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ECEN5553 Telecom Systems
Dr. George Scheets
Week #8
Readings:
[18a] "Trading at the Speed of Light"
[18b] "Is The U.S. Stock Market Rigged?"
Optional: "Flash Boys"
[16] "Voice over the Internet: A Tutorial"
Outline 7 October 2015, Lecture 22 (Live)
No later than 14 October (Remote DL)
No Class Friday (Fall Break)
Outlines
Received
due 7 October (local)
14 October (remote)
44 %
Packet Switch StatMux Trunking
Pure Internet (or Ethernet) Model
Fixed Rate Traffic
Bursty Data Traffic
Router
SONET & OTN
(Ethernet)
Assumptions:
All Fixed Rate Traffic is packetized.
All traffic is Statistically Multiplexed onto the trunk BW.
Internet Service Provider Backbone
Packet
Aware
Router
StatMux, Packet Switched Network, Full Duplex Trunks.
Access lines mostly attach to routers.
ATM Trunking
(In Nineties, claimed as Tomorrow's Network Model)
Fixed Rate Traffic
Bursty Data Traffic
ATM
Switch
SONET OC-N
Assumptions:
Fixed Rate Traffic gets CBR Virtual Circuits.
CBR traffic gets near-TDM like service.
Data Traffic is StatMuxed onto the remaining trunk BW.
ATM Backbone
Cell
Aware
ATM Switch
StatMux/TDM, Cell Switched Network, Full Duplex Trunks.
Access lines mostly attach to ATM switches, and "ATM capable"
routers, FR switches, TD Muxes, & cross connects.
Circuit Switch TDM Trunking
(Eighties 'Private Line' Network Model)
Fixed Rate Traffic
TDM
Switch
Bursty Data Traffic
Fiber, Cable,
& Microwave
Assumptions:
All Traffic receives trunk bandwidth based on peak
input rates.
No aggregation. Data traffic consists of many slower
speed, relatively lightly loaded circuits.
Carrier Leased Line Backbone
Byte
Aware
Cross-Connect
TDM, Circuit Switched Network, Full Duplex Trunks.
Access lines mostly attach to routers, FR & ATM
switches, TD Muxes, & cross connects of other carriers.
Hybrid TDM Trunking
(Network Model for older Carriers)
Fixed Rate
Bursty Data
Packet
Switch
TDM
Switch
SONET
Assumptions:
Bursty Data Traffic is all StatMuxed onto a common
fabric (such as Frame Relay).
Aggregate streams are TDM cross connected onto SONET.
Trunk BW assigned based on peak rates.
Hybrid Network
Byte
Aware
Cross-Connect
Fixed Rate Traffic: CSTDM bandwidth based on Peak Rates
Bursty Traffic: Access lines aggregated onto higher load trunk.
Packet Switch StatMux Trunks are CSTDM.
Voice Quality vs. Bit Rate
Quality
G.729
G.728
G.726
G.711
G.723.1
8
16
32
Bit Rate (Kbps)
64
Switched Network Carrying Capacities
High Speed Trunk
Hybrid
Carrying
Capacity
Cell Switch
StatMux
Packet Switch
StatMux
Circuit Switch
TDM
0% Bursty
100% Fixed Rate
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
Switched Network Carrying Capacities
Hybrid Network
Carrying
Capacity
all bursty data traffic groomed onto
packet network
Hybrid
Circuit Switch
TDM
0% Bursty
100% Fixed Rate
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
Switched Network Carrying Capacities
Hybrid Network
Carrying
Capacity
Hybrid
no data traffic groomed onto
packet network
0% Bursty
100% Fixed Rate
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
Switched Network Carrying Capacities
Hybrid Network
Carrying
Capacity
real world network
0% Bursty
100% Fixed Rate
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
Switched Network Carrying Capacities
Convergence
Carrying
Capacity
Cell Switch
StatMux
Packet Switch
StatMux
Circuit Switch
TDM
0% Bursty
100% Fixed Rate
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
70’s & 80’s Fixed Rate Voice Dominates
Data
Voice
70’s & 80’s
time
Switched Network Carrying Capacities
Convergence
Carrying
Capacity
Circuit Switch
TDM
0% Bursty
100% Fixed Rate
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
Turn of the Century
A Mixed Traffic Environment
Data
Voice
2000
time
Switched Network Carrying Capacities
Convergence
Carrying
Capacity
0% Bursty
100% Fixed Rate
Cell Switch
StatMux
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
By 2005, Data Dominated
Data
Voice
time
2005
Switched Network Carrying Capacities
Convergence
Carrying
Capacity
Packet Switch
StatMux
0% Bursty
100% Fixed Rate
Offered
Traffic Mix
100% Bursty
0% Fixed Rate
What's the impact of Video?

Video #1 since 2010, is a packet switched
statmux network best?
 Yes.

Most video coders are variable rate.
Two changes to make the network more video
friendly…
 Might
be a good idea to increase Ethernet's
maximum packet size.
 All packets with bit errors shouldn't be dropped
 Voice/Video dropped packet = lower quality
 Better quality possible if payload delivered
Carrying Capacity...
 Got bursty data traffic to move?
A packet switched system using statistical
multiplexing will allow you to service the most
users given a fixed chunk of bandwidth.
 Got fixed rate traffic to move?
A circuit switched system will allow you to
service the most customers given a fixed chunk
of bandwidth.
WAN Trends
60's - Fixed Rate Voice Dominates
 Voice Network moving data on the side
 Mid to Late 90's – Mixed Traffic Environment
 New Carriers – ATM
 Older Carriers – Hybrid
 Early 00's - Mostly Bursty Traffic
 Data Networks moving voice on the side
 10's - Mostly Video
 Data Networks moving video
Data & voice on the side

Example) Coding a
Microphone Output
m(t) volts (air pressure)
time (sec)
Energy from about 500 - 3,500 Hz.
A/D Convertor
m(t) volts (air pressure)
1/8000 second
time (sec)
Step #1)
Sample the waveform at rate > 2*Max Frequency.
Telephone voice is sampled at 8,000 samples/second.
A/D Convertor

Legacy Wired Telephone System uses PCM

Pulse Code Modulation
One of N possible equal length Code
Words is assigned to each Voltage
N Typically a Power of 2
Log2N bits per code word
 Wired
Phone System: N = 256 & 8 bits/word
 Compact Disk: N = 65,536 & 16 bits/word
A/D Convertor. 1 bit/sample.
Example) N = 2. Assign 0 or 1 to voltage.
3.62 v, output a 1
t1
time (sec)
0 < Voltage < +5v, Assign Logic 1
-5v < Voltage < 0, Assign Logic 0
Bit Stream Out = 1111110000111...
A/D Convertor. 1 bit/sample.
Example) N = 2. Assign 0 or 1 to voltage.
0 < Voltage < +5v, Assign Logic 1
-5v < Voltage < 0, Assign Logic 0
Far side gets... 1111110000111 (13 samples)
Needs to output 13 voltages.
What does a 1 represent? A 0?
Receive a 1? Output +2.5 v (mid-range)
Receive a 0? Output -2.5 v (mid-range)
Hold the voltage until next sample
A/D Convertor. 1 bit/sample.
Input to the transmitter.
Output at the receiver.
+2.5 v
-2.5 v
Considerable Round-Off error exists.
A/D Convertor. 2 bits/sample
Example) N = 4. Assign 00, 01, 10 or 11.
3.62 v, Assign 11
+2.5 v
time (sec)
t1
2.5 < Voltage < 5 , Assign 11
0 < Voltage < 2.5, Assign 10
-2.5 < Voltage < 0, Assign 00
-5 < Voltage < -2.5, Assign 01
-2.5 v
Bit Stream Out =
11111011111100
000000101011...
A/D Convertor. 2 bits/sample.
Input to the transmitter.
Output at the receiver.
+3.75 v
+1.25 v
-1.25 v
Receive 11? Output 3.75v
Receive 10? Output 1.25v
Receive 00? Output -1.25v
Receive 01? Output -3.75v
Reduced Round-Off error exists.
-3.75 v
Circuit Switched Voice (POTS)
 Bandwidth
≈ 3,500 Hertz
 A/D Converter
 samples
voice 8,000 times/second
 rounds off voice to one of 256 voltage levels
 transmits 8 bits per sample to far side
 D/A
Converter
 receives
8 bit code word
 outputs one of 256 voltage levels for 1/8000th
second
 64,000
bps (1 byte, 8000 times/second)
Compact Disk
 Bandwidth
≈ 20,000 Hertz
 A/D Converter
 samples
voice 44,100 times/second
 rounds off voice to one of 65,536 voltage levels
 transmits 16 bits per sample to far side
 D/A
Converter
 receives
16 bit code word
 outputs one of 65,536 voltage levels for
1/44100th second
 705,600
bps
Sampling & Quantizing Examples
 fs
= 16 KHz
 4096
quantiles
 256 quantiles (approximate phone quality)
 32 quantiles
 4 quantiles (generally 2 levels used!)
 4096
 fs
quantiles
= 16 KHz
 fs = 8 KHz (some interference)
 fs = 2 KHz
 fs = 1 KHz
1/8th Second of Voice
1/8th Second of Voice
1/8th Second of Voice
Sources of POTS delay
Source CO
POTS
TDM Trunk TSI
Trunk resources are dedicated
to each voice call via TDM.
PCM
Coder
...
Local Loop
PCM
Coder
POTS
Local Loop
TDM Trunk TSI
Destination CO
Intermediate
Digital
Voice
Switches
Sources of VoIP delay
Voice
Packet Transmission
Coder Assembler
Buffer
Packet
Switch
...
Trunk resources are randomly assigned to
each voice call via Statistical Multiplexing.
Voice
Decoder
Receiver
Buffer
StatMux
Trunks
Intermediate
Packet
Switches
Packet
Switch
Voice (Video) on LAN (WAN)
 More complex system than circuit switched
voice
 Packet Assembler
 Transmitter Buffer
 Receiver Buffer
 End-to-End Delays > Circuit Switch TDM
 Delay Variability > Circuit Switch TDM