1-2 61204659L1-1A
Section 1, Introduction MX2800 STS-1 User Manual
STS-1 Overview
Controller Card 1:1 Redundancy
The MX2800 STS-1 supports two hot-swappable controller cards which provide 1:1 redundancy for the T1
and STS-1 signals as well as the STS-1 connections. With two cards installed, the MX2800 STS-1 can
recover from circuit or network failure, depending on the configuration. Refer to Section 7, Circuit Redun-
dancy for more information.
2. STS-1 OVERVIEW
The MX2800 STS-1 multiplexer delivers up to 28 T1s or 21 E1s via the SONET Synchronous Transport
Signal Level One (STS-1) at a speed of 51.84 Mbps. This is a cost-effective method for providing T1/E1
signals without the need for costly and complex multi-level multiplexing/demultiplexing as in an M13
multiplexer. The T1/E1 signals can be directly multiplexed into the SONET STS-1 signal, allowing simpli-
fied add and drop functionality.
The MX2800 STS-1 multiplexer also implements VT hairpinning and VT cross-connect mapping. Any VT
can be hairpinned back to the STS-1 signal for dropping further down the SONET ring. Cross-connect
mapping permits a VT to be mapped to any of the 28 available physical ports. The relationship of MX2800
STS-1 components and SONET terminology is illustrated in Figure 1-1.
Figure 1-1. MX2800 STS-1 Components
STS-1 Framing Structure
The STS-1 frame is organized as 9 rows by 90 columns of bytes. See Table 1-1. This frame is transmitted
row by row, from left to right, and with the most significant bit (MSB) of each byte transmitted first. It is
defined to operate at the basic rate of 8 kHz or 125 microseconds per frame, or 8,000 frames per second at
a bit rate of 51.84 Mbps.
The frame is divided into two parts to physically segregate the layers:
• Transport Overhead
• Synchronous Payload Envelope
The first 3 columns make up the transport overhead (TOH); the remainder is the synchronous payload
envelope (SPE). The TOH has 3 rows for the section overhead (SOH) and 6 rows for the line overhead
(LOH). The SPE has one column for the path overhead (POH). The remaining 86 columns are for payload
data (49.536 Mbps).
A
C
T
N
E
T
A
L
M
P
R
F
A
C
T
N
E
T
A
L
M
P
R
F
Multiplexer MultiplexerAdd/Drop
Multiplexer
Repeater Repeater
SECTION (single run of fiber)
LINE (between multiplexers)
PATH (end-to-end)
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