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Access On LT Lines

Power Line Telephony

        As the Powerline is universal in nature,it will offer cost effective solution for last mile access and can severe as integrated
access network  providing range of services such as Telephony , Internet Access, AMR, Home Networking etc.

Architecture of a typical Powerline Access Communication System

        The typical architecture serving the purpose of last mile access is as shown below :

 In   the above architecture the area served by the step down Transformer is called service tree. In each service tree there
will be  a PLCG (PowerLine Communication Gateway ). PLCG enables the communication between PLCT's  to the external
communication  network such as PSTN ,and in between PLCT's with in each Service tree. PLCG enables all communication
services to external net work  through already existing links such as DSL, ADSL, RF based or through Optical Fiber or even
over HT-Line depending up on environment and availability .PLCT is the one which will couple the signal (voice/data)  from
customer premises /office  on to the LT line (230V) and will communicate only through PLCG. PLCT normally connected near
to  the  Step down Transformer.

Service Tree

        A typical service tree may support 20 25 voice calls , and is as shown below :

Connecting  each PLCG to the telephone network may be problem for network designers instead many PLCG s can be
connected to an Access switch, which in turn will get connected the telephone network or internet. The connection between a
PLCG to Access switch can be over a DSL.

 Communication between PLCT's

        A typical voice call originating  from a PLCT proceeds like this .The Subscriber indicates the terminal his intention  to call
another subscriber by pressing one or few keys .Then the module responsible  for voice service tells the management layer at
the PLCT that it requires so much bandwidth for constant Bit rate applications . The ML (Management layer ) at PLCT  in turn
request with the ML at the PLCG to allocate the required BW . The PLCG confirms the allocation by providing transaction  ID
and WBT (Wait Before Transmit time). Transaction ID will be used by the AL (Adaptation layer) to route the call and WBT
will be used by the MAC layer to Access the medium .This set of actions establishes a data path between the two adaptation
layers at the PLCG and PLCT. Any signaling exchanged between the exchange and the subscriber terminal goes transparently.
The data and signaling goes in the same pocket ,the AL is responsible for splitting and sending that to the server at the
appropriate format.