Public switched telephone network ppt

public switched telephone network pstn ppt and block diagram of telecommunication network
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Dr.NeerajMittal,India,Teacher
Published Date:19-07-2017
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Introduction to Telephony, Cable and Internet Technologies Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Connectivity:  direct (pt-pt, N-users),  indirect (switched, inter-networked)  Telephony, Internet, Cable Networks: Basic Concepts  Concepts: Topologies, Framing, Multiplexing, Flow/Error Control, Reliability, Multiple-access, Circuit/Packet- switching, Addressing/routing, Congestion control  Data link/MAC layer: SLIP, PPP, LAN technologies …  Interconnection Devices  S. Keshav book (Chapter 2), Opt Nets (Sec 11.1, 13.1, 13.2) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Connectivity...  Building Blocks links: coax cable, optical fiber... nodes: general-purpose workstations...  Direct connectivity: point-to-point multiple access Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Connectivity… (Continued)  Indirect Connectivity switched networks = switches inter-networks = routers Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4What is “Connectivity” ?  Direct or indirect access to every other node in the network  Connectivity is what you get instead of a direct physical link Key Tradeoff: Performance characteristics worse Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Connectivity …  Internet: Best-effort (no performance guarantees) Packet-by-packet  A pt-pt link: Always-connected Fixed bandwidth Fixed delay Zero-jitter Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Telephony Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7Telephone Network: What is It?  Specialized to carry voice traffic  Aggregates like T1, SONET OC-N can also carry data  Also carries  Telemetry, video, fax, modem calls  Internally, uses digital samples  Switches and switch controllers are special purpose computers Pieces: 1. End systems 2. Transmission 3. Switching 4. Signaling Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8Telephone Network: What is It?  Single basic service: two-way voice  low end-to-end delay  guarantee that an accepted call will run to completion  Endpoints connected by a circuit, like an electrical circuit  Signals flow both ways (full duplex)  Associated with reserved bandwidth and buffer resources Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9Telephone Network Design  Fully connected core  simple routing  telephone number is a hint about how to route a call  But not for 800/888/700/900 numbers: these are pointers to a directory that translates them into regular numbers  hierarchically allocated telephone number space Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10Telephone Network Design Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Telephone Pieces: End Systems Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Telephone Pieces: End Systems  Transducers: key to carrying voice on wires  Dialer  Ringer  Switch-hook Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13Last-Mile Transmission Environment  Wire gauges:19, 22, 24, 26 gauge(smaller better)  Diameters: 0.8, 0.6, 0.5, 0.4 mm (larger better)  Various forms of noise: (twisting reduces noise)  Bridged-tap noise: bit-energy diverted to extension phone sockets  Crosstalk  Ham radio  AM broadcast  Insertion loss: -140 dBm noise floor  100 million times more sensitive than normal modems  Bandwidth range = 600 kHz  Notch effects in insertion loss due to bridged-taps  Transmission PSD = -40dBm = 90 dBm budget Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 142-wire vs 4-wire: Sidetones and Echoes  Both trans & reception circuits need two wires  4 wires from every central office to home  Alternative: Use same pair of wires for both transmission and reception  Signal from transmission flows to receiver: sidetone  Reverse Effect: received signal at end-system bounces back to CO (esp if delay 20 ms): echo  Solutions: balance circuit (attenuate side-tone) + echo- cancellation circuit (cancel echoes). Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15Dialing  Pulse  sends a pulse per digit  collected by central office (CO)  Interpreted by CO switching system to place call or activate special features (eg: call forwarding, prepaid- calls etc)  Tone  key press (feep) sends a pair of tones = digit  also called Dual Tone Multifrequency (DTMF)  CO supplies the power for ringing the bell.  Standardized interface between CO and end-system = digital handsets, cordless/cellular phones Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16Telephone Pieces: Transmission Muxing  Trunks between central offices carry hundreds of conversations  Can’t run thick bundles Instead, send many calls on the same wire  Multiplexing (a.ka. Sharing)  Analog multiplexing  Band-limit call to 3.4 KHz and frequency shift onto higher bandwidth trunk  obsolete  Digital multiplexing  first convert voice to samples  1 sample = 8 bits of voice  8000 samples/sec = call = 64 Kbps Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Transmission Multiplexing (contd)  How to choose a sample?  256 quantization levels, logarithmically spaced (why?)  sample value = amplitude of nearest quantization level  Two choices of levels ( law and A law)  Time division multiplexing  Trunk carries bits at a faster bit rate than inputs  n input streams, each with a 1-byte buffer  Output interleaves samples  Need to serve all inputs in the time it takes one sample to arrive = output runs n times faster than input  Overhead bits mark end of frame (why?) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Transmission Multiplexing  Multiplexed trunks can be multiplexed further  Need a standard (why?)  US/Japan standard is called Digital Signaling hierarchy (DS) Digital Signal Number of Number of voice Bandwidth Number previous level circuits circuits DS0 1 64 Kbps DS1 24 24 1.544Mbps DS2 4 96 6.312 Mbps DS3 7 672 44.736 Mbps Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19Telephone Pieces: Switching Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20