public switched system. telecom infrastructure edge connection –terminal equipment phone fax modem...
TRANSCRIPT
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