Nortel Networks OPTera Metro 3500 - Manual (Page 301)

Hardware feature descriptions 3-73
Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
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 3-6 for 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
-5
to 10
-9
. If the bit error rate
(BER) drops below the threshold, an autonomous protection switch occurs.