Download ACCESS NETWORKING - CERN Computing Seminars

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
[email protected]
[email protected]
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Introduction
PSTN access
ISDN access
VOIP
Emergence of packet switching networks
BB Access Technologies
ADSL
Conclusions
Bibliography
Introduction
Telecomm. Tech. Devp. (chronology)
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Telecomm. With Morse code
First Telegraph in India (Cal.)
ITU established with 20 European countries
Trans-Atlantic cable (US - France)
(London - Bombay)
Invention of Telephone by Bell
First manual exchange in India (50 lines, Cal.)
Indian Telegraph Act
Sir J. C. Bose transmits on wireless
Marconi demonstrates wireless (UK - France)
Beginning of Bell company
Lee Deforest develops vaccume tube ampl.
PABX
1847-1845
1852
1865
1866
1870
1876
1882
1885
1895
1899
1903
1906
1910
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Under ground cable in US
Baird develops picture tube and picture tx.
Hartley introduces concept of information
as a measure of quantity of data in a message
Marconi discovers Microwaves
First co-axial cable manufactured
First SPC computer (ENIAC)
Transistor invented
Shannon’s theorem on channel capacity
Electronic switching
First artificial satellite (USSR Sputnik)
1915
1926
1927
1932
1936
1946
1947
1949
1955
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
• 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
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1965
1969
1972
1974
1979
1982
1989
1992
1995
2000
2002
Packet switching proposed (D. Davis UK, P. Baran US)
ARPANET Launched
Beginning of E-mail (Tomlinson USA)
First article on TCP/IP (Cerf/Kahn)
First research lab. Comp. Network (NSF, Univ. of wis)
Internet defined as TCP/IP connected n/w
No. of internet users reach 100,000 and IETF formed
WWW released, No. of nodes hits 1 Million
VOIP comes to market
No. of hosts break 300 M, voice traffic crosses over data
VOIP takes 13 % of long haul telephone traffic
Digital Divide
• In Africa
• In India
• USA
1 phone per 100 persons
4 phones per 100 persons
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
percent of them are in industrial world
• Africa and middle east has only 1 % of internet users
90
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)
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Concentrators of individual lines to T1/E1
Cellular antenna sites
PBX
Optical Network Units
Cable TV
Various Access Options
• Narrow band
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PSTN based access
ISDN based access
Cellular based (Cellular digital packet data)
PLCC based
• Broad band
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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
US A
Na me Calls Rat e
( Mbps)
DS0
1 . 064
DS1
24 1. 544
DS2*
96 6. 312
DS3
672 44. 736
DS4* 4032 274. 176
Eur ope/Indi a
Na me Calls Rat e
CEPT1
CEPT2
CEPT3
CEPT4
30
120
480
1920
2. 048
8. 448
34. 368
139. 264
SDH/SONET Multiplexing Hierarchy
• Multiplexing
Level
Data Rate
(MBPS)
USA
Name
European
Name
• 1
2
3
4
5
6
8
9
10
51.84
155.52
466.56
622.08
933.12
1244.16
1866.24
2488.32
9953.28
OC-1
OC-3
OC-9
OC-12
OC-18
OC-24
OC-36
OC-48
OC-192
Undefined
STM-1
STM-3
STM-4
STM-6
STM-8
STM-12
STM-16
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
– V.32
– V.34
– V.42bis
– V.90, V.92
– V.54
300 baud, FSK, 2-wire, async
9600 baud, QAM with trallis FEC and
Echo cancellation
28000 baud
ISDN 64/128 Kbps
With error correction and compression
56 Kbps voice band modem
100 Kbps leased line baseband modem
2 wire and 4 wire
Shannon’s theorem on channel capacity
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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
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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.
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
Int erface St r uct ure
Us er
Tot al
dat a rat e bit rat e
Basi c
Access
BRI
2B + D( 16)
144 Kbps
Pri mar y
Access
PRI
( USA)
23B + D( 64) 1. 536 Mbps 1. 544 Mbps
PRI
( Eur ope)
30B + D( 64) 1. 984 Mbps 2. 048 Mbps
192 Kbps
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
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 - 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
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
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Application
P, S, T
Network
Data link
• Physical
ftp, mail protocols sw, speech coders
TCP, UDP,
RTP, RTCP, SNMP
IP, ICMP, X.25
Ethernet
ATM,
V.34, 90
LLC, MAC Frame relay
HDLC, LAPB
10baseT
ISDN
SLIC
U, 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
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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
Voice
Very low
Med.
E-commerce Low
High
(Transactions)
E-mail
Low
High
Telnet
Low
High
Serious Browsing
Medium
Low FTP
High
Low Low Video conf.
Med. High High
delay Jitter
High
High
High
Low
Low Low
Med. Low
High High
Med.
High
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
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)
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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
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Line coding and error correction coding
Signal processing
Antenna design
TDMA/FDMA/SDMA/CDMA
FTTx Technology
• Advantages
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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
Altitude
MEO
1400
GEO
10,352
36,000
KM
Round 13
trip delay
Data rate
84
nx2 Mbps
250 msec
-
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 appln
Kolimbiris, Addison wesley, 2001