ECEN5553 Telecom SystemsDr. George ScheetsWeek #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)

OutlinesReceived

due 7 October (local)14 October (remote)

44 %

Packet Switch StatMux TrunkingPure Internet (or Ethernet) Model

RouterFixed Rate Traffic

Bursty Data Traffic

Assumptions: All Fixed Rate Traffic is packetized. All traffic is Statistically Multiplexed onto the trunk BW.

SONET & OTN(Ethernet)

Internet Service Provider Backbone

Router

TrunksLeased LinePacketAware

StatMux, Packet Switched Network, Full Duplex Trunks.Access lines mostly attach to routers.

ATM Trunking(In Nineties, claimed as Tomorrow's Network Model)

ATMSwitch

Fixed Rate Traffic

Bursty Data Traffic

Assumptions: Fixed Rate Traffic gets CBR Virtual Circuits. CBR traffic gets near-TDM like service. Data Traffic is StatMuxed onto the remaining trunk BW.

SONET OC-N

ATM Backbone

ATM SwitchATM Switch

TrunksLeased LineCell

Aware

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)

TDMSwitch

Fixed Rate Traffic

Bursty Data Traffic

Assumptions: All Traffic receives trunk bandwidth based on peak input rates. No aggregation. Data traffic consists of many slower speed, relatively lightly loaded circuits.

Fiber, Cable, & Microwave

Carrier Leased Line Backbone

Cross-ConnectCross-Connect

TrunksLeased LineByte

Aware

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)

TDMSwitch

Fixed Rate

Bursty DataPacketSwitch

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.

SONET

Hybrid Network

Cross-ConnectCross-Connect

TrunksLeased LineByte

Aware

Fixed Rate Traffic: CSTDM bandwidth based on Peak RatesBursty Traffic: Access lines aggregated onto higher load trunk.

Packet Switch StatMux Trunks are CSTDM.

Voice Quality vs. Bit Rate

Bit Rate (Kbps)

QualityG.728 G.711G.726

8 16 32 64

G.729

G.723.1

Switched Network Carrying CapacitiesHigh Speed Trunk

Carrying Capacity

Circuit Switch TDM

Packet Switch StatMux

Cell Switch StatMux

Hybrid

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

Switched Network Carrying CapacitiesHybrid Network

Carrying Capacity

Circuit Switch TDM

Hybrid

all bursty data traffic groomed onto packet network

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

Switched Network Carrying CapacitiesHybrid Network

Carrying Capacity Hybrid

no data traffic groomed onto packet network

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

Switched Network Carrying CapacitiesHybrid Network

Carrying Capacity

real world network

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

Switched Network Carrying CapacitiesConvergence

Carrying Capacity

Circuit Switch TDM

Packet Switch StatMux

Cell Switch StatMux

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

70’s & 80’s Fixed Rate Voice Dominates

Voice

Data

time70’s & 80’s

Switched Network Carrying CapacitiesConvergence

Carrying Capacity

Circuit Switch TDM

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

Turn of the CenturyA Mixed Traffic Environment

Voice

Data

time2000

Switched Network Carrying CapacitiesConvergence

Carrying Capacity

Cell Switch StatMux

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

By 2005, Data Dominated

Voice

Data

time

2005

Switched Network Carrying CapacitiesConvergence

Carrying Capacity

Packet Switch StatMux

0% Bursty 100% Bursty100% Fixed Rate 0% Fixed RateOffered

Traffic Mix

What's the impact of Video? Video #1 since 2010, is a packet switched statmux network best?Video #1 since 2010, is a packet switched statmux network best?

Yes. Most video coders are variable rate.Yes. Most video coders are variable rate. Two changes to make the network more video friendly… Two changes to make the network more video friendly…

Might be a good idea to increase Ethernet's maximum packet size.Might be a good idea to increase Ethernet's maximum packet size. All packets with bit errors shouldn't be droppedAll packets with bit errors shouldn't be dropped

Voice/Video dropped packet = lower qualityVoice/Video dropped packet = lower quality Better quality possible if payload deliveredBetter quality possible if payload delivered

Carrying Capacity... Got Got bursty data bursty data traffictraffic to move?to move?

A A packet switched system packet switched system using using statistical statistical multiplexing multiplexing will allow you to service the most will allow you to service the most users given a fixed chunk of bandwidth. users given a fixed chunk of bandwidth.

GotGot fixed rate fixed rate traffic to move?traffic to move?A A circuit switched circuit switched system will allow you to system will allow you to service the most customers given a fixed chunk service the most customers given a fixed chunk of bandwidth.of bandwidth.

WAN Trends 60's - Fixed Rate Voice Dominates60's - Fixed Rate Voice Dominates

Voice Network moving data on the sideVoice Network moving data on the side Mid to Late 90's – Mixed Traffic EnvironmentMid to Late 90's – Mixed Traffic Environment

New Carriers – ATMNew Carriers – ATM Older Carriers – HybridOlder Carriers – Hybrid

Early 00's - Mostly Bursty TrafficEarly 00's - Mostly Bursty Traffic Data Networks moving voice on the sideData Networks moving voice on the side

10's - Mostly Video10's - Mostly Video Data Networks moving video Data Networks moving video

Data & voice on the sideData & voice on the side

Example) Coding aMicrophone Output

time (sec)

m(t) volts (air pressure)

Energy from about 500 - 3,500 Hz.

A/D Convertor

time (sec)

m(t) volts (air pressure)

Step #1)Sample the waveform at rate > 2*Max Frequency.Telephone voice is sampled at 8,000 samples/second.

1/8000 second

A/D Convertor Legacy Wired Telephone System uses PCMLegacy Wired Telephone System uses PCM

Pulse Code ModulationPulse Code Modulation One of N possible equal length Code One of N possible equal length Code Words is Words is assigned to each Voltageassigned to each VoltageN Typically a Power of 2N Typically a Power of 2LogLog22N bits per code wordN bits per code word Wired Phone System: N = 256 & 8 bits/wordWired Phone System: N = 256 & 8 bits/word Compact Disk: N = 65,536 & 16 bits/wordCompact Disk: N = 65,536 & 16 bits/word

A/D Convertor. 1 bit/sample.

time (sec)

Example) N = 2. Assign 0 or 1 to voltage.

0 < Voltage < +5v, Assign Logic 1-5v < Voltage < 0, Assign Logic 0

3.62 v, output a 1

t1

Bit Stream Out = 1111110000111...

A/D Convertor. 1 bit/sample.Example) N = 2. Assign 0 or 1 to voltage.

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

0 < Voltage < +5v, Assign Logic 1-5v < Voltage < 0, Assign Logic 0

A/D Convertor. 1 bit/sample.

Input to the transmitter.Output at the receiver.

Considerable Round-Off error exists.

+2.5 v

-2.5 v

time (sec)

Example) N = 4. Assign 00, 01, 10 or 11.

2.5 < Voltage < 5 , Assign 110 < Voltage < 2.5, Assign 10-2.5 < Voltage < 0, Assign 00-5 < Voltage < -2.5, Assign 01

3.62 v, Assign 11

t1

Bit Stream Out =11111011111100 000000101011...

+2.5 v

-2.5 v

A/D Convertor. 2 bits/sample

A/D Convertor. 2 bits/sample.

Input to the transmitter.Output at the receiver.

Receive 11? Output 3.75vReceive 10? Output 1.25vReceive 00? Output -1.25vReceive 01? Output -3.75vReduced Round-Off error exists.

+3.75 v

+1.25 v

-1.25 v

-3.75 v

Circuit Switched Voice (POTS) Bandwidth ≈ 3,500 HertzBandwidth ≈ 3,500 Hertz A/D ConverterA/D Converter

samples voice 8,000 times/secondsamples voice 8,000 times/second rounds off voice to one of 256 voltage levelsrounds off voice to one of 256 voltage levels transmits 8 bits per sample to far sidetransmits 8 bits per sample to far side

D/A ConverterD/A Converter receives 8 bit code wordreceives 8 bit code word outputs one of 256 voltage levels for 1/8000th secondoutputs one of 256 voltage levels for 1/8000th second

64,000 bps (1 byte, 8000 times/second)64,000 bps (1 byte, 8000 times/second)

Compact Disk Bandwidth ≈ 20,000 HertzBandwidth ≈ 20,000 Hertz A/D ConverterA/D Converter

samples voice 44,100 times/secondsamples voice 44,100 times/second rounds off voice to one of 65,536 voltage levelsrounds off voice to one of 65,536 voltage levels transmits 16 bits per sample to far sidetransmits 16 bits per sample to far side

D/A ConverterD/A Converter receives 16 bit code wordreceives 16 bit code word outputs one of 65,536 voltage levels for 1/44100th secondoutputs one of 65,536 voltage levels for 1/44100th second

705,600 bps705,600 bps

Sampling & Quantizing Examples fs = 16 KHzfs = 16 KHz

4096 quantiles4096 quantiles 256 quantiles (approximate phone quality)256 quantiles (approximate phone quality) 32 quantiles32 quantiles 4 quantiles (generally 2 levels used!)4 quantiles (generally 2 levels used!)

4096 quantiles4096 quantiles fs = 16 KHzfs = 16 KHz fs = 8 KHz (some interference)fs = 8 KHz (some interference) fs = 2 KHzfs = 2 KHz fs = 1 KHzfs = 1 KHz

1/8th Second of Voice

1/8th Second of Voice

1/8th Second of Voice

Sources of POTS delay

Local Loop

PCMCoder TDM Trunk

POTSTSI

POTSTSI

IntermediateDigitalVoice

Switches

...

TDM TrunkLocal Loop

PCMCoder

Trunk resources are dedicatedto each voice call via TDM.

Source CO

Destination CO

Sources of VoIP delay

VoiceCoder

PacketSwitch

PacketSwitch

IntermediatePacket

Switches...

StatMuxTrunks

VoiceDecoder

Trunk resources are randomly assigned to each voice call via Statistical Multiplexing.

PacketAssembler

TransmissionBuffer

ReceiverBuffer

Voice (Video) on LAN (WAN) More complex system than circuit switched More complex system than circuit switched

voicevoice Packet AssemblerPacket Assembler Transmitter BufferTransmitter Buffer Receiver BufferReceiver Buffer

End-to-End Delays > Circuit Switch TDMEnd-to-End Delays > Circuit Switch TDM Delay Variability > Circuit Switch TDMDelay Variability > Circuit Switch TDM