Public Switched System
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
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
Analog Signaling
• Two Wires, Full Duplex
– Ring, tip
– Hybrid circuit,
– Protection circuit
• http://www.epanorama.net/circui
ts/teleinterface.html
• On hook
– DC: 48V
– Ringing: 80V, 20 Hz
• Off hook
–
–
–
–
DC: 23-80 mA, 5-10V
Dial tone: 350+440 Hz
Pulse or tone dialing
Ring tone 440+480Hz, or
line busy 480+620 Hz
– Connection
Indication of line status by tones!
http://www.telephonetribute.com/signal_
and_circuit_conditions.htm
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/ADS
L_Tutorial.pdf
Central Office
• Digitization
• Switching
– http://www.dmine.com/phworld/network/
• Multiplexing
• Inter Office Trunk Line
• Long Haul
Hierarchy
• Pre-Divestiture
• Local Exchange Carrier
– LATA
• Interexchange Carrier
– Long distance
• Common Channel
Signaling (SS7)
http://www.pt.com/tutorials/ss7/
585
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 bits+1 bit; 1.544 Mb/s DS1
– DS2, 3; OC1, 3, 12, 48, 192, 768
Switching
• Space Switch
– Historical electromechanical switch
– Electronic switch
http://en.wikipedia.org/wiki/List_of_telephone_switches
Switching
• Time Switch
– Tim Slot Swapping
• Memory
Switching
• TMS Switch
• Switching Fabric
– Contention
– Queuing
– Resource optimization
http://www.ecs.umass.edu/ece/wolf/courses/ECE697J/slides/EC
E697J-03-10-02.pdf
http://www.cs.bham.ac.uk/~gkt/Teaching/SEM335/Queenie/prog
ram/BatcherBanyanApplet.html
Circuit Switching
• Pre-Arranged Switches to Establish a Path
–
–
–
–
Fixed bandwidth
Low variance in delay
Set up overhead
Idle time
Data Flow Chart
circuit
establishment
data
transmission
circuit
termination
DATA
Packet Switching
• Datagram
Header
Data
Trailer
– Multiple Routes to Send
• Demo
– http://www.pbs.org/opb/nerds2.0.1/geek_glossary/packet_
switching_flash.html
• Flexible, efficient
• Variable delay, congestion
• Buffer, sequencing
• Virtual Circuit
– Set up; data always in sequence
• Systems
– ATM, Frame Relay, X.25
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
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
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.pdf
http://www.mfaforum.org/frame/tutorials/40142.shtml
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/ATM101.ppt.gz
Voice Over Digital Networks
• Digital Traffic >> 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
SONET or SDH Transport
• Synchronous
• Scalable
– Fiber friendly
•
http://www.cse.wustl.edu/~jain/cis777-99/ftp/g_9snt/sld001.htm
STS-1
• Overhead and Payload
• Transport
•
http://www.tek.com/Measurement/App_Notes/SONET/2RW_11407_2.pdf
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
More on SONET
• Introduction
– http://people.deas.harvard.edu/~jones/cscie129/nu_lectures/lecture12/son
et/sonet.html
• Chips
– http://www.lightreading.com/document.asp?doc_id=56058
• Future
– http://www.fujitsu.com/downloads/TEL/fnc/whitepapers/futureofsonetwp.pdf
– http://img.lightreading.com/heavyreading/pdf/hr20031114_esum.pdf