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 opticsTelephone Industry – The Economics Side of the Storyhttp://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/circuits/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/A

DSL_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)

585

http://www.pt.com/tutorials/ss7/

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 switchhttp://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/ECE697J-03-10-02.pdfhttp://www.cs.bham.ac.uk/~gkt/Teaching/SEM335/Queenie/program/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

data transmission

circuit termination

Packet Switching• Datagram

– 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

Header Data Trailer

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.pdfhttp://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/sonet/sonet.html

• Chips– http://www.lightreading.com/document.asp?doc_id=56058

• Future– http://www.fujitsu.com/downloads/TEL/fnc/whitepapers/futureofsonet-

wp.pdf– http://img.lightreading.com/heavyreading/pdf/hr20031114_esum.pdf