bayly e1 primer
TRANSCRIPT
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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 bits binary code.
• Putting these numbers together we have an:
• 8000 Hz (sample rate)
• x 8 bits (binary code)
• = 64000 bits per second (representing one time slot channel)
• The coding technique used for E-1 transmission systems is called “A-law” companding. In T-1 transmission systems, “µ-law” companding is used which uses a different method of representing of the amplitude in its 8 bit binary code.
• The technique used to convert analog to digital is Pulse Code Modulation or PCM
E1 Fundamentals
• A Frame;• An E1 system consists of 32 time slots which contain the 64 kbit/s consecutive samples. This is called a frame. • The Transmission Rate;• When combined together 32 time slots x 64 Kbits/s = 2048 Kbits/s which is the speed of the E-1 transmission
system.• ITU-T Specifications; • ITU-T Rec. G.703
– Bit rate: 2048 Kbit/s +/- 50 ppm– Code: HDB3 (high density bipolar 3)
Table 6/G.703Pulse shape(normally rectangular)
All marks of a valid signal must conform with the mask(see figure 15/G.703) irrespective of the sign. The value Vcorresponds to the peak value.
Pair(s) in each direction One coaxial pair One symmetrical pair
Test load impedance 75 ohms resistive 120 ohms resistive
Nominal peak voltage of a mask (pulse) 2.37 V 3 V
Peak voltage of a space (no pulse) 0 ± 0.237 V 0 ± 0.3 V
Nominal pulse width 244 ns
Ratio of the amplitude of positive and negative pulses atthe centre of the pulse interval
0.95 to 1.05
Ratio of the widths of positive and negative pulses at the normal half amplitude
0.95 to 1.05
Maximum peak-to peak jitter at an output port Refer to § 2 of Recommendation G.823
E1 Transmission Format
E1 Transmission Format
ITU-T Specifications;
• ITU-T Rec. fig.15/G.703
sample capture of an
E1 signal with the
pulse shape mask
ITU-T Rec. G.704
E1 CAS Transmission Format
• Time Slot 16 : Frames 2 through 15 are the same as frame 1• Time Slot 0: Even number frames 2 through 14 are the same as frame 0• Time Slot 0: Odd number frames 3 through 15 are the same as frame 1
1 = bit set to 1 0 = bit set to 0 1/0 = speech / signalling (varying data) X = unassigned bit (normally set to 1)
Fr. Ch. Ch.
1 1 16 2 2 17 3 3 18 : : :15 15 30
10 2 3 4 5 6 7 8 9 10 11 12 13 14 15Multiframe (16 frames)
Frame 0 (32 Time Slots)
10 2 3 4 5 6 7 8 9101112131415 1716 1819202122232425262728293031Frame 1 (32 Time Slots)
10 2 3 4 5 6 7 8 9101112131415 1716 1819202122232425262728293031
Time Slot 0 (8 bits)
0X 0 1 1 0 1 1 10
10
10
10
10
10
10
10
Time Slot 1 Speech (Ch. 1)
Time Slot 16 (8 bits)
00 0 0 X 0 X X
Time Slot 0 (8 bits)
1X 0 X X X X X
Time Slot 16 Signalling Bits10
10
10
10
10
10
10
10
SpeechCh. 1-15
SpeechCh. 16-30
SpeechCh. 1-15
SpeechCh. 16-30
Frame
Time Slot
Frame Alignment
Word
Multi-Frame
Alignment Word
Changes to 1 on loss of distant multiframe
Changes to 1 on loss of distant frame(remote alarm)
Not-Frame alignment word
A B CD A B CD
LSB
Applying this framing method to the Omniplexer. • TS 0 is used for framing and alarm information • TS 16 contains the voice signalling bits:
– the A bit is used for the call status indication.
– the B bit is used as a busy indication.
– bit C & D are not used in most voice applications.
• The Omniplexer assigns channel numbers 1 to 30, for usable transmission.
ITU-T G.704 (32 Time Slots)
10 2 3 4 5 6 7 8 9 101112131415 1716 1819202122232425262728293031
Omniplexer - 30 Channel Assignments
1- 2 3 4 5 6 7 8 9 101112131415 16- 1718192021222324252627282930
E1 CAS Transmission Format
E1 CCS Transmission Format
Applying this framing method to the OMNIBranch and OMNIFlex. • TS 0 is used for framing and alarm information • The OMNIBranch assigns channel numbers 1 to 31, for usable transmission.
CCITT G.704 (32 Time Slots)
10 2 3 4 5 6 7 8 9 101112131415 1716 1819202122232425262728293031
OMNIBranch / OMNIFlex - 31 Time Slot Assignments
1- 2 3 4 5 6 7 8 9 101112131415 1716 1819202122232425262728293031
Frame (32 Time Slots)
10 2 3 4 5 6 7 8 9101112131415 1716 1819202122232425262728293031
SpeechCh. 1-31
Time Slot
Time Slot 0 (8 bits)
0X 0 1 1 0 1 1 10
10
10
10
10
10
10
10
Time Slot 1 Speech (Ch. 1)
Frame Alignment
Word
ITU-T Rec. G.704
PDH Asynchronous Transmission Format
• PDH = Pleisiochronous Digital Hierarchy
• One time slot channel = 64000 bits per second or 64 Kbps
• 32 time slots = an E1 (2.048 Mbps)(30 user channels + 1 synchronization and 1 framing channel)
• 4 x E1 = E2 (8.448 Mbps), 120 channel PCM system
• 4 x E2 = E3 (34.368 Mbps) 480 channel PCM system
• 16 x E1 = E3 (34.368 Mbps) 480 channel PCM system
SDH Synchronous Transmission Format
• SDH = Synchronous Digital Hierarchy
• 32 time slots = 1 x E1 (2.048 Mbps)(30 user channels + sync and framing)
• 63 x E1 = STM1 (155 Mbps)
• 4 x STM1 = STM4 (622 Mbps)
• 4 x STM4 = STM16 (2500 Mbps or 2.5 Gbps)
• 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 multiple D/A and A/D conversion is cumulative across the system.» The overall high cost of the system» Increase in noise level
Site BDrop/Insert
Site CDrop/Insert
Site DDrop/Insert
Site AChannel Bank
Site EChannel
Bank
Drop/Insert analog channels
D/A A/D
Drop/Insert analog channels
D/A A/D
Drop/Insert analog channels
D/A A/D
E1 E1E1 E1
Theory of Drop & Insert
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.
BDrop/Insert
CDrop/Insert
DDrop/Insert
AChannel Bank
EChannel Bank
Drop/Insert channels
Drop/Insert channels
Drop/Insert channels
Drop Insert Pass through
Synchronization
Bi-Directional E1
Master Clock Source- Internal Stratum III clockOr- External Clock
Loop Time ModeRedirects incoming clockto outbound E1
• Only one E1 clock in the network• Far end is loop timed to keep both directions of E1 synchronized
E1 Tx with Clock
E1 Tx with Clock
E1 Rx
E1 Rx
Point - Point
Synchronization
Master Clock Source- Internal Stratum III Clock Or- External Clock
Loop Time Mode- Redirects incoming clock to outbound E1
• Only one E1 clock in the network• Drop/Insert terminal recovers clock from incoming E1• Far end is loop timed to keep both directions of E1 synchronized
Drop/Insert
Recovered Mode- Clock extracted from incoming E1
• Mux clock derived from West and East E1 clocks +/- 128 bit slip buffer
West E1 East E1
Point-to-Point E1
E1; 1 – 30 channels
• Voice• Full-Rate Data• Sub-Rate Data
• Voice• Full-Rate Data• Sub-Rate Data
Single Hop
Point-to-Point E1
3 Hops
E1; 12 channels
E1; 8 channels
E1; 10 channels
• Poor utilization of E1’s• Excessive multiplex equipment• Does not support multipoint interfaces
Drop/Insert E1
3 Hops
E1; 30 channels (12+8+10)
E1; 18 channels(8+10)
E1; 10 channels
• Good utilization of E1’s• Minimal multiplex equipment• Supports multipoint interfaces
• 30 channels
• 12 channels
• 8 channels
• 10 channels
Drop/Insert Advantages
• Supports time-slot 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
Drop/Insert
VF
VF
Site 1 Site 2 Site 3
TS #1D/I to Site 2
TS #1D/I to Site 1
VF
TS #1D/I to Site 3(Re-Use)
VF
TS #1D/I to Site 2
VF
TS #2To Site 3Pass Through Site 2
VF
TS #2To Site 1
• Time-slot #1 is re-used at Site 2• Individual channels may be dropped and re-used• Time-slots “pass through” site where channel is not accessed
Channel Re-Use
Drop/Insert
LSDCM
LSDCM
Site 1 Site 2 Site 3
Insert into TS-1Sub-ChannelsA,B to Site 2C,D to Site 3
Drop TS-1Sub-Ch A,Bfrom Site 1
LSDCM
Insert TS-1Sub-Ch A,Bto Site 3
LSDCM
Drop TS-1Sub-ChA,B from Site 2C,D fro Site 1
• Time slot divided into 8 data sub-channels • Individual sub-channels may be dropped and inserted
Sub-Channel Re-Use
Drop/Insert
Site 1 Site 2 Site 3
Insert into TS-1Multipoint Voice orData Channel
Drop TS-1Multidrop Voice orData Channel
Drop TS-1Multidrop Voice orData Channel
Applications:
• Polling Channels• SCADA Systems• Inter-Station communications• Maintenance Orderwire channels
Time slot digitally bridged anddropped at each site
Multidrop Interfaces
E1 Bit Error Rate Testing
Site 1 Site 2 Site 3
E1Test Set
• From one location, technician can selectively test each link• E1 remote loopback enabled sequentially to test link-by-link• Testing performed in both “West” and “East” directions (using drop/insert E1 test set)• Can test entire E1 bandwidth or time slot 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• OMNIPlexer’s built-in E1 error rate testing will raise alarm if error rate rises above pre-programmed threshold (10E-6 to 10E-9)
Laptop or PC connected to Local Port
E1 Testing
Data Channel Testing
Site 1 Site 2 Site 3
• 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 time slot, multiple time slots or sub-rate time slot 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
DCM
DCM
DataTest Set
E1 Testing
Voice Channel Testing
Site 1 Site 2 Site 3
• 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
E&M
E&M
Analog Signal Generator
Analog LevelMeter
E1 Testing
Products
• OMNIPlexer Intelligent T1 and E1 Drop/Insert Multiplexer
edge of network access and backhaul solutions
• OMNISkip E3 to 16 E1 Multiplexer
• OMNIBranch & OMNIFlex Compact Digital Cross-Connect Switches - 4 to 8 T1 ports - Data port options