Teknillinen korkeakoulu IP Telephony - · PDF fileŁ Transfer technology for...
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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
Voice over ATM, Voice over ADSL, and Voice over CATV
Erik Väkevä6.4.2001
IP TelephonyIP Telephony- Introduction -- Introduction -
S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 2
Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over ATM, ADSL, CATVVoice over ATM, ADSL, CATV- Introduction -- 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, andVoCATV).
� 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 ofnetworks bi-directional
S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 3
Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over ATMVoice over ATM- Networks -- 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 TVchannels.
� inflexible, bandwidth like 64 kbps and its� multiplies 32*64 kbps
� inefficient, 64 kbps point-to-point channel through a telecommunications networkfor one phone connection
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over ATMVoice over ATM- ATM Adaptation Layer -- 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 andleased 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)
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over ATMVoice over ATM- Protocols, ATM and AAL2 -- Protocols, ATM and AAL2 -
ATM trunking (AAL2)� for narrowband
services� between two
InterworkingFunctions (IWF) tointerconnect pairs ofnon-ATM trunks.
S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 6
Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over ATMVoice over ATM- Protocols, ATM and AAL2 -- 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)
S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 7
Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over ATMATM- Delays and Echo- 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 interfaceof each speech circuit into the ATM network
� Delays and echo are important variables on speech quality (ITU-T G.114)� Acceptable delays are about 15-30 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 ofATM cells 6) build-out delay for accommodating packet delay variation (PDV)
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over ATMATM- Services and descriptors- Services and descriptors - -
ATM services have two different main descriptors; 1) Traffic descriptors 2) QoSdescriptors
Traffic descriptors
� Peak Cell Rate (PCR), defines the maximum cell rate over connections that sourcecan submit
� Sustainable Cell Rate (SCR), defines average cell rate upper limit to connectionswithout traffic violation
� Maximum Burst Size (MBS), defines maximum number of cells that can be sentback-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
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over ATMVoice over ATM- Services and descriptors -- Services and descriptors -
The QoS descriptors
� Maximum Cell Transfer Delay (maxCTD), CTD is a delay that is generated when cellis transferred from start point to end point on the network and maxCTD is an upperlimit on CDT.
� Cell Delay Variation (CDV), defines maximum cell transfer delay time difference inthe 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.
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over ATMVoice over ATM- Services classes -- 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 signallingand 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
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over ADSLADSL- ADSL & DSL- 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 4.3125 kHz.
� data part is continuously connected, voice connection will be created
� maximum line length is 12000 foots (12000*30,48 cm ~ 3.660 m)
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over ADSLADSL- End user's ADSL network- 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 separatedwith High-pass-Filter(HPF)
� voice is separated withLow-pass-Filter (LPF)
� passive splitter is reliablein a power failuresituation.
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over ADSLADSL- VoDSL- VoDSL - -
� VoDSL technology is a platform
� equipment or Network Elements (NE)
� voice or data to customer over Public Switched Telephony Network (PSTN) orover 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 thevoice and data traffic
� Digital Subscriber Line AccessMultiplexer (DSLAM)
� voice gateway, filter voice trafficfrom data network
� Class 5 Switch, voice services
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over ADSLADSL- Physical layer- Physical layer and standards-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
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- Cable Television- 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 twoclasses
� distributive services
� interactive services, two-transmissionpath
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- CATV network- CATV network - -
S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 17
Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- Standardisation- Standardisation and organisations-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 300 800
� 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
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- DVB/DAVIC standards 1(2)- DVB/DAVIC standards 1(2) - -
DAVIC since in 1994, memberships that represent all sectors
� memberships that represent all sectors, manufacturing, service, researchorganisations, 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, andTransmission
DAVIC and ETSI have worked together
� DVB specification and DAVIC specification are identical.
S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 19
Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- - DVB/DAVIC DVB/DAVIC standards 2(2) 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 videoservices.
� 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.
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- - MCNS/DOCSIS standardMCNS/DOCSIS standard - -
MCNS standards
� multi cable service operators (MSO) and media companies from NorthAmerican
� 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 thespecification.
� The DOCSIS 1.1 specification; fragmentation in the upstream anddownstream, support QoS, and tiered services.
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Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- - DVB/DAVIC versus DOCSISDVB/DAVIC versus DOCSIS - -
S38_130_IP_Telephony.ppt/ 06.04.2001 / Erik Väkevä page: 22
Teknillinen korkeakoulu
S-38.130 Licentiate course on Telecommunications Technology: IP Telephony
Voice over Voice over CATVCATV- - ConclusionConclusion - -
Conclusion
� The ATM is lower layer technology but VoDSL and VoCATV are modemtechnologies
� 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 quaranteecertain traffic class level ---> no important delays or latencies
� DSL technology; modem technology, better transfer speed, copper lines, line lengthto a few kilometres
� CATV technology; old technology, two different services, distributive services andinteractive services. Two standards, DVB/DAVIC from European andMCNS/DOCSIS from North American, dominated other specifications.