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3 F
UNCTIONAL DESCRIPTION
TM-77 and MD-77 devices perform the following functions:
1. processing of electrical signals at the bit rate of 2.048 Mbit/s in HDB-3 three-level code into
a digital signal in the natural code;
2. multiplexing of four data streams at the bit rate of 2.048 Mbit/s according to the G.742
recommendation;
3. encoding in 5B/6B code;
4. processing an electrical signal into an optical one;
5. receiving of an optical signal and processing it into an electrical signal;
6. decoding of a data stream encoded in 5B/6B code;
7. demultiplexing of four data streams at the bit rate of 2.048 Mbit/s;
8. encoding of a data stream at the bit rate of 2.048 Mbit/s in HDB-3 code;
9. control and signaling of the basic parameters of the multiplexer operation and generation
of alarms in the event of failures.
3.1
Diagnostic and signaling systems
TM-77 and MD-77 type devices automatically control the parameters of E1/G.703 local
interface and linear optical signal, and detect and signalize the following conditions and values:
G.703 E1 local interface
• loss of interface input signal
• receiving of AIS signal coming from E1 interface
• receiving of AIS signal coming from demultiplexer
• HDB3 code violation
Linear optical interface:
• loss of linear input signal
• loss of frame synchronization of the received signal
• block error rates 1x10
• receiving of the AIS bit in G.742 frame signaling a remote alarm
An alarm condition is indicated as follows:
• appropriate local interface LED is switched on: LOES
• appropriate optical interface LED is switched on: LOOS, LOF, 10
• shorting of UALA, NUALA alarm relay terminals in TM-72 telecommunication rack.
When a failure is detected, a "non-urgent" alarm – NUA (indicating a failure condition,
which does not interrupt transmission) or an "urgent" alarm – UA (meaning a transmission
interruption - an immediate operator's response is necessary) is generated.
MD-77 device card signalizes generation of an urgent or non-urgent alarm by sending
a signal to activate the alarm relays in TM-72 rack. The urgent and non-urgent alarm signaling
relay contacts in the telecommunication rack are connected to DSUB- 9 female socket.
The detected failure conditions and actions taken are shown in Table 1.
IOA77-1F
4
E1/G.703 P
X
LESIOCHRONOUS
O
PERATING
-3
-6
and 1x10
exceeded
M
ULTIPLEXER
M
ANUAL
8
-3
-6
, 10
, RAL, LDF
May 2007
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