[nsp] clock extraction

[Carlson Per]

> From: Kostas Anagnopoulos [mailto:kostas.anagnopoulos at oteglobe.net]
> 
> Thank you very much for your reply.However,still it is not very clear to
> me how the receiver derives a clock from the bitstream of a 
> fractional e1/t1 etc. while it cannot do the same from the bitstream of an

> unclocked circuit, and requires a terminal to send the clock.
> 
> Is there a difference in the clock recovery method of the two.

No, it's not. A terminal using "clock source line" cannot tell whether the
circuit is clocked by the SP or the other terminal (as long the clock source
complies with G.703). 

As long as one of the terminals or the SP is clocking the circuit,
everything
should work fine. The hard part is figuring out if the SP clocks the circuit
;-)

The rules of thumb are (as said before):
Fractional circuits: Clocked by SP
OC-n/STM-n circuits: Clocked by SP
Full PDH-circuits: Must be clocked by one of the terminals

Of course, this implies the circuit is provided by a SP. E.g. a local
POS-circuit
(without any intervening SONET/SDH-equipment) must be clocked by one
of the terminals.

Pelle