ACCESS NETWORKING

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ACCESS NETWORKING

• Dr. Prakash D. Vyavahare
• Dept. of Electronics Telecomm.Engg.
• S. G. S. Inst. Of Tech. And Science,
• 23 Park Road, INDORE 452 003
• pvyavahare_at_hotmail.com
• prakash_at_sgsits.ac.in

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• Introduction
• PSTN access
• ISDN access
• VOIP
• Emergence of packet switching networks
• BB Access Technologies
• ADSL
• Conclusions
• Bibliography

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IntroductionTelecomm. Tech. Devp. (chronology)

• Telecomm. With Morse code 1847-1845
• First Telegraph in India (Cal.) 1852
• ITU established with 20 European countries 1865
• Trans-Atlantic cable (US - France) 1866
• (London -
  Bombay) 1870
• Invention of Telephone by Bell 1876
• First manual exchange in India (50 lines,
  Cal.) 1882
• Indian Telegraph Act 1885
• Sir J. C. Bose transmits on wireless 1895
• Marconi demonstrates wireless (UK - France) 1899
• Beginning of Bell company 1903
• Lee Deforest develops vaccume tube ampl. 1906
• PABX 1910

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• Under ground cable in US 1915
• Baird develops picture tube and picture tx. 1926
• Hartley introduces concept of information
• as a measure of quantity of data in a
  message 1927
• Marconi discovers Microwaves 1932
• First co-axial cable manufactured 1936
• First SPC computer (ENIAC) 1946
• Transistor invented 1947
• Shannons theorem on channel capacity 1949
• Electronic switching 1955
• First artificial satellite (USSR Sputnik) 1957

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• Kilby at TI invents IC 1958
• Paul Baran of Rand Corp. proposes packet
  switching 1960
• STD in India (Kanpur - Lucknow) 1960
• Paging system, Telstar satellite 1962
• ARPANET using packet switching (TCP/IP)
  1964 - 69
• First email on ARPANET 1971
• Cellular telephone in Tokyo 1979
• IBM - PC Microsoft - DOS 1981
• Portable cellular (Motorola) 1984
• GSM in 13 European countries 1988

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• Tim Burner Lee at CERN proposes Hyper-text
  info. System (Birth of WWW) 1990
• Digital mobile network in USA 1993
• Indian Telecom. Policy opens for private
  sec. 1994
• Internet service launched in India 1995
• Telecomm. Reg. Authority of India set-up 1997
• GMPCS (Iridium) starts 1998
• Long distance telephony opened for competition
  in India 1999 Lucent, Motorola, Microsoft
  opens office in India
• IT bill passed 2000
• Wireless in Local Loop makes its presence in
  India 2001
• Net Telephones legally introduced in INDIA 1
  April 2002

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Brief History of Internet

• 1965 Packet switching proposed (D. Davis UK, P.
  Baran US)
• 1969 ARPANET Launched
• 1972 Beginning of E-mail (Tomlinson USA)
• 1974 First article on TCP/IP (Cerf/Kahn)
• 1979 First research lab. Comp. Network (NSF,
  Univ. of wis)
• 1982 Internet defined as TCP/IP connected n/w
• 1989 No. of internet users reach 100,000 and
  IETF formed
• 1992 WWW released, No. of nodes hits 1 Million
• 1995 VOIP comes to market
• 2000 No. of hosts break 300 M, voice traffic
  crosses over data
• 2002 VOIP takes 13 of long haul telephone
  traffic

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Digital Divide

• In Africa 1 phone per 100 persons
• In India 4 phones per 100 persons
• USA 2 phones per persons
• Email Growth 1999 3.3 Billion,
  2003 11 Billion
• 5 Billion people in the world but Only 5 to
  6 of world population has access to internet
  and 90 percent of them are in industrial world
• Africa and middle east has only 1 of internet
  users

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Technology Development (Services)

• Principles of wire/wireless comm., for point
  to point (or multi-point) developed (modulation,
  line, source and channel coding)
• First stage of switching technology (FDMA,
  TDMA, Time and space switch)
• Second stage of switching technology (packet
  switching, Network management, optical fibers
  multiple services (Multi-media - voice, data,
  fax, video)
• Selection of the appropriate technology for
  accessing the core network by end user for
  multiple services with economy and QOS becomes
  main issue)

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Definitions

• Core Network Combination of switching centers
  and transmission systems connecting switching
  centers. (In India core network, till now,
  extended up to national boundaries, now the core
  networks of various TELCOs will be connected by
  the inter-exchange networks)
• Access Networks The portion of public switched
  network that connects access node (edge of access
  n/w) to the individual subscriber
  Access
  network in India is predominantly twisted copper
  wire (approx. 750 million of copper lines in the
  world)

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• Access Nodes (Access Network Interface or ANI)
• Concentrators of individual lines to T1/E1
• Cellular antenna sites
• PBX
• Optical Network Units
• Cable TV

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Various Access Options

• Narrow band
• PSTN based access
• ISDN based access
• Cellular based (Cellular digital packet data)
• PLCC based
• Broad band
• xDSL
• Cable modems
• Fixed wireless
• FTTx (PON)

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Traditional Local Loops

• In 1970s
• Residence to CO by copper line carrying analog
  voice/data (CO interconnected by T1/E1 or
  microwaves)
• Business Premises PABX connected to CO by number
  of lines for carrying analog voice/data
• In 1980s
• Residence to RLU by copper wire carrying analog
  voice/data or Digital voice (ISDN), RLU to CO by
  OFC
• Business premises PABX to MUX on digital trunk
  lines like T1/E1 (Mux to CO by T3/E3)
• Some business houses also use satellite links

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Local Loops (cont.)

• Residence to power line company center on
  electric wire
• Fiber to the home or cabinet (FTTH/FTTC)
• Residence to ONU on twisted pair/ co-axial/fiber
  
• ONU then connects to optical MUX/DEMUX
• Business PABX connects to a MUX switch by trunk
  lines which connects to the SDH/SONET optical
  ring

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Digital transmission Hierarchy
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SDH/SONET Multiplexing Hierarchy

• Multiplexing Data Rate USA European Level
  (MBPS) Name Name
• 1 51.84 OC-1 Undefined 2 155.52 OC-3 STM
  -1 3 466.56 OC-9 STM-3
  4 622.08 OC-12 STM-4
  5 933.12 OC-18 STM-6
  6 1244.16 OC-24 STM-8
  8 1866.24 OC-36 STM-12
  9 2488.32 OC-48 STM-16
  10 9953.28 OC-192 STM-64

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Internet Access to Home (PSTN Modems)

• The Client work station connects to modem which
  is connected through the PSTN twisted pair to CO
  and finally to the modem pool at the server
• PSTN MODEM STANDARDS
• V.21/Bell - 301 300 baud, FSK, 2-wire, async
• V.32 9600 baud, QAM with trallis FEC and
  Echo cancellation
• V.34 28000 baud
• V.42bis ISDN 64/128 Kbps With error
  correction and compression
• V.90, V.92 56 Kbps voice band modem
• V.54 100 Kbps leased line baseband modem 2
  wire and 4 wire

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Shannons theorem on channel capacity

• C lt B log (1 S/N)
  .
  - 2
• For B 4 KHz and S/N 30 dB C 40 KBps
  approx.
• Assumption AWGN,
• Modulation Technique and Coding technique not
  defined
• Cross talk and ISI are major issues in PSTN lines

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Issues in PSTN based access to Internet

• Slow connect time to server (via local switch)
  (Not suitable for on-line
  transaction processing)
• Low band width
• Cost of connect time on PSTN even when not being
  used for data transmission
• Not suitable for many high BW applications like
  video conferencing, Bulk file transfer etc.

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Accessing Network using ISDN

• Digital Network Access
• Networks are digital
• Services are integrated
• Two types of access
• (One for home and another for business (PABX))
• Considerable economy in terms of access time and
  ease in operation and maintenance

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ISDN (cont.)

• Uses two wires (basic access) or 4 wires (primary
  access) for getting connected to the central
  office digital switc
• ISDN based equipment (TE!) can be directly
  connected to the network Terminator
• Non-ISDN based equipment (TE2) can be connected
  via Terminal Adapter (TA)
• Network Terminator - 2 (NT2) can connect multiple
  number of equipments
• Various ISDN reference interfaces R, S, T, U for
  interfacing between NT1/2, TA and TE1/2

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ISDN Services Access Network Interface (ANI)
structure
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ISDN Merits

• Simultaneous voice and data transmission
• 128 Kbps delivery rate
• Integration of multiple services on single line
• cost effective than PSTN
• Most local loops can be used without modification
• Lower error rate
• Faster connect time to server

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Voice Over IP (VOIP)

• VOIP is the fastest growing area in comm. Today
• Carries voice traffic as data packets over packet
  switched data networks instead of as asynchronous
  stream of binary data over a circuit switched TDM
  voice network
• Address and control info of IP packet carries
  voice to dest.
• Convenient to talk with multi-media PC
• VOIP on LAN is convenient since no additional
  resources are needed (PC should be on all the
  time)
• Saves resources as against circuit switched
  network
• Economical and with reduced maintenance cost
• Alternatively voice enabled cable modem, or DSL
  boxes

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Steps Involved in VoIP

• Analog voice digitized at 8 K samples per second
  generating 64 Kbps bit stream, non-linear ADC,
  A-law (India)
• Digital filtering to remove line echo, remove
  silence period, time stamping, (add comfort noise
  at the rx end )
• Voice frame formation and data compression
  64 Kbps compressed to 8 Kbps,
  10 msec frame (10 byte data)
• IP packet preparation, Real-time Transport
  Protocol (RTP) with 12 byte header, 8 byte UDP
  header, 20 byte IP header
• IP packet transmission on internet (hubs,
  switches, routers)
• Steps 1 to 5 are executed in reverse order at
  the rx. end

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End-to-end VoIP packet latency (Delay)

• Delay source Typical values in msec.
  Recording (in PC) 10 - 40 Encoding
  (codec) 5 - 10 Compression 5 -
  10 Internet delivery 70 - 120 Jitter
  buffer 50 - 200 De-compression 5 -
  10 Decode 5 - 10
  --------------------------------------------------
  ---------------- Average delay 150 - 400
  msec

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PSTN v/s VoIP

• PSTN delay is less than 30 msec across
  globe, VoIP delay is approx. 150 msec
• QOS (delay) and QOV are variable and not
  guaranteed
• PC should be on all the time
• Annoying echoes due to larger delays (echo
  suppression can not be used, complex echo
  cancellation need to be used)
• Larger overhead per packet
• Much lower monthly is the main motivating factor

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Protocol Stacks

• Application ftp, mail protocols sw, speech
  coders
• P, S, T TCP, UDP, RTP, RTCP, SNMP
• Network IP, ICMP, X.25
• Data link Ethernet ATM, V.34, 90 LLC,
  MAC Frame relay HDLC, LAPB
• Physical 10baseT ISDN SLIC U, S, T
  int. codec LAN ISDN, WAN POTS

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QOS in Internet networks

• QOS is a measure of how quickly and reliably the
  data is transferred from source to the
  destination. (data Time sensitive
  financial transactions, still images, larger
  data files, voice, video)
• How to quantify and measure QOS
• Each service may require different types of QOS
• Subscriber Lease Agreement (SLA) must mention how
  QOS will be measured, conveyed to the customer,
  and what are the compensation clauses if it is
  not met.

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5 Important performance of QOS

• Availability 100 theoretically, 99.8 (90
  minutes down time per month) 99.9999 (2.6
  secs/month)
• Throughput (is not maximum capacity of the
  network)
• Sharing network lowers throughput
• Overhead of extra-bits per packet reduces the
  effective transfer rate
• The service provider must guarantee minimum rate
  of throughput for an application

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QOS (cont.)

• Packet loss Buffered queues get overflow or
  errors Retransmission adds delay
• Normal value of less than 1 average delay per
  month
• Latency (Delay)
• PSTN less than 30 msec,
• Internet 150 msec (digitizatin, compression,
  queuing )
• Jitter
• Variation in queue length
• Variation in processing time
• Time to re-order segmented packets

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Sensitivity of data types to QOS on internet

• Traffic Type Bandwidth Loss delay Jitter V
  oice Very low Med. High High E-commerce Low High
  High Low (Transactions) E-mail Low High Lo
  w Low Telnet Low High Med. Low Serious
  Browsing Medium High High Low FTP High Med. Low
  Low Video conf. High Med. High High

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Provisions for QOS

• IP Best effort, no guarantee on delivery or
  delay
• TCP Checks for sequence number of rx. Packet
  and requests for retransmission (slow)
• UDP Runs faster than TCP
• ATM Extensive provisions for QOS tags
• Soln IPV-6, IP over ATM, Edge routers

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Broadband Access Technologies

• xDSL Technologies (Digital subscriber line)
• CATV Technology
• Fiber To The Home/Cabinet (FTTx) Technology
• Wireless access
• Satellite Technology
• Power line Technology

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Various DSL Technologies

• IDSL ISDN based DSL (128 kbps modem banks)
• HDSL High Data rate DSL (T1/E1 speed) earlier DSL
• ADSL Asymmetric DSL (1.5 to 9 Mbps
  downstream) (16 to 800 Kbps upstream depending
  on dis.)
• UDSL, SDSL Unidirectional, Symmetric
• VDSL 12.9 Mbps (4500 ft) - 52.8 (1000 ft)
• Uses twisted copper wire, future local loops

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DSL Application

• High speed internet access, real-time access on
  remote LAN
• Distance learning (school, colleges, libraries),
  always on
• Video conferencing
• Combined voice and high speed data on same line
• Video on demand in apartment blocks using VDSL

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Advantages of ADSL (over cable or satellite)

• Low infra structure investments (shares telephone
  line)
• Can adapt to varying line conditions
• As secure as dial-up modem or T1 connection
• Asymmetric matches with future internet
  applications
• High dedicated BW (unlike sharing in cable TV)
• ADSL switches bypass the telephone switches that
  are getting overloaded with data traffic
• 40 times faster than ISDN and 100 times than 28 K
  modem

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Key features of ADSL

• 4 KHz is reserved for POTS
• The high bit rate data is line encoded using
  efficient and robust line coding techniques like
  DMT or CAP
• Multiplexed at CO by DSLAM (Digital
  Subscriber Line Access Multiplexor)
• Uses DSP techniques for echo-cancellation of
  Near-End (NEXT) and Far-End (FEXT) cross talk of
  multi-pair
• Line is properly terminated to reduce loading of
  loop
• better UTP category cable used

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ADSL Modulation

• CAP - Carrierless Amplitude/phase modulation
• a version of QAM in which incoming data modulates
  a single carrier which is them transmitted, the
  carrier itself is suppressed
• DMT - Discrete Multi-tone
• a version of multi-carrier modulation in which
  incoming data is collected and then distributed
  over a large number of small individual carriers
  each of which uses QAM

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Wireless Access Techniques

• 2G 1991 GSM (Digital circuit switched) 16 Kbps
• 2.5G 2001 HSCSD/EDGE 192 Kbps (High Speed
  Circuit Switched Data)
• 3G 2004 EDGE_2, 3G_IP (ckt packet) upto 2
  Mbps
• Broadband wireless access
• 13 frequencies allocated by ITU (700 MHz to 40
  GHz)

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Broadband access in wireless

• Challenges
• Spectral allocation and BW limitations
• Noise environment and interference
• Techniques used
• Line coding and error correction coding
• Signal processing
• Antenna design
• TDMA/FDMA/SDMA/CDMA

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FTTx Technology

• Advantages
• Bandwidth for large number of users at a site
• Growth potential (cost of fiber reducing)
• QOS
• can directly connect to SDH/SONEt
• Topologies bus, ring or star (Unidirectional)
• Access TDMA, WDMA

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Cable Modems

• Set-top box interfaces TV at customer premises
  with cable modem connected by co-axial cable to
  cable operator
• Uses collision resolution protocol (request for
  mini-slots)
• Uses 64 or 256 QAM
• 6 MHz channel (30 - 40 Mbps (shared), 450 - 750
  MHz
• 17 Million cable connections, security is an issue

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Satellite Constallation

• Orbit LEO MEO GEO Altitude 1400 10,352
  36,000 KM Round 13 84 250 msec trip
  delay Data rate nx2 Mbps - 128
  Kbps

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Conclusions

• The ability to access broadbase contents from
  internet regardless of physical location is
  beneficial in increasing productivity through
  telecommuting
• At global level, data comm. Is moving to a
  single, public networking environment environment
  with multi-gigabit tx. Rates, optical fiber based
  SDH (SONET) at physical layer with ease in
  mux/demux of low data rate traffic in high speed
  links
• (Core networks and transmission between exchanges
  are capable of carrying high bit rate user data)

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• Types of services significantly increased at user
  premises
• Access at high speed from customer premises and
  QOS is the main issue
• Many options Dial-up, ISDN, cable, ADSL
• More options in future FTTX, satellite, mobile,
  PLCC
• Availability, reliability and economy as deciding
  factor
• No unique solution
• Knowledge of access technologies, their QOS and
  cost and market trends are important in making
  long term investmens

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Bibliography

• www.xdsl.com
• The cost of quality in internet-style
  networks Amitya Dutta-Roy, IEEE spectrum,
  Sept. 2000
• Internet Telephony going like
  crazy Thomsen Jani, IEEE spectrum, May 2000
• Dr. Dobba journal, May 2000
• An engineering approach to computer
  networking S. Kesav, 1999, Addison wesley
• Telecommunication Transmission systems R. G.
  Winch, 1993, McGraw Hill
• Digital Communications Glover and Grant,
  1998, prentice Hall

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• Telecommunications Network management Aidarous
  and Plevyak, IEEE press, 2001
• Security for Telecomm. Network Manag. Rozenblit,
  IEEE press, 2001
• Fundamentals of Digital Switching McDonald,
  Plenum press
• IP technology History, current state and
  prospects Yanovsky, St. Petersburg univ, Russian
  fed.
• IT and Telecomm. Impact on developing
  countries W. Luther, FCC, USA
• Chaotic electronics in telecomm. Kennedy CRC
  press
• Digital comm. Systems with sat. and fiber optics
  appln Kolimbiris, Addison wesley, 2001

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