Bayly Presentation

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T1 Fundamentals
Analog to Digital Conversion of a Voice Signal

• For quality voice transmission the sample rate
  needs to be at least two times the highest
  frequency, typically 3500 Hz. For this reason a
  sample rate of 8000 times per second is used.
• Each sample of the signal has an amplitude
  component this is represented by an 8 bit binary
  code.
• Putting these numbers together we have an
• 8000 Hz (sample rate)
• x 8 bits (binary code)
• 64000 bits per second
• The coding technique used for T-1 transmission
  systems is called µ-law companding.

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T1 Transmission Format

• T-1 vs DS-1, these terms are used interchangeably
• T1 is a designator for T-Carrier/ Type 1
• T-Carrier indicates time division multiplexing
  (TDM)
• Type 1 defines the type format of the digital
  transmission medium
• Describes the physical characteristics Twisted
  pair, copper wire, etc.
• Defines the speed and number of 64Kbps voice and
  data channels
• DS-1 means Digital Signal Level One which defines
  the electrical characteristics of the T1 signal.
• Bipolar signal, /-3V base-to-peak, 125us frame
  interval, etc.

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T1 Transmission Format

• To determine the T-1 systems format
• 24 channels per frame
• X8 bits per channel
• 192 bits 1 framing bit 193 bits per frame
• 193 bits per frame
• X 8000 frames per second
• 1544 Kbits per second
• There are types of operation for the T-1 signal
• SF - Super Frame, sometimes called D4
• ESF - Extended Super Frame

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D4 (SF) Framing

• Voice Channels
• 24 voice circuits operating at 64Kbps 1536 Kbps
• Framing bit 8Kbps (F bit) for
• Errors detected at the CSU are Format errors only
• Bipolar Violations (BPV)
• Loss of signal (LOS)
• Loss of Frame (LOF)
• Average (ones) Density Violations
• Excessive zeros
• Logic error may not cause format errors
• Errors might not occur in the framing bits

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D4 (SF) Framing
1544 Kbps DS1
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Extended Superframe (ESF) Framing

• Voice Channels
• 24 voice circuits operating at 64Kbps 1536 Kbps
• Framing bit 8Kbps (F bit) for
• Frame synchronization
• 2Kbps are used for the frame alignment.
• CRC6 (Cyclic Redundancy Check)
• 2Kbps are used for CRC6 (Cyclic Redundancy
  Check).
• CRC-6 is a calculation of the total of bits in
  the entire extended superframe

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Extended Superframe (ESF) Framing

• Facility Datalink channel (FDL)
• 4 Kbps are used for FDL that could be used for
• remote access of CSUs commands through the
  datalink.
• Non-service affecting status messages may be sent
  through the datalink.
• Service affecting loopbacks may also be set
  through the link

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Extended Superframe (ESF) Framing
Multiframe (24 frames)
24 Frames
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24 Channels
Framing bit (F bit)
Speech Ch. 1-24
Speech Ch. 1-24
Channels
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Line Codes

• Alternate Mark Inversion (AMI)
• The output signal has both positive and negative
  components, this reduces the DC component.
• Each pulse is the opposite polarity of the one
  before.
• Because each pulse is opposite in polarity of the
  one before, this is called, Alternate Mark
  Inversion.

Unipolar
Bipolar
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Line Codes

• Bipolar 8 Zero Substitution (B8ZS)
• Similar to AMI with addition of 8 zero
  substitution
• If 8 zeros are transmitted simultaneously, a 1
  will be inserted to avoid a false alarm

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Theory of Drop Insert

• The conventional way of performing drop and
  insert is with the use of back-to-back channel
  banks.
• At a Drop/Insert site all channels are converted
  to analog levels.

• While this technique works, there are several
  draw backs including
• Distortion caused by the D/A and A/D conversion
  compiled over the system.
• The overall high cost of the system
• Increase in noise level

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OMNIPlexer Drop Insert

• The Omniplexer allows for drop and insert at
  every site but only converts to analog the
  channels that are required. The remaining are
  passed through digitally.

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Synchronization
Point - Point
T1 Tx with Clock
T1 Rx
Bi-Directional T1
T1 Tx with Clock
T1 Rx
Master Clock Source - Internal Stratum III
clock Or - External Clock
Loop Time Mode Redirects incoming clock to
outbound T1

• Only one T1 clock in the network
• Far end is loop timed to keep both directions of
  T1 synchronized

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Synchronization
Drop/Insert
West T1
East T1

• Mux clock derived from
• West and East T1 clocks
• /- 128 bit slip buffer

Master Clock Source - Internal Stratum III Clock
Or - External Clock
Loop Time Mode - Redirects incoming clock to
outbound T1

• Recovered Mode
• Clock extracted from
• incoming T1

• Only one T1 clock in the network
• Drop/Insert terminal recovers clock from
  incoming T1
• Far end is loop timed to keep both directions of
  T1 synchronized

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Point-to-Point T1
Single Hop
T1 1 24 channels

• Voice
• Full-Rate Data
• Sub-Rate Data

• Voice
• Full-Rate Data
• Sub-Rate Data

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Point-to-Point T1
3 Hops
T1 6 channels
T1 8 channels
T1 10 channels

• Poor utilization of T1s
• Excessive multiplex equipment
• Does not support multipoint interfaces

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Drop/Insert T1
3 Hops
T1 24 channels (6810)
T1 18 channels (810)

• 6 channels

• 24 channels

• 8 channels

• Good utilization of T1s
• Minimal multiplex equipment
• Supports multipoint interfaces

T1 10 channels

• 10 channels

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Drop/Insert Advantages

• Supports DS-0 channel re-use
• Supports sub-rate data channel re-use
• Supports multipoint (miltidrop) voice and data
  interfaces
• Low throughput delay (less than 100 microseconds)
• Low jitter accumulation

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Drop/Insert
Channel Re-Use
Site 1
Site 2
Site 3
V F
V F
V F
V F
V F
V F
DS-0 1 D/I to Site 1
DS-0 1 D/I to Site 2
DS-0 1 D/I to Site 3 (Re-Use)
DS-0 1 D/I to Site 2
DS-0 2 To Site 3 Pass Through Site 2
DS-0 2 To Site 1

• DS-0 1 is re-used at Site 2
• Individual channels may be dropped and re-used
• DS-0s pass through site where channel is not
  accessed

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Drop/Insert
Sub-Channel Re-Use
Site 1
Site 2
Site 3
L S D C M
L S D C M
L S D C M
L S D C M
Drop TS-1 Sub-Ch A,B from Site 1
Insert into TS-1 Sub-Channels A,B to Site 2 C,D
to Site 3
Insert TS-1 Sub-Ch A,B to Site 3
Drop TS-1 Sub-Ch A,B from Site 2 C,D fro Site 1

• Time slot divided into 8 data sub-channels
• Individual sub-channels may be dropped and
  inserted

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Drop/Insert
Multidrop Interfaces
Site 1
Site 2
Site 3
Insert into TS-1 Multipoint Voice or Data Channel
Drop TS-1 Multidrop Voice or Data Channel
Drop TS-1 Multidrop Voice or Data Channel

• Applications
• Polling Channels
• SCADA Systems
• Inter-Station communications
• Maintenance Orderwire channels

Time slot digitally bridged and dropped at each
site
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T1 Testing
T1 Bit Error Rate Testing
Site 1
Site 2
Site 3
T1 Test Set
Laptop or PC connected to Local Port

• From one location, technician can selectively
  test each link
• T1 remote loopback enabled sequentially to test
  link-by-link
• Testing performed in both West and East
  directions (using drop/insert T1 test set)
• Can test entire T1 bandwidth or DS-0 increments
• Duration of test is ½ to 1 hour
• Error rate of 10E-6 is acceptable, error rate of
  10E-8 to 10E-9 is expected
• OMNIPlexers built-in T1 error rate testing will
  raise alarm if error rate rises above
  pre-programmed
• threshold (10E-6 to 10E-9)

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T1 Testing
Data Channel Testing
Site 1
Site 2
Site 3
D C M
D C M

• From one location, technician can perform
  end-to-end bit error rate test for each data
  circuit
• Data channel remote loopback enabled
• Can test entire one DS-0, multiple DS-0s or
  sub-rate DS-0 data channels
• Duration of test is ½ to 1 hour
• Error rate of 10E-6 is acceptable, error rate of
  10E-8 to 10E-9 is expected

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T1 Testing
Voice Channel Testing
Site 1
Site 2
Site 3
E M
E M

• From one location, technician can perform
  end-to-end bit test for each analog circuit
• Analog channel remote loopback enabled
• Measure analog level, signal-to-noise ratio,
  noise floor, distortion

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Products

• OMNIPlexer Intelligent T1 Multiplexer
• - Drop/Insert operation
• - Point-to-point and multipoint interfaces
• - Remote management and T1 performance monitoring

• OMNIBranch OMNIFlex Digital Cross-Connect
  Switches
• - Compact size
• 4 to 8 T1 ports
• Data port options

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