one OC-12 optical interface circuit pack in each shelf. The additional OC-12 optical interface circuit packs can be installed in the shelf to provide OC-12 tributaries.

Unidirectional path switched rings (UPSRs)

UPSRs operating at an OC-12 line rate require two OC-12 circuit packs in each shelf.

OC-12 Protection switching

OC-12 traffic is protected by linear and path protection.

OC-12 linear protection switching is 1+1 non-revertive, unidirectional, or bidirectional. If a fiber cut occurs in either the receive or transmit fibers of the active fiber path, or the transmitter or receiver OC-12 optical interface circuit pack fails at either end of the active fiber path, traffic is switched from the active OC-12 transmitter or receiver to the standby OC-12 transmitter or receiver. Switching can also take place under user control.

For bidirectional protection switching, if one of the two fibers fails, traffic on both fibers is switched to protection. For unidirectional protection switching, if one fiber fails, traffic from that fiber is switched to protection, traffic on the other fiber remains on the fiber. Both OC-12 interface circuit packs are active if unidirectional switching occurs and one fiber fails.

The signal degrade threshold is user-provisionable for the working OC-12 facility of a 1+1 linear protected OC-12 pair. The default value is 10-6. The threshold is provisionable within the range 10-5to 10-9. If the bit error rate (BER) drops below the threshold, an autonomous protection switch occurs.

Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004