DATA COMMUNICATIONRECOVERY (E1 Tapping)

USMAN TARIQ s470.05M. SHAHZAIB ABBAS s471.05NOMAN MUMTAZ ALI s481.05S.M. ALI ABBAS RIZVI s488.05

A Project in collaboration with Snoopy Devices & Systems

TAPPING

• “Decoding a Communication of any Entity.”• Born with Wars; Concept of Tapping.• Telegraph; Tapping Morse code• Radio; Intercepting Air interface• Telephone; Intercepting any junction point from

Local Loop to Exchange• Optical Fiber taps; Connecting Mirror in series• Ideal taps; Transparent and invisible• Tapping of E-Carrier (E1)

PCM

• “Information present in periodic samples of an Analog Signal represented by digital words in a bit stream”

• Analog to Digital Conversion• High Noise Immunity, Easy Detection.

PCM

• Sampling; Recording Instantaneous values of signals

• Quantization; Assign Discrete amplitudes to each sample

• Coding; Replacing Discrete amplitudes with equivalent Binary codes.

• PCM30/E1; PCM 24/T1

PCM30/E-Carrier (E1)

• 30 users accommodated in one frame using TDM , with one user/timeslot.

• 2 additional time slots used for frame synchronization and signaling.

• 32 time slots with 8 bits each results in 32timeslots*8bits/timeslot=256 bits/frame.

• Each timeslot 64kbits/sec bit rate, resulting in a 2.048 Mbits/s data rate.

• Frame duration = 125microseconds

Tapping of E1• Transmitted E1 frames captured inform of a bit

stream.• Timeslot “0” and Timeslot “16” stripped off

leaving behind payload in 30 timeslots.• Each user assigned its own channel in a separate

file.• Suitable header appended to file of each user to

ensure playing compatibility.• Result = playable user voice in their individual

files/channels.

PROJECT COMPONENTS

MATLAB E1-Simulator

MATLAB E1-Simulator

• MATLAB GUIDE Application.• Works on Matrix manipulation.• Programmed to produce E1-Stream as input

for E1-Tapping Application• Flexible

Building Blocks

• Configuration Block• Audio Recorder• PCM Generator• Graph Plotter• E1 Generator

Configuration Block

• Accommodation of 30 users.• Assignment of unique id’s to each user.• Storing user data in a “flat file” database.

Audio Recorder

• Built-in function.• Takes input on the basis of

3 parameters (Sampling Rate = 8000samples/sec, no of bits/sample = 8 bits/sample, no of channels=1)

• File saved in a Structure.• Structure to Vector/Array

conversion.

PCM Generator

• Same as practical PCM systems used.• Input: 30 Recorded Voice Arrays.• Sampling• Quantization• Coding• Output: PCM Pulse Train; 1s and 0s.

Graph Plotter

• Two Dimensional graph plotting of different forms of 30 input signals.

• Voice Input Signal• Sampled Input Signal• Quantized PAM Signal• 30 Pulse train containing PCM bits.

E1 Generator• Input: Generated PCM

Pulse trains.• Individual byte taken from

each user to make 30 timeslots.

• Appends 2 additional bytes for Synchronization and Signaling.

• Frame Interleaving to form E1 Stream.

• Binary to Decimal conversion to be written in file.

E1-Simulator

C# E1 Tapping Application

C# E1 Tapping Application

• .NET Windows Form Application• Works on different Controls and Methods• Accepts the E1 stream generated by MATLAB

E1 Simulator.• User friendly• Flexible

Work Modules

• Module # 1: Payload Extractor• Module # 2: Channel Allocator• Module # 3: E1 Voice Recovery Unit

Payload extractor

• Calculates Frame Count.• Iterative block used to

remove Ts0/Ts16 (Synchronization/Signaling) Headers from input E1 stream.

• Uses Frame Count as an iterative count for separating headers & payload.

• Displays error message if Frame Count = 0

Header Information

Voice Information

Payload Extractor

Payload

–E1 Frames –Frame Count

Channel Allocator• Receives extracted

payload from Module # 1.• Extracts individual

timeslots from the payload.

• Writes the data of each timeslot in its respective file.

• Displays error message if there is no payload.

Channel Allocator

Extracted Payload

File Writer

Time SlotSeparator

ALL

OC

AT

ION

ALG

OR

ITH

M

Time Slot # 01

Time Slot # 02

Time Slot # 30

File # 01

File # 02

File # 30

.

.

.

....

E1 Voice Recovery Unit

• Takes individual timeslot data files from module # 2.

• Appends suitable header to each file, converting it in a playable form.

• Plays the files in standard VLC player.

Header Appender E1 Voice Player

File # 01

File # 02

File # 03

File # 30

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.

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.

.

.

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VoiceFile # 01

VoiceFile # 02

VoiceFile # 03

VoiceFile # 30

Voice Output

E1 Voice Recovery Unit

E1-Tapping Application

Stream Viewer

Module 1 Module 2

Module 3

E1 StreamE1Frames Payload

.

.

.

File # 01

File # 02

File # 30

Voice File # 01

Voice File # 02

Voice File # 30

.

.

.

VoiceOutputs

Headers

Ts

# 0/

Ts

# 16

FrameCount

Count

No. of Frames

Final Design

Simulation and Results

E1-Simulator

E1-Simulator: Audio Recorder

• Small voice amplitudes in 2D graph.

• Voice amplitudes in bordering segment of A-Law Curve.

• Voice: -15 to 20 dB • >0 dB; Noise

E1-Simulator (Sampler)

• Sampling done in accordance with Nyquist criteria.

• Voice frequency range: 300-3400 Hz

• Sampling rate = 8000 samples/s.

E1-Simulator (Quantizer)

• Sampled signal compressed by A-Law, Non Uniform Quantization.

• Less quantization noise.

• Double line effect in 2D graph shows quantized signal.

E1-Simulator (Encoder)

• Assigns 8-bit code to discrete quantized amplitudes.

• Gives PCM Pulse train consisting of 1’s and 0’s as output in 2D graph.

Simulation Results

E1-Tapping Application

E1-Tapping Application (Payload Extractor)

• 3 parameters shown:• Binary Stream• Frame Count• Extracted Payload

(without headers)

E1-Tapping Application (Channel Allocator)

• 30 timeslots in their respective channels shown in output.

• Channels used for writing individual user files.

E1-Tapping Application (E1 Voice Recovery Unit)

• Appends header to each individual file/channel.

• Transparent to the user.

Conclusion

• E1 tapping achieved

E1Stream

Voice I/P Voice O/P