PSTN Architecture Overview (1)
• PSTN: Public Switched
Telephone Network
• History: From American Bell
to AT&T
• Hierarchical and layer
structures
• Planned as a national network
• Design for Ilities
– Service availability,
– Sound Quality,…
• Early realization of necessary
basic research on ilities
Satellite links
Submarine
cables
International gateway
exchange (Centre de Transit 3)
International
network
National tandem exchanges
(Tertiary trunk switching
centers)
Trunk network
Regional tandem exchanges
(Secondary trunk switching
centers)
Local tandem exchanges
(Primary trunk switching
centers)
Local
network
Local
exchanges
Subscriber lines
Figure by MIT OCW.
© 2005 Student: Jijun Lin, Daniel Livengood, Chintan Vaishnav, Engineering Systems Division, Massachusetts Institute of Technology
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PSTN Architecture Overview (2)
• Switching Hierarchy
–
–
–
–
–
RC
Regional Center
Sectional Center
Primary Center
Toll Center
End Office
ES
ES
RC
Trunk Circuit 0.5 to 1.5dB
VNL
SC
SC
Class 2 Offices
Trunk Circuit 0.5 to 1.5dB
VNL
PC
PC
Class 3 Offices
Trunk Circuit 0.5 to 1.5dB
VNL
TC
TC
VNL + 2
EO
Class 1 Offices
Junction Circuit 2 to 4dB
Junction Circuit
Junction Circuit
Junction Circuit
T
x
Subscriber
T
Class 4 Offices
EO
Class 5 Offices
Junction Circuit
Final Route
High Usage
Route
ES
Echo Suppressor
Tandem Office
SC
Sectional Centre
Ave
Average
TC
Toll Centre
EO
End (Local) Office
RC
Regional Centre
VNL
Via Net Loss
PC
Primary Centre
REGIONAL CENTERS
Figure by MIT OCW.
Regional Centers (1972)(12)
Figure by MIT OCW.
Five level switching plan in use from 1950s
© 2005 Student: Jijun Lin, Daniel Livengood, Chintan Vaishnav, Engineering Systems Division, Massachusetts Institute of Technology
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PSTN History
(Collection by Prof. Whitney)
• Classification divides the PSTN into 5 levels (post1950):
–
–
–
–
–
Class 1: Regional Center, top level, 8 centers in 1930, 12 centers in 1972
Class 2: Sectional Center (not a part of the 1930 network)
Class 3: Primary Center
Class 4: Toll Center
Class 5: End Office
Image removed for copyright reasons.
Map of a U.S. telephone network.
What/Where is the Data behind this Graphic?
© 2005 Student: Jijun Lin, Daniel Livengood, Chintan Vaishnav, Engineering Systems Division, Massachusetts Institute of Technology
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PSTN Definitions and Metrics
• Our network definitions
– Node: Switching center
– Link: Cable connecting switching centers
• Our metric focus
– Geodesic length between two points: with mechanical switches,
the goal was to have this be 3 or less
– Bandwidth: where are the choke points?
• Betweenness
–
–
–
–
Centrality
Scale-free
Preferential Attachment (911? Critical infrastructure lines)
Motifs
© 2005 Student: Jijun Lin, Daniel Livengood, Chintan Vaishnav, Engineering Systems Division, Massachusetts Institute of Technology
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Historical Connection Plans
Connection plan to help decrease the
geodesic length in 1930 V (notice the
motifs) and 1950 -->
Class 1
Regional Center
Class 2
Sectional Center
National
Class 3
Primary Center
Class 4
Toll Center
Local
Class 5
End Office
Five-level toll switching plan in use from the 1950s.
A variety of routings was possible with a maximum
of nine trunks in tandem.
Figure by MIT OCW. After Andrews & Hatch, 1971.
Figure by MIT OCW.
Improved quality via level skipping
© 2005 Student: Jijun Lin, Daniel Livengood, Chintan Vaishnav, Engineering Systems Division, Massachusetts Institute of Technology
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Questions and Supporting Data
Predicting/Explaining Structure
Which algorithms does the analysis of the actual structure
substantiate?
Data available: Switching Centers, Links in between, bandwidths
Predicting/Explaining Properties
What are the properties of the structure as a result of adding
availability?
Data available: 911-Tandem Links, Diverse Routing, Location
Routing Numbers
Observing systems
What motifs do we see?
Data available: Hierarchical view constructed from the data
Sources
Telcordia LERG Database, Quest Current Access Line Counts Database,
Bellcore’s BOC Notes on intraLATA Network
© 2005 Student: Jijun Lin, Daniel Livengood, Chintan Vaishnav, Engineering Systems Division, Massachusetts Institute of Technology
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