09-10-2012, 04:22 PM
SDH and GFP
SDH and GFP.pdf (Size: 441.31 KB / Downloads: 76)
The transmission is organized into frames.
• Each frame contains a fixed number of time slots.
• Each time slot is pre-assigned to a specific input
link. The duration of a time slot is either a bit or a
byte.
• If the buffer of an input link has no data, then its
associated time slot is transmitted empty.
• A time slot dedicated to an input link repeats
continuously frame after frame, thus forming a
channel or a trunk.
Pulse code modulation
• TDM is used in telephony
• Voice analog signals are digitized at the
end office using Pulse Code Modulation.
• A voice signal is sampled 8000 times/sec,
or every 125 μsec.
• A 7-bit or 8-bit number is created every
125 μsec.
The Digital Signal (DS) and ITU-T standard
• A North American standard that specifies how to
multiplex several voice calls onto a single link.
• The DS standard is a North American standard and
it is not the same as the international hierarchy
standardized by ITU-T.
• Both standards are independent of the transmission.
Fractional T1/E1
• Fractional T1 or E1 allows the use of only
a fraction of the T1 or E1 capacity.
• For example: if N=2, then only two time
slots are used per frame, which corresponds
to a channel with total bandwidth of 128
Kbps.
The terminal multiplexer :
It multiplexes a number of DS-n or E1 signals
into a single OC-N signal
• It consists of a controller, low-speed interfaces
for DS-n or E1 signals, an OC-N interface, and a
time slot interchanger (TSI)
• It works also as a demultiplexer