Public Switched Telephone Network (pstn)

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1 " ' ' 2 # $ %&#'(&#'(&#'( #' ( $) $) &$ *+ $ $ , . , /& $ $ - ) . + / $ 0# , ! .+ " # $ ! 4. ,' +$ )5 , 3 " 2 # $ ! 4. ,' 7 )5 , " 6 9 3 ! 7 8 &; ! #' ( &#' 4. ,' )5 , " : &$ ! < * & ! $ ; = $ X.21 Cell switching - works with cells (packets) having a fixed size : offers bounded delay guarantees (QoS compatible, long packets won’t stuck cells) ! (fixed length) CSPDN: Circuit switched public data net* PSPDN: Packet switched public data net** DQDB: Distributed queue dual bus * Used by European Telecom’s that use X.21 in circuit switched nets **Used by British Telecom’s Packet-switched Service (PSS), Data Pac (Canada) ... > $) &# Circuit switching - dedicated path - constant delay/bandwidth - voice/data - paid by time - examples: PSTN, GSM? Time switch - Makes switching between time slots - In the figure incoming slot 3 is switched to outgoing slot 3 for one voice direction - Each coming timeslot stored in Speech Store (SS) - Control store (CS) determines the order the slot are read from SS - The info in CS is determined during setup phase of the call Space switch - makes switching between PCM lines - works with electronic gates controlled by CS ! Cross-point Cross-point controlled controlled by byCS CS TDM 1? $) ; * ) ) 7 & & & & # $ ! . . . . $ + $0 $0 . . . . . .. . . . $ . . . 7 , $ . . $ $ 11 $ example Packet structure Seq: sequence number Op code: message/control identifier CRC: Cyclic Redundancy Code Node structure Note: - source address required for retransmission in ARQ - byte count could be also an end flag ! 1" *+ 0 ,/ 4 / 8 Version IHL 16 Type of service Identification Time to live 19 24 31 Total length Flags Protocol Fragment offset Header checksum Source IP address Destination IP address Options /-6 / ! Padding . 12 *+ & . 7 $, &@&9 =?" : LAN Function - transport units have a constant length - access units access known subscribers in access unit’s subnets and route packets access unit for them - access protocol applies token ring Properties - decentralized (distributed switching as in FDDI*) - for ATM compatible MANs (metropolitan area networks) - rates: up to 155 Mbps - geographical limit up to 200 km access unit . . access unit LAN access unit * FDDI: Fiber Distributed Data Interface for description, see the supplementary material of this lecture ! Transport Unit (same as in ATM) 16 $) ; General characteristics can use packets of varying length packet is assigned an address and the necessary control information packets are placed in frames Each sent frame stored in a buffer (store & forward) in a receiving node and its information is checked before resending -> delays but errorless transmission possible In summary: packet handing by nodes consists of checking the packet format checking for errors (link level - OSI 2) waiting for available outgoing path capacity ! 18 ) $ Connection oriented - Applies same route - QoS well defined - Phases - Connection setup - Data transmission - Release - Packets received in same order - Example: ATM, frame relay, PCM ! Connectionless - Use of different routes for each packet possible - Each packet has address fields - QoS not guaranteed - Packets may come in different order - Example: IP (Internet Protocol), TCP takes care of cleaning the mess 1: . 0 Transfer modes PSTN Circuit switching for voice ISDN -- developed nowadays also for data PCM - well-specified delays - echo problems Packet switching - developed for data - nowadays also for voice - statistical multiplexing - traditionally variable delays IP, Frame-relay ATM ! 3 Connection types ATM Connection oriented Frame-relay - hand-shaking - strict error requirements X.25 - for fast data transfer Connectionless - especially for broadcasting/ streaming - modest error rates often accepted - for fast data in good channels X.25, IP, UDP* *User Datagram Protocol1< &- .+ $ $ A&# &# SPC: Stored program control FDM:Freq. div. multiplexing TDM:Time div. multiplexing WDM:Wavelength div. mult. %&# ! 1= * ;+ $ 1=<: ' 5 9 1=<= . 1=>1. 9 $ , ' 1?? $ + . "1 $, ! $ ;' ; , - See further info also at: http://www.seg.co.uk/telecomm/ ! $ ; $ + via selectors + Topology of the first network using Strowger switch ) 1> ' ; ) ;) $ 9B, 1?? + , ) LS1 10 CF1 $ 1 GS1 A-subs. B-subs. 10 CF10 GS10 1 LS10 #'/ '4 , ) . % )5 5 ) ! Call setup: 1. A-sub. picks up handset (CF detects) - exchange sends line available -tone 2. A-sub. sends pulses (GS, LS activated) - exchange sends ringing tone 9B, - 9 *+ $ "? # + $ Signaling (SS7) with users and other exchanges to other exchanges PBX ETC Announcement equipment Signaling equipment Third-party equipment Traffic concentration - Operation & maintenance support (Q.513) - Charging Control system - Supplementary (IN) services (as credit card call) - Subscriber data, switch control conference calls, call waiting, broadcasting ... ! Test/measurement equipment Recorded announcements: faults/subscriber services Switch Group switch Control Subscriber stage O&M HW ETC: Exchange terminal circuit IN: Intelligent network "1 $ Connects to: digit receivers, info tones, test equipment Concentrator MUX To ETC internet access (DSLAM) centrex* service Control system: subscriber authentication, routing, billing, O & M, ... ETC: Exchange terminal circuit Speech store: shift registers storing bits for time switching Control store: gates guiding speech store switches * leased PBX function from local exchange ! "" *+ $ - . . . . $ . $ 3 . ./ . . - 7 ; Sample of Intelligent network (IN) services ! "2 *+ $ - + - $ , , $ $ , $ , ) . $ ! , , ) $ $ ;. ! ; "6 ) ) Cross-bar switch (space division matrix) . ; . $ , ! ) +.+ # . + ,9 - . . ; ; $ , #) ; "8 ) . . ; % 1??. ) 7 . / . .+ $ )C )C ! ( + 1> : " 1>" # $ . $ .7 ;% .1>" # .. ",1 . .1> : "?? ; $ ": ) ) A + . $ $ ;1?,1D 2,1 # . 7 . .) $ $ $ + Time switch Space switch Subscriber stage Time switch Question: Why time or space switch is not always enough? ! "< /& + . @81" $ E1 E" ' V4 * * * * B E2 /& '9B * E8 ' Peek to Q-recommendations ! * 9 * , * ,*+ , ' ,' , $ /& , "= *+ $ .+ + $ E1, ' 9 /& E1). " 9 H & "+:6 $ . . $ /& ! . E1 $ $ 3 F /& G/& ) 9B , H 1: ; 3 - . $ ; . 5>:1 "> *+ $ . E")E6 E", / . - ; ; "?6= ( $ 2?9 H & * 5>" ! 2? *+ $ 9 "?6= . E8 + $ ( . . . ' $ /& ) * E8 ! . 5 $ $ $ $ /& # % $ $ 8 41 4" $ + $ ; < $ $ $ $ $ $, $, ) ). & $ $ . 9) K ) $, ') $ ; 9) *A-subscriber’s on-hook message transmitted to B exchange ! 6? $ $ $ . . . . , $ $ $ $$ . $ $ ! + $ $ 61 # ; to international level Transit exchange Regional transport level Local transport level Local exchange Access transport level ! 6" ; + % ; $ $ + ; ; $ . . ; + $ . . $ $ $ # 5 ; ); . . &A&# & 4 . . . A - $ &- * & # +$ SDH - transport of 1.5/2/6/34/45/140 Mbps within a transmission rate of 155.52 Mbps - carries for instance ATM and IP within rates that are integer multiples of 155.52 Mbps ! 62 &$ # + $*7 5:1 International exchange (Finland) * ! 1:5 DCME & #*% &$ " 8,1H ; '(& . & #* 5<:2 DCME Q.50 signaling International exchange (US) # .2" $, *+ 1 18 # ( "#( ) ') ( ; ; *1 DCME A: Digital line interface B: Time-slot switching C: Voice interpolation (DSI) D: ADPCM E: Variable bit rate (for overload) 66 @812 ' &. . E . < - ; - , $ - ., $ . $ . ; / + ! 3 $ - - 7 68 - Value Added Basic Supplementary - ( - , ) - ' ; 7 ; 11= + $ - / ; G@=" " L 3 ; $0 $$ E ; ; ! $( /& $ - $ L . $GL 7 / / $ $G 3 . . . 6: 5 . - 4. ,M*% , $ ! 6< $ + $, *7 Distribution point On-line subscriber with several telephones ADSL modem Cross connection point Twisted pair - connections & '# ISDN 2B+D 144 kb/s Q.512 specifies exchange interfaces Wireless access (or radio access point) ISDN connection example: 30B+D (2.048 Mb/s) Business subscriber ! Multiplexer Private Branch Exchange 6= ' $ . Loop current used for signaling & message Digital-lines to ISDN central office Analog-line ! per trunk signaling in local loop: - long setup time - hacking easy - voice grade circuits - interference & cross-talk sensitive - expensive 6> 9 ' ; $I . ; # ; - ) $ - ! 8? & ) $ & ) $ 9) * ! -; ; 81 # & $ . / . ' # . / . '( & &( ' 7 ; - & # & $ ! 8" 300 Hz - 3.6 kHz # / ) . E": 11( == ) "6?? 6) E"< 11( == ) 6=?? . . E"> 11( == ) >:?? ) ) 6) E>? ?>( >= ) 8: ??? ( :?? ( . E2: E2< ) 6= ! (0 . 22 $ :?)1?= 3 82 # . & * / 4 & * $ ) $ .7 . . . #7 ) ; 3 $ $ $ # ) ) E6" # 8 E6" # 1? -N ') 7 $ E>? . ,E"6 ." 6 ( * $ ! 86 ' $ $ . . V.34 V.24 / . & # Analog exchange Interface & $ V.24 / . V.34 G.711 decoder G.711 G.711 encoder & # Digital exchange Interface & $ G.711 (11/88) - Pulse code modulation (PCM) of voice frequencies V.34 (02/98) - A modem operating (up to 33 600 bit/s) for use in 2-wire analog PSTN ! V.34 G.711 G.711 Digital Digital modems: modems: Generate Generate G.711 G.711 signals signals and and receive receive V.34 V.34 signals signals passed passed through through G.711 G.711 encoder. encoder. Connected through aa digital digital interface interface Connected to to aa digital digital switched switched network network through Analog Analog modems: modems: Generate Generate V.34 V.34 signals signals and and receive receive G.711 G.711 signals signals that that have have been been passed passed through through G.711 G.711 decoder decoder in in an an analog analog PSTN PSTN local local loop loop 88 %+ - %+ . / *** ?"( >1 ) A %+ 5 5 5 5 *+ E1< . . 16 6?? ( 1 O:= , " O<: , 2 O=?, 6 O=6 , $ , ' $ ' $ &$ &$ . $ "6?? ( $ 6=?? ( $ 166?? ( $ :6 ( /& $ 5 ; ; Scanning Scanning Coding Compression Compression Modem Modem(D/A) (D/A) Coding $ . . . $.+ , '6( 1166 ! # 2 @'# E"< E"> ( 8: / ) $ &4 *4 )5 ) - 54 $ ; /4 /& #4 $ . . - . ) )/ $ ) ; ; - $ , ;. ITU: International Telecommunications Union ! 8< # $ 4 ) 4 ) . . $ 7 7 ; @4 $ $ ; 41 4" / ) E4 ! ) ,6 8 : )& $ < 4$ $ $ $ $ , - 8= *+ , @) $ , $ $K (Illustrative examples denoted by arrows) ! *http://www.itu.int/rec/recommendation.asp?type=products&lang=e&parent=T-REC-Q 8> $ ! $ $ :?