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S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 1 Teknillinen korkeakoulu S-38.130 Licentiate course on Telecommunications Technology: IP Telephony.

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Presentation on theme: "S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 1 Teknillinen korkeakoulu S-38.130 Licentiate course on Telecommunications Technology: IP Telephony."— Presentation transcript:

1 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 1 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM, Voice over ADSL, and Voice over CATV Erik Väkevä IP Telephony - Introduction -

2 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 2 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM, ADSL, CATV - Introduction - The telephone networks of today are changing from traditionally circuit-based networks (TDM, PCM, PDH, SDH) to the packet-based networks (VoIP, VoA) opens challenges to new voice technologies. (VoIP, VoA, VoDSL, and VoCATV). This presentation presents the basic information VoA, based on cell technology, asynchronous, high transfer speed e.g. 622 Mbps The VoDSL is local loop access technology and transfer speed is up to 9 Mbps. Community Antenna Television (CATV) was unidirectional but now topology of networks bi-directional

3 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 3 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - Networks - Asynchronous Transfer Mode (ATM), packet switching technology service-independent 53-byte fixed-size cell (5 bytes header and 48 bytes payload ---> efficiency 90.6 %. International Telecommunication Union (ITU) has selected ATM as Transfer technology for Broadband-Integrated Services Digital Network (B-ISDN) traditional telecommunications networks (PDH, SDH and CATV) service dependence, PDH and SDH networks for voice carry and CATV for TV channels. inflexible, bandwidth like 64 kbps and its’ multiplies 32*64 kbps inefficient, 64 kbps point-to-point channel through a telecommunications network for one phone connection

4 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 4 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - ATM Adaptation Layer - Five ATM Adaptation Layer (AAL) types. Layers carry diverse message streams, same ATM cell format (53 bytes). AAL Type 1: Constant Bit Rate (CBR) Services; for isochronous information streams, voice (64 kbps), uncompressed video and leased lines AAL Type 2: Variable Bit Rate (VBR) Services; audio and compressed video (MPEG2) AAL Type 3/4: Connection-oriented VBR Services; Data Transfer on packet switching networks AAL Type 5: Connectionless VBR Services; Data Communications (TCP/IP)

5 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 5 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - Protocols, ATM and AAL2 - ATM trunking (AAL2) for narrowband services between two Interworking Functions (IWF) to interconnect pairs of non-ATM trunks.

6 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 6 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - Protocols, ATM and AAL2 - AAL2 benefits compared to other methods bandwidth allocation is less per cell, silence removal releases bandwidth no encoded speech information no empty ATM cells operator can route and switch narrowband calls on a per call basis AAL2 layer is better for bursty traffic (VBR)

7 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 7 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - Delays and Echo - 7) cells transmission time in physical network Echo is caused by hybrid networks 2-wire cables and 4-wire cables acoustical feedback at the end user's terminal are used. When speech channels are carried in ATM cells then echo cancellers are required at the interface of each speech circuit into the ATM network Delays and echo are important variables on speech quality (ITU-T G.114) Acceptable delays are about ms without echo cancellers and 150 ms in international speech connections with echo cancellers. An acceptable latency is 300 ms and 450 ms latency is unacceptable Delays appear from 1) voice compressing and decompressing 2) voice packaging to ATM cell 3) different buffers 4) Quality of Service (QoS) queues 5) switching of ATM cells 6) build-out delay for accommodating packet delay variation (PDV)

8 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 8 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - Services and descriptors - ATM services have two different main descriptors; 1) Traffic descriptors 2) QoS descriptors Traffic descriptors Peak Cell Rate (PCR), defines the maximum cell rate over connections that source can submit Sustainable Cell Rate (SCR), defines average cell rate upper limit to connections without traffic violation Maximum Burst Size (MBS), defines maximum number of cells that can be sent back-to-back at the peak rate Minimum Cell Rate (MCR), parameter that is set by the MCR commitment request Cell Delay Variation Tolerance (CDVT), defines the maximum cell delay variance

9 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 9 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - Services and descriptors - The QoS descriptors Maximum Cell Transfer Delay (maxCTD), CTD is a delay that is generated when cell is transferred from start point to end point on the network and maxCTD is an upper limit on CDT. Cell Delay Variation (CDV), defines maximum cell transfer delay time difference in the network. CDV is the maxCTD (worst case) minus fixed delay (best case). Cell Loss Ratio (CLR), defines ratio to the ratio of lost cells to total cells transmitted. Cell loss causes e.g. buffer overflow situation or wrong routing.

10 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 10 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ATM - Services classes -  Constant Bit Rate (CBR) services --> nickname “Continuous Bit Rate”.  rigorous timing controls and performance parameters.  video, single voice channel, N*64kbps, DSn, En, Q.931 N-ISDN D-channel signalling and circuit emulation.  Variable Bit Rate (VBR) services, real-time-VBR (rt-VBR) and non-real-time-VBR (nrt- VBR)  a bursty traffic, voice channel with silence removal and compressed video packets.  Available Bit Rate (ABR) services  elastic applications, Client-Server applications, TCP/IP, LAN applications, Q.2931 ATM signalling.  Unspecified Bit Rate (UBR) services  Used to fill bandwidth with data stream  provides “best-effort” service

11 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 11 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ADSL - ADSL & DSL - Two different working groups have originally developed DSL the Asymmetric Digital Subscriber Line (ADSL) Forum the Universal ADSL Working Group (UAWG) ADSL is a local loop access technology a modem technology, copper twisted-pair wire data, voice, and video 256 frequency channels for downstream transmission, from 1.5 Mbps to 9 Mbps 32 channels for upstream transmission, from 64 kbps to 1.5 Mbps channels’ bandwidth is kHz. data part is continuously connected, voice connection will be created maximum line length is foots (12000*30,48 cm ~ m)

12 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 12 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ADSL - End user's ADSL network - End user needs an ADSL modem with filter the filter can be included to the ADSL modem, “Splitterless Installation” cheaper than splittered installation Plain Old Telephony Server (POTS) splitter is used, "splittered installation" data stream is separated with High-pass-Filter (HPF) voice is separated with Low-pass-Filter (LPF) passive splitter is reliable in a power failure situation.

13 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 13 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ADSL - VoDSL - VoDSL technology is a platform equipment or Network Elements (NE) voice or data to customer over Public Switched Telephony Network (PSTN) or over Packet Backbone Network. Equipment or Network Elements (NE) are customer equipment (e.g. telephones, fax, and modem), Integrated Access Device (IAD) like ADSL modem, interface to the voice and data traffic Digital Subscriber Line Access Multiplexer (DSLAM) voice gateway, filter voice traffic from data network Class 5 Switch, voice services

14 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 14 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over ADSL - Physical layer and standards- Physical transport layer Frame Relay (FR), ATM, or Internet Protocol (IP). FR is common used technology, ATM has useful Quality of Service (QoS) traffic classify, AAL1 and AAL2 IP is future technology Standards Physical layer standards ---> ANSI, ETSI, and ITU ATM standards ---> ITU and the ATM Forum IP standards ---> Internet Engineering Task Force (IETF) ADSL architectures ---> ADSL Forum Several working groups, one of which is VoDSL group and it has several sub- working groups

15 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 15 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - Cable Television - Traditional CATV one-way transmission network system sent TV programs to a downstream direction network structure is point-to-point Nowadays CATV two-way transmission network provides fast data transmission cable modems (CM) speed is from 3 Mbps to 50 Mbps line distance can be over 100 km network topology is a tree model. coaxial cables, last kilometres Hybrid Fiber Coax (HFC) cable converters near the subscriber different services, classified to two classes distributive services interactive services, two-transmission path

16 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 16 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - CATV network -

17 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 17 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - Standardisation and organisations- Multimedia Cable Network System (MCNS) partners cable operators and media companies from North America standard named Data over Cable Service Interface Specification (DOCSIS) used in North America area and in Asian area European Telecommunication Standards Institute (ETSI) standard named Digital Video Broadcasting (DVB), ETS used in European area, in Asian area, and South American area Other standard is named Digital Audio Video Council (DAVIC) International Telecommunication Union (ITU) Both DVB/DAVIC and MCNS standards are nowadays ITU standards MCNS and DVB/DAVIC standards are dominated markets over world

18 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 18 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - DVB/DAVIC standards 1(2) - DAVIC since in 1994, memberships that represent all sectors memberships that represent all sectors, manufacturing, service, research organisations, and governments. standard named DAVIC 1.4 architecture, interfaces, protocol layers, security, and interoperability DVB standard was accepted by ETSI organisation in 1997 DVB specification includes Audio, Conditional Access, Interactivity, Interfacing, Measurement, Multimedia Home Platform (MHP), Multiplexing, Subtitling, and Transmission DAVIC and ETSI have worked together DVB specification and DAVIC specification are identical.

19 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 19 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - DVB/DAVIC standards 2(2) - DVB/DAVIC standards have been created to European markets. European Union (EU) directive that digital TV transmission must be based on DVB specification recommended to use DVB/DAVIC standards on digital audio and video services. The European Cable Communications Association (ECCA) recommends using these standards on equipment cable operators demand that CMs are compatible to DVB/DAVIC standards. Physical layer is based on ATM technology (QoS) two user equipment to home, Set-Top-Box (STB); interactive TV applications and Internet applications CM; video, data, and voice applications.

20 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 20 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - MCNS/DOCSIS standard - MCNS standards multi cable service operators (MSO) and media companies from North American The DOCSIS specification, beginning of 1998 transmission of data over cable network North American TV standards First version didn’t support QoS, but now QoS has been added to the specification. The DOCSIS 1.1 specification; fragmentation in the upstream and downstream, support QoS, and tiered services.

21 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 21 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - DVB/DAVIC versus DOCSIS -

22 S38_130_IP_Telephony.ppt/ / Erik Väkevä page: 22 Teknillinen korkeakoulu S Licentiate course on Telecommunications Technology: IP Telephony Voice over CATV - Conclusion - Conclusion The ATM is lower layer technology but VoDSL and VoCATV are modem technologies VoATM, VoDSL, and VoCATV, offer new transfer methods to carry voice traffic. Circuit based networks are inefficient ATM technology; structure is cell, QoS service classes, QoS plus TOS quarantee certain traffic class level ---> no important delays or latencies DSL technology; modem technology, better transfer speed, copper lines, line length to a few kilometres CATV technology; old technology, two different services, distributive services and interactive services. Two standards, DVB/DAVIC from European and MCNS/DOCSIS from North American, dominated other specifications.


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