This is the information structure used to support information pay load and over
head information field organized in a block frame structure which repeats every
125 micro seconds.
• CONTAINER :
The first entry point of the PDH signal is the container in which the signal is
prepared so that it can enter into the next stage i.e. virtual container. In container-
1 the signal speed is increased from 32 bytes to 34 bytes in the case of 2Mbps.
• VIRTUAL CONTAINER :
In virtual container the path over head {POH) fields are organized in a block
frame structure either 125 micro seconds or 500 micro seconds. The POH
information consists of only 1 byte in VC-1 for 125 micro seconds frame.
In VC-3 and VC-4, POH is 1 column of 9 bytes. The types of virtual container
identified are orders VCs VC-1 and VC-2 and higher order VC-3 and VC-4.
• TRIBUTARY UNIT(TU) :
A tributary unit is a information structure which provides adaption between the
lower order path layer and the higher order path layer . It consists of a information
pay load.
• TRIBUTARY UNIT GROUP :
One or more tributaries are contained in tributary unit group. A TUG-2 consist of
homogenous assembly of identical TU-1s or TU-2. TUG-3 consists of a
homogenous assembly of TUG-2s or TU-3
• NETWORK NODE INTERFACE(NNI):
The interface at a network node which is used to interconnect with another
network node.
• ADMINISTRATIVE UNIT(AU) :
It is the information structure which provides adaptation between the higher order
path layer and the multiplex section layer.
• ADMINISTRATIVE GROUP :
It is a group of same type AU.
SDH SYSTEM :
It may functionally be subdivided into four parts :
1. Mechanical system
2. Transport System
3. Management System
4. Power System
1. MECHANICAL SYSTEM : This part covers the mechanical parts.
These mechanical parts are :
• RACK : It is a rectangular box of size :
600mm x 2200mm & 600mm x 1600mm
• SUBRACK : It is a mechanical frame that can be mounted in a rack. It holds the
moduls of the system. Upto three mother board groups can be mounted in this
subrack. One NE uses one, two or all three motherboard groups in the subrack. The
connections between motherboard groups are made by cables. Upto three NEs can
placed in the subrack.Empty positions in the subrack are to be covered by a
coverplate. Each motherboard section has a width which is 1/3 of the total width.
• MODULE : It is a physical unit that can be plugged into a subrack and pulled out
again.
• RCF(RACK CONNECTION FIELD) : It provides the connection of power,
protection against surge voltages with secondary power fuses or ckt breakers are
available for rack. The RCF also includes rack alarm output and LEDs.
• SRCF(SUBRACK CONNECTION FIELD) : For wide subracks with rear cable
access as RCF.
• CABLES : Optical signals are connected on the modules in both rear and front
access systems.
2. POWER SYSTEM :
SECONDARY SUPPLY FROM STATION :
Dual DC supply with positive terminal to ground. One supply can be used as
protection supply for other one.
NOMINAL VOLTAGE : -48V
OPERATING RANGE : -36V TO -75V
TERTIARY SUPPLY( INTERNAL SYSTEM) :
OUT PUT FROM POWER SUPPLY MODULE +5V & -5V
OPERATION LIFE : 15YRS
INSTALLING OPTICAL MODULES :
1. Use of adjustements or performance of procedures other than those
specified here in may result in hazards radiation exposure.
2. Keep connectors and bare fibre ends at least 25cm away from eyes.
To completely eleminate the possibility of eye damage, the far end optical module
must be turned off.
3. Never use microscopes or magnifying glasses in connection with
laser beam (from fibre ends or connection).
4. To avoid damage to sensitive ckts, use an antistatic bracelet.
APPLICATIONS-
1. RING APPLICATION
In access network it is common to have STM-1and STM-4 ring where a limited
number of signals.
Example-2Mbit/s signals are collected from different nodes into one central node
which comprises the local exchange.By using the FIBCOM FOCUS AC1 for this
application most of the small nodes can be implemented by using only one ADM module.
monitoring of the signal at the customer side .Two customers with different
availability requirements are connected to an STM-4 ring .
The concept of STM-1 signal with a payload of 1/3 the bandwidth brings the
STM-1 supervisory function to the signal delivery point without sacrificing the
overall bandwidth of the ring.
The signals are connected to the Head end ADM-4 for further processing in a
telephone switch or a cross connect device.
STM-4 ring with STM-1 branches bringing the supervisory function to the signal
delivery point.
2. LINE APPLICATION
This type of application is a simple point to point system with two terminal
multiplexers.
This application can also be expanded with line add/drop multiplexers where an
ADM is inserted in each direction.
