Public Switched System

1

• Public Switched System

2
Telecom Infrastructure

• Edge Connection
• Terminal Equipment
• Phone
• Fax
• Modem
• DSL
• Subscriber Loop
• Core Switching
• Central office
• Switching hierarchy
• Circuit switching
• Packet switching
• Metro Area Network
• Long Haul Transmission
• Coax and microwave links
• Fiber optics
• Telephone Industry The Economics Side of the
  Story
• http//elsa.berkeley.edu/woroch/dance.pdf

3
Phone

• Electrical
• Parts
• Carbon microphone, electromagnet speaker, bell,
  dial
• Signaling
• DC
• AC 300-3400 Hz
• Electronic
• Dial tone and push button
• DTMF http//en.wikipedia.org/wiki/DTMF

4
Analog Signaling

• Two Wires, Full Duplex
• Ring, tip
• Hybrid circuit,
• Protection circuit
• http//www.epanorama.net/circuits/teleinterface.ht
  ml
• On hook
• DC 48V
• Ringing 80V, 20 Hz
• Off hook
• DC 23-80 mA, 5-10V
• Dial tone 350440 Hz
• Pulse or tone dialing
• Ring tone 440480Hz, or
• line busy 480620 Hz
• Connection
• Indication of line status by tones!
• http//www.telephonetribute.com/signal_and_circuit
  _conditions.htm

5
Subscriber Loop

• Twisted Wires
• 22-26 gauge
• Frequency dependent loss
• Loading
• Splice and repeater
• A tour
• http//www.epanorama.net/links/telephone.html
• DSL
• www.iol.unh.edu/services/testing/dsl/training/ADSL
  _Tutorial.pdf

6
Central Office

• Digitization
• Switching
• http//www.dmine.com/phworld/network/
• Multiplexing
• Inter Office Trunk Line
• Long Haul

7
Hierarchy

• Pre-Divestiture
• Local Exchange Carrier
• LATA
• Interexchange Carrier
• Long distance
• Common Channel Signaling (SS7)

http//www.pt.com/tutorials/ss7/
585
8
Digital Signaling

• Bandpass
• 4 kHz band limited filtering
• Digitization
• 8 kHz sampling
• 256 A-law companding
• 8-bit resolution
• 64 kb/s DS0
• Time Division Multiplexing
• x24 lines of 8 bits1 bit 1.544 Mb/s DS1
• DS2, 3 OC1, 3, 12, 48, 192, 768

9
Switching

• Space Switch
• Historical electromechanical switch
• Electronic switch
• http//en.wikipedia.org/wiki/List_of_telephone_swi
  tches

10
Switching

• Time Switch
• Tim Slot Swapping
• Memory

11
Switching

• TMS Switch
• Switching Fabric
• Contention
• Queuing
• Resource optimization
• http//www.ecs.umass.edu/ece/wolf/courses/ECE697J/
  slides/ECE697J-03-10-02.pdf
• http//www.cs.bham.ac.uk/gkt/Teaching/SEM335/Quee
  nie/program/BatcherBanyanApplet.html

12
Circuit Switching

• Pre-Arranged Switches to Establish a Path
• Fixed bandwidth
• Low variance in delay
• Set up overhead
• Idle time

13
Data Flow Chart
circuit establishment
14
Packet Switching

• Datagram
• Multiple Routes to Send
• Demo
• http//www.pbs.org/opb/nerds2.0.1/geek_glossary/pa
  cket_switching_flash.html
• Flexible, efficient
• Variable delay, congestion
• Buffer, sequencing
• Virtual Circuit
• Set up data always in sequence
• Systems
• ATM, Frame Relay, X.25

15
ISDN

• Digital Telephony With Voice and Data
• B Channel
• Service at 64 kbs
• D Channel
• Control at 16 kbs
• Speed
• Basic 144 kbs
• Primary 1.536 Mbps
• B-ISDN H channels
• Introduction to ISDN
• http//www.ralphb.net/ISDN/index.html

16
Frame Relay

• Characteristics
• Resource sharing using packet switching
• Dynamic bandwidth allocation supporting bursty
  data
• Low latency, high throughput
• WAN
• Protocol
• Synchronization
• Flag Field
• Destination
• Address
• Data link connection identifier virtual
  connection
• Flow Control
• Forward explicit congestion notification
• Backward explicit congestion notification
• Discard eligibility
• Information Field
• Up to 16 kB
• Error Handling
• Frame check sequence

17
ATM

• Characteristics
• Asynchronous
• Efficient
• Near real time response
• Support multiple services
• Protocol
• Header 5 B
• Generic Flow Control
• Virtual Path Identifier
• Virtual Channel Identifier
• Payload Type Identifier
• Cell Loss Priority
• Header Error Control
• Payload 48 B
• http//www.uniforum.chi.il.us/slides/atmintro/ATM1
  01.ppt.gz

18
Voice Over Digital Networks

• Digital Traffic gtgt Voice Traffic
• Voice Support by Digital Networks
• Conversion
• Digitization
• Compression
• Prioritization
• Fragmentation
• Other Issues
• Jitter
• Silence suppression
• Echo cancellation
• Voice Over IP
• http//www.solwise.co.uk/voiceoverip_intro.htm
• Voice Over ATM, IP, and Frame Relay
• http//www.protocols.com/papers/voe.htm

19
SONET or SDH Transport

• Synchronous
• Scalable
• Fiber friendly
• http//www.cse.wustl.edu/jain/cis777-99/ftp/g_9sn
  t/sld001.htm

20
STS-1

• Overhead and Payload
• Transport
• http//www.tek.com/Measurement/App_Notes/SONET/2RW
  _11407_2.pdf

21
Characteristics of SONET

• Synchronization
• Accurate timing, no bit stuffing
• Data Compatibility
• Direct mux or demux
• System Compatibility
• Vendor, data rate
• Service Compatibility
• ATM, IP, video, etc.
• Networking Capable

22
More on SONET

• Introduction
• http//people.deas.harvard.edu/jones/cscie129/nu_
  lectures/lecture12/sonet/sonet.html
• Chips
• http//www.lightreading.com/document.asp?doc_id56
  058
• Future
• http//www.fujitsu.com/downloads/TEL/fnc/whitepape
  rs/futureofsonet-wp.pdf
• http//img.lightreading.com/heavyreading/pdf/hr200
  31114_esum.pdf