1 / 54

Voice over Packet

Voice over Packet. Yaakov (J) Stein Chief Scientist RAD Data Communications. Voice over Packet. What is this course all about? NOT course on Voice over IP (although we may use VoIP as an example) Voice means “telephony voice” (not high-quality or communications-quality)

derora
Download Presentation

Voice over Packet

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. VoiceoverPacket Yaakov (J) Stein Chief ScientistRAD Data Communications

  2. Voice over Packet What is this course all about? NOT course on Voice over IP (although we may use VoIP as an example) Voice means “telephony voice” (not high-quality or communications-quality) Packet means any cell or packet-based data network (FR,ATM,IP,etc) Most of the course is about the over all the mechanisms needed to carry voice on a packet network Everything in common to VoIP, VoATM, VoFR, VoDSL, VoCATV, etc

  3. TOC Course Outline -1- • Introduction • PSTN Review history and terminology • Packet networks IP,FR, ATM • The case for VoP • PSTN Emulation • Digital Voice Processing • Speech production mechanisms pitch, formants, LPC, cepstrum • Speech perception mechanisms hearing, psychophysics • Simple Voice DSP gain, AGC, simple-VAD • Complex Voice DSP correlation, pitch, U/V, LPC, LSP • Speech Compression • Simple coders G.711, ADPCM • ABS CELP coders G.723.1, G.728, G.729 • Other coders MELP, MBE, STC, WI

  4. TOC Course Outline -2- • Other features • Echo cancellation • Modem/fax relay • Qos • Paying for QoS • Speech quality measurement PSQM, PESQ, E-model • VoX • VoIP • VoFR • VoATM • VoDSL • VoCATV • TDMoIP • VoCATV

  5. PSTN Review

  6. PSTN Review The PSTN circa 1900 pair of copper wires “local loop” manual routing at local exchange office • Analog voltage travels over copper wire end-to-end • Voice signal arrives at destination severely attenuated and distorted • Routing performed manually at exchanges office(s) • Routing is expensive and lengthy operation • Route is maintained for duration of call

  7. PSTN Review f t Multiplexing 1900: 25% of telephony revenues went to copper mines • standard was 18 gauge, long distance even heavier • two wires per loop to combat cross-talk • needed method to place multiple conversations on a single trunk 1918: “Carrier system” (FDM) • 5 conversations on single trunk • later extended to 12 (group) • still later supergroups, master groups, supermaster groups 1963: T-carrier system (TDM) • T1 = 24 conversations per trunk • later T3 = 28 T1s • still later SDH rates with 1000s of conversations per trunk channels timeslots

  8. PSTN Review Local Exchange PSTN Topology Many local telephone exchanges had sprung up Bell Telephone acquired them and interconnected them for long distance local loop Local Exchange Local Exchange Long distance network trunk circuit subscriber line

  9. PSTN Review Switching / routing Originally • All switching was manual • All routing was unprincipled Both were expensive and performed once per call 1879 Connolly & McTigthe invent automatic switching 1888 Strowger invents dial telephone and automatic telephone exchange 1892 first public automatic exchange (La Porte, Indiana) 1902 first rotary dial phone 1917 Blauvelt invents large city numbering plan 1930 tandem crossbar switch 1953 centralized automatic message accounting (call billing) 1963 touch-tone dialing 1970 Erna Hoover invents computerized telephony switch

  10. PSTN Review Old US PSTN Class 1 Regional centers Class 2 Class 2 Sectional centers Class 3 Class 3 Class 3 Primary centers Class 4 Class 4 Class 4 Class 4 Toll (tandem) offices circuits,trunks Class 5 Class 5 Class 5 Class 5 Class 5 Central (end) offices local loop subscriber lines last mile Class 5 switch is the sole interface to the subscriber lines

  11. PSTN Review Optimized Telephony Routing Circuit switching (route is maintained for duration of call) Route “set-up” is an expensive operation, just as it was for manual switching Today, complex least cost routing algorithms are used Call duration consists of set-up, voice and tear-down phases

  12. PSTN Review Signaling PSTN with automatic switching requires signaling The present PSTN has thousands of features and all require signaling support Examples: On-hook / off-hook Pulse / Tone dialing Receiver off-hook Call waiting Caller number identification Call forwarding Hook-flash Fax transmission detect Inter-CO messaging Echo cancellation Voice mail Conference calls Coin-drop Billing

  13. PSTN Review Signaling Methods Signaling can be performed by several methods • Analog voltage signaling E&M, ground-start, loop-start • In-band signaling DTMF, MFR1, MFR2 • Channel associated signaling (CAS) AB bits, ABCD bits • Common channel signaling (CCS) SS7, QSIG • Trunk Associated CCS • Separate signaling network CCS

  14. PSTN Review The PSTN circa 1960 trunks circuits local loop subscriber line automatic routing through universal telephone network • Analog voltages used throughout, but extensive Frequency Division Multiplexing • Voice signal arrives at destination after amplification and filtering to 4 KHz • Automatic routing • Universal dial-tone • Voltage and tone signaling • Circuit switching (route is maintained for duration of call)

  15. PSTN Review The Digitalization of the PSTN Shannon (Bell Labs) proved is better than and the PSTN became digital Better means • More efficient use of resources (e.g. more channels on trunks) • Higher voice quality (less noise, less distortion) • Added features Digital Communications Analog Communications

  16. PSTN Review Timing In addition to voice, the digital PSTN transports timing • This timing information is essential because of • the universal use of TDM • the requirement of accurate playback (especially for fax/modem) • Receiving switches can recover the clock of the transmitting switch • Every telephony network has an accurate clock called “stratum 1” Clocks synchronized to it are called “stratum 2” Clocks synchronized to them are called “stratum 3” and so on

  17. PSTN Review The Present PSTN core backbone PSTN Network subscriber line • Analog voltages and copper wire used only in “last mile”, • but core designed to mimic original situation • Voice signal filtered to 4 KHz at input to digital network • Time Division Multiplexing of digital signals in the network • Extensive use of fiber optic and wireless physical links • T1/E1, PDH and SONET/SDH “synchronous” protocols • Signaling can be channel/trunk associated or via separate network (SS7) • Automatic routing • Circuit switching (route is maintained for duration of call) • Complex routing optimization algorithms (LP, Karmarkar, etc)

  18. PSTN Review VoP course Nonvoice services The PSTN can even be used to transport non-voice signals such as FAX or DATA • These services disguise themselves as voice by using a modem • Proper timing is essential • Special signaling is required • turn off LEC • turn off call waiting • service recognition PSTN • capabilities negotiation • mutual identification • end of page/document • modem recognition • modem training • data compression

  19. PSTN Review Digital Loop Carrier Pushes the digital PSTN closer to customer AT&T SLC-40, SLC-96,Nortel DMS P-phone, “pair-gain” Access Network TR-08 Mode 1pair-gain: Replace 96 pairs with 5 T1s (one spare for “span protection”) 96 – 10 = 86 TR-08 Mode 2pair-gain: Replace 96 pairs with 2 T1s (without “span protection”) 96 – 4 = 92 CLASS 5 UTP/coax/fiber Street cabinet CPE FTTB/FTTC pedestal UTP TR-08 multiplex 96 lines on: Mode 1: 4 T1s Mode 2: 2 T1s (2:1 concentration) GR303/V5.1/V5.2 multiplex up to 2048 lines

  20. Packet Networks

  21. Packet Networks Earliest Data Comm Earliest data communications were serial bit streams Basic data unit is the character (5, 6, 7, or 8 bits) Start-stop protocol delineates individual characters Rate limited to thousands of characters per second Initially range limited to tens of meters … later modems extended range Terminal – computer and computer – computer used the same protocol RS 232

  22. Packet Networks Data in Packets Problems with serial communications protocols • Large overhead (encapsulation per character) • Dedicated resources 1961 Kleinrock article on packet switching network 1962 ARPA computer program begins 1967 first use of word “packet” 1969 ARPANET becomes operational (UCLA, SRI, UCSB, Utah) 1972 first email

  23. Packet Networks Packet Switched Networks • US DOD project to design a data communications network • Design goal was reliability under attack • Advanced switch technology enabled routing-on-the-fly • Design produced Internet Protocol • Data stream divided in variable-length packets • Each packet routed individually (connectionless) • Perhaps less optimal, but it’s only for one packet! • Consecutive packets may take different paths • Best-effort packet delivery • No inherent timing, QoS or traffic-engineering mechanisms • Packets can • be corrupted or lost • arrive out-of-order • be duplicated

  24. Packet Networks Different PSNs Many different Packet Switched Networks Internet Protocol TCP, UDP, SCTP, RTP Frame Relay ATM MPLS Ethernet LAN, GbE, EFM DSL HDSL, SHDSL, ADSL, VDSL L2TP L2TP/UDP, L2TPv3

  25. header payload trailer header trailer header payload trailer Commonality • Layered structure not always OSI 7-layer model • Use of headers, trailers and payload • Payload may be adapted • Successive SDU -> PDU Headers more prevalent OSI uses only headers Service Data Unit Protocol Data Unit

  26. Packet Networks IP • designed to robustly interconnect data terminals • protocol suite for intranets and internets • defines all layers except physical (layer 1) Eth, ATM, SONET • variable length packets • best effort packet delivery, no QoS guarantees • connectionless, virtual connection TCP, SCTP • unreliable UDP, reliable TCP, highly reliable SCTP • RT support RTP, RTCP, RTSP • tunneling support PPP, L2TP • standards body: IETF

  27. Packet Networks src port dest port seq num ver len TOS total len ack num ID flgs frag offs offs res flags window TTL prot hdr chksum chksum urgent ptr src IP add options padding dest IP add options padding payload IP TCP UDP src port dest port length chksum

  28. Packet Networks Frame Relay (FR) • designed as WAN to connect LANs over low-speed link • low overhead and simple processing • defines layers 1 (physical) and 2 (data-link) • variable length packets • best effort packet delivery, no QoS guarantees • connection oriented • unreliable, but committed info rate • standards bodies: ITU-T, FRF

  29. Packet Networks payload flag FR header FCS flag 8 8 16 8 F E C N B E C N DLCI C/R EA DLCI DE EA 4 6 1 1 1 1 1 1 Frame Relay (FR)

  30. Packet Networks ATM Asynchronous Transfer Mode • designed as wideband ISDN • fast switching • defines layers 1-4 (physical, data-link, network, transport) • small constant length packets (cells) 53=5+48 cell tax • multiservice (data, CBR/VBR voice/video) • QoS levels and guarantees • connection oriented • standards bodies: ITU-T, ATMF

  31. Packet Networks (GFC) VPI VCI PTI CLP HEC 5-byte header 48 byte payload ATM AAL1 connection orientedCBR AAL2 connection orientedVBR AAL5 connectionless data packets GFC General Flow Control VPI Virtual Path Indentifier VCI Virtual Channel Indentifier PTI Payload Type Identifier CLP Cell Loss Priority HEC Header Error Control VC VP VC

  32. DSL • designed to reuse subscriber lines for broadband • layer 1 (physical) protocol (modem) • many varieties HDSL, SHDSL, ADSL, VDSL • FDM of data with POTS • synchronous but transports packet data • cVoDSL for synchronous voice • standards bodies : ITU-T, ETSI TM6, T1E1.4, DSLF

  33. Packet Networks … … … 1 2 3 4 23 24 1 2 3 S S frame 32 B frame 193b … … … E1 1 2 3 4 31 32 1 2 3 … … TDM / PDH / SDH Same data rate even when no data! The PSTN is not a PSN ! T1 Frame every 125 msec STM-1 frame 9 * 270 B

  34. The Casefor VoP

  35. VoP Case Voice over PSN We saw that data transported over voice network Should we “turn the tables” and transport voice over data networks? • Economics PSTN keeps circuit open for call duration packet networks use only resources truly needed • Convergence we need only maintain a single network • Added value enables new applications (video, white-boards, ftp, presence, voice browsing, etc.)

  36. VoP Case Voice over PSN There are a few problems … • Voice has to be “packetized”(what size packets?, preprocessing?) • Not a synchronous stream; no timing distribution • Packets arrive after random delays • Packets may arrive out-of-order • Packets may be lost • Reliability

  37. VoP Case PSTN Accessibility The PSTN has • 560 Million subscriber lines worldwide (156 M in US) • Total traffic CAGR 5% • 100 Million fax machines (45 M in US) • Fax traffic CAGR 12% • >1.5 Billion people with access to fax Is there any business reason to transport voice otherwise?

  38. VoP Case Relative Capacity 250 200 150 Voice Traffic Growth 5% /yr 100 50 Data Traffic Growth 300% /yr 0 1996 1997 1998 1999 2000 2001 Data Traffic Growth Data traffic growing much faster than voice (already more) Internet capacity increasing by factor of 10 each year

  39. VoP Case Revenue Breakdown AT&T 1998 figures • 51% switched (long distance) voice (incl. fax) service • 45.3% leased line service • 1.6% FR • 1.5% IP • 0.7% ATM So data traffic is increasing fast because it’s cheap! The killer-app from revenue point of view is voice

  40. VoP Case Typical VoP Applications • PC – PC communications (VoIP,VoDSL) • Integrated Access Devices (VoATM,VoIP) • Enterprise/campus convergence (VoFR,VoATM) • Toll-bypass (VoFR, TDMoIP) • Access networks (VoDSL, VoATM, VoCATV)

  41. PSTN Emulation

  42. PSTN Emulation header TDM payload trailer Encapsulation We would like to use the standard PSN technique but TDM payloads have no natural size packet ! The header will typically contain • addresses • identifiers • status, alarms • sequence number • timestamp • control information

  43. PSTN Emulation 135 136 138 139 Sequence Numbers Packet numbering is needed to • detect packet loss (mainly for timing - RT systems do not retransmit) • correct for misordering • supply timing when source is synchronous 135 137 136 138

  44. PSTN Emulation Timing PSNs introduce delay variation (jitter) How does PSTN emulation replicate timing? • Station clock • Clock distribution • Adaptive clock

  45. PSTN Emulation RTP with IP/UDP IP header (5 dwords) UDP header (2 dwords) RTP header (> 3 dwords) PAYLOAD

  46. PSTN Emulation RTP Header (RFC 1889) 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 V P X CSRC M PAYLD TYPESEQUENCE NUMBER TIMESTAMP SSRC ID V version number P padding indicator X extension indicator CSRC contributing source M marker bit SSRC sync source identifier

  47. PSTN Emulation Types of PSTN Emulation Call (session) emulation • Emulates single call • Voice and end-user signaling Loop emulation • Emulates trunk composed of individual loops • Only transports active loops (timeslots) Circuit emulation • Emulates entire circuit (trunk) • Does not deal with individual timeslots

  48. PSTN Emulation header N voice samples … header 4 31 32 1 2 … header 1 2 3 4 31 32 … … … 1 2 3 4 31 32 1 2 ptr 3 4 31 32 1 2 … TS1 TS2 TS3 TSn Payload Types • Call emulation • Leased line emulation • H.225 • CES (AAL1) • LES (AAL2)

  49. PSTN Emulation Extent of Emulation End-to-end emulation Edge-to-edge emulation Link emulation core switches edge switch edge switch

  50. PSTN Emulation PSN PSTN GW Emulation Elements PSTN emulations may have the following elements • End-points phone, user agent (UAC,UAS), terminal • Gateways IWF, SoftSwitch • Intermediaries • Proxies, Redirectors • Mixers • Address and location servers gatekeeper, registrar

More Related