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--- E1 and T1--- SDH and PDH
--- DWDM--- CDMA
--- Clocking
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T1/E1 Overview
Digital Telephony
Digital voice
Basic Time Division Multiplexing
T1 and E1 Applications
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Digital Telephony
Advantages of digital telephony are:
More efficient because multiple voice channels are multiplexed andtransmitted over a common transmission path.
More economical when compared to the number of equivalentanalog lines that would be required.
More reliable in that repeaters maintain the integrity of the digitalsignals over long distances.
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Digital Voice
Product of Analog to digital conversion.
Involves sampling, quantization and bitencoding.
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Basic Time Division Multiplexing
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PCM
Sampling
Quantization
Bit encoding
Adaptive Differential PCM
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T1/E1 Technology
T1/E1 Multiplexing
T1/E1 Framing
T1/E1 Signaling
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Industrial Standards For T1
AT&T Publication 43801
AT&T Publication 54016
AT&T Publication 62411
ANSI T1.403-1989
Bell core TR-TSY-000194
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Industrial Standards For E1
ITU-T Recommendation G.703
ITU-T Recommendation G.704
ITU-T Recommendation G.706
ITU-T Recommendation G.711
ITU-T Recommendation G.732 ITU-T Recommendation G.823
ITU-T Recommendation I.431
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Summary
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DWDM
Increase the bit rate
Nonlinear effects that can affect waveform quality.
Increase the number of wavelengths
Several wavelengths, or light colors, can simultaneously
multiplex signals of 2.5 to 40 Gbps each over a strand of
fiber.
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Sonet and TDM
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TDM interfaces
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WDM interfaces
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Process Of DWDM
OC-48c/STM-16c interface operating atthe 1310-nm wavelength.
Conversion of incoming optical signals intothe precise ITU-standard wavelengths tobe multiplexed, transponders are currentlya key determinant of the openness of
DWDM systems.
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Transponder converts the client optical signalfrom back to an electrical signal. This electricalsignal is then used to drive the WDM laser. Eachtransponder within the system converts itsclient's signal to a slightly different wavelength.The wavelengths from all of the transponders inthe system are then optically multiplexed. In thereceive direction of the DWDM system, thereverse process takes place. Individualwavelengths are filtered from the multiplexedfiber and fed to individual transponders, which
convert the signal to electrical and drive astandard interface to the client.
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Access Schemes:
FDMA:
Each pair of communicators is allocatedpart of the spectrum for all of the time.
TDMA:
Each pair of communicators is allocated all
(or at least a large part) of the spectrumfor part of the time.
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CDMA
Every communicator will be allocated the
entire spectrum all of the time.
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Coding
CDMA uses unique spreading codes to spreadthe baseband data before transmission.
The receiver then uses a correlator to despread
the wanted signal, which is passed through alowpass filter.
The rate of a spreading code is referred to aschip rate rather than bit rate.
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The Spreading Process
CDMA uses Direct Sequence spreading bycombining the baseband information tohigh chip rate binary code. The SpreadingFactor is the ratio of the chips(3.84Mchips/s) to baseband informationrate. Spreading factors vary from 4 to
512.
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Clocking
A reference source of timinginformation
Free run clocking occurs when local
oscillator is lost with externalsynchronization reference.
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Synchronization Techniques
Loop Clock Settings
Local Clock Settings
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Clocking Levels
Stratum 1
Completely autonomous timing source,
Stratum 1 timing is an atomic standard orreference oscillator
Example:
Primary Reference Source (PRS) asdefined in ANSI T1.101.
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Stratum 2:
Tracks an input and holds to the last bestestimate of the input reference frequency
The drift of a Stratum 2 with no inputreference is required to be less than 1.6 x10-8 per year.
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Stratum 3:
Stratum Level 3 is defined as a clocksystem that tracks an input as in
Stratum 2, but over a wider range.
A Stratum Level 3 clock system requires a
minimum adjustment range of 4.6 x 10-6.
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Stratum 4:
Stratum Level 4 is defined as a clocksystem that tracks an input, except that theadjustment and drift range is 3.2 x 10-5.
Stratum 4 clock has no holdover capabilityso in the absence of a reference it free
runs within the adjustment range limits.
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