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Circuit Pack Descriptions
7-78 Issue 3 June 2001
Detailed Description of Operation 7
Figure 7-30 is a block diagram of the STS1E circuit pack. The STS1E circuit pack
has two modes of operation determined by the setting of a hardware switch, VT-G
to and from EC-1 (high-speed mode) or STS-1 to and from EC-1 (low-speed
mode).
In the high-speed mode, the STS1E circuit pack receives eight incoming VT-G
channels (seven service and one protection) from the eight low-speed DS1/
DS1PM circuit packs and selects seven channels. These seven channels, along
with STS-1 path overhead, transport overhead, a valid STS-1 pointer, and parity
are byte-interleaved into an STS-1 formatted signal and transmitted as an EC-1
signal. In the receive direction, the incoming EC-1 signal is demultiplexed into
seven VT-G signals.
In the low-speed mode, the STS1E circuit pack selects an STS-1 signal, either
service or protection, from the OLIU circuit pack backplane and sends the signal
to the EC-1 interface (receive direction). In the transmit direction, the incoming
EC-1 signal is processed and routed to the backplane as an STS-1 signal.
In the low-speed mode, the STS1E circuit pack can be configured for a VT-based
STS-1. In this case, the STS-1 path overhead (POH) for the EC-1 is terminated.
For non-VT-based STS-1s, the STS-1 path is sent through the STS1E circuit pack
unaffected.
Regardless of the operating mode, the STS1E circuit pack:
â– Inserts transport overhead
â– Provides scrambling and descrambling
â– Provides B3ZS encoding and decoding
â– Provides waveshaping
â– Provides optional LBO for transmission to the STSX-1.
Control Circuitry 7
The STS1E circuit pack interfaces with the SYSCTL and OHCTL circuit packs.
The SYSCTL receives maintenance elements for reporting the status of the circuit
pack, the status of the incoming signal, and inventory information (
CLEI
code,
date of manufacture, etc.). These maintenance elements are used for fault
detection and isolation. Conversely, the STS1E circuit pack responds to signals
from the SYSCTL including protection switching and LED control commands.
The STS1E circuit pack accesses the SONET transport overhead and routes it,
via the transport overhead channel interface, to the OHCTL.
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