Control, Transmission, and Synchronization Interfaces
5-6 Issue 8.0 July 2002
The FT-2000 OC-48 Add/Drop-Rings Terminal for 2-Fiber Rings interfaces with up
to 48 bidirectional DS3 equivalent signals (DS3, EC-1, and/or OC-3
*
)and2
OC-48 high speed lines (1E and 1W). Each OC-48 high speed line consists of
sixteen 155 Mb/s (STS-3) tributaries. The STS-3 tributaries 1 through 8 are the
service tributaries, and STS-3 tributaries 9 through 16 are the protection
tributaries. In Figure 5-3, the eastbound service STS-3 tributaries are identified
as
Service 1
and the westbound service tributaries are identified as
Service 2
.
The eastbound protection STS-3 tributaries are identified as
Protection 2
and the
westbound protection STS-3 tributaries are identified as
Protection 1
.
If a failure occurs, the eastbound service STS-3 tributaries (Service 1) are
protected by the westbound protection STS-3 tributaries (Protection 1). The
westbound service STS-3 tributaries (Service 2) are protected by the eastbound
protection STS-3 tributaries (Protection 2). For more information about 2-fiber
ring protection switching, electrical low speed protection switching, and optical low
speed protection switching, refer to Volume I, Section 9, "Maintenance
Description."
Internally, the FT-2000 OC-48 Add/Drop-Rings Terminal for 2-Fiber Rings employs
standard synchronous multiplexing for add/drop and through traffic. (Refer to
Appendix A, "A SONET Overview.") To add DS3 or EC-1 electrical low speed
signals, each electrical low speed interface circuit pack (DS3 or STS1E) accepts
up to three low speed signals (DS3 or EC-1) and maps them into
155 Mb/s signals (STS-3 tributaries). To add OC-3 optical low speed signals, each
OC3 (1.3 STD) circuit pack accepts one OC-3 low speed signal and maps it into
an STS-3 tributary. These add/drop STS-3 tributaries are combined with the
through STS-3 tributaries, multiplexed to one STS-48 signal, and converted to an
optical OC-48 signal for transmission over high speed line 1E or 1W.
To drop DS3, EC-1, OC-3, and/or OC-12 low speed signals, the incoming optical
OC-48 signal is converted back to an electrical STS-48 signal and is
demultiplexed to sixteen STS-3 tributaries. The STS-3 tributaries that are
designated to be dropped are demultiplexed into DS3, EC-1, and/or OC-3 low
speed signals. The STS-3 tributaries not designated to be dropped are the
through traffic. The through traffic is combined with the add traffic for transmission
in the opposite direction.
* One OC-3 signal is equivalent to three DS3 or EC-1 signals.
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