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Appendix J: Telecom Technology
Basic SDH Signal
The basic format of an SDH signal allows it to carry many different
services in its Virtual Container (VC) because it is bandwidth flex-
ible. This capability will allow for such things as the transmission of
high speed, packet switched services, ATM, contribution video and
distribution video. However, SDH still permits transport and
networking at the 2 Mbit/s, 34 Mbit/s and 140 Mbit/s levels,
accommodating the existing digital hierarchy signals. In addition,
SDH supports the transport of signals based on the 1.5 Mbit/s
hierarchy.
CTS850 Test Set, SDH/PDH
Transmission hierarchies
The following tables compare the Non synchronous and
Synchronous transmission hierarchies.
Table J 1. Non SynchronousHierarchy
Signal Digital Bit Rate Channels
64 kbit/s 64 kbit/s One 64 kbit/s
E1 2.048 Mbit/s 32 E0
E2 8.448 Mbit/s 128 E0
E3 34.368 Mbit/s 16 E1
E4 139.264 Mbit/s 64 E1
CTS850 Test Set, SDH/PDH User Manual J 1
Appendix J: Telecom Technology
Table J 2. SDH Hierarchy
Bit Rate Abbr. SDH SDH Capacity
51.840 Mbit/s 51 Mbit/s STM 0 21 E1
155.520 Mbit/s 155 Mbit/s STM 1 63 E1 or 1 E4
622.080 Mbit/s 622 Mbit/s STM 4 252 E1 or 4 E4
2488.320 Mbit/s 2.4 Gbit/s STM 16 1008 E1 or 16 E4
9953.280 Mbit/s 10 Gbit/s STM 64 4032 E1 or 64 E4
STM = Synchronous Transport Module
PDH Basics
Plesiochronous Data Hierarchy (PDH) is a telecommunications
transmission technology, implemented thirty years ago, based on
PCM (Pulse Code Modulation) and TDM (time division multiplex-
ing).
PDH is tailored to voice communication; has dedicated bandwidth
for each voice channel and a fixed channel assignment. PDH is
worldwide compatible only at the 64 kbit/s digitized voice level.
Pulse Code Modulation (PCM)
In the early 1970's, digital transmission began to appear in the
world's telephone network, utilizing a method known as Pulse Code
Modulation. PCM allowed analogue waveforms, such as the human
voice, to be represented in binary form. Using this PCM method, it
was possible to represent a standard 4 kHz analogue telephone signal
as a 64 kbit/s digital bit stream.
J 2 CTS850 Test Set, SDH/PDH User Manual
Appendix J: Telecom Technology
Anti Alias Sample
Filter
Quantizer
Encoder
8,000 samples/second x 8 bits/sample =
64 kb/s digital bit stream (one timeslot)
Figure J 1:Pulse Code Modulation
Engineers saw the potential to produce more cost effective
transmission systems by combining several PCM channels and
transmitting them down the same copper twisted pair as had
previously been occupied by a single analogue signal.
The method used to combine multiple 64 kbit/s channels into a
single high speed bit stream is known as Time Division Multiplex-
ing (TDM). In simple terms, a byte from each incoming channel is
transmitted in turn down the outgoing high speed channel. This
process is sometimes referred to as "sequential byte interleaving."
CTS850 Test Set, SDH/PDH User Manual J 3
Appendix J: Telecom Technology
analogue to
digital converter
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