Nortel Networks OPTera Metro 3500 - Manual (Page 306)

3-78 Hardware feature descriptions
OPTera Metro 3500 Multiservice Platform NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
Optical receive
The OC-3 optical interface circuit pack receives an optical signal on the optical
receive channel. The optical signal is converted into an STS-3 or STS-3c
electrical signal and routed to the STX or VTX-series circuit packs.
Since the receiver sensitivity is 0 dBm, VOAs are not required for OC-3 optical
interface circuit packs.
Equipping rules
The OC-3 optical interface circuit pack can be installed in slots 3 through 10.
See
Table 3-3 on page 3-6 for operational temperature ranges.
1+1 linear
A protected 1+1 linear system operating at an OC-3 line rate requires two
OC-3 circuit packs in each shelf. Unprotected OC-3 linear systems require
only one OC-3 circuit pack in each shelf.
Unidirectional path switched rings (UPSRs)
UPSRs operating at an OC-3 line rate require two OC-3 circuit packs in each
shelf.
OC-3 Protection switching
OC-3 traffic is protected by linear and path protection.
OC-3 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-3 optical interface circuit
pack fails at either end of the active fiber path, traffic is switched from the
active OC-3 transmitter or receiver to the standby OC-3 transmitter or receiver.
Switching can also take place under user control.
For bidirectional protection switching, if one of the two fibers fail, 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-3 interface circuit packs are active if
f unidirectional switching occurs and one fiber fails.
The signal degrade threshold is user-provisionable for the working OC-3
facility of a 1+1 linear protected OC-3 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.
OC-3 path switching uses nonrevertive protection. There are no permanent
VT1.5, STS-1, or STS-3cprotection or working paths. The network element
receives two incoming VT1.5, STS-1, or STS-3c signals: one from the
provisioned working optical interface circuit pack and one from the
switchmate optical interface circuit pack. The network element selects the
better of the two signals.