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@hotmail.com

prakash@sgsits.ac.in

• Introduction

• PSTN access

• ISDN access

• VOIP

• Emergence of packet switching networks

• BB Access Technologies

• ADSL

• Conclusions

• Bibliography

Introduction

Telecomm. 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

• 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

• Shannon’s theorem on channel capacity 1949

• Electronic switching 1955

• First artificial satellite (USSR Sputnik) 1957

• 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

• 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

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

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 butOnly 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

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)

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)

• Access Nodes (Access Network Interface or ANI)

• Concentrators of individual lines to T1/E1

• Cellular antenna sites

• PBX

• Optical Network Units

• Cable TV

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)

Traditional Local Loops

• In 1970’s– 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 1980’s– 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

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

Digital transmission Hierarchy

USA Eur ope/Indi aNa me Calls Rat e

( Mbps)Na me Calls Rat e

DS0 1 .064DS1 24 1. 544 CEPT1 30 2. 048DS2* 96 6. 312 CEPT2 120 8. 448DS3 672 44. 736 CEPT3 480 34. 368DS4* 4032 274. 176 CEPT4 1920 139. 264

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

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

Shannon’s theorem on channel capacity

• C < 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

•

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.

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

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

ISDN Services & Access Network Interface (ANI) structure

Interface Struct ure Userdat a rate

Tot albit rate

Basi cAccess

BRI 2B + D( 16) 144 Kbps 192 Kbps

Pri mar yAccess

PRI( USA)

23B + D( 64) 1. 536 Mbps 1. 544 Mbps

PRI( Europe)

30B + D( 64) 1. 984 Mbps 2. 048 Mbps

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

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

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

End-to-end VoIP packet latency (Delay)

• Delay source Typical values in msec.

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

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

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 relayHDLC, LAPB

• Physical 10baseT ISDN SLICU, S, T int. codec

LAN ISDN, WAN POTS

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.

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

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

Sensitivity of data types to QOS on internet

• Traffic Type Bandwidth Loss delay Jitter

Voice Very low Med. High HighE-commerce Low High High Low(Transactions)E-mail Low High Low LowTelnet Low High Med. LowSerious Browsing Medium High HighLow FTP High Med.Low Low Video conf. HighMed. High High

Provisions for QOS

• IP Best effort, no guarantee on delivery or delay

• TCP Checks for sequence number of rx. Packet andrequests for retransmission (slow)

• UDP Runs faster than TCP

• ATM Extensive provisions for QOS tags

• Soln : IPV-6, IP over ATM, Edge routers

Broadband Access Technologies

• xDSL Technologies (Digital subscriber line)

• CATV Technology

• Fiber To The Home/Cabinet (FTTx) Technology

• Wireless access

• Satellite Technology

• Power line Technology

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

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

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

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

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

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)

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

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

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

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

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)

• 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

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. Dobb’a 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

• 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 applnKolimbiris, Addison wesley, 2001